diff --git a/.github/scripts/install-musl-build-tools.sh b/.github/scripts/install-musl-build-tools.sh
index e2af7528d5..634fe04d71 100644
--- a/.github/scripts/install-musl-build-tools.sh
+++ b/.github/scripts/install-musl-build-tools.sh
@@ -32,30 +32,132 @@ case "${TARGET}" in
     ;;
 esac
 
-if command -v clang++ >/dev/null; then
-  cxx="$(command -v clang++)"
-  echo "CXXFLAGS=--target=${TARGET} -stdlib=libc++ -pthread" >> "$GITHUB_ENV"
-  echo "CFLAGS=--target=${TARGET} -pthread" >> "$GITHUB_ENV"
-  if command -v clang >/dev/null; then
-    cc="$(command -v clang)"
-    echo "CC=${cc}" >> "$GITHUB_ENV"
-    echo "TARGET_CC=${cc}" >> "$GITHUB_ENV"
-    target_cc_var="CC_${TARGET}"
-    target_cc_var="${target_cc_var//-/_}"
-    echo "${target_cc_var}=${cc}" >> "$GITHUB_ENV"
-  fi
-elif command -v "${arch}-linux-musl-g++" >/dev/null; then
-  cxx="$(command -v "${arch}-linux-musl-g++")"
-elif command -v musl-g++ >/dev/null; then
-  cxx="$(command -v musl-g++)"
+# Use the musl toolchain as the Rust linker to avoid Zig injecting its own CRT.
+if command -v "${arch}-linux-musl-gcc" >/dev/null; then
+  musl_linker="$(command -v "${arch}-linux-musl-gcc")"
 elif command -v musl-gcc >/dev/null; then
-  cxx="$(command -v musl-gcc)"
-  echo "CFLAGS=-pthread" >> "$GITHUB_ENV"
+  musl_linker="$(command -v musl-gcc)"
 else
-  echo "musl g++ not found after install; arch=${arch}" >&2
+  echo "musl gcc not found after install; arch=${arch}" >&2
   exit 1
 fi
 
+zig_target="${TARGET/-unknown-linux-musl/-linux-musl}"
+runner_temp="${RUNNER_TEMP:-/tmp}"
+tool_root="${runner_temp}/codex-musl-tools-${TARGET}"
+mkdir -p "${tool_root}"
+
+sysroot=""
+if command -v zig >/dev/null; then
+  zig_bin="$(command -v zig)"
+  cc="${tool_root}/zigcc"
+  cxx="${tool_root}/zigcxx"
+
+  cat >"${cc}" <<EOF
+#!/usr/bin/env bash
+set -euo pipefail
+
+args=()
+skip_next=0
+for arg in "\$@"; do
+  if [[ "\${skip_next}" -eq 1 ]]; then
+    skip_next=0
+    continue
+  fi
+  case "\${arg}" in
+    --target)
+      skip_next=1
+      continue
+      ;;
+    --target=*|-target=*|-target)
+      # Drop any explicit --target/-target flags. Zig expects -target and
+      # rejects Rust triples like *-unknown-linux-musl.
+      if [[ "\${arg}" == "-target" ]]; then
+        skip_next=1
+      fi
+      continue
+      ;;
+  esac
+  args+=("\${arg}")
+done
+
+exec "${zig_bin}" cc -target "${zig_target}" "\${args[@]}"
+EOF
+  cat >"${cxx}" <<EOF
+#!/usr/bin/env bash
+set -euo pipefail
+
+args=()
+skip_next=0
+for arg in "\$@"; do
+  if [[ "\${skip_next}" -eq 1 ]]; then
+    skip_next=0
+    continue
+  fi
+  case "\${arg}" in
+    --target)
+      skip_next=1
+      continue
+      ;;
+    --target=*|-target=*|-target)
+      if [[ "\${arg}" == "-target" ]]; then
+        skip_next=1
+      fi
+      continue
+      ;;
+  esac
+  args+=("\${arg}")
+done
+
+exec "${zig_bin}" c++ -target "${zig_target}" "\${args[@]}"
+EOF
+  chmod +x "${cc}" "${cxx}"
+
+  sysroot="$("${zig_bin}" cc -target "${zig_target}" -print-sysroot 2>/dev/null || true)"
+else
+  cc="${musl_linker}"
+
+  if command -v "${arch}-linux-musl-g++" >/dev/null; then
+    cxx="$(command -v "${arch}-linux-musl-g++")"
+  elif command -v musl-g++ >/dev/null; then
+    cxx="$(command -v musl-g++)"
+  else
+    cxx="${cc}"
+  fi
+fi
+
+if [[ -n "${sysroot}" && "${sysroot}" != "/" ]]; then
+  echo "BORING_BSSL_SYSROOT=${sysroot}" >> "$GITHUB_ENV"
+  boring_sysroot_var="BORING_BSSL_SYSROOT_${TARGET}"
+  boring_sysroot_var="${boring_sysroot_var//-/_}"
+  echo "${boring_sysroot_var}=${sysroot}" >> "$GITHUB_ENV"
+fi
+
+cflags="-pthread"
+cxxflags="-pthread"
+if [[ "${TARGET}" == "aarch64-unknown-linux-musl" ]]; then
+  # BoringSSL enables -Wframe-larger-than=25344 under clang and treats warnings as errors.
+  cflags="${cflags} -Wno-error=frame-larger-than"
+  cxxflags="${cxxflags} -Wno-error=frame-larger-than"
+fi
+
+echo "CFLAGS=${cflags}" >> "$GITHUB_ENV"
+echo "CXXFLAGS=${cxxflags}" >> "$GITHUB_ENV"
+echo "CC=${cc}" >> "$GITHUB_ENV"
+echo "TARGET_CC=${cc}" >> "$GITHUB_ENV"
+target_cc_var="CC_${TARGET}"
+target_cc_var="${target_cc_var//-/_}"
+echo "${target_cc_var}=${cc}" >> "$GITHUB_ENV"
 echo "CXX=${cxx}" >> "$GITHUB_ENV"
+echo "TARGET_CXX=${cxx}" >> "$GITHUB_ENV"
+target_cxx_var="CXX_${TARGET}"
+target_cxx_var="${target_cxx_var//-/_}"
+echo "${target_cxx_var}=${cxx}" >> "$GITHUB_ENV"
+
+cargo_linker_var="CARGO_TARGET_${TARGET^^}_LINKER"
+cargo_linker_var="${cargo_linker_var//-/_}"
+echo "${cargo_linker_var}=${musl_linker}" >> "$GITHUB_ENV"
+
+echo "CMAKE_C_COMPILER=${cc}" >> "$GITHUB_ENV"
 echo "CMAKE_CXX_COMPILER=${cxx}" >> "$GITHUB_ENV"
 echo "CMAKE_ARGS=-DCMAKE_HAVE_THREADS_LIBRARY=1 -DCMAKE_USE_PTHREADS_INIT=1 -DCMAKE_THREAD_LIBS_INIT=-pthread -DTHREADS_PREFER_PTHREAD_FLAG=ON" >> "$GITHUB_ENV"
diff --git a/.github/workflows/rust-ci.yml b/.github/workflows/rust-ci.yml
index a6bf51369b..a8efec1089 100644
--- a/.github/workflows/rust-ci.yml
+++ b/.github/workflows/rust-ci.yml
@@ -261,6 +261,12 @@ jobs:
             /var/cache/apt
           key: apt-${{ matrix.runner }}-${{ matrix.target }}-v1
 
+      - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
+        name: Install Zig
+        uses: mlugg/setup-zig@v2
+        with:
+          version: 0.14.0
+
       - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
         name: Install musl build tools
         env:
diff --git a/.github/workflows/rust-release.yml b/.github/workflows/rust-release.yml
index 9033d058d7..3625c830dd 100644
--- a/.github/workflows/rust-release.yml
+++ b/.github/workflows/rust-release.yml
@@ -104,6 +104,12 @@ jobs:
             ${{ github.workspace }}/codex-rs/target/
           key: cargo-${{ matrix.runner }}-${{ matrix.target }}-release-${{ hashFiles('**/Cargo.lock') }}
 
+      - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
+        name: Install Zig
+        uses: mlugg/setup-zig@v2
+        with:
+          version: 0.14.0
+
       - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
         name: Install musl build tools
         env:
diff --git a/.github/workflows/shell-tool-mcp.yml b/.github/workflows/shell-tool-mcp.yml
index 0e03fea43c..a8a01b5f6a 100644
--- a/.github/workflows/shell-tool-mcp.yml
+++ b/.github/workflows/shell-tool-mcp.yml
@@ -97,6 +97,12 @@ jobs:
         with:
           targets: ${{ matrix.target }}
 
+      - if: ${{ matrix.install_musl }}
+        name: Install Zig
+        uses: mlugg/setup-zig@v2
+        with:
+          version: 0.14.0
+
       - if: ${{ matrix.install_musl }}
         name: Install musl build dependencies
         env:
diff --git a/codex-rs/Cargo.lock b/codex-rs/Cargo.lock
index 633899b68e..d0b3a0ec37 100644
--- a/codex-rs/Cargo.lock
+++ b/codex-rs/Cargo.lock
@@ -1096,6 +1096,7 @@ dependencies = [
  "serial_test",
  "shlex",
  "tempfile",
+ "time",
  "tokio",
  "toml 0.9.5",
  "tracing",
diff --git a/codex-rs/app-server-protocol/src/protocol/v2.rs b/codex-rs/app-server-protocol/src/protocol/v2.rs
index acf08be990..e282e924fc 100644
--- a/codex-rs/app-server-protocol/src/protocol/v2.rs
+++ b/codex-rs/app-server-protocol/src/protocol/v2.rs
@@ -5,6 +5,7 @@ use crate::protocol::common::AuthMode;
 use codex_protocol::account::PlanType;
 use codex_protocol::approvals::ExecPolicyAmendment as CoreExecPolicyAmendment;
 use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::config_types::ForcedLoginMethod;
 use codex_protocol::config_types::Personality;
 use codex_protocol::config_types::ReasoningSummary;
@@ -30,6 +31,7 @@ use codex_protocol::protocol::SkillErrorInfo as CoreSkillErrorInfo;
 use codex_protocol::protocol::SkillInterface as CoreSkillInterface;
 use codex_protocol::protocol::SkillMetadata as CoreSkillMetadata;
 use codex_protocol::protocol::SkillScope as CoreSkillScope;
+use codex_protocol::protocol::SubAgentSource as CoreSubAgentSource;
 use codex_protocol::protocol::TokenUsage as CoreTokenUsage;
 use codex_protocol::protocol::TokenUsageInfo as CoreTokenUsageInfo;
 use codex_protocol::user_input::ByteRange as CoreByteRange;
@@ -700,6 +702,7 @@ pub enum SessionSource {
     VsCode,
     Exec,
     AppServer,
+    SubAgent(CoreSubAgentSource),
     #[serde(other)]
     Unknown,
 }
@@ -711,7 +714,7 @@ impl From<CoreSessionSource> for SessionSource {
             CoreSessionSource::VSCode => SessionSource::VsCode,
             CoreSessionSource::Exec => SessionSource::Exec,
             CoreSessionSource::Mcp => SessionSource::AppServer,
-            CoreSessionSource::SubAgent(_) => SessionSource::Unknown,
+            CoreSessionSource::SubAgent(sub) => SessionSource::SubAgent(sub),
             CoreSessionSource::Unknown => SessionSource::Unknown,
         }
     }
@@ -724,6 +727,7 @@ impl From<SessionSource> for CoreSessionSource {
             SessionSource::VsCode => CoreSessionSource::VSCode,
             SessionSource::Exec => CoreSessionSource::Exec,
             SessionSource::AppServer => CoreSessionSource::Mcp,
+            SessionSource::SubAgent(sub) => CoreSessionSource::SubAgent(sub),
             SessionSource::Unknown => CoreSessionSource::Unknown,
         }
     }
@@ -934,7 +938,7 @@ pub struct CollaborationModeListParams {}
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
 pub struct CollaborationModeListResponse {
-    pub data: Vec<CollaborationMode>,
+    pub data: Vec<CollaborationModeMask>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
@@ -1083,6 +1087,7 @@ pub struct ThreadStartParams {
     pub base_instructions: Option<String>,
     pub developer_instructions: Option<String>,
     pub personality: Option<Personality>,
+    pub ephemeral: Option<bool>,
     /// If true, opt into emitting raw response items on the event stream.
     ///
     /// This is for internal use only (e.g. Codex Cloud).
@@ -1466,7 +1471,7 @@ pub struct Thread {
     #[ts(type = "number")]
     pub updated_at: i64,
     /// [UNSTABLE] Path to the thread on disk.
-    pub path: PathBuf,
+    pub path: Option<PathBuf>,
     /// Working directory captured for the thread.
     pub cwd: PathBuf,
     /// Version of the CLI that created the thread.
diff --git a/codex-rs/app-server/Cargo.toml b/codex-rs/app-server/Cargo.toml
index f31df68b3f..9fa2044058 100644
--- a/codex-rs/app-server/Cargo.toml
+++ b/codex-rs/app-server/Cargo.toml
@@ -35,6 +35,7 @@ serde = { workspace = true, features = ["derive"] }
 serde_json = { workspace = true }
 mcp-types = { workspace = true }
 tempfile = { workspace = true }
+time = { workspace = true }
 toml = { workspace = true }
 tokio = { workspace = true, features = [
     "io-std",
diff --git a/codex-rs/app-server/src/bespoke_event_handling.rs b/codex-rs/app-server/src/bespoke_event_handling.rs
index 931c1073aa..68e233b843 100644
--- a/codex-rs/app-server/src/bespoke_event_handling.rs
+++ b/codex-rs/app-server/src/bespoke_event_handling.rs
@@ -1006,7 +1006,15 @@ pub(crate) async fn apply_bespoke_event_handling(
             };
 
             if let Some(request_id) = pending {
-                let rollout_path = conversation.rollout_path();
+                let Some(rollout_path) = conversation.rollout_path() else {
+                    let error = JSONRPCErrorError {
+                        code: INVALID_REQUEST_ERROR_CODE,
+                        message: "thread has no persisted rollout".to_string(),
+                        data: None,
+                    };
+                    outgoing.send_error(request_id, error).await;
+                    return;
+                };
                 let response = match read_summary_from_rollout(
                     rollout_path.as_path(),
                     fallback_model_provider.as_str(),
diff --git a/codex-rs/app-server/src/codex_message_processor.rs b/codex-rs/app-server/src/codex_message_processor.rs
index daf0fb3d73..d0b8c7f949 100644
--- a/codex-rs/app-server/src/codex_message_processor.rs
+++ b/codex-rs/app-server/src/codex_message_processor.rs
@@ -134,6 +134,7 @@ use codex_core::InitialHistory;
 use codex_core::NewThread;
 use codex_core::RolloutRecorder;
 use codex_core::SessionMeta;
+use codex_core::ThreadConfigSnapshot;
 use codex_core::ThreadManager;
 use codex_core::ThreadSortKey as CoreThreadSortKey;
 use codex_core::auth::CLIENT_ID;
@@ -172,6 +173,7 @@ use codex_protocol::config_types::ForcedLoginMethod;
 use codex_protocol::config_types::Personality;
 use codex_protocol::items::TurnItem;
 use codex_protocol::models::ResponseItem;
+use codex_protocol::protocol::AgentStatus;
 use codex_protocol::protocol::GitInfo as CoreGitInfo;
 use codex_protocol::protocol::McpAuthStatus as CoreMcpAuthStatus;
 use codex_protocol::protocol::McpServerRefreshConfig;
@@ -192,7 +194,6 @@ use std::sync::Arc;
 use std::sync::atomic::AtomicBool;
 use std::sync::atomic::Ordering;
 use std::time::Duration;
-use tokio::select;
 use tokio::sync::Mutex;
 use tokio::sync::broadcast;
 use tokio::sync::oneshot;
@@ -1378,11 +1379,23 @@ impl CodexMessageProcessor {
                     session_configured,
                     ..
                 } = new_thread;
+                let rollout_path = match session_configured.rollout_path {
+                    Some(path) => path,
+                    None => {
+                        let error = JSONRPCErrorError {
+                            code: INTERNAL_ERROR_CODE,
+                            message: "rollout path missing for v1 conversation".to_string(),
+                            data: None,
+                        };
+                        self.outgoing.send_error(request_id, error).await;
+                        return;
+                    }
+                };
                 let response = NewConversationResponse {
                     conversation_id: thread_id,
                     model: session_configured.model,
                     reasoning_effort: session_configured.reasoning_effort,
-                    rollout_path: session_configured.rollout_path,
+                    rollout_path,
                 };
                 self.outgoing.send_response(request_id, response).await;
             }
@@ -1398,7 +1411,7 @@ impl CodexMessageProcessor {
     }
 
     async fn thread_start(&mut self, request_id: RequestId, params: ThreadStartParams) {
-        let typesafe_overrides = self.build_thread_config_overrides(
+        let mut typesafe_overrides = self.build_thread_config_overrides(
             params.model,
             params.model_provider,
             params.cwd,
@@ -1408,6 +1421,7 @@ impl CodexMessageProcessor {
             params.developer_instructions,
             params.personality,
         );
+        typesafe_overrides.ephemeral = Some(params.ephemeral.unwrap_or_default());
 
         let config =
             match derive_config_from_params(&self.cli_overrides, params.config, typesafe_overrides)
@@ -1429,50 +1443,45 @@ impl CodexMessageProcessor {
             Ok(new_conv) => {
                 let NewThread {
                     thread_id,
+                    thread,
                     session_configured,
                     ..
                 } = new_conv;
-                let rollout_path = session_configured.rollout_path.clone();
+                let config_snapshot = thread.config_snapshot().await;
                 let fallback_provider = self.config.model_provider_id.as_str();
 
                 // A bit hacky, but the summary contains a lot of useful information for the thread
                 // that unfortunately does not get returned from thread_manager.start_thread().
-                let thread = match read_summary_from_rollout(
-                    rollout_path.as_path(),
-                    fallback_provider,
-                )
-                .await
-                {
-                    Ok(summary) => summary_to_thread(summary),
-                    Err(err) => {
-                        self.send_internal_error(
-                            request_id,
-                            format!(
-                                "failed to load rollout `{}` for thread {thread_id}: {err}",
-                                rollout_path.display()
-                            ),
-                        )
-                        .await;
-                        return;
+                let thread = match session_configured.rollout_path.as_ref() {
+                    Some(rollout_path) => {
+                        match read_summary_from_rollout(rollout_path.as_path(), fallback_provider)
+                            .await
+                        {
+                            Ok(summary) => summary_to_thread(summary),
+                            Err(err) => {
+                                self.send_internal_error(
+                                    request_id,
+                                    format!(
+                                        "failed to load rollout `{}` for thread {thread_id}: {err}",
+                                        rollout_path.display()
+                                    ),
+                                )
+                                .await;
+                                return;
+                            }
+                        }
                     }
+                    None => build_ephemeral_thread(thread_id, &config_snapshot),
                 };
 
-                let SessionConfiguredEvent {
-                    model,
-                    model_provider_id,
-                    cwd,
-                    approval_policy,
-                    sandbox_policy,
-                    ..
-                } = session_configured;
                 let response = ThreadStartResponse {
                     thread: thread.clone(),
-                    model,
-                    model_provider: model_provider_id,
-                    cwd,
-                    approval_policy: approval_policy.into(),
-                    sandbox: sandbox_policy.into(),
-                    reasoning_effort: session_configured.reasoning_effort,
+                    model: config_snapshot.model,
+                    model_provider: config_snapshot.model_provider_id,
+                    cwd: config_snapshot.cwd,
+                    approval_policy: config_snapshot.approval_policy.into(),
+                    sandbox: config_snapshot.sandbox_policy.into(),
+                    reasoning_effort: config_snapshot.reasoning_effort,
                 };
 
                 // Auto-attach a thread listener when starting a thread.
@@ -1725,7 +1734,7 @@ impl CodexMessageProcessor {
         self.outgoing.send_response(request_id, response).await;
     }
 
-    async fn thread_read(&self, request_id: RequestId, params: ThreadReadParams) {
+    async fn thread_read(&mut self, request_id: RequestId, params: ThreadReadParams) {
         let ThreadReadParams {
             thread_id,
             include_turns,
@@ -1744,15 +1753,8 @@ impl CodexMessageProcessor {
             match find_thread_path_by_id_str(&self.config.codex_home, &thread_uuid.to_string())
                 .await
             {
-                Ok(Some(path)) => path,
-                Ok(None) => {
-                    self.send_invalid_request_error(
-                        request_id,
-                        format!("no rollout found for thread id {thread_uuid}"),
-                    )
-                    .await;
-                    return;
-                }
+                Ok(Some(path)) => Some(path),
+                Ok(None) => None,
                 Err(err) => {
                     self.send_invalid_request_error(
                         request_id,
@@ -1763,24 +1765,45 @@ impl CodexMessageProcessor {
                 }
             };
 
-        let fallback_provider = self.config.model_provider_id.as_str();
-        let mut thread = match read_summary_from_rollout(&rollout_path, fallback_provider).await {
-            Ok(summary) => summary_to_thread(summary),
-            Err(err) => {
-                self.send_internal_error(
+        let mut thread = if let Some(rollout_path) = rollout_path.as_ref() {
+            let fallback_provider = self.config.model_provider_id.as_str();
+            match read_summary_from_rollout(rollout_path, fallback_provider).await {
+                Ok(summary) => summary_to_thread(summary),
+                Err(err) => {
+                    self.send_internal_error(
+                        request_id,
+                        format!(
+                            "failed to load rollout `{}` for thread {thread_uuid}: {err}",
+                            rollout_path.display()
+                        ),
+                    )
+                    .await;
+                    return;
+                }
+            }
+        } else {
+            let Ok(thread) = self.thread_manager.get_thread(thread_uuid).await else {
+                self.send_invalid_request_error(
                     request_id,
-                    format!(
-                        "failed to load rollout `{}` for thread {thread_uuid}: {err}",
-                        rollout_path.display()
-                    ),
+                    format!("thread not loaded: {thread_uuid}"),
+                )
+                .await;
+                return;
+            };
+            let config_snapshot = thread.config_snapshot().await;
+            if include_turns {
+                self.send_invalid_request_error(
+                    request_id,
+                    "ephemeral threads do not support includeTurns".to_string(),
                 )
                 .await;
                 return;
             }
+            build_ephemeral_thread(thread_uuid, &config_snapshot)
         };
 
-        if include_turns {
-            match read_event_msgs_from_rollout(&rollout_path).await {
+        if include_turns && let Some(rollout_path) = rollout_path.as_ref() {
+            match read_event_msgs_from_rollout(rollout_path).await {
                 Ok(events) => {
                     thread.turns = build_turns_from_event_msgs(&events);
                 }
@@ -1967,6 +1990,14 @@ impl CodexMessageProcessor {
                     initial_messages,
                     ..
                 } = session_configured;
+                let Some(rollout_path) = rollout_path else {
+                    self.send_internal_error(
+                        request_id,
+                        format!("rollout path missing for thread {thread_id}"),
+                    )
+                    .await;
+                    return;
+                };
                 // Auto-attach a thread listener when resuming a thread.
                 if let Err(err) = self
                     .attach_conversation_listener(thread_id, false, ApiVersion::V2)
@@ -2170,6 +2201,14 @@ impl CodexMessageProcessor {
             initial_messages,
             ..
         } = session_configured;
+        let Some(rollout_path) = rollout_path else {
+            self.send_internal_error(
+                request_id,
+                format!("rollout path missing for thread {thread_id}"),
+            )
+            .await;
+            return;
+        };
         // Auto-attach a conversation listener when forking a thread.
         if let Err(err) = self
             .attach_conversation_listener(thread_id, false, ApiVersion::V2)
@@ -2919,6 +2958,18 @@ impl CodexMessageProcessor {
                 session_configured,
                 ..
             }) => {
+                let rollout_path = match session_configured.rollout_path.clone() {
+                    Some(path) => path,
+                    None => {
+                        let error = JSONRPCErrorError {
+                            code: INTERNAL_ERROR_CODE,
+                            message: "rollout path missing for resumed conversation".to_string(),
+                            data: None,
+                        };
+                        self.outgoing.send_error(request_id, error).await;
+                        return;
+                    }
+                };
                 self.outgoing
                     .send_server_notification(ServerNotification::SessionConfigured(
                         SessionConfiguredNotification {
@@ -2928,7 +2979,7 @@ impl CodexMessageProcessor {
                             history_log_id: session_configured.history_log_id,
                             history_entry_count: session_configured.history_entry_count,
                             initial_messages: session_configured.initial_messages.clone(),
-                            rollout_path: session_configured.rollout_path.clone(),
+                            rollout_path: rollout_path.clone(),
                         },
                     ))
                     .await;
@@ -2941,7 +2992,7 @@ impl CodexMessageProcessor {
                     conversation_id: thread_id,
                     model: session_configured.model.clone(),
                     initial_messages,
-                    rollout_path: session_configured.rollout_path.clone(),
+                    rollout_path,
                 };
                 self.outgoing.send_response(request_id, response).await;
             }
@@ -3117,6 +3168,19 @@ impl CodexMessageProcessor {
             }
         };
 
+        let rollout_path = match session_configured.rollout_path.clone() {
+            Some(path) => path,
+            None => {
+                let error = JSONRPCErrorError {
+                    code: INTERNAL_ERROR_CODE,
+                    message: "rollout path missing for forked conversation".to_string(),
+                    data: None,
+                };
+                self.outgoing.send_error(request_id, error).await;
+                return;
+            }
+        };
+
         self.outgoing
             .send_server_notification(ServerNotification::SessionConfigured(
                 SessionConfiguredNotification {
@@ -3126,7 +3190,7 @@ impl CodexMessageProcessor {
                     history_log_id: session_configured.history_log_id,
                     history_entry_count: session_configured.history_entry_count,
                     initial_messages: session_configured.initial_messages.clone(),
-                    rollout_path: session_configured.rollout_path.clone(),
+                    rollout_path: rollout_path.clone(),
                 },
             ))
             .await;
@@ -3139,7 +3203,7 @@ impl CodexMessageProcessor {
             conversation_id: thread_id,
             model: session_configured.model.clone(),
             initial_messages,
-            rollout_path: session_configured.rollout_path.clone(),
+            rollout_path,
         };
         self.outgoing.send_response(request_id, response).await;
     }
@@ -3250,51 +3314,27 @@ impl CodexMessageProcessor {
         // If the thread is active, request shutdown and wait briefly.
         if let Some(conversation) = self.thread_manager.remove_thread(&thread_id).await {
             info!("thread {thread_id} was active; shutting down");
-            let conversation_clone = conversation.clone();
-            let notify = Arc::new(tokio::sync::Notify::new());
-            let notify_clone = notify.clone();
-
-            // Establish the listener for ShutdownComplete before submitting
-            // Shutdown so it is not missed.
-            let is_shutdown = tokio::spawn(async move {
-                // Create the notified future outside the loop to avoid losing notifications.
-                let notified = notify_clone.notified();
-                tokio::pin!(notified);
-                loop {
-                    select! {
-                        _ = &mut notified => { break; }
-                        event = conversation_clone.next_event() => {
-                            match event {
-                                Ok(event) => {
-                                    if matches!(event.msg, EventMsg::ShutdownComplete) { break; }
-                                }
-                                // Break on errors to avoid tight loops when the agent loop has exited.
-                                Err(_) => { break; }
-                            }
-                        }
-                    }
-                }
-            });
             // Request shutdown.
             match conversation.submit(Op::Shutdown).await {
                 Ok(_) => {
-                    // Successfully submitted Shutdown; wait before proceeding.
-                    select! {
-                        _ = is_shutdown => {
-                            // Normal shutdown: proceed with archive.
-                        }
-                        _ = tokio::time::sleep(Duration::from_secs(10)) => {
-                            warn!("thread {thread_id} shutdown timed out; proceeding with archive");
-                            // Wake any waiter; use notify_waiters to avoid missing the signal.
-                            notify.notify_waiters();
-                            // Perhaps we lost a shutdown race, so let's continue to
-                            // clean up the .jsonl file.
+                    // Poll agent status rather than consuming events so attached listeners do not block shutdown.
+                    let wait_for_shutdown = async {
+                        loop {
+                            if matches!(conversation.agent_status().await, AgentStatus::Shutdown) {
+                                break;
+                            }
+                            tokio::time::sleep(Duration::from_millis(50)).await;
                         }
+                    };
+                    if tokio::time::timeout(Duration::from_secs(10), wait_for_shutdown)
+                        .await
+                        .is_err()
+                    {
+                        warn!("thread {thread_id} shutdown timed out; proceeding with archive");
                     }
                 }
                 Err(err) => {
                     error!("failed to submit Shutdown to thread {thread_id}: {err}");
-                    notify.notify_waiters();
                 }
             }
         }
@@ -3809,23 +3849,29 @@ impl CodexMessageProcessor {
             );
         }
 
-        let rollout_path = review_thread.rollout_path();
         let fallback_provider = self.config.model_provider_id.as_str();
-        match read_summary_from_rollout(rollout_path.as_path(), fallback_provider).await {
-            Ok(summary) => {
-                let thread = summary_to_thread(summary);
-                let notif = ThreadStartedNotification { thread };
-                self.outgoing
-                    .send_server_notification(ServerNotification::ThreadStarted(notif))
-                    .await;
-            }
-            Err(err) => {
-                tracing::warn!(
-                    "failed to load summary for review thread {}: {}",
-                    session_configured.session_id,
-                    err
-                );
+        if let Some(rollout_path) = review_thread.rollout_path() {
+            match read_summary_from_rollout(rollout_path.as_path(), fallback_provider).await {
+                Ok(summary) => {
+                    let thread = summary_to_thread(summary);
+                    let notif = ThreadStartedNotification { thread };
+                    self.outgoing
+                        .send_server_notification(ServerNotification::ThreadStarted(notif))
+                        .await;
+                }
+                Err(err) => {
+                    tracing::warn!(
+                        "failed to load summary for review thread {}: {}",
+                        session_configured.session_id,
+                        err
+                    );
+                }
             }
+        } else {
+            tracing::warn!(
+                "review thread {} has no rollout path",
+                session_configured.session_id
+            );
         }
 
         let turn_id = review_thread
@@ -4228,7 +4274,7 @@ impl CodexMessageProcessor {
 
     async fn resolve_rollout_path(&self, conversation_id: ThreadId) -> Option<PathBuf> {
         match self.thread_manager.get_thread(conversation_id).await {
-            Ok(conv) => Some(conv.rollout_path()),
+            Ok(conv) => conv.rollout_path(),
             Err(_) => None,
         }
     }
@@ -4493,6 +4539,23 @@ async fn read_updated_at(path: &Path, created_at: Option<&str>) -> Option<String
     updated_at.or_else(|| created_at.map(str::to_string))
 }
 
+fn build_ephemeral_thread(thread_id: ThreadId, config_snapshot: &ThreadConfigSnapshot) -> Thread {
+    let now = time::OffsetDateTime::now_utc().unix_timestamp();
+    Thread {
+        id: thread_id.to_string(),
+        preview: String::new(),
+        model_provider: config_snapshot.model_provider_id.clone(),
+        created_at: now,
+        updated_at: now,
+        path: None,
+        cwd: config_snapshot.cwd.clone(),
+        cli_version: env!("CARGO_PKG_VERSION").to_string(),
+        source: config_snapshot.session_source.clone().into(),
+        git_info: None,
+        turns: Vec::new(),
+    }
+}
+
 pub(crate) fn summary_to_thread(summary: ConversationSummary) -> Thread {
     let ConversationSummary {
         conversation_id,
@@ -4521,7 +4584,7 @@ pub(crate) fn summary_to_thread(summary: ConversationSummary) -> Thread {
         model_provider,
         created_at: created_at.map(|dt| dt.timestamp()).unwrap_or(0),
         updated_at: updated_at.map(|dt| dt.timestamp()).unwrap_or(0),
-        path,
+        path: Some(path),
         cwd,
         cli_version,
         source: source.into(),
diff --git a/codex-rs/app-server/tests/suite/v2/collaboration_mode_list.rs b/codex-rs/app-server/tests/suite/v2/collaboration_mode_list.rs
index cb9ff3e18e..7d25810261 100644
--- a/codex-rs/app-server/tests/suite/v2/collaboration_mode_list.rs
+++ b/codex-rs/app-server/tests/suite/v2/collaboration_mode_list.rs
@@ -16,7 +16,7 @@ use codex_app_server_protocol::CollaborationModeListResponse;
 use codex_app_server_protocol::JSONRPCResponse;
 use codex_app_server_protocol::RequestId;
 use codex_core::models_manager::test_builtin_collaboration_mode_presets;
-use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::config_types::ModeKind;
 use pretty_assertions::assert_eq;
 use tempfile::TempDir;
@@ -45,13 +45,23 @@ async fn list_collaboration_modes_returns_presets() -> Result<()> {
     let CollaborationModeListResponse { data: items } =
         to_response::<CollaborationModeListResponse>(response)?;
 
-    let expected = vec![
+    let expected = [
         plan_preset(),
         code_preset(),
         pair_programming_preset(),
         execute_preset(),
     ];
-    assert_eq!(expected, items);
+    assert_eq!(expected.len(), items.len());
+    for (expected_mask, actual_mask) in expected.iter().zip(items.iter()) {
+        assert_eq!(expected_mask.name, actual_mask.name);
+        assert_eq!(expected_mask.mode, actual_mask.mode);
+        assert_eq!(expected_mask.model, actual_mask.model);
+        assert_eq!(expected_mask.reasoning_effort, actual_mask.reasoning_effort);
+        assert_eq!(
+            expected_mask.developer_instructions,
+            actual_mask.developer_instructions
+        );
+    }
     Ok(())
 }
 
@@ -59,11 +69,11 @@ async fn list_collaboration_modes_returns_presets() -> Result<()> {
 ///
 /// If the defaults change in the app server, this helper should be updated alongside the
 /// contract, or the test will fail in ways that imply a regression in the API.
-fn plan_preset() -> CollaborationMode {
+fn plan_preset() -> CollaborationModeMask {
     let presets = test_builtin_collaboration_mode_presets();
     presets
         .into_iter()
-        .find(|p| p.mode == ModeKind::Plan)
+        .find(|p| p.mode == Some(ModeKind::Plan))
         .unwrap()
 }
 
@@ -71,20 +81,20 @@ fn plan_preset() -> CollaborationMode {
 ///
 /// The helper keeps the expected model and reasoning defaults co-located with the test
 /// so that mismatches point directly at the API contract being exercised.
-fn pair_programming_preset() -> CollaborationMode {
+fn pair_programming_preset() -> CollaborationModeMask {
     let presets = test_builtin_collaboration_mode_presets();
     presets
         .into_iter()
-        .find(|p| p.mode == ModeKind::PairProgramming)
+        .find(|p| p.mode == Some(ModeKind::PairProgramming))
         .unwrap()
 }
 
 /// Builds the code preset that the list response is expected to return.
-fn code_preset() -> CollaborationMode {
+fn code_preset() -> CollaborationModeMask {
     let presets = test_builtin_collaboration_mode_presets();
     presets
         .into_iter()
-        .find(|p| p.mode == ModeKind::Code)
+        .find(|p| p.mode == Some(ModeKind::Code))
         .unwrap()
 }
 
@@ -92,10 +102,10 @@ fn code_preset() -> CollaborationMode {
 ///
 /// The execute preset uses a different reasoning effort to capture the higher-effort
 /// execution contract the server currently exposes.
-fn execute_preset() -> CollaborationMode {
+fn execute_preset() -> CollaborationModeMask {
     let presets = test_builtin_collaboration_mode_presets();
     presets
         .into_iter()
-        .find(|p| p.mode == ModeKind::Execute)
+        .find(|p| p.mode == Some(ModeKind::Execute))
         .unwrap()
 }
diff --git a/codex-rs/app-server/tests/suite/v2/thread_fork.rs b/codex-rs/app-server/tests/suite/v2/thread_fork.rs
index 32abc237e3..c06f387fd2 100644
--- a/codex-rs/app-server/tests/suite/v2/thread_fork.rs
+++ b/codex-rs/app-server/tests/suite/v2/thread_fork.rs
@@ -77,8 +77,9 @@ async fn thread_fork_creates_new_thread_and_emits_started() -> Result<()> {
     assert_ne!(thread.id, conversation_id);
     assert_eq!(thread.preview, preview);
     assert_eq!(thread.model_provider, "mock_provider");
-    assert!(thread.path.is_absolute());
-    assert_ne!(thread.path, original_path);
+    let thread_path = thread.path.clone().expect("thread path");
+    assert!(thread_path.is_absolute());
+    assert_ne!(thread_path, original_path);
     assert!(thread.cwd.is_absolute());
     assert_eq!(thread.source, SessionSource::VsCode);
 
diff --git a/codex-rs/app-server/tests/suite/v2/thread_read.rs b/codex-rs/app-server/tests/suite/v2/thread_read.rs
index 8704a25468..d8ca3aa696 100644
--- a/codex-rs/app-server/tests/suite/v2/thread_read.rs
+++ b/codex-rs/app-server/tests/suite/v2/thread_read.rs
@@ -64,7 +64,7 @@ async fn thread_read_returns_summary_without_turns() -> Result<()> {
     assert_eq!(thread.id, conversation_id);
     assert_eq!(thread.preview, preview);
     assert_eq!(thread.model_provider, "mock_provider");
-    assert!(thread.path.is_absolute());
+    assert!(thread.path.as_ref().expect("thread path").is_absolute());
     assert_eq!(thread.cwd, PathBuf::from("/"));
     assert_eq!(thread.cli_version, "0.0.0");
     assert_eq!(thread.source, SessionSource::Cli);
diff --git a/codex-rs/app-server/tests/suite/v2/thread_resume.rs b/codex-rs/app-server/tests/suite/v2/thread_resume.rs
index 183532ea7d..6129c0de2f 100644
--- a/codex-rs/app-server/tests/suite/v2/thread_resume.rs
+++ b/codex-rs/app-server/tests/suite/v2/thread_resume.rs
@@ -117,7 +117,7 @@ async fn thread_resume_returns_rollout_history() -> Result<()> {
     assert_eq!(thread.id, conversation_id);
     assert_eq!(thread.preview, preview);
     assert_eq!(thread.model_provider, "mock_provider");
-    assert!(thread.path.is_absolute());
+    assert!(thread.path.as_ref().expect("thread path").is_absolute());
     assert_eq!(thread.cwd, PathBuf::from("/"));
     assert_eq!(thread.cli_version, "0.0.0");
     assert_eq!(thread.source, SessionSource::Cli);
@@ -169,7 +169,7 @@ async fn thread_resume_prefers_path_over_thread_id() -> Result<()> {
     .await??;
     let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(start_resp)?;
 
-    let thread_path = thread.path.clone();
+    let thread_path = thread.path.clone().expect("thread path");
     let resume_id = mcp
         .send_thread_resume_request(ThreadResumeParams {
             thread_id: "not-a-valid-thread-id".to_string(),
diff --git a/codex-rs/cli/src/main.rs b/codex-rs/cli/src/main.rs
index 332f6314b5..103cc4b349 100644
--- a/codex-rs/cli/src/main.rs
+++ b/codex-rs/cli/src/main.rs
@@ -396,8 +396,7 @@ fn run_update_action(action: UpdateAction) -> anyhow::Result<()> {
     if !status.success() {
         anyhow::bail!("`{cmd_str}` failed with status {status}");
     }
-    println!();
-    println!("🎉 Update ran successfully! Please restart Codex.");
+    println!("\n🎉 Update ran successfully! Please restart Codex.");
     Ok(())
 }
 
diff --git a/codex-rs/codex-api/src/requests/headers.rs b/codex-rs/codex-api/src/requests/headers.rs
index 02f08724ff..02f8c61c31 100644
--- a/codex-rs/codex-api/src/requests/headers.rs
+++ b/codex-rs/codex-api/src/requests/headers.rs
@@ -15,13 +15,12 @@ pub(crate) fn subagent_header(source: &Option<SessionSource>) -> Option<String>
         return None;
     };
     match sub {
+        codex_protocol::protocol::SubAgentSource::Review => Some("review".to_string()),
+        codex_protocol::protocol::SubAgentSource::Compact => Some("compact".to_string()),
+        codex_protocol::protocol::SubAgentSource::ThreadSpawn { .. } => {
+            Some("collab_spawn".to_string())
+        }
         codex_protocol::protocol::SubAgentSource::Other(label) => Some(label.clone()),
-        other => Some(
-            serde_json::to_value(other)
-                .ok()
-                .and_then(|v| v.as_str().map(std::string::ToString::to_string))
-                .unwrap_or_else(|| "other".to_string()),
-        ),
     }
 }
 
diff --git a/codex-rs/core/src/agent/control.rs b/codex-rs/core/src/agent/control.rs
index 6c5ebf9f02..611c0d164c 100644
--- a/codex-rs/core/src/agent/control.rs
+++ b/codex-rs/core/src/agent/control.rs
@@ -39,12 +39,20 @@ impl AgentControl {
         &self,
         config: crate::config::Config,
         prompt: String,
+        session_source: Option<codex_protocol::protocol::SessionSource>,
     ) -> CodexResult<ThreadId> {
         let state = self.upgrade()?;
         let reservation = self.state.reserve_spawn_slot(config.agent_max_threads)?;
 
         // The same `AgentControl` is sent to spawn the thread.
-        let new_thread = state.spawn_new_thread(config, self.clone()).await?;
+        let new_thread = match session_source {
+            Some(session_source) => {
+                state
+                    .spawn_new_thread_with_source(config, self.clone(), session_source)
+                    .await?
+            }
+            None => state.spawn_new_thread(config, self.clone()).await?,
+        };
         reservation.commit(new_thread.thread_id);
 
         // Notify a new thread has been created. This notification will be processed by clients
@@ -268,7 +276,7 @@ mod tests {
         let control = AgentControl::default();
         let (_home, config) = test_config().await;
         let err = control
-            .spawn_agent(config, "hello".to_string())
+            .spawn_agent(config, "hello".to_string(), None)
             .await
             .expect_err("spawn_agent should fail without a manager");
         assert_eq!(
@@ -370,7 +378,7 @@ mod tests {
         let harness = AgentControlHarness::new().await;
         let thread_id = harness
             .control
-            .spawn_agent(harness.config.clone(), "spawned".to_string())
+            .spawn_agent(harness.config.clone(), "spawned".to_string(), None)
             .await
             .expect("spawn_agent should succeed");
         let _thread = harness
@@ -417,12 +425,12 @@ mod tests {
             .expect("start thread");
 
         let first_agent_id = control
-            .spawn_agent(config.clone(), "hello".to_string())
+            .spawn_agent(config.clone(), "hello".to_string(), None)
             .await
             .expect("spawn_agent should succeed");
 
         let err = control
-            .spawn_agent(config, "hello again".to_string())
+            .spawn_agent(config, "hello again".to_string(), None)
             .await
             .expect_err("spawn_agent should respect max threads");
         let CodexErr::AgentLimitReached {
@@ -455,7 +463,7 @@ mod tests {
         let control = manager.agent_control();
 
         let first_agent_id = control
-            .spawn_agent(config.clone(), "hello".to_string())
+            .spawn_agent(config.clone(), "hello".to_string(), None)
             .await
             .expect("spawn_agent should succeed");
         let _ = control
@@ -464,7 +472,7 @@ mod tests {
             .expect("shutdown agent");
 
         let second_agent_id = control
-            .spawn_agent(config.clone(), "hello again".to_string())
+            .spawn_agent(config.clone(), "hello again".to_string(), None)
             .await
             .expect("spawn_agent should succeed after shutdown");
         let _ = control
@@ -490,12 +498,12 @@ mod tests {
         let cloned = control.clone();
 
         let first_agent_id = cloned
-            .spawn_agent(config.clone(), "hello".to_string())
+            .spawn_agent(config.clone(), "hello".to_string(), None)
             .await
             .expect("spawn_agent should succeed");
 
         let err = control
-            .spawn_agent(config, "hello again".to_string())
+            .spawn_agent(config, "hello again".to_string(), None)
             .await
             .expect_err("spawn_agent should respect shared guard");
         let CodexErr::AgentLimitReached { max_threads } = err else {
diff --git a/codex-rs/core/src/agent/guards.rs b/codex-rs/core/src/agent/guards.rs
index c384ed7cd8..2f146f2f80 100644
--- a/codex-rs/core/src/agent/guards.rs
+++ b/codex-rs/core/src/agent/guards.rs
@@ -1,6 +1,8 @@
 use crate::error::CodexErr;
 use crate::error::Result;
 use codex_protocol::ThreadId;
+use codex_protocol::protocol::SessionSource;
+use codex_protocol::protocol::SubAgentSource;
 use std::collections::HashSet;
 use std::sync::Arc;
 use std::sync::Mutex;
@@ -19,6 +21,25 @@ pub(crate) struct Guards {
     total_count: AtomicUsize,
 }
 
+/// Initial agent is depth 0.
+pub(crate) const MAX_THREAD_SPAWN_DEPTH: i32 = 1;
+
+fn session_depth(session_source: &SessionSource) -> i32 {
+    match session_source {
+        SessionSource::SubAgent(SubAgentSource::ThreadSpawn { depth, .. }) => *depth,
+        SessionSource::SubAgent(_) => 0,
+        _ => 0,
+    }
+}
+
+pub(crate) fn next_thread_spawn_depth(session_source: &SessionSource) -> i32 {
+    session_depth(session_source).saturating_add(1)
+}
+
+pub(crate) fn exceeds_thread_spawn_depth_limit(depth: i32) -> bool {
+    depth > MAX_THREAD_SPAWN_DEPTH
+}
+
 impl Guards {
     pub(crate) fn reserve_spawn_slot(
         self: &Arc<Self>,
@@ -102,6 +123,30 @@ mod tests {
     use super::*;
     use pretty_assertions::assert_eq;
 
+    #[test]
+    fn session_depth_defaults_to_zero_for_root_sources() {
+        assert_eq!(session_depth(&SessionSource::Cli), 0);
+    }
+
+    #[test]
+    fn thread_spawn_depth_increments_and_enforces_limit() {
+        let session_source = SessionSource::SubAgent(SubAgentSource::ThreadSpawn {
+            parent_thread_id: ThreadId::new(),
+            depth: 1,
+        });
+        let child_depth = next_thread_spawn_depth(&session_source);
+        assert_eq!(child_depth, 2);
+        assert!(exceeds_thread_spawn_depth_limit(child_depth));
+    }
+
+    #[test]
+    fn non_thread_spawn_subagents_default_to_depth_zero() {
+        let session_source = SessionSource::SubAgent(SubAgentSource::Review);
+        assert_eq!(session_depth(&session_source), 0);
+        assert_eq!(next_thread_spawn_depth(&session_source), 1);
+        assert!(!exceeds_thread_spawn_depth_limit(1));
+    }
+
     #[test]
     fn reservation_drop_releases_slot() {
         let guards = Arc::new(Guards::default());
diff --git a/codex-rs/core/src/agent/mod.rs b/codex-rs/core/src/agent/mod.rs
index 180f70dbe6..03652e43e5 100644
--- a/codex-rs/core/src/agent/mod.rs
+++ b/codex-rs/core/src/agent/mod.rs
@@ -1,10 +1,12 @@
 pub(crate) mod control;
-// Do not put in `pub` or `pub(crate)`. This code should not be used somewhere else.
 mod guards;
 pub(crate) mod role;
 pub(crate) mod status;
 
 pub(crate) use codex_protocol::protocol::AgentStatus;
 pub(crate) use control::AgentControl;
+pub(crate) use guards::MAX_THREAD_SPAWN_DEPTH;
+pub(crate) use guards::exceeds_thread_spawn_depth_limit;
+pub(crate) use guards::next_thread_spawn_depth;
 pub(crate) use role::AgentRole;
 pub(crate) use status::agent_status_from_event;
diff --git a/codex-rs/core/src/client.rs b/codex-rs/core/src/client.rs
index f0f2b125fd..437380deef 100644
--- a/codex-rs/core/src/client.rs
+++ b/codex-rs/core/src/client.rs
@@ -226,13 +226,11 @@ impl ModelClient {
 
         let mut extra_headers = ApiHeaderMap::new();
         if let SessionSource::SubAgent(sub) = &self.state.session_source {
-            let subagent = if let crate::protocol::SubAgentSource::Other(label) = sub {
-                label.clone()
-            } else {
-                serde_json::to_value(sub)
-                    .ok()
-                    .and_then(|v| v.as_str().map(std::string::ToString::to_string))
-                    .unwrap_or_else(|| "other".to_string())
+            let subagent = match sub {
+                crate::protocol::SubAgentSource::Review => "review".to_string(),
+                crate::protocol::SubAgentSource::Compact => "compact".to_string(),
+                crate::protocol::SubAgentSource::ThreadSpawn { .. } => "collab_spawn".to_string(),
+                crate::protocol::SubAgentSource::Other(label) => label.clone(),
             };
             if let Ok(val) = HeaderValue::from_str(&subagent) {
                 extra_headers.insert("x-openai-subagent", val);
diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 25c2b225a3..9fc2bae165 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -89,6 +89,7 @@ use crate::client::ModelClient;
 use crate::client::ModelClientSession;
 use crate::client_common::Prompt;
 use crate::client_common::ResponseEvent;
+use crate::codex_thread::ThreadConfigSnapshot;
 use crate::compact::collect_user_messages;
 use crate::config::Config;
 use crate::config::Constrained;
@@ -192,6 +193,7 @@ pub struct Codex {
     pub(crate) rx_event: Receiver<Event>,
     // Last known status of the agent.
     pub(crate) agent_status: watch::Receiver<AgentStatus>,
+    pub(crate) session: Arc<Session>,
 }
 
 /// Wrapper returned by [`Codex::spawn`] containing the spawned [`Codex`],
@@ -345,12 +347,13 @@ impl Codex {
         let thread_id = session.conversation_id;
 
         // This task will run until Op::Shutdown is received.
-        tokio::spawn(submission_loop(session, config, rx_sub));
+        tokio::spawn(submission_loop(Arc::clone(&session), config, rx_sub));
         let codex = Codex {
             next_id: AtomicU64::new(0),
             tx_sub,
             rx_event,
             agent_status: agent_status_rx,
+            session,
         };
 
         #[allow(deprecated)]
@@ -394,6 +397,11 @@ impl Codex {
     pub(crate) async fn agent_status(&self) -> AgentStatus {
         self.agent_status.borrow().clone()
     }
+
+    pub(crate) async fn thread_config_snapshot(&self) -> ThreadConfigSnapshot {
+        let state = self.session.state.lock().await;
+        state.session_configuration.thread_config_snapshot()
+    }
 }
 
 /// Context for an initialized model agent
@@ -495,6 +503,19 @@ pub(crate) struct SessionConfiguration {
 }
 
 impl SessionConfiguration {
+    fn thread_config_snapshot(&self) -> ThreadConfigSnapshot {
+        ThreadConfigSnapshot {
+            model: self.collaboration_mode.model().to_string(),
+            model_provider_id: self.original_config_do_not_use.model_provider_id.clone(),
+            approval_policy: self.approval_policy.value(),
+            sandbox_policy: self.sandbox_policy.get().clone(),
+            cwd: self.cwd.clone(),
+            reasoning_effort: self.collaboration_mode.reasoning_effort(),
+            personality: self.personality,
+            session_source: self.session_source.clone(),
+        }
+    }
+
     pub(crate) fn apply(&self, updates: &SessionSettingsUpdate) -> ConstraintResult<Self> {
         let mut next_configuration = self.clone();
         if let Some(collaboration_mode) = updates.collaboration_mode.clone() {
@@ -652,7 +673,15 @@ impl Session {
         // - initialize RolloutRecorder with new or resumed session info
         // - perform default shell discovery
         // - load history metadata
-        let rollout_fut = RolloutRecorder::new(&config, rollout_params);
+        let rollout_fut = async {
+            if config.ephemeral {
+                Ok(None)
+            } else {
+                RolloutRecorder::new(&config, rollout_params)
+                    .await
+                    .map(Some)
+            }
+        };
 
         let history_meta_fut = crate::message_history::history_metadata(&config);
         let auth_manager_clone = Arc::clone(&auth_manager);
@@ -679,7 +708,9 @@ impl Session {
             error!("failed to initialize rollout recorder: {e:#}");
             anyhow::Error::from(e)
         })?;
-        let rollout_path = rollout_recorder.rollout_path.clone();
+        let rollout_path = rollout_recorder
+            .as_ref()
+            .map(|rec| rec.rollout_path.clone());
 
         let mut post_session_configured_events = Vec::<Event>::new();
 
@@ -768,7 +799,7 @@ impl Session {
             mcp_startup_cancellation_token: Mutex::new(CancellationToken::new()),
             unified_exec_manager: UnifiedExecProcessManager::default(),
             notifier: UserNotifier::new(config.notify.clone()),
-            rollout: Mutex::new(Some(rollout_recorder)),
+            rollout: Mutex::new(rollout_recorder),
             user_shell: Arc::new(default_shell),
             show_raw_agent_reasoning: config.show_raw_agent_reasoning,
             exec_policy,
diff --git a/codex-rs/core/src/codex_delegate.rs b/codex-rs/core/src/codex_delegate.rs
index b855612113..9a94f988d5 100644
--- a/codex-rs/core/src/codex_delegate.rs
+++ b/codex-rs/core/src/codex_delegate.rs
@@ -92,6 +92,7 @@ pub(crate) async fn run_codex_thread_interactive(
         tx_sub: tx_ops,
         rx_event: rx_sub,
         agent_status: codex.agent_status.clone(),
+        session: Arc::clone(&codex.session),
     })
 }
 
@@ -134,6 +135,7 @@ pub(crate) async fn run_codex_thread_one_shot(
     let (tx_bridge, rx_bridge) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
     let ops_tx = io.tx_sub.clone();
     let agent_status = io.agent_status.clone();
+    let session = Arc::clone(&io.session);
     let io_for_bridge = io;
     tokio::spawn(async move {
         while let Ok(event) = io_for_bridge.next_event().await {
@@ -166,6 +168,7 @@ pub(crate) async fn run_codex_thread_one_shot(
         rx_event: rx_bridge,
         tx_sub: tx_closed,
         agent_status,
+        session,
     })
 }
 
@@ -442,15 +445,15 @@ mod tests {
         let (tx_events, rx_events) = bounded(1);
         let (tx_sub, rx_sub) = bounded(SUBMISSION_CHANNEL_CAPACITY);
         let (_agent_status_tx, agent_status) = watch::channel(AgentStatus::PendingInit);
+        let (session, ctx, _rx_evt) = crate::codex::make_session_and_context_with_rx().await;
         let codex = Arc::new(Codex {
             next_id: AtomicU64::new(0),
             tx_sub,
             rx_event: rx_events,
             agent_status,
+            session: Arc::clone(&session),
         });
 
-        let (session, ctx, _rx_evt) = crate::codex::make_session_and_context_with_rx().await;
-
         let (tx_out, rx_out) = bounded(1);
         tx_out
             .send(Event {
diff --git a/codex-rs/core/src/codex_thread.rs b/codex-rs/core/src/codex_thread.rs
index 6d132a9256..152679d146 100644
--- a/codex-rs/core/src/codex_thread.rs
+++ b/codex-rs/core/src/codex_thread.rs
@@ -4,18 +4,35 @@ use crate::error::Result as CodexResult;
 use crate::protocol::Event;
 use crate::protocol::Op;
 use crate::protocol::Submission;
+use codex_protocol::config_types::Personality;
+use codex_protocol::openai_models::ReasoningEffort;
+use codex_protocol::protocol::AskForApproval;
+use codex_protocol::protocol::SandboxPolicy;
+use codex_protocol::protocol::SessionSource;
 use std::path::PathBuf;
 use tokio::sync::watch;
 
+#[derive(Clone, Debug)]
+pub struct ThreadConfigSnapshot {
+    pub model: String,
+    pub model_provider_id: String,
+    pub approval_policy: AskForApproval,
+    pub sandbox_policy: SandboxPolicy,
+    pub cwd: PathBuf,
+    pub reasoning_effort: Option<ReasoningEffort>,
+    pub personality: Option<Personality>,
+    pub session_source: SessionSource,
+}
+
 pub struct CodexThread {
     codex: Codex,
-    rollout_path: PathBuf,
+    rollout_path: Option<PathBuf>,
 }
 
 /// Conduit for the bidirectional stream of messages that compose a thread
 /// (formerly called a conversation) in Codex.
 impl CodexThread {
-    pub(crate) fn new(codex: Codex, rollout_path: PathBuf) -> Self {
+    pub(crate) fn new(codex: Codex, rollout_path: Option<PathBuf>) -> Self {
         Self {
             codex,
             rollout_path,
@@ -43,7 +60,11 @@ impl CodexThread {
         self.codex.agent_status.clone()
     }
 
-    pub fn rollout_path(&self) -> PathBuf {
+    pub fn rollout_path(&self) -> Option<PathBuf> {
         self.rollout_path.clone()
     }
+
+    pub async fn config_snapshot(&self) -> ThreadConfigSnapshot {
+        self.codex.thread_config_snapshot().await
+    }
 }
diff --git a/codex-rs/core/src/config/mod.rs b/codex-rs/core/src/config/mod.rs
index fae370ec0e..ca3ccc1ffd 100644
--- a/codex-rs/core/src/config/mod.rs
+++ b/codex-rs/core/src/config/mod.rs
@@ -89,7 +89,7 @@ pub use codex_git::GhostSnapshotConfig;
 /// files are *silently truncated* to this size so we do not take up too much of
 /// the context window.
 pub(crate) const PROJECT_DOC_MAX_BYTES: usize = 32 * 1024; // 32 KiB
-pub(crate) const DEFAULT_AGENT_MAX_THREADS: Option<usize> = None;
+pub(crate) const DEFAULT_AGENT_MAX_THREADS: Option<usize> = Some(6);
 
 pub const CONFIG_TOML_FILE: &str = "config.toml";
 
@@ -261,6 +261,9 @@ pub struct Config {
     /// Settings that govern if and what will be written to `~/.codex/history.jsonl`.
     pub history: History,
 
+    /// When true, session is not persisted on disk. Default to `false`
+    pub ephemeral: bool,
+
     /// Optional URI-based file opener. If set, citations to files in the model
     /// output will be hyperlinked using the specified URI scheme.
     pub file_opener: UriBasedFileOpener,
@@ -1158,6 +1161,7 @@ pub struct ConfigOverrides {
     pub include_apply_patch_tool: Option<bool>,
     pub show_raw_agent_reasoning: Option<bool>,
     pub tools_web_search_request: Option<bool>,
+    pub ephemeral: Option<bool>,
     /// Additional directories that should be treated as writable roots for this session.
     pub additional_writable_roots: Vec<PathBuf>,
 }
@@ -1246,6 +1250,7 @@ impl Config {
             include_apply_patch_tool: include_apply_patch_tool_override,
             show_raw_agent_reasoning,
             tools_web_search_request: override_tools_web_search_request,
+            ephemeral,
             additional_writable_roots,
         } = overrides;
 
@@ -1530,6 +1535,7 @@ impl Config {
             codex_home,
             config_layer_stack,
             history,
+            ephemeral: ephemeral.unwrap_or_default(),
             file_opener: cfg.file_opener.unwrap_or(UriBasedFileOpener::VsCode),
             codex_linux_sandbox_exe,
 
@@ -3687,10 +3693,11 @@ model_verbosity = "high"
                 project_doc_max_bytes: PROJECT_DOC_MAX_BYTES,
                 project_doc_fallback_filenames: Vec::new(),
                 tool_output_token_limit: None,
-                agent_max_threads: None,
+                agent_max_threads: DEFAULT_AGENT_MAX_THREADS,
                 codex_home: fixture.codex_home(),
                 config_layer_stack: Default::default(),
                 history: History::default(),
+                ephemeral: false,
                 file_opener: UriBasedFileOpener::VsCode,
                 codex_linux_sandbox_exe: None,
                 hide_agent_reasoning: false,
@@ -3768,10 +3775,11 @@ model_verbosity = "high"
             project_doc_max_bytes: PROJECT_DOC_MAX_BYTES,
             project_doc_fallback_filenames: Vec::new(),
             tool_output_token_limit: None,
-            agent_max_threads: None,
+            agent_max_threads: DEFAULT_AGENT_MAX_THREADS,
             codex_home: fixture.codex_home(),
             config_layer_stack: Default::default(),
             history: History::default(),
+            ephemeral: false,
             file_opener: UriBasedFileOpener::VsCode,
             codex_linux_sandbox_exe: None,
             hide_agent_reasoning: false,
@@ -3864,10 +3872,11 @@ model_verbosity = "high"
             project_doc_max_bytes: PROJECT_DOC_MAX_BYTES,
             project_doc_fallback_filenames: Vec::new(),
             tool_output_token_limit: None,
-            agent_max_threads: None,
+            agent_max_threads: DEFAULT_AGENT_MAX_THREADS,
             codex_home: fixture.codex_home(),
             config_layer_stack: Default::default(),
             history: History::default(),
+            ephemeral: false,
             file_opener: UriBasedFileOpener::VsCode,
             codex_linux_sandbox_exe: None,
             hide_agent_reasoning: false,
@@ -3946,10 +3955,11 @@ model_verbosity = "high"
             project_doc_max_bytes: PROJECT_DOC_MAX_BYTES,
             project_doc_fallback_filenames: Vec::new(),
             tool_output_token_limit: None,
-            agent_max_threads: None,
+            agent_max_threads: DEFAULT_AGENT_MAX_THREADS,
             codex_home: fixture.codex_home(),
             config_layer_stack: Default::default(),
             history: History::default(),
+            ephemeral: false,
             file_opener: UriBasedFileOpener::VsCode,
             codex_linux_sandbox_exe: None,
             hide_agent_reasoning: false,
diff --git a/codex-rs/core/src/features.rs b/codex-rs/core/src/features.rs
index 9a9527aa7a..5e2a0d5d50 100644
--- a/codex-rs/core/src/features.rs
+++ b/codex-rs/core/src/features.rs
@@ -434,11 +434,7 @@ pub const FEATURES: &[FeatureSpec] = &[
     FeatureSpec {
         id: Feature::Collab,
         key: "collab",
-        stage: Stage::Experimental {
-            name: "Multi-agents",
-            menu_description: "Allow Codex to spawn and collaborate with other agents on request (formerly named `collab`).",
-            announcement: "NEW! Codex can now spawn other agents and work with them to solve your problems. Enable in /experimental!",
-        },
+        stage: Stage::Beta,
         default_enabled: false,
     },
     FeatureSpec {
diff --git a/codex-rs/core/src/lib.rs b/codex-rs/core/src/lib.rs
index 41d33a4ce4..2042e330ef 100644
--- a/codex-rs/core/src/lib.rs
+++ b/codex-rs/core/src/lib.rs
@@ -15,6 +15,7 @@ pub mod codex;
 mod codex_thread;
 mod compact_remote;
 pub use codex_thread::CodexThread;
+pub use codex_thread::ThreadConfigSnapshot;
 mod agent;
 mod codex_delegate;
 mod command_safety;
diff --git a/codex-rs/core/src/models_manager/collaboration_mode_presets.rs b/codex-rs/core/src/models_manager/collaboration_mode_presets.rs
index ac1334c56c..aff111b1ad 100644
--- a/codex-rs/core/src/models_manager/collaboration_mode_presets.rs
+++ b/codex-rs/core/src/models_manager/collaboration_mode_presets.rs
@@ -1,6 +1,5 @@
-use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::config_types::ModeKind;
-use codex_protocol::config_types::Settings;
 use codex_protocol::openai_models::ReasoningEffort;
 
 const COLLABORATION_MODE_PLAN: &str = include_str!("../../templates/collaboration_mode/plan.md");
@@ -10,7 +9,7 @@ const COLLABORATION_MODE_PAIR_PROGRAMMING: &str =
 const COLLABORATION_MODE_EXECUTE: &str =
     include_str!("../../templates/collaboration_mode/execute.md");
 
-pub(super) fn builtin_collaboration_mode_presets() -> Vec<CollaborationMode> {
+pub(super) fn builtin_collaboration_mode_presets() -> Vec<CollaborationModeMask> {
     vec![
         plan_preset(),
         code_preset(),
@@ -20,50 +19,46 @@ pub(super) fn builtin_collaboration_mode_presets() -> Vec<CollaborationMode> {
 }
 
 #[cfg(any(test, feature = "test-support"))]
-pub fn test_builtin_collaboration_mode_presets() -> Vec<CollaborationMode> {
+pub fn test_builtin_collaboration_mode_presets() -> Vec<CollaborationModeMask> {
     builtin_collaboration_mode_presets()
 }
 
-fn plan_preset() -> CollaborationMode {
-    CollaborationMode {
-        mode: ModeKind::Plan,
-        settings: Settings {
-            model: "gpt-5.2-codex".to_string(),
-            reasoning_effort: Some(ReasoningEffort::High),
-            developer_instructions: Some(COLLABORATION_MODE_PLAN.to_string()),
-        },
+fn plan_preset() -> CollaborationModeMask {
+    CollaborationModeMask {
+        name: "Plan".to_string(),
+        mode: Some(ModeKind::Plan),
+        model: None,
+        reasoning_effort: Some(Some(ReasoningEffort::High)),
+        developer_instructions: Some(Some(COLLABORATION_MODE_PLAN.to_string())),
     }
 }
 
-fn code_preset() -> CollaborationMode {
-    CollaborationMode {
-        mode: ModeKind::Code,
-        settings: Settings {
-            model: "gpt-5.2-codex".to_string(),
-            reasoning_effort: Some(ReasoningEffort::Medium),
-            developer_instructions: Some(COLLABORATION_MODE_CODE.to_string()),
-        },
+fn code_preset() -> CollaborationModeMask {
+    CollaborationModeMask {
+        name: "Code".to_string(),
+        mode: Some(ModeKind::Code),
+        model: None,
+        reasoning_effort: None,
+        developer_instructions: Some(Some(COLLABORATION_MODE_CODE.to_string())),
     }
 }
 
-fn pair_programming_preset() -> CollaborationMode {
-    CollaborationMode {
-        mode: ModeKind::PairProgramming,
-        settings: Settings {
-            model: "gpt-5.2-codex".to_string(),
-            reasoning_effort: Some(ReasoningEffort::Medium),
-            developer_instructions: Some(COLLABORATION_MODE_PAIR_PROGRAMMING.to_string()),
-        },
+fn pair_programming_preset() -> CollaborationModeMask {
+    CollaborationModeMask {
+        name: "Pair Programming".to_string(),
+        mode: Some(ModeKind::PairProgramming),
+        model: None,
+        reasoning_effort: Some(Some(ReasoningEffort::Medium)),
+        developer_instructions: Some(Some(COLLABORATION_MODE_PAIR_PROGRAMMING.to_string())),
     }
 }
 
-fn execute_preset() -> CollaborationMode {
-    CollaborationMode {
-        mode: ModeKind::Execute,
-        settings: Settings {
-            model: "gpt-5.2-codex".to_string(),
-            reasoning_effort: Some(ReasoningEffort::High),
-            developer_instructions: Some(COLLABORATION_MODE_EXECUTE.to_string()),
-        },
+fn execute_preset() -> CollaborationModeMask {
+    CollaborationModeMask {
+        name: "Execute".to_string(),
+        mode: Some(ModeKind::Execute),
+        model: None,
+        reasoning_effort: Some(Some(ReasoningEffort::High)),
+        developer_instructions: Some(Some(COLLABORATION_MODE_EXECUTE.to_string())),
     }
 }
diff --git a/codex-rs/core/src/models_manager/manager.rs b/codex-rs/core/src/models_manager/manager.rs
index efa60507ea..58049b4747 100644
--- a/codex-rs/core/src/models_manager/manager.rs
+++ b/codex-rs/core/src/models_manager/manager.rs
@@ -14,7 +14,7 @@ use crate::models_manager::model_presets::builtin_model_presets;
 use codex_api::ModelsClient;
 use codex_api::ReqwestTransport;
 use codex_app_server_protocol::AuthMode;
-use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ModelPreset;
 use codex_protocol::openai_models::ModelsResponse;
@@ -91,7 +91,7 @@ impl ModelsManager {
     /// List collaboration mode presets.
     ///
     /// Returns a static set of presets seeded with the configured model.
-    pub fn list_collaboration_modes(&self) -> Vec<CollaborationMode> {
+    pub fn list_collaboration_modes(&self) -> Vec<CollaborationModeMask> {
         builtin_collaboration_mode_presets()
     }
 
diff --git a/codex-rs/core/src/thread_manager.rs b/codex-rs/core/src/thread_manager.rs
index 70d8cb7900..bc5cd4f19e 100644
--- a/codex-rs/core/src/thread_manager.rs
+++ b/codex-rs/core/src/thread_manager.rs
@@ -19,7 +19,7 @@ use crate::rollout::RolloutRecorder;
 use crate::rollout::truncation;
 use crate::skills::SkillsManager;
 use codex_protocol::ThreadId;
-use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::openai_models::ModelPreset;
 use codex_protocol::protocol::InitialHistory;
 use codex_protocol::protocol::McpServerRefreshConfig;
@@ -158,7 +158,7 @@ impl ThreadManager {
             .await
     }
 
-    pub fn list_collaboration_modes(&self) -> Vec<CollaborationMode> {
+    pub fn list_collaboration_modes(&self) -> Vec<CollaborationModeMask> {
         self.state.models_manager.list_collaboration_modes()
     }
 
@@ -314,11 +314,22 @@ impl ThreadManagerState {
         config: Config,
         agent_control: AgentControl,
     ) -> CodexResult<NewThread> {
-        self.spawn_thread(
+        self.spawn_new_thread_with_source(config, agent_control, self.session_source.clone())
+            .await
+    }
+
+    pub(crate) async fn spawn_new_thread_with_source(
+        &self,
+        config: Config,
+        agent_control: AgentControl,
+        session_source: SessionSource,
+    ) -> CodexResult<NewThread> {
+        self.spawn_thread_with_source(
             config,
             InitialHistory::New,
             Arc::clone(&self.auth_manager),
             agent_control,
+            session_source,
         )
         .await
     }
@@ -330,6 +341,24 @@ impl ThreadManagerState {
         initial_history: InitialHistory,
         auth_manager: Arc<AuthManager>,
         agent_control: AgentControl,
+    ) -> CodexResult<NewThread> {
+        self.spawn_thread_with_source(
+            config,
+            initial_history,
+            auth_manager,
+            agent_control,
+            self.session_source.clone(),
+        )
+        .await
+    }
+
+    pub(crate) async fn spawn_thread_with_source(
+        &self,
+        config: Config,
+        initial_history: InitialHistory,
+        auth_manager: Arc<AuthManager>,
+        agent_control: AgentControl,
+        session_source: SessionSource,
     ) -> CodexResult<NewThread> {
         let CodexSpawnOk {
             codex, thread_id, ..
@@ -339,7 +368,7 @@ impl ThreadManagerState {
             Arc::clone(&self.models_manager),
             Arc::clone(&self.skills_manager),
             initial_history,
-            self.session_source.clone(),
+            session_source,
             agent_control,
         )
         .await?;
diff --git a/codex-rs/core/src/tools/handlers/collab.rs b/codex-rs/core/src/tools/handlers/collab.rs
index 56463e644a..83ee53905b 100644
--- a/codex-rs/core/src/tools/handlers/collab.rs
+++ b/codex-rs/core/src/tools/handlers/collab.rs
@@ -78,6 +78,11 @@ impl ToolHandler for CollabHandler {
 mod spawn {
     use super::*;
     use crate::agent::AgentRole;
+    use crate::agent::MAX_THREAD_SPAWN_DEPTH;
+    use crate::agent::exceeds_thread_spawn_depth_limit;
+    use crate::agent::next_thread_spawn_depth;
+    use codex_protocol::protocol::SessionSource;
+    use codex_protocol::protocol::SubAgentSource;
     use std::sync::Arc;
 
     #[derive(Debug, Deserialize)]
@@ -105,6 +110,13 @@ mod spawn {
                 "Empty message can't be sent to an agent".to_string(),
             ));
         }
+        let session_source = turn.client.get_session_source();
+        let child_depth = next_thread_spawn_depth(&session_source);
+        if exceeds_thread_spawn_depth_limit(child_depth) {
+            return Err(FunctionCallError::RespondToModel(format!(
+                "agent depth limit reached: max depth is {MAX_THREAD_SPAWN_DEPTH}"
+            )));
+        }
         session
             .send_event(
                 &turn,
@@ -125,7 +137,14 @@ mod spawn {
         let result = session
             .services
             .agent_control
-            .spawn_agent(config, prompt.clone())
+            .spawn_agent(
+                config,
+                prompt.clone(),
+                Some(SessionSource::SubAgent(SubAgentSource::ThreadSpawn {
+                    parent_thread_id: session.conversation_id,
+                    depth: child_depth,
+                })),
+            )
             .await
             .map_err(collab_spawn_error);
         let (new_thread_id, status) = match &result {
@@ -573,7 +592,6 @@ fn build_agent_spawn_config(
     config.model_reasoning_summary = turn.client.get_reasoning_summary();
     config.developer_instructions = turn.developer_instructions.clone();
     config.compact_prompt = turn.compact_prompt.clone();
-    config.user_instructions = turn.user_instructions.clone();
     config.shell_environment_policy = turn.shell_environment_policy.clone();
     config.codex_linux_sandbox_exe = turn.codex_linux_sandbox_exe.clone();
     config.cwd = turn.cwd.clone();
@@ -597,13 +615,17 @@ mod tests {
     use super::*;
     use crate::CodexAuth;
     use crate::ThreadManager;
+    use crate::agent::MAX_THREAD_SPAWN_DEPTH;
     use crate::built_in_model_providers;
+    use crate::client::ModelClient;
     use crate::codex::make_session_and_context;
     use crate::config::types::ShellEnvironmentPolicy;
     use crate::function_tool::FunctionCallError;
     use crate::protocol::AskForApproval;
     use crate::protocol::Op;
     use crate::protocol::SandboxPolicy;
+    use crate::protocol::SessionSource;
+    use crate::protocol::SubAgentSource;
     use crate::turn_diff_tracker::TurnDiffTracker;
     use codex_protocol::ThreadId;
     use pretty_assertions::assert_eq;
@@ -723,6 +745,45 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn spawn_agent_rejects_when_depth_limit_exceeded() {
+        let (mut session, mut turn) = make_session_and_context().await;
+        let manager = thread_manager();
+        session.services.agent_control = manager.agent_control();
+
+        let session_source = SessionSource::SubAgent(SubAgentSource::ThreadSpawn {
+            parent_thread_id: session.conversation_id,
+            depth: MAX_THREAD_SPAWN_DEPTH,
+        });
+        turn.client = ModelClient::new(
+            turn.client.config(),
+            Some(session.services.auth_manager.clone()),
+            turn.client.get_model_info(),
+            turn.client.get_otel_manager(),
+            turn.client.get_provider(),
+            turn.client.get_reasoning_effort(),
+            turn.client.get_reasoning_summary(),
+            session.conversation_id,
+            session_source,
+        );
+
+        let invocation = invocation(
+            Arc::new(session),
+            Arc::new(turn),
+            "spawn_agent",
+            function_payload(json!({"message": "hello"})),
+        );
+        let Err(err) = CollabHandler.handle(invocation).await else {
+            panic!("spawn should fail when depth limit exceeded");
+        };
+        assert_eq!(
+            err,
+            FunctionCallError::RespondToModel(format!(
+                "agent depth limit reached: max depth is {MAX_THREAD_SPAWN_DEPTH}"
+            ))
+        );
+    }
+
     #[tokio::test]
     async fn send_input_rejects_empty_message() {
         let (session, turn) = make_session_and_context().await;
@@ -1073,7 +1134,6 @@ mod tests {
         };
         turn.developer_instructions = Some("dev".to_string());
         turn.compact_prompt = Some("compact".to_string());
-        turn.user_instructions = Some("user".to_string());
         turn.shell_environment_policy = ShellEnvironmentPolicy {
             use_profile: true,
             ..ShellEnvironmentPolicy::default()
@@ -1093,7 +1153,6 @@ mod tests {
         expected.model_reasoning_summary = turn.client.get_reasoning_summary();
         expected.developer_instructions = turn.developer_instructions.clone();
         expected.compact_prompt = turn.compact_prompt.clone();
-        expected.user_instructions = turn.user_instructions.clone();
         expected.shell_environment_policy = turn.shell_environment_policy.clone();
         expected.codex_linux_sandbox_exe = turn.codex_linux_sandbox_exe.clone();
         expected.cwd = turn.cwd.clone();
@@ -1107,4 +1166,31 @@ mod tests {
             .expect("sandbox policy set");
         assert_eq!(config, expected);
     }
+
+    #[tokio::test]
+    async fn build_agent_spawn_config_preserves_base_user_instructions() {
+        let (session, mut turn) = make_session_and_context().await;
+        let session_source = turn.client.get_session_source();
+        let mut base_config = (*turn.client.config()).clone();
+        base_config.user_instructions = Some("base-user".to_string());
+        turn.user_instructions = Some("resolved-user".to_string());
+        turn.client = ModelClient::new(
+            Arc::new(base_config.clone()),
+            Some(session.services.auth_manager.clone()),
+            turn.client.get_model_info(),
+            turn.client.get_otel_manager(),
+            turn.client.get_provider(),
+            turn.client.get_reasoning_effort(),
+            turn.client.get_reasoning_summary(),
+            session.conversation_id,
+            session_source,
+        );
+        let base_instructions = BaseInstructions {
+            text: "base".to_string(),
+        };
+
+        let config = build_agent_spawn_config(&base_instructions, &turn).expect("spawn config");
+
+        assert_eq!(config.user_instructions, base_config.user_instructions);
+    }
 }
diff --git a/codex-rs/core/templates/collab/experimental_prompt.md b/codex-rs/core/templates/collab/experimental_prompt.md
index 9763592e27..c6cd6f7ac4 100644
--- a/codex-rs/core/templates/collab/experimental_prompt.md
+++ b/codex-rs/core/templates/collab/experimental_prompt.md
@@ -13,6 +13,3 @@ This feature must be used wisely. For simple or straightforward tasks, you don't
 * When you're done with a sub-agent, don't forget to close it using `close_agent`.
 * Be careful on the `timeout_ms` parameter you choose for `wait`. It should be wisely scaled.
 * Sub-agents have access to the same set of tools as you do so you must tell them if they are allowed to spawn sub-agents themselves or not.
-
-## Global
-You're name is Batman
diff --git a/codex-rs/core/templates/collaboration_mode/plan.md b/codex-rs/core/templates/collaboration_mode/plan.md
index 7d78645de2..3d0447c729 100644
--- a/codex-rs/core/templates/collaboration_mode/plan.md
+++ b/codex-rs/core/templates/collaboration_mode/plan.md
@@ -1,283 +1,41 @@
-# Collaboration Style: Plan
+# Plan Mode (Conversational)
 
-You work in **two phases**:
+You work in 2 phases and you should *chat your way* to a great plan before finalizing it.
 
-- **PHASE 1 — Understand user intent**: Align on what the user is trying to accomplish and what “success” means. Focus on intent, scope, constraints, and preference tradeoffs.
-- **PHASE 2 — Technical spec & implementation plan**: Convert the intent into a decision‑complete technical spec and an implementation plan detailed enough that another agent could execute with minimal follow‑ups.
+PHASE 1 — Intent chat (what they actually want)
+- Keep asking until you can clearly state: goal + success criteria, audience, in/out of scope, constraints, current state, and the key preferences/tradeoffs.
+- Bias toward questions over guessing: if any high‑impact ambiguity remains, do NOT plan yet—ask.
+- Include a “Confirm my understanding” question in each round (so the user can correct you early).
 
----
+PHASE 2 — Implementation chat (what/how we’ll build)
+- Once intent is stable, keep asking until the spec is decision‑complete: approach, interfaces (APIs/schemas/I/O), data flow, edge cases/failure modes, testing + acceptance criteria, rollout/monitoring, and any migrations/compat constraints.
 
 ## Hard interaction rule (critical)
-
-Every assistant turn MUST be **exactly one** of:
-
-**A) A `request_user_input` tool call** (to gather requirements and iterate), OR  
-**B) The final plan output** (**plan‑only**, with a good title).
-
-Constraints:
-- **Do NOT ask questions in free text.** All questions MUST be asked via `request_user_input`.
-- **Do NOT mix** a `request_user_input` call with plan content in the same turn.
-- You may use internal tools to explore (repo search, file reading, environment inspection) **before** emitting either A or B, but the user‑visible output must still be exactly A or B.
-
----
-
-## Two types of uncertainty (treat differently)
-
-### Type 1 — Discoverable facts (repo/system truth)
-Examples: “Where is app‑server 2 defined?”, “Which config sets turn duration?”, “Which service emits this metric?”
-
-Rule: **Evidence-first exploration applies.** Don’t ask the user until you’ve searched.
-
-### Type 2 — Preferences & tradeoffs (product and engineering intent)
-
-Rule: **Ask early** These are often *not discoverable* and should not be silently assumed when multiple approaches are viable.
-
----
-
-## Evidence‑first exploration (precondition to asking discoverable questions)
-
-When a repo / codebase / workspace is available (or implied), you MUST attempt to resolve discoverable questions by **exploring first**.
-
-Before calling `request_user_input` for a discoverable fact, do a quick investigation pass:
-- Run at least **2 targeted searches** (exact match + a likely variant/synonym).
-- Check the most likely “source of truth” surfaces (service manifests, infra configs, env/config files, entrypoints, schemas/types/constants).
-
-You may ask the user ONLY if, after exploration:
-- There are **multiple plausible candidates** and picking wrong would materially change the implementation, OR
-- Nothing is found and you need a **missing identifier**, environment name, external dependency, or non-repo context, OR
-- The repo reveals ambiguity that must be resolved by product intent (not code).
-
-If you found a **single best match**, DO NOT ask the user — proceed and record it as an assumption in the final plan.
-
-If you must ask, incorporate what you already found:
-- Provide **options listing the candidates** you discovered (paths/service names), with a **recommended** option.
-- Do NOT ask the user to “point to the path” unless you have **zero candidates** after searching.
-
----
-
-## Preference capture (you SHOULD ask when it changes the plan)
-
-If there are **multiple reasonable implementation approaches** with meaningful tradeoffs, you SHOULD ask the user to choose their preference even if you could assume a default.
-
-Treat tradeoff choice as **high-impact** unless the user explicitly said:
-- “Use your best judgement,” or
-- “Pick whatever is simplest,” or
-- “I don’t care—ship fast.”
-
-When asking a preference question:
-- Provide **2–4 mutually exclusive options**.
-- Include a **recommended default** that matches the user’s apparent goals.
-- If the user doesn’t answer, proceed with the recommended option and record it as an assumption.
-
----
-
-## No‑trivia rule for questions (guardrail)
-
-You MUST NOT ask questions whose answers are likely to be found by:
-- repo text search,
-- reading config/infra manifests,
-- following imports/types/constants,
-unless you already attempted those and can summarize what you found.
-
-Every `request_user_input` question must:
-- materially change an implementation decision, OR
-- disambiguate between **concrete candidates** you already found, OR
-- capture a **preference/tradeoff** that is not discoverable from the repo.
-
----
-
-## PHASE 1 — Understand user intent
-
-### Purpose
-Identify what the user actually wants, what matters most, and what constraints + preferences shape the solution.
-
-### Phase 1 principles
-- State what you think the user cares about (speed vs quality, prototype vs production, etc.).
-- Think out loud briefly when it helps weigh tradeoffs.
-- Use reasonable suggestions with explicit assumptions; make it easy to accept/override.
-- Ask fewer, better questions. Ask only what materially changes the spec/plan OR captures a real tradeoff.
-- Think ahead: propose helpful suggestions the user may need (testing, debug mode, observability, migration path).
-
-### Phase 1 exit criteria (Intent gate)
-Before moving to Phase 2, ensure you have either a **user answer** OR an **explicit assumption** for:
-
-**Intent basics**
-- Primary goal + success criteria (how we know it worked)
-- Primary user / audience
-- In-scope and out-of-scope
-- Constraints (time, budget, platform, security/compliance)
-- Current context (what exists today: code/system/data)
-
-**Preference profile (don’t silently assume if unclear and high-impact)**
-- Risk posture: prototype vs production quality bar
-- Tradeoff priority: ship fast vs robust/maintainable
-- Compatibility expectations: backward compatibility / migrations / downtime tolerance (if relevant)
-
-Use `request_user_input` to deeply understand the user's intent after exploring your environment.
-
----
-
-## PHASE 2 — Technical spec & implementation plan
-
-### Purpose
-Turn the intent into a buildable, decision-complete technical spec.
-
-### Phase 2 exit criteria (Spec gate)
-Before finalizing the plan, ensure you’ve pinned down (answer or assumption):
-- Chosen approach + 1–2 alternatives with tradeoffs
-- Interfaces (APIs, schemas, inputs/outputs)
-- Data flow + key edge cases / failure modes
-- Testing + acceptance criteria
-- Rollout/monitoring expectations
-- Any key preference/tradeoff decisions (and rationale)
-
-If something is high-impact and unknown, ask via `request_user_input`. Otherwise assume defaults and proceed.
-
----
-
-## Using `request_user_input` in Plan Mode
-
-Use `request_user_input` when either:
-1) You are genuinely blocked on a decision that materially changes the plan and cannot be resolved via evidence-first exploration, OR  
-2) There is a meaningful **preference/tradeoff** the user should choose among.
-3) When an answer is skipped, assume the recommended path.
-
+Every assistant turn MUST be exactly one of:
+A) a `request_user_input` tool call (questions/options only), OR
+B) the final output: a titled, plan‑only document.
 Rules:
-- **Default to options** when there are ≤ 4 common outcomes; include a **recommended** option.
-- Use **free-form only** when truly unbounded (e.g., “paste schema”, “share constraints”, “provide examples”).
-- Every question must be tied to a decision that changes the spec (A→X, B→Y).
-- If you found candidates in the repo, options MUST reference them (paths/service names) so the user chooses among concrete items.
+- No questions in free text (only via `request_user_input`).
+- Never mix a `request_user_input` call with plan content.
+- Internal tool/repo exploration is allowed privately before A or B.
 
-Do **not** use `request_user_input` to ask:
-- “is my plan ready?” / “should I proceed?”
-- “where is X?” when repo search can answer it.
+## Ask a lot, but never ask trivia
+You SHOULD ask many questions, but each question must:
+- materially change the spec/plan, OR
+- confirm/lock an assumption, OR
+- choose between meaningful tradeoffs.
+Batch questions (e.g., 4–10) per `request_user_input` call to keep momentum.
 
-(If your environment enforces a limit, aim to resolve within ~5 `request_user_input` calls; if still blocked, ask only the most decision-critical remaining question(s) and proceed with explicit assumptions.)
+## Two kinds of unknowns (treat differently)
+1) Discoverable facts (repo/system truth): explore first.
+   - Before asking, run ≥2 targeted searches (exact + variant) and check likely sources of truth (configs/manifests/entrypoints/schemas/types/constants).
+   - Ask only if: multiple plausible candidates; nothing found but you need a missing identifier/context; or ambiguity is actually product intent.
+   - If asking, present concrete candidates (paths/service names) + recommend one.
 
-### Examples (technical, schema-populated)
+2) Preferences/tradeoffs (not discoverable): ask early.
+   - Provide 2–4 mutually exclusive options + a recommended default.
+   - If unanswered, proceed with the recommended option and record it as an assumption in the final plan.
 
-**1) Boolean (yes/no), no free-form**
-```json
-{
-  "questions": [
-    {
-      "id": "enable_migration",
-      "header": "Migrate",
-      "question": "Enable the database migration in this release?",
-      "options": [
-        { "label": "Yes (Recommended)", "description": "Ship the migration with this rollout." },
-        { "label": "No", "description": "Defer the migration to a later release." }
-      ]
-    }
-  ]
-}
-````
-
-**2) Preference/tradeoff question (recommended + options)**
-
-```json
-{
-  "questions": [
-    {
-      "id": "tradeoff_priority",
-      "header": "Tradeoff",
-      "question": "Which priority should guide the implementation?",
-      "options": [
-        { "label": "Ship fast (Recommended)", "description": "Minimal changes, pragmatic shortcuts, faster delivery." },
-        { "label": "Robust & maintainable", "description": "Cleaner abstractions, more refactor, better long-term stability." },
-        { "label": "Performance-first", "description": "Optimize latency/throughput even if complexity rises." },
-        { "label": "Other", "description": "Specify a different priority or constraint." }
-      ]
-    }
-  ]
-}
-```
-
-**3) Free-form only (no options)**
-
-```json
-{
-  "questions": [
-    {
-      "id": "acceptance_criteria",
-      "header": "Success",
-      "question": "What are the acceptance criteria or success metrics we should optimize for?"
-    }
-  ]
-}
-```
-
----
-
-## Iterating and final output
-
-Only AFTER you have all the information (or explicit assumptions for remaining low-impact unknowns), write the full plan.
-
-A good plan here is **decision-complete**: it contains the concrete choices, interfaces, acceptance criteria, and rollout details needed for another agent to execute with minimal back-and-forth.
-
-### Plan output (what to include)
-
-Your plan MUST include the sections below. Keep them concise but specific; include only what’s relevant to the task.
-
-1. **Title**
-
-* A clear, specific title describing what will be built/delivered.
-
-2. **Goal & Success Criteria**
-
-* What outcome we’re driving.
-* Concrete acceptance criteria (tests, metrics, or observable behavior). Prefer “done when …”.
-
-3. **Non-goals / Out of Scope**
-
-* Explicit boundaries to prevent scope creep.
-
-4. **Assumptions**
-
-* Any defaults you assumed due to missing info, labeled clearly.
-
-5. **Proposed Solution**
-
-* The chosen approach (with rationale).
-* 1–2 alternatives considered and why they were not chosen (brief tradeoffs).
-
-6. **System Design**
-
-* Architecture / components / data flow (only as deep as needed).
-* Key invariants, edge cases, and failure modes (and how they’re handled).
-
-7. **Interfaces & Data Contracts**
-
-* APIs, schemas, inputs/outputs, event formats, config flags, etc.
-* Validation rules and backward/forward compatibility expectations if applicable.
-
-8. **Execution Details**
-
-* Concrete implementation steps and ordering.
-* **Codebase specifics are conditional**: include file/module/function names, directories, migrations, and dependencies **only when relevant and known** (or when you can reasonably infer them).
-* If unknown, specify what to discover and how (e.g., “search for X symbol”, “locate Y service entrypoint”).
-
-9. **Testing & Quality**
-
-* Test strategy (unit/integration/e2e) proportional to risk.
-* How to verify locally and in staging; include any test data or harness needs.
-
-10. **Rollout, Observability, and Ops**
-
-* Release strategy (flags, gradual rollout, migration plan).
-* Monitoring/alerts/logging and dashboards to add or update.
-* Rollback strategy and operational playbook notes (brief).
-
-11. **Risks & Mitigations**
-
-* Top risks (technical, product, security, privacy, performance).
-* Specific mitigations and “watch-outs”.
-
-12. **Open Questions**
-
-* Only if something truly must be resolved later; include how to resolve and what decision it affects.
-
-### Plan output (strict)
-
-**The final output should contain the plan and plan only with a good title.**
-PLEASE DO NOT confirm the plan with the user before ending. The user will be responsible for telling us to update, iterate or execute the plan.
\ No newline at end of file
+## Finalization rule
+Only output the final plan when remaining unknowns are low‑impact and explicitly listed as assumptions.
+Final output must be plan‑only with a good title (no “should I proceed?”).
\ No newline at end of file
diff --git a/codex-rs/core/tests/suite/collaboration_instructions.rs b/codex-rs/core/tests/suite/collaboration_instructions.rs
index 3c6619fcea..f7183b817e 100644
--- a/codex-rs/core/tests/suite/collaboration_instructions.rs
+++ b/codex-rs/core/tests/suite/collaboration_instructions.rs
@@ -422,7 +422,11 @@ async fn resume_replays_collaboration_instructions() -> Result<()> {
 
     let mut builder = test_codex();
     let initial = builder.build(&server).await?;
-    let rollout_path = initial.session_configured.rollout_path.clone();
+    let rollout_path = initial
+        .session_configured
+        .rollout_path
+        .clone()
+        .expect("rollout path");
     let home = initial.home.clone();
 
     let collab_text = "resume instructions";
diff --git a/codex-rs/core/tests/suite/compact.rs b/codex-rs/core/tests/suite/compact.rs
index 230ab57840..1ecac3afe0 100644
--- a/codex-rs/core/tests/suite/compact.rs
+++ b/codex-rs/core/tests/suite/compact.rs
@@ -154,7 +154,7 @@ async fn summarize_context_three_requests_and_instructions() {
         session_configured,
         ..
     } = thread_manager.start_thread(config).await.unwrap();
-    let rollout_path = session_configured.rollout_path;
+    let rollout_path = session_configured.rollout_path.expect("rollout path");
 
     // 1) Normal user input – should hit server once.
     codex
@@ -1237,7 +1237,11 @@ async fn auto_compact_runs_after_resume_when_token_usage_is_over_limit() {
     });
     let initial = builder.build(&server).await.unwrap();
     let home = initial.home.clone();
-    let rollout_path = initial.session_configured.rollout_path.clone();
+    let rollout_path = initial
+        .session_configured
+        .rollout_path
+        .clone()
+        .expect("rollout path");
 
     // A single over-limit completion should not auto-compact until the next user message.
     mount_sse_once(
@@ -1429,7 +1433,7 @@ async fn auto_compact_persists_rollout_entries() {
     codex.submit(Op::Shutdown).await.unwrap();
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::ShutdownComplete)).await;
 
-    let rollout_path = session_configured.rollout_path;
+    let rollout_path = session_configured.rollout_path.expect("rollout path");
     let text = std::fs::read_to_string(&rollout_path).unwrap_or_else(|e| {
         panic!(
             "failed to read rollout file {}: {e}",
diff --git a/codex-rs/core/tests/suite/compact_remote.rs b/codex-rs/core/tests/suite/compact_remote.rs
index a2cf73e110..2fc5ba53c2 100644
--- a/codex-rs/core/tests/suite/compact_remote.rs
+++ b/codex-rs/core/tests/suite/compact_remote.rs
@@ -230,7 +230,12 @@ async fn remote_compact_persists_replacement_history_in_rollout() -> Result<()>
     )
     .await?;
     let codex = harness.test().codex.clone();
-    let rollout_path = harness.test().session_configured.rollout_path.clone();
+    let rollout_path = harness
+        .test()
+        .session_configured
+        .rollout_path
+        .clone()
+        .expect("rollout path");
 
     let responses_mock = responses::mount_sse_once(
         harness.server(),
diff --git a/codex-rs/core/tests/suite/compact_resume_fork.rs b/codex-rs/core/tests/suite/compact_resume_fork.rs
index b7ce49abbe..f6047ac733 100644
--- a/codex-rs/core/tests/suite/compact_resume_fork.rs
+++ b/codex-rs/core/tests/suite/compact_resume_fork.rs
@@ -1013,7 +1013,7 @@ async fn compact_conversation(conversation: &Arc<CodexThread>) {
 }
 
 async fn fetch_conversation_path(conversation: &Arc<CodexThread>) -> std::path::PathBuf {
-    conversation.rollout_path()
+    conversation.rollout_path().expect("rollout path")
 }
 
 async fn resume_conversation(
diff --git a/codex-rs/core/tests/suite/fork_thread.rs b/codex-rs/core/tests/suite/fork_thread.rs
index 2a9f604c3d..8698991846 100644
--- a/codex-rs/core/tests/suite/fork_thread.rs
+++ b/codex-rs/core/tests/suite/fork_thread.rs
@@ -80,7 +80,7 @@ async fn fork_thread_twice_drops_to_first_message() {
     }
 
     // Request history from the base conversation to obtain rollout path.
-    let base_path = codex.rollout_path();
+    let base_path = codex.rollout_path().expect("rollout path");
 
     // GetHistory flushes before returning the path; no wait needed.
 
@@ -135,7 +135,7 @@ async fn fork_thread_twice_drops_to_first_message() {
         .await
         .expect("fork 1");
 
-    let fork1_path = codex_fork1.rollout_path();
+    let fork1_path = codex_fork1.rollout_path().expect("rollout path");
 
     // GetHistory on fork1 flushed; the file is ready.
     let fork1_items = read_items(&fork1_path);
@@ -154,7 +154,7 @@ async fn fork_thread_twice_drops_to_first_message() {
         .await
         .expect("fork 2");
 
-    let fork2_path = codex_fork2.rollout_path();
+    let fork2_path = codex_fork2.rollout_path().expect("rollout path");
     // GetHistory on fork2 flushed; the file is ready.
     let fork1_items = read_items(&fork1_path);
     let fork1_user_inputs = find_user_input_positions(&fork1_items);
diff --git a/codex-rs/core/tests/suite/image_rollout.rs b/codex-rs/core/tests/suite/image_rollout.rs
index b6dad6a227..6aebe6630d 100644
--- a/codex-rs/core/tests/suite/image_rollout.rs
+++ b/codex-rs/core/tests/suite/image_rollout.rs
@@ -136,7 +136,7 @@ async fn copy_paste_local_image_persists_rollout_request_shape() -> anyhow::Resu
     codex.submit(Op::Shutdown).await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::ShutdownComplete)).await;
 
-    let rollout_path = codex.rollout_path();
+    let rollout_path = codex.rollout_path().expect("rollout path");
     let rollout_text = read_rollout_text(&rollout_path).await?;
     let actual = find_user_message_with_image(&rollout_text)
         .expect("expected user message with input image in rollout");
@@ -217,7 +217,7 @@ async fn drag_drop_image_persists_rollout_request_shape() -> anyhow::Result<()>
     codex.submit(Op::Shutdown).await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::ShutdownComplete)).await;
 
-    let rollout_path = codex.rollout_path();
+    let rollout_path = codex.rollout_path().expect("rollout path");
     let rollout_text = read_rollout_text(&rollout_path).await?;
     let actual = find_user_message_with_image(&rollout_text)
         .expect("expected user message with input image in rollout");
diff --git a/codex-rs/core/tests/suite/override_updates.rs b/codex-rs/core/tests/suite/override_updates.rs
index 3ceb847daa..d995446864 100644
--- a/codex-rs/core/tests/suite/override_updates.rs
+++ b/codex-rs/core/tests/suite/override_updates.rs
@@ -129,7 +129,7 @@ async fn override_turn_context_records_permissions_update() -> Result<()> {
     test.codex.submit(Op::Shutdown).await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::ShutdownComplete)).await;
 
-    let rollout_path = test.codex.rollout_path();
+    let rollout_path = test.codex.rollout_path().expect("rollout path");
     let rollout_text = read_rollout_text(&rollout_path).await?;
     let developer_texts = rollout_developer_texts(&rollout_text);
     let approval_texts: Vec<&String> = developer_texts
@@ -172,7 +172,7 @@ async fn override_turn_context_records_environment_update() -> Result<()> {
     test.codex.submit(Op::Shutdown).await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::ShutdownComplete)).await;
 
-    let rollout_path = test.codex.rollout_path();
+    let rollout_path = test.codex.rollout_path().expect("rollout path");
     let rollout_text = read_rollout_text(&rollout_path).await?;
     let env_texts = rollout_environment_texts(&rollout_text);
     let new_cwd_text = new_cwd.path().display().to_string();
@@ -209,7 +209,7 @@ async fn override_turn_context_records_collaboration_update() -> Result<()> {
     test.codex.submit(Op::Shutdown).await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::ShutdownComplete)).await;
 
-    let rollout_path = test.codex.rollout_path();
+    let rollout_path = test.codex.rollout_path().expect("rollout path");
     let rollout_text = read_rollout_text(&rollout_path).await?;
     let developer_texts = rollout_developer_texts(&rollout_text);
     let collab_text = collab_xml(collab_text);
diff --git a/codex-rs/core/tests/suite/permissions_messages.rs b/codex-rs/core/tests/suite/permissions_messages.rs
index 9a32a7d9f9..f3d9e8d47b 100644
--- a/codex-rs/core/tests/suite/permissions_messages.rs
+++ b/codex-rs/core/tests/suite/permissions_messages.rs
@@ -202,7 +202,11 @@ async fn resume_replays_permissions_messages() -> Result<()> {
         config.approval_policy = Constrained::allow_any(AskForApproval::OnRequest);
     });
     let initial = builder.build(&server).await?;
-    let rollout_path = initial.session_configured.rollout_path.clone();
+    let rollout_path = initial
+        .session_configured
+        .rollout_path
+        .clone()
+        .expect("rollout path");
     let home = initial.home.clone();
 
     initial
@@ -280,7 +284,11 @@ async fn resume_and_fork_append_permissions_messages() -> Result<()> {
         config.approval_policy = Constrained::allow_any(AskForApproval::OnRequest);
     });
     let initial = builder.build(&server).await?;
-    let rollout_path = initial.session_configured.rollout_path.clone();
+    let rollout_path = initial
+        .session_configured
+        .rollout_path
+        .clone()
+        .expect("rollout path");
     let home = initial.home.clone();
 
     initial
diff --git a/codex-rs/core/tests/suite/resume.rs b/codex-rs/core/tests/suite/resume.rs
index d0718a334d..a7be42f430 100644
--- a/codex-rs/core/tests/suite/resume.rs
+++ b/codex-rs/core/tests/suite/resume.rs
@@ -26,7 +26,11 @@ async fn resume_includes_initial_messages_from_rollout_events() -> Result<()> {
     let initial = builder.build(&server).await?;
     let codex = Arc::clone(&initial.codex);
     let home = initial.home.clone();
-    let rollout_path = initial.session_configured.rollout_path.clone();
+    let rollout_path = initial
+        .session_configured
+        .rollout_path
+        .clone()
+        .expect("rollout path");
 
     let initial_sse = sse(vec![
         ev_response_created("resp-initial"),
@@ -85,7 +89,11 @@ async fn resume_includes_initial_messages_from_reasoning_events() -> Result<()>
     let initial = builder.build(&server).await?;
     let codex = Arc::clone(&initial.codex);
     let home = initial.home.clone();
-    let rollout_path = initial.session_configured.rollout_path.clone();
+    let rollout_path = initial
+        .session_configured
+        .rollout_path
+        .clone()
+        .expect("rollout path");
 
     let initial_sse = sse(vec![
         ev_response_created("resp-initial"),
@@ -143,7 +151,11 @@ async fn resume_switches_models_preserves_base_instructions() -> Result<()> {
     let initial = builder.build(&server).await?;
     let codex = Arc::clone(&initial.codex);
     let home = initial.home.clone();
-    let rollout_path = initial.session_configured.rollout_path.clone();
+    let rollout_path = initial
+        .session_configured
+        .rollout_path
+        .clone()
+        .expect("rollout path");
 
     let initial_sse = sse(vec![
         ev_response_created("resp-initial"),
diff --git a/codex-rs/core/tests/suite/review.rs b/codex-rs/core/tests/suite/review.rs
index 3a66e320b6..df678f9e9d 100644
--- a/codex-rs/core/tests/suite/review.rs
+++ b/codex-rs/core/tests/suite/review.rs
@@ -120,7 +120,7 @@ async fn review_op_emits_lifecycle_and_review_output() {
 
     // Also verify that a user message with the header and a formatted finding
     // was recorded back in the parent session's rollout.
-    let path = codex.rollout_path();
+    let path = codex.rollout_path().expect("rollout path");
     let text = std::fs::read_to_string(&path).expect("read rollout file");
 
     let mut saw_header = false;
@@ -627,7 +627,7 @@ async fn review_input_isolated_from_parent_history() {
     assert_eq!(instructions, REVIEW_PROMPT);
 
     // Also verify that a user interruption note was recorded in the rollout.
-    let path = codex.rollout_path();
+    let path = codex.rollout_path().expect("rollout path");
     let text = std::fs::read_to_string(&path).expect("read rollout file");
     let mut saw_interruption_message = false;
     for line in text.lines() {
diff --git a/codex-rs/docs/codex_mcp_interface.md b/codex-rs/docs/codex_mcp_interface.md
index 19e1d91581..1aa5aa12ae 100644
--- a/codex-rs/docs/codex_mcp_interface.md
+++ b/codex-rs/docs/codex_mcp_interface.md
@@ -101,7 +101,8 @@ Each response yields:
 
 Fetch the built-in collaboration mode presets with `collaborationMode/list`. This endpoint does not accept pagination and returns the full list in one response:
 
-- `data` – ordered list of collaboration mode presets
+- `data` – ordered list of collaboration mode masks (partial settings to apply on top of the base mode)
+  - For tri-state fields like `reasoning_effort` and `developer_instructions`, omit the field to keep the current value, set it to `null` to clear it, or set a concrete value to update it.
 
 ## Event stream
 
diff --git a/codex-rs/exec/src/lib.rs b/codex-rs/exec/src/lib.rs
index 7679891287..441041aa68 100644
--- a/codex-rs/exec/src/lib.rs
+++ b/codex-rs/exec/src/lib.rs
@@ -229,6 +229,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         include_apply_patch_tool: None,
         show_raw_agent_reasoning: oss.then_some(true),
         tools_web_search_request: None,
+        ephemeral: None,
         additional_writable_roots: add_dir,
     };
 
diff --git a/codex-rs/exec/tests/event_processor_with_json_output.rs b/codex-rs/exec/tests/event_processor_with_json_output.rs
index e0b2509667..43de1f95f8 100644
--- a/codex-rs/exec/tests/event_processor_with_json_output.rs
+++ b/codex-rs/exec/tests/event_processor_with_json_output.rs
@@ -85,7 +85,7 @@ fn session_configured_produces_thread_started_event() {
             history_log_id: 0,
             history_entry_count: 0,
             initial_messages: None,
-            rollout_path,
+            rollout_path: Some(rollout_path),
         }),
     );
     let out = ep.collect_thread_events(&ev);
diff --git a/codex-rs/mcp-server/src/outgoing_message.rs b/codex-rs/mcp-server/src/outgoing_message.rs
index b7c66592ff..2069db69d0 100644
--- a/codex-rs/mcp-server/src/outgoing_message.rs
+++ b/codex-rs/mcp-server/src/outgoing_message.rs
@@ -267,7 +267,7 @@ mod tests {
                 history_log_id: 1,
                 history_entry_count: 1000,
                 initial_messages: None,
-                rollout_path: rollout_file.path().to_path_buf(),
+                rollout_path: Some(rollout_file.path().to_path_buf()),
             }),
         };
 
@@ -307,7 +307,7 @@ mod tests {
             history_log_id: 1,
             history_entry_count: 1000,
             initial_messages: None,
-            rollout_path: rollout_file.path().to_path_buf(),
+            rollout_path: Some(rollout_file.path().to_path_buf()),
         };
         let event = Event {
             id: "1".to_string(),
@@ -371,7 +371,7 @@ mod tests {
             history_log_id: 1,
             history_entry_count: 1000,
             initial_messages: None,
-            rollout_path: rollout_file.path().to_path_buf(),
+            rollout_path: Some(rollout_file.path().to_path_buf()),
         };
         let event = Event {
             id: "1".to_string(),
diff --git a/codex-rs/protocol/src/config_types.rs b/codex-rs/protocol/src/config_types.rs
index 444901bf75..ae956797ea 100644
--- a/codex-rs/protocol/src/config_types.rs
+++ b/codex-rs/protocol/src/config_types.rs
@@ -188,21 +188,21 @@ impl CollaborationMode {
     ///
     /// - `model`: `Some(s)` to update the model, `None` to keep the current model
     /// - `effort`: `Some(Some(e))` to set effort to `e`, `Some(None)` to clear effort, `None` to keep current effort
-    /// - `developer_instructions`: `Some(s)` to update developer instructions, `None` to keep current
+    /// - `developer_instructions`: `Some(Some(s))` to set instructions, `Some(None)` to clear them, `None` to keep current
     ///
     /// Returns a new `CollaborationMode` with updated values, preserving the mode.
     pub fn with_updates(
         &self,
         model: Option<String>,
         effort: Option<Option<ReasoningEffort>>,
-        developer_instructions: Option<String>,
+        developer_instructions: Option<Option<String>>,
     ) -> Self {
         let settings = self.settings_ref();
         let updated_settings = Settings {
             model: model.unwrap_or_else(|| settings.model.clone()),
             reasoning_effort: effort.unwrap_or(settings.reasoning_effort),
             developer_instructions: developer_instructions
-                .or_else(|| settings.developer_instructions.clone()),
+                .unwrap_or_else(|| settings.developer_instructions.clone()),
         };
 
         CollaborationMode {
@@ -210,6 +210,26 @@ impl CollaborationMode {
             settings: updated_settings,
         }
     }
+
+    /// Applies a mask to this collaboration mode, returning a new collaboration mode
+    /// with the mask values applied. Fields in the mask that are `Some` will override
+    /// the corresponding fields, while `None` values will preserve the original values.
+    ///
+    /// The `name` field in the mask is ignored as it's metadata for the mask itself.
+    pub fn apply_mask(&self, mask: &CollaborationModeMask) -> Self {
+        let settings = self.settings_ref();
+        CollaborationMode {
+            mode: mask.mode.unwrap_or(self.mode),
+            settings: Settings {
+                model: mask.model.clone().unwrap_or_else(|| settings.model.clone()),
+                reasoning_effort: mask.reasoning_effort.unwrap_or(settings.reasoning_effort),
+                developer_instructions: mask
+                    .developer_instructions
+                    .clone()
+                    .unwrap_or_else(|| settings.developer_instructions.clone()),
+            },
+        }
+    }
 }
 
 /// Settings for a collaboration mode.
@@ -219,3 +239,49 @@ pub struct Settings {
     pub reasoning_effort: Option<ReasoningEffort>,
     pub developer_instructions: Option<String>,
 }
+
+/// A mask for collaboration mode settings, allowing partial updates.
+/// All fields except `name` are optional, enabling selective updates.
+#[derive(Clone, PartialEq, Eq, Hash, Debug, Serialize, Deserialize, JsonSchema, TS)]
+pub struct CollaborationModeMask {
+    pub name: String,
+    pub mode: Option<ModeKind>,
+    pub model: Option<String>,
+    pub reasoning_effort: Option<Option<ReasoningEffort>>,
+    pub developer_instructions: Option<Option<String>>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    #[test]
+    fn apply_mask_can_clear_optional_fields() {
+        let mode = CollaborationMode {
+            mode: ModeKind::Code,
+            settings: Settings {
+                model: "gpt-5.2-codex".to_string(),
+                reasoning_effort: Some(ReasoningEffort::High),
+                developer_instructions: Some("stay focused".to_string()),
+            },
+        };
+        let mask = CollaborationModeMask {
+            name: "Clear".to_string(),
+            mode: None,
+            model: None,
+            reasoning_effort: Some(None),
+            developer_instructions: Some(None),
+        };
+
+        let expected = CollaborationMode {
+            mode: ModeKind::Code,
+            settings: Settings {
+                model: "gpt-5.2-codex".to_string(),
+                reasoning_effort: None,
+                developer_instructions: None,
+            },
+        };
+        assert_eq!(expected, mode.apply_mask(&mask));
+    }
+}
diff --git a/codex-rs/protocol/src/protocol.rs b/codex-rs/protocol/src/protocol.rs
index 1f35fed60e..7bf3c90eab 100644
--- a/codex-rs/protocol/src/protocol.rs
+++ b/codex-rs/protocol/src/protocol.rs
@@ -1518,6 +1518,10 @@ pub enum SessionSource {
 pub enum SubAgentSource {
     Review,
     Compact,
+    ThreadSpawn {
+        parent_thread_id: ThreadId,
+        depth: i32,
+    },
     Other(String),
 }
 
@@ -1539,6 +1543,12 @@ impl fmt::Display for SubAgentSource {
         match self {
             SubAgentSource::Review => f.write_str("review"),
             SubAgentSource::Compact => f.write_str("compact"),
+            SubAgentSource::ThreadSpawn {
+                parent_thread_id,
+                depth,
+            } => {
+                write!(f, "thread_spawn_{parent_thread_id}_d{depth}")
+            }
             SubAgentSource::Other(other) => f.write_str(other),
         }
     }
@@ -2139,7 +2149,9 @@ pub struct SessionConfiguredEvent {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub initial_messages: Option<Vec<EventMsg>>,
 
-    pub rollout_path: PathBuf,
+    /// Path in which the rollout is stored. Can be `None` for ephemeral threads
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub rollout_path: Option<PathBuf>,
 }
 
 /// User's decision in response to an ExecApprovalRequest.
@@ -2491,7 +2503,7 @@ mod tests {
                 history_log_id: 0,
                 history_entry_count: 0,
                 initial_messages: None,
-                rollout_path: rollout_file.path().to_path_buf(),
+                rollout_path: Some(rollout_file.path().to_path_buf()),
             }),
         };
 
diff --git a/codex-rs/tui/src/app.rs b/codex-rs/tui/src/app.rs
index 7063f8f5ba..1d53f5d70d 100644
--- a/codex-rs/tui/src/app.rs
+++ b/codex-rs/tui/src/app.rs
@@ -12,6 +12,7 @@ use crate::bottom_pane::SelectionViewParams;
 use crate::bottom_pane::popup_consts::standard_popup_hint_line;
 use crate::chatwidget::ChatWidget;
 use crate::chatwidget::ExternalEditorState;
+use crate::cwd_prompt::CwdPromptAction;
 use crate::diff_render::DiffSummary;
 use crate::exec_command::strip_bash_lc_and_escape;
 use crate::external_editor;
@@ -36,6 +37,8 @@ use codex_core::AuthManager;
 use codex_core::CodexAuth;
 use codex_core::ThreadManager;
 use codex_core::config::Config;
+use codex_core::config::ConfigBuilder;
+use codex_core::config::ConfigOverrides;
 use codex_core::config::edit::ConfigEdit;
 use codex_core::config::edit::ConfigEditsBuilder;
 use codex_core::config_loader::ConfigLayerStackOrdering;
@@ -44,12 +47,14 @@ use codex_core::features::Feature;
 use codex_core::models_manager::manager::RefreshStrategy;
 use codex_core::models_manager::model_presets::HIDE_GPT_5_1_CODEX_MAX_MIGRATION_PROMPT_CONFIG;
 use codex_core::models_manager::model_presets::HIDE_GPT5_1_MIGRATION_PROMPT_CONFIG;
+use codex_core::protocol::AskForApproval;
 use codex_core::protocol::DeprecationNoticeEvent;
 use codex_core::protocol::Event;
 use codex_core::protocol::EventMsg;
 use codex_core::protocol::FinalOutput;
 use codex_core::protocol::ListSkillsResponseEvent;
 use codex_core::protocol::Op;
+use codex_core::protocol::SandboxPolicy;
 use codex_core::protocol::SessionSource;
 use codex_core::protocol::SkillErrorInfo;
 use codex_core::protocol::TokenUsage;
@@ -60,6 +65,7 @@ use codex_protocol::openai_models::ModelPreset;
 use codex_protocol::openai_models::ModelUpgrade;
 use codex_protocol::openai_models::ReasoningEffort as ReasoningEffortConfig;
 use codex_protocol::protocol::SessionConfiguredEvent;
+use codex_utils_absolute_path::AbsolutePathBuf;
 use color_eyre::eyre::Result;
 use color_eyre::eyre::WrapErr;
 use crossterm::event::KeyCode;
@@ -87,6 +93,7 @@ use tokio::sync::broadcast;
 use tokio::sync::mpsc;
 use tokio::sync::mpsc::error::TryRecvError;
 use tokio::sync::mpsc::unbounded_channel;
+use toml::Value as TomlValue;
 
 const EXTERNAL_EDITOR_HINT: &str = "Save and close external editor to continue.";
 const THREAD_EVENT_CHANNEL_CAPACITY: usize = 1024;
@@ -498,6 +505,10 @@ pub(crate) struct App {
     /// Config is stored here so we can recreate ChatWidgets as needed.
     pub(crate) config: Config,
     pub(crate) active_profile: Option<String>,
+    cli_kv_overrides: Vec<(String, TomlValue)>,
+    harness_overrides: ConfigOverrides,
+    runtime_approval_policy_override: Option<AskForApproval>,
+    runtime_sandbox_policy_override: Option<SandboxPolicy>,
 
     pub(crate) file_search: FileSearchManager,
 
@@ -545,6 +556,23 @@ struct WindowsSandboxState {
     skip_world_writable_scan_once: bool,
 }
 
+fn normalize_harness_overrides_for_cwd(
+    mut overrides: ConfigOverrides,
+    base_cwd: &Path,
+) -> Result<ConfigOverrides> {
+    if overrides.additional_writable_roots.is_empty() {
+        return Ok(overrides);
+    }
+
+    let mut normalized = Vec::with_capacity(overrides.additional_writable_roots.len());
+    for root in overrides.additional_writable_roots.drain(..) {
+        let absolute = AbsolutePathBuf::resolve_path_against_base(root, base_cwd)?;
+        normalized.push(absolute.into_path_buf());
+    }
+    overrides.additional_writable_roots = normalized;
+    Ok(overrides)
+}
+
 impl App {
     pub fn chatwidget_init_for_forked_or_resumed_thread(
         &self,
@@ -567,6 +595,38 @@ impl App {
         }
     }
 
+    async fn rebuild_config_for_cwd(&self, cwd: PathBuf) -> Result<Config> {
+        let mut overrides = self.harness_overrides.clone();
+        overrides.cwd = Some(cwd.clone());
+        let cwd_display = cwd.display().to_string();
+        ConfigBuilder::default()
+            .codex_home(self.config.codex_home.clone())
+            .cli_overrides(self.cli_kv_overrides.clone())
+            .harness_overrides(overrides)
+            .build()
+            .await
+            .wrap_err_with(|| format!("Failed to rebuild config for cwd {cwd_display}"))
+    }
+
+    fn apply_runtime_policy_overrides(&mut self, config: &mut Config) {
+        if let Some(policy) = self.runtime_approval_policy_override.as_ref()
+            && let Err(err) = config.approval_policy.set(*policy)
+        {
+            tracing::warn!(%err, "failed to carry forward approval policy override");
+            self.chat_widget.add_error_message(format!(
+                "Failed to carry forward approval policy override: {err}"
+            ));
+        }
+        if let Some(policy) = self.runtime_sandbox_policy_override.as_ref()
+            && let Err(err) = config.sandbox_policy.set(policy.clone())
+        {
+            tracing::warn!(%err, "failed to carry forward sandbox policy override");
+            self.chat_widget.add_error_message(format!(
+                "Failed to carry forward sandbox policy override: {err}"
+            ));
+        }
+    }
+
     async fn shutdown_current_thread(&mut self) {
         if let Some(thread_id) = self.chat_widget.thread_id() {
             // Clear any in-flight rollback guard when switching threads.
@@ -824,6 +884,8 @@ impl App {
         tui: &mut tui::Tui,
         auth_manager: Arc<AuthManager>,
         mut config: Config,
+        cli_kv_overrides: Vec<(String, TomlValue)>,
+        harness_overrides: ConfigOverrides,
         active_profile: Option<String>,
         initial_prompt: Option<String>,
         initial_images: Vec<PathBuf>,
@@ -838,6 +900,8 @@ impl App {
         emit_deprecation_notice(&app_event_tx, ollama_chat_support_notice);
         emit_project_config_warnings(&app_event_tx, &config);
 
+        let harness_overrides =
+            normalize_harness_overrides_for_cwd(harness_overrides, &config.cwd)?;
         let thread_manager = Arc::new(ThreadManager::new(
             config.codex_home.clone(),
             auth_manager.clone(),
@@ -979,6 +1043,10 @@ impl App {
             auth_manager: auth_manager.clone(),
             config,
             active_profile,
+            cli_kv_overrides,
+            harness_overrides,
+            runtime_approval_policy_override: None,
+            runtime_sandbox_policy_override: None,
             file_search,
             enhanced_keys_supported,
             transcript_cells: Vec::new(),
@@ -1203,6 +1271,34 @@ impl App {
                 .await?
                 {
                     SessionSelection::Resume(path) => {
+                        let current_cwd = self.config.cwd.clone();
+                        let resume_cwd = match crate::resolve_cwd_for_resume_or_fork(
+                            tui,
+                            &current_cwd,
+                            &path,
+                            CwdPromptAction::Resume,
+                            true,
+                        )
+                        .await?
+                        {
+                            Some(cwd) => cwd,
+                            None => current_cwd.clone(),
+                        };
+                        let mut resume_config = if crate::cwds_differ(&current_cwd, &resume_cwd) {
+                            match self.rebuild_config_for_cwd(resume_cwd).await {
+                                Ok(cfg) => cfg,
+                                Err(err) => {
+                                    self.chat_widget.add_error_message(format!(
+                                        "Failed to rebuild configuration for resume: {err}"
+                                    ));
+                                    return Ok(AppRunControl::Continue);
+                                }
+                            }
+                        } else {
+                            // No rebuild needed: current_cwd comes from self.config.cwd.
+                            self.config.clone()
+                        };
+                        self.apply_runtime_policy_overrides(&mut resume_config);
                         let summary = session_summary(
                             self.chat_widget.token_usage(),
                             self.chat_widget.thread_id(),
@@ -1210,7 +1306,7 @@ impl App {
                         match self
                             .server
                             .resume_thread_from_rollout(
-                                self.config.clone(),
+                                resume_config.clone(),
                                 path.clone(),
                                 self.auth_manager.clone(),
                             )
@@ -1218,6 +1314,11 @@ impl App {
                         {
                             Ok(resumed) => {
                                 self.shutdown_current_thread().await;
+                                self.config = resume_config;
+                                self.file_search = FileSearchManager::new(
+                                    self.config.cwd.clone(),
+                                    self.app_event_tx.clone(),
+                                );
                                 let init = self.chatwidget_init_for_forked_or_resumed_thread(
                                     tui,
                                     self.config.clone(),
@@ -1401,10 +1502,8 @@ impl App {
             AppEvent::UpdateModel(model) => {
                 self.chat_widget.set_model(&model);
             }
-            AppEvent::UpdateCollaborationMode(mode) => {
-                let model = mode.model().to_string();
-                self.chat_widget.set_collaboration_mode(mode);
-                self.chat_widget.set_model(&model);
+            AppEvent::UpdateCollaborationMode(mask) => {
+                self.chat_widget.set_collaboration_mask(mask);
             }
             AppEvent::OpenReasoningPopup { model } => {
                 self.chat_widget.open_reasoning_popup(model);
@@ -1660,6 +1759,13 @@ impl App {
                 }
             }
             AppEvent::UpdateAskForApprovalPolicy(policy) => {
+                self.runtime_approval_policy_override = Some(policy);
+                if let Err(err) = self.config.approval_policy.set(policy) {
+                    tracing::warn!(%err, "failed to set approval policy on app config");
+                    self.chat_widget
+                        .add_error_message(format!("Failed to set approval policy: {err}"));
+                    return Ok(AppRunControl::Continue);
+                }
                 self.chat_widget.set_approval_policy(policy);
             }
             AppEvent::UpdateSandboxPolicy(policy) => {
@@ -1688,6 +1794,8 @@ impl App {
                         .add_error_message(format!("Failed to set sandbox policy: {err}"));
                     return Ok(AppRunControl::Continue);
                 }
+                self.runtime_sandbox_policy_override =
+                    Some(self.config.sandbox_policy.get().clone());
 
                 // If sandbox policy becomes workspace-write or read-only, run the Windows world-writable scan.
                 #[cfg(target_os = "windows")]
@@ -2014,14 +2122,14 @@ impl App {
                     history_log_id: 0,
                     history_entry_count: 0,
                     initial_messages: None,
-                    rollout_path: PathBuf::new(),
+                    rollout_path: Some(PathBuf::new()),
                 });
         session_configured.session_id = thread_id;
         session_configured.forked_from_id = None;
         session_configured.history_log_id = 0;
         session_configured.history_entry_count = 0;
         session_configured.initial_messages = None;
-        session_configured.rollout_path = PathBuf::new();
+        session_configured.rollout_path = Some(PathBuf::new());
         session_configured
     }
 
@@ -2236,6 +2344,7 @@ mod tests {
     use codex_core::CodexAuth;
     use codex_core::ThreadManager;
     use codex_core::config::ConfigBuilder;
+    use codex_core::config::ConfigOverrides;
     use codex_core::models_manager::manager::ModelsManager;
     use codex_core::protocol::AskForApproval;
     use codex_core::protocol::Event;
@@ -2254,6 +2363,25 @@ mod tests {
     use std::sync::atomic::AtomicBool;
     use tempfile::tempdir;
 
+    #[test]
+    fn normalize_harness_overrides_resolves_relative_add_dirs() -> Result<()> {
+        let temp_dir = tempdir()?;
+        let base_cwd = temp_dir.path().join("base");
+        std::fs::create_dir_all(&base_cwd)?;
+
+        let overrides = ConfigOverrides {
+            additional_writable_roots: vec![PathBuf::from("rel")],
+            ..Default::default()
+        };
+        let normalized = normalize_harness_overrides_for_cwd(overrides, &base_cwd)?;
+
+        assert_eq!(
+            normalized.additional_writable_roots,
+            vec![base_cwd.join("rel")]
+        );
+        Ok(())
+    }
+
     async fn make_test_app() -> App {
         let (chat_widget, app_event_tx, _rx, _op_rx) = make_chatwidget_manual_with_sender().await;
         let config = chat_widget.config_ref().clone();
@@ -2275,6 +2403,10 @@ mod tests {
             auth_manager,
             config,
             active_profile: None,
+            cli_kv_overrides: Vec::new(),
+            harness_overrides: ConfigOverrides::default(),
+            runtime_approval_policy_override: None,
+            runtime_sandbox_policy_override: None,
             file_search,
             transcript_cells: Vec::new(),
             overlay: None,
@@ -2323,6 +2455,10 @@ mod tests {
                 auth_manager,
                 config,
                 active_profile: None,
+                cli_kv_overrides: Vec::new(),
+                harness_overrides: ConfigOverrides::default(),
+                runtime_approval_policy_override: None,
+                runtime_sandbox_policy_override: None,
                 file_search,
                 transcript_cells: Vec::new(),
                 overlay: None,
@@ -2576,7 +2712,7 @@ mod tests {
                 history_log_id: 0,
                 history_entry_count: 0,
                 initial_messages: None,
-                rollout_path: PathBuf::new(),
+                rollout_path: Some(PathBuf::new()),
             };
             Arc::new(new_session_info(
                 app.chat_widget.config_ref(),
@@ -2628,7 +2764,7 @@ mod tests {
                 history_log_id: 0,
                 history_entry_count: 0,
                 initial_messages: None,
-                rollout_path: PathBuf::new(),
+                rollout_path: Some(PathBuf::new()),
             }),
         });
 
@@ -2673,7 +2809,7 @@ mod tests {
             history_log_id: 0,
             history_entry_count: 0,
             initial_messages: None,
-            rollout_path: PathBuf::new(),
+            rollout_path: Some(PathBuf::new()),
         };
 
         app.chat_widget.handle_codex_event(Event {
diff --git a/codex-rs/tui/src/app_event.rs b/codex-rs/tui/src/app_event.rs
index f6ed6e8abc..9a2d979f1c 100644
--- a/codex-rs/tui/src/app_event.rs
+++ b/codex-rs/tui/src/app_event.rs
@@ -23,7 +23,7 @@ use crate::history_cell::HistoryCell;
 use codex_core::features::Feature;
 use codex_core::protocol::AskForApproval;
 use codex_core::protocol::SandboxPolicy;
-use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::openai_models::ReasoningEffort;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -103,8 +103,8 @@ pub(crate) enum AppEvent {
     /// Update the current model slug in the running app and widget.
     UpdateModel(String),
 
-    /// Update the current collaboration mode in the running app and widget.
-    UpdateCollaborationMode(CollaborationMode),
+    /// Update the active collaboration mask in the running app and widget.
+    UpdateCollaborationMode(CollaborationModeMask),
 
     /// Persist the selected model and reasoning effort to the appropriate config.
     PersistModelSelection {
@@ -240,10 +240,10 @@ pub(crate) enum AppEvent {
     /// Open the custom prompt option from the review popup.
     OpenReviewCustomPrompt,
 
-    /// Submit a user message with an explicit collaboration mode.
+    /// Submit a user message with an explicit collaboration mask.
     SubmitUserMessageWithMode {
         text: String,
-        collaboration_mode: CollaborationMode,
+        collaboration_mode: CollaborationModeMask,
     },
 
     /// Open the approval popup.
diff --git a/codex-rs/tui/src/bottom_pane/chat_composer.rs b/codex-rs/tui/src/bottom_pane/chat_composer.rs
index 47c2c46251..d1f8d691a2 100644
--- a/codex-rs/tui/src/bottom_pane/chat_composer.rs
+++ b/codex-rs/tui/src/bottom_pane/chat_composer.rs
@@ -2039,15 +2039,6 @@ impl ChatComposer {
         {
             self.handle_paste(pasted);
         }
-        // Backspace at the start of an image placeholder should delete that placeholder (rather
-        // than deleting content before it). Do this without scanning the full text by consulting
-        // the textarea's element list.
-        if matches!(input.code, KeyCode::Backspace)
-            && self.try_remove_image_element_at_cursor_start()
-        {
-            return (InputResult::None, true);
-        }
-
         // For non-char inputs (or after flushing), handle normally.
         // Track element removals so we can drop any corresponding placeholders without scanning
         // the full text. (Placeholders are atomic elements; when deleted, the element disappears.)
@@ -2086,29 +2077,6 @@ impl ChatComposer {
         (InputResult::None, true)
     }
 
-    fn try_remove_image_element_at_cursor_start(&mut self) -> bool {
-        if self.attached_images.is_empty() {
-            return false;
-        }
-
-        let p = self.textarea.cursor();
-        let Some(payload) = self.textarea.element_payload_starting_at(p) else {
-            return false;
-        };
-        let Some(idx) = self
-            .attached_images
-            .iter()
-            .position(|img| img.placeholder == payload)
-        else {
-            return false;
-        };
-
-        self.textarea.replace_range(p..p + payload.len(), "");
-        self.attached_images.remove(idx);
-        self.relabel_attached_images_and_update_placeholders();
-        true
-    }
-
     fn reconcile_deleted_elements(&mut self, elements_before: Vec<String>) {
         let elements_after: HashSet<String> =
             self.textarea.element_payloads().into_iter().collect();
@@ -4662,8 +4630,7 @@ mod tests {
         assert!(!composer.textarea.text().contains(&placeholder));
         assert!(composer.attached_images.is_empty());
 
-        // Re-add and test backspace in middle: should break the placeholder string
-        // and drop the image mapping (same as text placeholder behavior).
+        // Re-add and ensure backspace at element start does not delete the placeholder.
         composer.attach_image(path);
         let placeholder2 = composer.attached_images[0].placeholder.clone();
         // Move cursor to roughly middle of placeholder
@@ -4671,8 +4638,8 @@ mod tests {
             let mid_pos = start_pos + (placeholder2.len() / 2);
             composer.textarea.set_cursor(mid_pos);
             composer.handle_key_event(KeyEvent::new(KeyCode::Backspace, KeyModifiers::NONE));
-            assert!(!composer.textarea.text().contains(&placeholder2));
-            assert!(composer.attached_images.is_empty());
+            assert!(composer.textarea.text().contains(&placeholder2));
+            assert_eq!(composer.attached_images.len(), 1);
         } else {
             panic!("Placeholder not found in textarea");
         }
@@ -4852,7 +4819,7 @@ mod tests {
         assert_eq!(composer.textarea.text(), "[Image #1][Image #2]");
         assert_eq!(composer.attached_images.len(), 2);
 
-        // Delete the first element using normal textarea editing (Delete at cursor start).
+        // Delete the first element using normal textarea editing (forward Delete at cursor start).
         composer.textarea.set_cursor(0);
         composer.handle_key_event(KeyEvent::new(KeyCode::Delete, KeyModifiers::NONE));
 
diff --git a/codex-rs/tui/src/bottom_pane/textarea.rs b/codex-rs/tui/src/bottom_pane/textarea.rs
index 3a849822b1..0235f7a9c1 100644
--- a/codex-rs/tui/src/bottom_pane/textarea.rs
+++ b/codex-rs/tui/src/bottom_pane/textarea.rs
@@ -766,12 +766,6 @@ impl TextArea {
             .collect()
     }
 
-    pub fn element_payload_starting_at(&self, pos: usize) -> Option<String> {
-        let pos = pos.min(self.text.len());
-        let elem = self.elements.iter().find(|e| e.range.start == pos)?;
-        self.text.get(elem.range.clone()).map(str::to_string)
-    }
-
     /// Renames a single text element in-place, keeping it atomic.
     ///
     /// Use this when the element payload is an identifier (e.g. a placeholder) that must be
@@ -1327,6 +1321,21 @@ mod tests {
         assert_eq!(t.text(), "b");
     }
 
+    #[test]
+    fn delete_forward_deletes_element_at_left_edge() {
+        let mut t = TextArea::new();
+        t.insert_str("a");
+        t.insert_element("<element>");
+        t.insert_str("b");
+
+        let elem_start = t.elements[0].range.start;
+        t.set_cursor(elem_start);
+        t.delete_forward(1);
+
+        assert_eq!(t.text(), "ab");
+        assert_eq!(t.cursor(), elem_start);
+    }
+
     #[test]
     fn delete_backward_word_and_kill_line_variants() {
         // delete backward word at end removes the whole previous word
diff --git a/codex-rs/tui/src/chatwidget.rs b/codex-rs/tui/src/chatwidget.rs
index 1f7fad3ea7..ce87b33eed 100644
--- a/codex-rs/tui/src/chatwidget.rs
+++ b/codex-rs/tui/src/chatwidget.rs
@@ -93,6 +93,7 @@ use codex_protocol::ThreadId;
 use codex_protocol::account::PlanType;
 use codex_protocol::approvals::ElicitationRequestEvent;
 use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::config_types::ModeKind;
 use codex_protocol::config_types::Settings;
 use codex_protocol::models::local_image_label_text;
@@ -415,12 +416,12 @@ pub(crate) struct ChatWidget {
     /// where the overlay may briefly treat new tail content as already cached.
     active_cell_revision: u64,
     config: Config,
-    /// Stored collaboration mode with model and reasoning effort.
+    /// The unmasked collaboration mode settings (always Custom mode).
     ///
-    /// When collaboration modes feature is enabled, this is initialized to the first preset.
-    /// When disabled, this is Custom. The model and reasoning effort are stored here instead of
-    /// being read from config or current_model.
-    stored_collaboration_mode: CollaborationMode,
+    /// Masks are applied on top of this base mode to derive the effective mode.
+    current_collaboration_mode: CollaborationMode,
+    /// The currently active collaboration mask, if any.
+    active_collaboration_mask: Option<CollaborationModeMask>,
     auth_manager: Arc<AuthManager>,
     models_manager: Arc<ModelsManager>,
     otel_manager: OtelManager,
@@ -727,20 +728,16 @@ impl ChatWidget {
         self.set_skills(None);
         self.thread_id = Some(event.session_id);
         self.forked_from = event.forked_from_id;
-        self.current_rollout_path = Some(event.rollout_path.clone());
+        self.current_rollout_path = event.rollout_path.clone();
         let initial_messages = event.initial_messages.clone();
         let model_for_header = event.model.clone();
         self.session_header.set_model(&model_for_header);
-        // Only update stored collaboration settings when collaboration modes are disabled.
-        // When enabled, we preserve the selected variant (Plan/Pair/Execute/Custom) and its
-        // instructions as-is; the session configured event should not override it.
-        if !self.collaboration_modes_enabled() {
-            self.stored_collaboration_mode = self.stored_collaboration_mode.with_updates(
-                Some(model_for_header.clone()),
-                Some(event.reasoning_effort),
-                None,
-            );
-        }
+        self.current_collaboration_mode = self.current_collaboration_mode.with_updates(
+            Some(model_for_header.clone()),
+            Some(event.reasoning_effort),
+            None,
+        );
+        self.refresh_model_display();
         let session_info_cell = history_cell::new_session_info(
             &self.config,
             &model_for_header,
@@ -910,7 +907,7 @@ impl ChatWidget {
         if !self.queued_user_messages.is_empty() {
             return;
         }
-        if self.stored_collaboration_mode.mode != ModeKind::Plan {
+        if self.active_mode_kind() != ModeKind::Plan {
             return;
         }
         let has_message = last_agent_message.is_some_and(|message| !message.trim().is_empty());
@@ -932,14 +929,14 @@ impl ChatWidget {
     }
 
     fn open_plan_implementation_prompt(&mut self) {
-        let code_mode = collaboration_modes::code_mode(self.models_manager.as_ref());
-        let (implement_actions, implement_disabled_reason) = match code_mode {
-            Some(collaboration_mode) => {
+        let code_mask = collaboration_modes::code_mask(self.models_manager.as_ref());
+        let (implement_actions, implement_disabled_reason) = match code_mask {
+            Some(mask) => {
                 let user_text = PLAN_IMPLEMENTATION_CODING_MESSAGE.to_string();
                 let actions: Vec<SelectionAction> = vec![Box::new(move |tx| {
                     tx.send(AppEvent::SubmitUserMessageWithMode {
                         text: user_text.clone(),
-                        collaboration_mode: collaboration_mode.clone(),
+                        collaboration_mode: mask.clone(),
                     });
                 })];
                 (actions, None)
@@ -1930,23 +1927,25 @@ impl ChatWidget {
         let placeholder = PLACEHOLDERS[rng.random_range(0..PLACEHOLDERS.len())].to_string();
         let codex_op_tx = spawn_agent(config.clone(), app_event_tx.clone(), thread_manager);
 
-        let model_for_header = model.unwrap_or_else(|| DEFAULT_MODEL_DISPLAY_NAME.to_string());
+        let model_override = model.as_deref();
+        let model_for_header = model
+            .clone()
+            .unwrap_or_else(|| DEFAULT_MODEL_DISPLAY_NAME.to_string());
+        let active_collaboration_mask =
+            Self::initial_collaboration_mask(&config, models_manager.as_ref(), model_override);
+        let header_model = active_collaboration_mask
+            .as_ref()
+            .and_then(|mask| mask.model.clone())
+            .unwrap_or_else(|| model_for_header.clone());
         let fallback_custom = Settings {
-            model: model_for_header.clone(),
+            model: header_model.clone(),
             reasoning_effort: None,
             developer_instructions: None,
         };
-        let stored_collaboration_mode = if config.features.enabled(Feature::CollaborationModes) {
-            initial_collaboration_mode(
-                models_manager.as_ref(),
-                fallback_custom,
-                config.experimental_mode,
-            )
-        } else {
-            CollaborationMode {
-                mode: ModeKind::Custom,
-                settings: fallback_custom,
-            }
+        // Collaboration modes start in Custom mode (not activated).
+        let current_collaboration_mode = CollaborationMode {
+            mode: ModeKind::Custom,
+            settings: fallback_custom,
         };
 
         let active_cell = Some(Self::placeholder_session_header_cell(&config));
@@ -1970,11 +1969,12 @@ impl ChatWidget {
             config,
             skills_all: Vec::new(),
             skills_initial_state: None,
-            stored_collaboration_mode,
+            current_collaboration_mode,
+            active_collaboration_mask,
             auth_manager,
             models_manager,
             otel_manager,
-            session_header: SessionHeader::new(model_for_header),
+            session_header: SessionHeader::new(header_model),
             initial_user_message,
             token_info: None,
             rate_limit_snapshot: None,
@@ -2051,23 +2051,25 @@ impl ChatWidget {
         let mut rng = rand::rng();
         let placeholder = PLACEHOLDERS[rng.random_range(0..PLACEHOLDERS.len())].to_string();
 
-        let model_for_header = model.unwrap_or_else(|| DEFAULT_MODEL_DISPLAY_NAME.to_string());
+        let model_override = model.as_deref();
+        let model_for_header = model
+            .clone()
+            .unwrap_or_else(|| DEFAULT_MODEL_DISPLAY_NAME.to_string());
+        let active_collaboration_mask =
+            Self::initial_collaboration_mask(&config, models_manager.as_ref(), model_override);
+        let header_model = active_collaboration_mask
+            .as_ref()
+            .and_then(|mask| mask.model.clone())
+            .unwrap_or_else(|| model_for_header.clone());
         let fallback_custom = Settings {
-            model: model_for_header.clone(),
+            model: header_model.clone(),
             reasoning_effort: None,
             developer_instructions: None,
         };
-        let stored_collaboration_mode = if config.features.enabled(Feature::CollaborationModes) {
-            initial_collaboration_mode(
-                models_manager.as_ref(),
-                fallback_custom,
-                config.experimental_mode,
-            )
-        } else {
-            CollaborationMode {
-                mode: ModeKind::Custom,
-                settings: fallback_custom,
-            }
+        // Collaboration modes start in Custom mode (not activated).
+        let current_collaboration_mode = CollaborationMode {
+            mode: ModeKind::Custom,
+            settings: fallback_custom,
         };
 
         let active_cell = Some(Self::placeholder_session_header_cell(&config));
@@ -2091,11 +2093,12 @@ impl ChatWidget {
             config,
             skills_all: Vec::new(),
             skills_initial_state: None,
-            stored_collaboration_mode,
+            current_collaboration_mode,
+            active_collaboration_mask,
             auth_manager,
             models_manager,
             otel_manager,
-            session_header: SessionHeader::new(model_for_header),
+            session_header: SessionHeader::new(header_model),
             initial_user_message,
             token_info: None,
             rate_limit_snapshot: None,
@@ -2171,7 +2174,16 @@ impl ChatWidget {
         let mut rng = rand::rng();
         let placeholder = PLACEHOLDERS[rng.random_range(0..PLACEHOLDERS.len())].to_string();
 
-        let header_model = model.unwrap_or_else(|| session_configured.model.clone());
+        let model_override = model.as_deref();
+        let header_model = model
+            .clone()
+            .unwrap_or_else(|| session_configured.model.clone());
+        let active_collaboration_mask =
+            Self::initial_collaboration_mask(&config, models_manager.as_ref(), model_override);
+        let header_model = active_collaboration_mask
+            .as_ref()
+            .and_then(|mask| mask.model.clone())
+            .unwrap_or(header_model);
 
         let codex_op_tx =
             spawn_agent_from_existing(conversation, session_configured, app_event_tx.clone());
@@ -2181,17 +2193,10 @@ impl ChatWidget {
             reasoning_effort: None,
             developer_instructions: None,
         };
-        let stored_collaboration_mode = if config.features.enabled(Feature::CollaborationModes) {
-            initial_collaboration_mode(
-                models_manager.as_ref(),
-                fallback_custom,
-                config.experimental_mode,
-            )
-        } else {
-            CollaborationMode {
-                mode: ModeKind::Custom,
-                settings: fallback_custom,
-            }
+        // Collaboration modes start in Custom mode (not activated).
+        let current_collaboration_mode = CollaborationMode {
+            mode: ModeKind::Custom,
+            settings: fallback_custom,
         };
 
         let mut widget = Self {
@@ -2213,7 +2218,8 @@ impl ChatWidget {
             config,
             skills_all: Vec::new(),
             skills_initial_state: None,
-            stored_collaboration_mode,
+            current_collaboration_mode,
+            active_collaboration_mask,
             auth_manager,
             models_manager,
             otel_manager,
@@ -2816,18 +2822,24 @@ impl ChatWidget {
             }
         }
 
+        let effective_mode = self.effective_collaboration_mode();
+        let collaboration_mode = if self.collaboration_modes_enabled() {
+            self.active_collaboration_mask
+                .as_ref()
+                .map(|_| effective_mode.clone())
+        } else {
+            None
+        };
         let op = Op::UserTurn {
             items,
             cwd: self.config.cwd.clone(),
             approval_policy: self.config.approval_policy.value(),
             sandbox_policy: self.config.sandbox_policy.get().clone(),
-            model: self.stored_collaboration_mode.model().to_string(),
-            effort: self.stored_collaboration_mode.reasoning_effort(),
+            model: effective_mode.model().to_string(),
+            effort: effective_mode.reasoning_effort(),
             summary: self.config.model_reasoning_summary,
             final_output_json_schema: None,
-            collaboration_mode: self
-                .collaboration_modes_enabled()
-                .then(|| self.stored_collaboration_mode.clone()),
+            collaboration_mode,
             personality: None,
         };
 
@@ -3180,7 +3192,7 @@ impl ChatWidget {
             .map(|ti| &ti.total_token_usage)
             .unwrap_or(&default_usage);
         let collaboration_mode = self.collaboration_mode_label();
-        let reasoning_effort_override = Some(self.stored_collaboration_mode.reasoning_effort());
+        let reasoning_effort_override = Some(self.effective_reasoning_effort());
         self.add_to_history(crate::status::new_status_output(
             &self.config,
             self.auth_manager.as_ref(),
@@ -3558,23 +3570,24 @@ impl ChatWidget {
             return;
         }
 
+        let current_kind = self
+            .active_collaboration_mask
+            .as_ref()
+            .and_then(|mask| mask.mode)
+            .or_else(|| {
+                collaboration_modes::default_mask(self.models_manager.as_ref())
+                    .and_then(|mask| mask.mode)
+            });
         let items: Vec<SelectionItem> = presets
             .into_iter()
-            .map(|preset| {
-                let name = match preset.mode {
-                    ModeKind::Plan => "Plan",
-                    ModeKind::Code => "Code",
-                    ModeKind::PairProgramming => "Pair Programming",
-                    ModeKind::Execute => "Execute",
-                    ModeKind::Custom => "Custom",
-                };
-                let is_current =
-                    collaboration_modes::same_variant(&self.stored_collaboration_mode, &preset);
+            .map(|mask| {
+                let name = mask.name.clone();
+                let is_current = current_kind == mask.mode;
                 let actions: Vec<SelectionAction> = vec![Box::new(move |tx| {
-                    tx.send(AppEvent::UpdateCollaborationMode(preset.clone()));
+                    tx.send(AppEvent::UpdateCollaborationMode(mask.clone()));
                 })];
                 SelectionItem {
-                    name: name.to_string(),
+                    name,
                     is_current,
                     actions,
                     dismiss_on_select: true,
@@ -3690,7 +3703,7 @@ impl ChatWidget {
         let model_slug = preset.model.to_string();
         let is_current_model = self.current_model() == preset.model.as_str();
         let highlight_choice = if is_current_model {
-            self.stored_collaboration_mode.reasoning_effort()
+            self.effective_reasoning_effort()
         } else {
             default_choice
         };
@@ -4548,21 +4561,15 @@ impl ChatWidget {
         }
         if feature == Feature::CollaborationModes {
             self.bottom_pane.set_collaboration_modes_enabled(enabled);
-            let settings = self.stored_collaboration_mode.settings.clone();
-            let fallback_custom = settings.clone();
-            self.stored_collaboration_mode = if enabled {
-                initial_collaboration_mode(
-                    self.models_manager.as_ref(),
-                    fallback_custom,
-                    self.config.experimental_mode,
-                )
-            } else {
-                CollaborationMode {
-                    mode: ModeKind::Custom,
-                    settings,
-                }
+            let settings = self.current_collaboration_mode.settings.clone();
+            self.current_collaboration_mode = CollaborationMode {
+                mode: ModeKind::Custom,
+                settings,
             };
+            self.active_collaboration_mask = None;
             self.update_collaboration_mode_indicator();
+            self.refresh_model_display();
+            self.request_redraw();
         }
     }
 
@@ -4591,31 +4598,52 @@ impl ChatWidget {
 
     /// Set the reasoning effort in the stored collaboration mode.
     pub(crate) fn set_reasoning_effort(&mut self, effort: Option<ReasoningEffortConfig>) {
-        self.stored_collaboration_mode =
-            self.stored_collaboration_mode
+        self.current_collaboration_mode =
+            self.current_collaboration_mode
                 .with_updates(None, Some(effort), None);
+        if self.collaboration_modes_enabled()
+            && let Some(mask) = self.active_collaboration_mask.as_mut()
+        {
+            mask.reasoning_effort = Some(effort);
+        }
     }
 
     /// Set the model in the widget's config copy and stored collaboration mode.
     pub(crate) fn set_model(&mut self, model: &str) {
-        self.session_header.set_model(model);
-        self.stored_collaboration_mode =
-            self.stored_collaboration_mode
+        self.current_collaboration_mode =
+            self.current_collaboration_mode
                 .with_updates(Some(model.to_string()), None, None);
+        if self.collaboration_modes_enabled()
+            && let Some(mask) = self.active_collaboration_mask.as_mut()
+        {
+            mask.model = Some(model.to_string());
+        }
+        self.refresh_model_display();
     }
 
     pub(crate) fn current_model(&self) -> &str {
-        self.stored_collaboration_mode.model()
+        if !self.collaboration_modes_enabled() {
+            return self.current_collaboration_mode.model();
+        }
+        self.active_collaboration_mask
+            .as_ref()
+            .and_then(|mask| mask.model.as_deref())
+            .unwrap_or_else(|| self.current_collaboration_mode.model())
     }
 
     #[allow(dead_code)] // Used in tests
-    pub(crate) fn stored_collaboration_mode(&self) -> &CollaborationMode {
-        &self.stored_collaboration_mode
+    pub(crate) fn current_collaboration_mode(&self) -> &CollaborationMode {
+        &self.current_collaboration_mode
     }
 
     #[cfg(test)]
     pub(crate) fn current_reasoning_effort(&self) -> Option<ReasoningEffortConfig> {
-        self.stored_collaboration_mode.reasoning_effort()
+        self.effective_reasoning_effort()
+    }
+
+    #[cfg(test)]
+    pub(crate) fn active_collaboration_mode_kind(&self) -> ModeKind {
+        self.active_mode_kind()
     }
 
     fn is_session_configured(&self) -> bool {
@@ -4626,6 +4654,57 @@ impl ChatWidget {
         self.config.features.enabled(Feature::CollaborationModes)
     }
 
+    fn initial_collaboration_mask(
+        config: &Config,
+        models_manager: &ModelsManager,
+        model_override: Option<&str>,
+    ) -> Option<CollaborationModeMask> {
+        if !config.features.enabled(Feature::CollaborationModes) {
+            return None;
+        }
+        let mut mask = match config.experimental_mode {
+            Some(kind) => collaboration_modes::mask_for_kind(models_manager, kind)?,
+            None => collaboration_modes::default_mask(models_manager)?,
+        };
+        if let Some(model_override) = model_override {
+            mask.model = Some(model_override.to_string());
+        }
+        Some(mask)
+    }
+
+    fn active_mode_kind(&self) -> ModeKind {
+        self.active_collaboration_mask
+            .as_ref()
+            .and_then(|mask| mask.mode)
+            .unwrap_or(ModeKind::Custom)
+    }
+
+    fn effective_reasoning_effort(&self) -> Option<ReasoningEffortConfig> {
+        if !self.collaboration_modes_enabled() {
+            return self.current_collaboration_mode.reasoning_effort();
+        }
+        let current_effort = self.current_collaboration_mode.reasoning_effort();
+        self.active_collaboration_mask
+            .as_ref()
+            .and_then(|mask| mask.reasoning_effort)
+            .unwrap_or(current_effort)
+    }
+
+    fn effective_collaboration_mode(&self) -> CollaborationMode {
+        if !self.collaboration_modes_enabled() {
+            return self.current_collaboration_mode.clone();
+        }
+        self.active_collaboration_mask.as_ref().map_or_else(
+            || self.current_collaboration_mode.clone(),
+            |mask| self.current_collaboration_mode.apply_mask(mask),
+        )
+    }
+
+    fn refresh_model_display(&mut self) {
+        let effective = self.effective_collaboration_mode();
+        self.session_header.set_model(effective.model());
+    }
+
     fn model_display_name(&self) -> &str {
         let model = self.current_model();
         if model.is_empty() {
@@ -4640,7 +4719,7 @@ impl ChatWidget {
         if !self.collaboration_modes_enabled() {
             return None;
         }
-        match self.stored_collaboration_mode.mode {
+        match self.active_mode_kind() {
             ModeKind::Plan => Some("Plan"),
             ModeKind::Code => Some("Code"),
             ModeKind::PairProgramming => Some("Pair Programming"),
@@ -4653,7 +4732,7 @@ impl ChatWidget {
         if !self.collaboration_modes_enabled() {
             return None;
         }
-        match self.stored_collaboration_mode.mode {
+        match self.active_mode_kind() {
             ModeKind::Plan => Some(CollaborationModeIndicator::Plan),
             ModeKind::Code => Some(CollaborationModeIndicator::Code),
             ModeKind::PairProgramming => Some(CollaborationModeIndicator::PairProgramming),
@@ -4673,26 +4752,25 @@ impl ChatWidget {
             return;
         }
 
-        if let Some(next_mode) = collaboration_modes::next_mode(
+        if let Some(next_mask) = collaboration_modes::next_mask(
             self.models_manager.as_ref(),
-            &self.stored_collaboration_mode,
+            self.active_collaboration_mask.as_ref(),
         ) {
-            self.set_collaboration_mode(next_mode);
+            self.set_collaboration_mask(next_mask);
         }
     }
 
-    /// Update the stored collaboration mode.
+    /// Update the active collaboration mask.
     ///
-    /// When collaboration modes are enabled, the current mode is attached to *every*
-    /// submission as `Op::UserTurn { collaboration_mode: Some(...) }`.
-    pub(crate) fn set_collaboration_mode(&mut self, mode: CollaborationMode) {
+    /// When collaboration modes are enabled and a preset is selected (not Custom),
+    /// the current mode is attached to submissions as `Op::UserTurn { collaboration_mode: Some(...) }`.
+    pub(crate) fn set_collaboration_mask(&mut self, mask: CollaborationModeMask) {
         if !self.collaboration_modes_enabled() {
             return;
         }
-        let old_model = self.stored_collaboration_mode.model().to_string();
-        let mode = mode.with_updates(Some(old_model), None, None);
-        self.stored_collaboration_mode = mode;
+        self.active_collaboration_mask = Some(mask);
         self.update_collaboration_mode_indicator();
+        self.refresh_model_display();
         self.request_redraw();
     }
 
@@ -4875,11 +4953,9 @@ impl ChatWidget {
     pub(crate) fn submit_user_message_with_mode(
         &mut self,
         text: String,
-        collaboration_mode: CollaborationMode,
+        collaboration_mode: CollaborationModeMask,
     ) {
-        let model = collaboration_mode.model().to_string();
-        self.set_collaboration_mode(collaboration_mode);
-        self.set_model(&model);
+        self.set_collaboration_mask(collaboration_mode);
         self.submit_user_message(text.into());
     }
 
@@ -5306,29 +5382,6 @@ fn extract_first_bold(s: &str) -> Option<String> {
     None
 }
 
-fn initial_collaboration_mode(
-    models_manager: &ModelsManager,
-    fallback_custom: Settings,
-    desired_mode: Option<ModeKind>,
-) -> CollaborationMode {
-    if let Some(kind) = desired_mode {
-        if kind == ModeKind::Custom {
-            return CollaborationMode {
-                mode: ModeKind::Custom,
-                settings: fallback_custom,
-            };
-        }
-        if let Some(mode) = collaboration_modes::mode_for_kind(models_manager, kind) {
-            return mode;
-        }
-    }
-
-    collaboration_modes::default_mode(models_manager).unwrap_or(CollaborationMode {
-        mode: ModeKind::Custom,
-        settings: fallback_custom,
-    })
-}
-
 async fn fetch_rate_limits(base_url: String, auth: CodexAuth) -> Option<RateLimitSnapshot> {
     match BackendClient::from_auth(base_url, &auth) {
         Ok(client) => match client.get_rate_limits().await {
diff --git a/codex-rs/tui/src/chatwidget/tests.rs b/codex-rs/tui/src/chatwidget/tests.rs
index 6a7401ce6c..e76abdbd7a 100644
--- a/codex-rs/tui/src/chatwidget/tests.rs
+++ b/codex-rs/tui/src/chatwidget/tests.rs
@@ -89,6 +89,7 @@ use tempfile::NamedTempFile;
 use tempfile::tempdir;
 use tokio::sync::mpsc::error::TryRecvError;
 use tokio::sync::mpsc::unbounded_channel;
+use toml::Value as TomlValue;
 
 #[cfg(target_os = "windows")]
 fn set_windows_sandbox_enabled(enabled: bool) {
@@ -160,7 +161,7 @@ async fn resumed_initial_messages_render_history() {
                 message: "assistant reply".to_string(),
             }),
         ]),
-        rollout_path: rollout_file.path().to_path_buf(),
+        rollout_path: Some(rollout_file.path().to_path_buf()),
     };
 
     chat.handle_codex_event(Event {
@@ -221,7 +222,7 @@ async fn replayed_user_message_preserves_text_elements_and_local_images() {
             text_elements: text_elements.clone(),
             local_images: local_images.clone(),
         })]),
-        rollout_path: rollout_file.path().to_path_buf(),
+        rollout_path: Some(rollout_file.path().to_path_buf()),
     };
 
     chat.handle_codex_event(Event {
@@ -268,7 +269,7 @@ async fn submission_preserves_text_elements_and_local_images() {
         history_log_id: 0,
         history_entry_count: 0,
         initial_messages: None,
-        rollout_path: rollout_file.path().to_path_buf(),
+        rollout_path: Some(rollout_file.path().to_path_buf()),
     };
     chat.handle_codex_event(Event {
         id: "initial".into(),
@@ -777,29 +778,16 @@ async fn make_chatwidget_manual(
     let auth_manager = AuthManager::from_auth_for_testing(CodexAuth::from_api_key("test"));
     let codex_home = cfg.codex_home.clone();
     let models_manager = Arc::new(ModelsManager::new(codex_home, auth_manager.clone()));
-    let collaboration_modes_enabled = cfg.features.enabled(Feature::CollaborationModes);
     let reasoning_effort = None;
-    let stored_collaboration_mode = if collaboration_modes_enabled {
-        collaboration_modes::default_mode(models_manager.as_ref()).unwrap_or_else(|| {
-            CollaborationMode {
-                mode: ModeKind::Custom,
-                settings: Settings {
-                    model: resolved_model.clone(),
-                    reasoning_effort,
-                    developer_instructions: None,
-                },
-            }
-        })
-    } else {
-        CollaborationMode {
-            mode: ModeKind::Custom,
-            settings: Settings {
-                model: resolved_model.clone(),
-                reasoning_effort,
-                developer_instructions: None,
-            },
-        }
+    let base_mode = CollaborationMode {
+        mode: ModeKind::Custom,
+        settings: Settings {
+            model: resolved_model.clone(),
+            reasoning_effort,
+            developer_instructions: None,
+        },
     };
+    let current_collaboration_mode = base_mode;
     let widget = ChatWidget {
         app_event_tx,
         codex_op_tx: op_tx,
@@ -807,7 +795,8 @@ async fn make_chatwidget_manual(
         active_cell: None,
         active_cell_revision: 0,
         config: cfg,
-        stored_collaboration_mode,
+        current_collaboration_mode,
+        active_collaboration_mask: None,
         auth_manager,
         models_manager,
         otel_manager,
@@ -1214,7 +1203,7 @@ async fn plan_implementation_popup_yes_emits_submit_message_event() {
         panic!("expected SubmitUserMessageWithMode, got {event:?}");
     };
     assert_eq!(text, PLAN_IMPLEMENTATION_CODING_MESSAGE);
-    assert_eq!(collaboration_mode.mode, ModeKind::Code);
+    assert_eq!(collaboration_mode.mode, Some(ModeKind::Code));
 }
 
 #[tokio::test]
@@ -1223,7 +1212,7 @@ async fn submit_user_message_with_mode_sets_coding_collaboration_mode() {
     chat.thread_id = Some(ThreadId::new());
     chat.set_feature_enabled(Feature::CollaborationModes, true);
 
-    let code_mode = collaboration_modes::code_mode(chat.models_manager.as_ref())
+    let code_mode = collaboration_modes::code_mask(chat.models_manager.as_ref())
         .expect("expected code collaboration mode");
     chat.submit_user_message_with_mode("Implement the plan.".to_string(), code_mode);
 
@@ -1247,14 +1236,10 @@ async fn submit_user_message_with_mode_sets_coding_collaboration_mode() {
 async fn plan_implementation_popup_skips_replayed_turn_complete() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
     chat.set_feature_enabled(Feature::CollaborationModes, true);
-    chat.stored_collaboration_mode = CollaborationMode {
-        mode: ModeKind::Plan,
-        settings: Settings {
-            model: chat.current_model().to_string(),
-            reasoning_effort: None,
-            developer_instructions: None,
-        },
-    };
+    let plan_mask =
+        collaboration_modes::mask_for_kind(chat.models_manager.as_ref(), ModeKind::Plan)
+            .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
 
     chat.replay_initial_messages(vec![EventMsg::TurnComplete(TurnCompleteEvent {
         last_agent_message: Some("Plan details".to_string()),
@@ -1271,14 +1256,10 @@ async fn plan_implementation_popup_skips_replayed_turn_complete() {
 async fn plan_implementation_popup_skips_when_messages_queued() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
     chat.set_feature_enabled(Feature::CollaborationModes, true);
-    chat.stored_collaboration_mode = CollaborationMode {
-        mode: ModeKind::Plan,
-        settings: Settings {
-            model: chat.current_model().to_string(),
-            reasoning_effort: None,
-            developer_instructions: None,
-        },
-    };
+    let plan_mask =
+        collaboration_modes::mask_for_kind(chat.models_manager.as_ref(), ModeKind::Plan)
+            .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
     chat.bottom_pane.set_task_running(true);
     chat.queue_user_message("Queued message".into());
 
@@ -1295,14 +1276,10 @@ async fn plan_implementation_popup_skips_when_messages_queued() {
 async fn plan_implementation_popup_shows_on_plan_update_without_message() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
     chat.set_feature_enabled(Feature::CollaborationModes, true);
-    chat.stored_collaboration_mode = CollaborationMode {
-        mode: ModeKind::Plan,
-        settings: Settings {
-            model: chat.current_model().to_string(),
-            reasoning_effort: None,
-            developer_instructions: None,
-        },
-    };
+    let plan_mask =
+        collaboration_modes::mask_for_kind(chat.models_manager.as_ref(), ModeKind::Plan)
+            .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
 
     chat.on_task_started();
     chat.on_plan_update(UpdatePlanArgs {
@@ -1327,14 +1304,10 @@ async fn plan_implementation_popup_skips_when_rate_limit_prompt_pending() {
     chat.auth_manager =
         AuthManager::from_auth_for_testing(CodexAuth::create_dummy_chatgpt_auth_for_testing());
     chat.set_feature_enabled(Feature::CollaborationModes, true);
-    chat.stored_collaboration_mode = CollaborationMode {
-        mode: ModeKind::Plan,
-        settings: Settings {
-            model: chat.current_model().to_string(),
-            reasoning_effort: None,
-            developer_instructions: None,
-        },
-    };
+    let plan_mask =
+        collaboration_modes::mask_for_kind(chat.models_manager.as_ref(), ModeKind::Plan)
+            .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
 
     chat.on_task_started();
     chat.on_plan_update(UpdatePlanArgs {
@@ -2222,22 +2195,25 @@ async fn collab_mode_shift_tab_cycles_only_when_enabled_and_idle() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(None).await;
     chat.set_feature_enabled(Feature::CollaborationModes, false);
 
-    let initial = chat.stored_collaboration_mode.clone();
+    let initial = chat.current_collaboration_mode().clone();
     chat.handle_key_event(KeyEvent::from(KeyCode::BackTab));
-    assert_eq!(chat.stored_collaboration_mode, initial);
+    assert_eq!(chat.current_collaboration_mode(), &initial);
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Custom);
 
     chat.set_feature_enabled(Feature::CollaborationModes, true);
 
     chat.handle_key_event(KeyEvent::from(KeyCode::BackTab));
-    assert_eq!(chat.stored_collaboration_mode.mode, ModeKind::Plan);
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Plan);
+    assert_eq!(chat.current_collaboration_mode(), &initial);
 
     chat.handle_key_event(KeyEvent::from(KeyCode::BackTab));
-    assert_eq!(chat.stored_collaboration_mode.mode, ModeKind::Code);
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Code);
+    assert_eq!(chat.current_collaboration_mode(), &initial);
 
     chat.on_task_started();
-    let before = chat.stored_collaboration_mode.clone();
+    let before = chat.active_collaboration_mode_kind();
     chat.handle_key_event(KeyEvent::from(KeyCode::BackTab));
-    assert_eq!(chat.stored_collaboration_mode, before);
+    assert_eq!(chat.active_collaboration_mode_kind(), before);
 }
 
 #[tokio::test]
@@ -2254,11 +2230,11 @@ async fn collab_slash_command_opens_picker_and_updates_mode() {
     );
 
     chat.handle_key_event(KeyEvent::from(KeyCode::Enter));
-    let selected_mode = match rx.try_recv() {
-        Ok(AppEvent::UpdateCollaborationMode(mode)) => mode,
+    let selected_mask = match rx.try_recv() {
+        Ok(AppEvent::UpdateCollaborationMode(mask)) => mask,
         other => panic!("expected UpdateCollaborationMode event, got {other:?}"),
     };
-    chat.set_collaboration_mode(selected_mode);
+    chat.set_collaboration_mask(selected_mask);
 
     chat.bottom_pane
         .set_composer_text("hello".to_string(), Vec::new(), Vec::new());
@@ -2298,7 +2274,119 @@ async fn collab_slash_command_opens_picker_and_updates_mode() {
 }
 
 #[tokio::test]
-async fn collab_mode_defaults_to_coding_when_enabled() {
+async fn collaboration_modes_defaults_to_code_on_startup() {
+    let codex_home = tempdir().expect("tempdir");
+    let cfg = ConfigBuilder::default()
+        .codex_home(codex_home.path().to_path_buf())
+        .cli_overrides(vec![(
+            "features.collaboration_modes".to_string(),
+            TomlValue::Boolean(true),
+        )])
+        .build()
+        .await
+        .expect("config");
+    let resolved_model = ModelsManager::get_model_offline(cfg.model.as_deref());
+    let otel_manager = test_otel_manager(&cfg, resolved_model.as_str());
+    let thread_manager = Arc::new(ThreadManager::with_models_provider(
+        CodexAuth::from_api_key("test"),
+        cfg.model_provider.clone(),
+    ));
+    let auth_manager = AuthManager::from_auth_for_testing(CodexAuth::from_api_key("test"));
+    let init = ChatWidgetInit {
+        config: cfg,
+        frame_requester: FrameRequester::test_dummy(),
+        app_event_tx: AppEventSender::new(unbounded_channel::<AppEvent>().0),
+        initial_user_message: None,
+        enhanced_keys_supported: false,
+        auth_manager,
+        models_manager: thread_manager.get_models_manager(),
+        feedback: codex_feedback::CodexFeedback::new(),
+        is_first_run: true,
+        model: Some(resolved_model.clone()),
+        otel_manager,
+    };
+
+    let chat = ChatWidget::new(init, thread_manager);
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Code);
+    assert_eq!(chat.current_model(), resolved_model);
+}
+
+#[tokio::test]
+async fn experimental_mode_plan_applies_on_startup() {
+    let codex_home = tempdir().expect("tempdir");
+    let cfg = ConfigBuilder::default()
+        .codex_home(codex_home.path().to_path_buf())
+        .cli_overrides(vec![
+            (
+                "features.collaboration_modes".to_string(),
+                TomlValue::Boolean(true),
+            ),
+            (
+                "tui.experimental_mode".to_string(),
+                TomlValue::String("plan".to_string()),
+            ),
+        ])
+        .build()
+        .await
+        .expect("config");
+    let resolved_model = ModelsManager::get_model_offline(cfg.model.as_deref());
+    let otel_manager = test_otel_manager(&cfg, resolved_model.as_str());
+    let thread_manager = Arc::new(ThreadManager::with_models_provider(
+        CodexAuth::from_api_key("test"),
+        cfg.model_provider.clone(),
+    ));
+    let auth_manager = AuthManager::from_auth_for_testing(CodexAuth::from_api_key("test"));
+    let init = ChatWidgetInit {
+        config: cfg,
+        frame_requester: FrameRequester::test_dummy(),
+        app_event_tx: AppEventSender::new(unbounded_channel::<AppEvent>().0),
+        initial_user_message: None,
+        enhanced_keys_supported: false,
+        auth_manager,
+        models_manager: thread_manager.get_models_manager(),
+        feedback: codex_feedback::CodexFeedback::new(),
+        is_first_run: true,
+        model: Some(resolved_model.clone()),
+        otel_manager,
+    };
+
+    let chat = ChatWidget::new(init, thread_manager);
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Plan);
+    assert_eq!(chat.current_model(), resolved_model);
+}
+
+#[tokio::test]
+async fn set_model_updates_active_collaboration_mask() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.1")).await;
+    chat.set_feature_enabled(Feature::CollaborationModes, true);
+    let plan_mask =
+        collaboration_modes::mask_for_kind(chat.models_manager.as_ref(), ModeKind::Plan)
+            .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
+
+    chat.set_model("gpt-5.1-codex-mini");
+
+    assert_eq!(chat.current_model(), "gpt-5.1-codex-mini");
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Plan);
+}
+
+#[tokio::test]
+async fn set_reasoning_effort_updates_active_collaboration_mask() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.1")).await;
+    chat.set_feature_enabled(Feature::CollaborationModes, true);
+    let plan_mask =
+        collaboration_modes::mask_for_kind(chat.models_manager.as_ref(), ModeKind::Plan)
+            .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
+
+    chat.set_reasoning_effort(None);
+
+    assert_eq!(chat.current_reasoning_effort(), None);
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Plan);
+}
+
+#[tokio::test]
+async fn collab_mode_is_not_sent_until_selected() {
     let (mut chat, _rx, mut op_rx) = make_chatwidget_manual(None).await;
     chat.thread_id = Some(ThreadId::new());
     chat.set_feature_enabled(Feature::CollaborationModes, true);
@@ -2308,25 +2396,24 @@ async fn collab_mode_defaults_to_coding_when_enabled() {
     chat.handle_key_event(KeyEvent::from(KeyCode::Enter));
     match next_submit_op(&mut op_rx) {
         Op::UserTurn {
-            collaboration_mode:
-                Some(CollaborationMode {
-                    mode: ModeKind::Code,
-                    ..
-                }),
+            collaboration_mode,
             personality: None,
             ..
-        } => {}
+        } => {
+            assert_eq!(collaboration_mode, None);
+        }
         other => {
-            panic!("expected Op::UserTurn with code collab mode, got {other:?}")
+            panic!("expected Op::UserTurn, got {other:?}")
         }
     }
 }
 
 #[tokio::test]
-async fn collab_mode_enabling_sets_coding_default() {
+async fn collab_mode_enabling_keeps_custom_until_selected() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(None).await;
     chat.set_feature_enabled(Feature::CollaborationModes, true);
-    assert_eq!(chat.stored_collaboration_mode.mode, ModeKind::Code);
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Custom);
+    assert_eq!(chat.current_collaboration_mode().mode, ModeKind::Custom);
 }
 
 #[tokio::test]
diff --git a/codex-rs/tui/src/collaboration_modes.rs b/codex-rs/tui/src/collaboration_modes.rs
index c66010b57a..95908d8e90 100644
--- a/codex-rs/tui/src/collaboration_modes.rs
+++ b/codex-rs/tui/src/collaboration_modes.rs
@@ -1,70 +1,61 @@
 use codex_core::models_manager::manager::ModelsManager;
-use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::config_types::ModeKind;
 
-fn mode_kind(mode: &CollaborationMode) -> ModeKind {
-    mode.mode
-}
-
 fn is_tui_mode(kind: ModeKind) -> bool {
     matches!(kind, ModeKind::Plan | ModeKind::Code)
 }
 
-fn filtered_presets(models_manager: &ModelsManager) -> Vec<CollaborationMode> {
+fn filtered_presets(models_manager: &ModelsManager) -> Vec<CollaborationModeMask> {
     models_manager
         .list_collaboration_modes()
         .into_iter()
-        .filter(|preset| is_tui_mode(mode_kind(preset)))
+        .filter(|mask| mask.mode.is_some_and(is_tui_mode))
         .collect()
 }
 
-pub(crate) fn presets_for_tui(models_manager: &ModelsManager) -> Vec<CollaborationMode> {
+pub(crate) fn presets_for_tui(models_manager: &ModelsManager) -> Vec<CollaborationModeMask> {
     filtered_presets(models_manager)
 }
 
-pub(crate) fn default_mode(models_manager: &ModelsManager) -> Option<CollaborationMode> {
+pub(crate) fn default_mask(models_manager: &ModelsManager) -> Option<CollaborationModeMask> {
     let presets = filtered_presets(models_manager);
     presets
         .iter()
-        .find(|preset| preset.mode == ModeKind::Code)
+        .find(|mask| mask.mode == Some(ModeKind::Code))
         .cloned()
         .or_else(|| presets.into_iter().next())
 }
 
-pub(crate) fn mode_for_kind(
+pub(crate) fn mask_for_kind(
     models_manager: &ModelsManager,
     kind: ModeKind,
-) -> Option<CollaborationMode> {
+) -> Option<CollaborationModeMask> {
     if !is_tui_mode(kind) {
         return None;
     }
-    let presets = filtered_presets(models_manager);
-    presets.into_iter().find(|preset| mode_kind(preset) == kind)
-}
-
-pub(crate) fn same_variant(a: &CollaborationMode, b: &CollaborationMode) -> bool {
-    mode_kind(a) == mode_kind(b)
+    filtered_presets(models_manager)
+        .into_iter()
+        .find(|mask| mask.mode == Some(kind))
 }
 
 /// Cycle to the next collaboration mode preset in list order.
-pub(crate) fn next_mode(
+pub(crate) fn next_mask(
     models_manager: &ModelsManager,
-    current: &CollaborationMode,
-) -> Option<CollaborationMode> {
+    current: Option<&CollaborationModeMask>,
+) -> Option<CollaborationModeMask> {
     let presets = filtered_presets(models_manager);
     if presets.is_empty() {
         return None;
     }
-    let current_kind = mode_kind(current);
+    let current_kind = current.and_then(|mask| mask.mode);
     let next_index = presets
         .iter()
-        .position(|preset| mode_kind(preset) == current_kind)
+        .position(|mask| mask.mode == current_kind)
         .map_or(0, |idx| (idx + 1) % presets.len());
     presets.get(next_index).cloned()
 }
 
-pub(crate) fn code_mode(models_manager: &ModelsManager) -> Option<CollaborationMode> {
-    filtered_presets(models_manager)
-        .into_iter()
-        .find(|preset| mode_kind(preset) == ModeKind::Code)
+pub(crate) fn code_mask(models_manager: &ModelsManager) -> Option<CollaborationModeMask> {
+    mask_for_kind(models_manager, ModeKind::Code)
 }
diff --git a/codex-rs/tui/src/cwd_prompt.rs b/codex-rs/tui/src/cwd_prompt.rs
new file mode 100644
index 0000000000..2a9c016a1e
--- /dev/null
+++ b/codex-rs/tui/src/cwd_prompt.rs
@@ -0,0 +1,286 @@
+use std::path::Path;
+
+use crate::key_hint;
+use crate::render::Insets;
+use crate::render::renderable::ColumnRenderable;
+use crate::render::renderable::Renderable;
+use crate::render::renderable::RenderableExt as _;
+use crate::selection_list::selection_option_row;
+use crate::tui::FrameRequester;
+use crate::tui::Tui;
+use crate::tui::TuiEvent;
+use color_eyre::Result;
+use crossterm::event::KeyCode;
+use crossterm::event::KeyEvent;
+use crossterm::event::KeyEventKind;
+use crossterm::event::KeyModifiers;
+use ratatui::buffer::Buffer;
+use ratatui::layout::Rect;
+use ratatui::prelude::Widget;
+use ratatui::style::Stylize as _;
+use ratatui::text::Line;
+use ratatui::widgets::Clear;
+use ratatui::widgets::WidgetRef;
+use tokio_stream::StreamExt;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) enum CwdPromptAction {
+    Resume,
+    Fork,
+}
+
+impl CwdPromptAction {
+    fn verb(self) -> &'static str {
+        match self {
+            CwdPromptAction::Resume => "resume",
+            CwdPromptAction::Fork => "fork",
+        }
+    }
+
+    fn past_participle(self) -> &'static str {
+        match self {
+            CwdPromptAction::Resume => "resumed",
+            CwdPromptAction::Fork => "forked",
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) enum CwdSelection {
+    Current,
+    Session,
+}
+
+impl CwdSelection {
+    fn next(self) -> Self {
+        match self {
+            CwdSelection::Current => CwdSelection::Session,
+            CwdSelection::Session => CwdSelection::Current,
+        }
+    }
+
+    fn prev(self) -> Self {
+        match self {
+            CwdSelection::Current => CwdSelection::Session,
+            CwdSelection::Session => CwdSelection::Current,
+        }
+    }
+}
+
+pub(crate) async fn run_cwd_selection_prompt(
+    tui: &mut Tui,
+    action: CwdPromptAction,
+    current_cwd: &Path,
+    session_cwd: &Path,
+) -> Result<CwdSelection> {
+    let mut screen = CwdPromptScreen::new(
+        tui.frame_requester(),
+        action,
+        current_cwd.display().to_string(),
+        session_cwd.display().to_string(),
+    );
+    tui.draw(u16::MAX, |frame| {
+        frame.render_widget_ref(&screen, frame.area());
+    })?;
+
+    let events = tui.event_stream();
+    tokio::pin!(events);
+
+    while !screen.is_done() {
+        if let Some(event) = events.next().await {
+            match event {
+                TuiEvent::Key(key_event) => screen.handle_key(key_event),
+                TuiEvent::Paste(_) => {}
+                TuiEvent::Draw => {
+                    tui.draw(u16::MAX, |frame| {
+                        frame.render_widget_ref(&screen, frame.area());
+                    })?;
+                }
+            }
+        } else {
+            break;
+        }
+    }
+
+    Ok(screen.selection().unwrap_or(CwdSelection::Session))
+}
+
+struct CwdPromptScreen {
+    request_frame: FrameRequester,
+    action: CwdPromptAction,
+    current_cwd: String,
+    session_cwd: String,
+    highlighted: CwdSelection,
+    selection: Option<CwdSelection>,
+}
+
+impl CwdPromptScreen {
+    fn new(
+        request_frame: FrameRequester,
+        action: CwdPromptAction,
+        current_cwd: String,
+        session_cwd: String,
+    ) -> Self {
+        Self {
+            request_frame,
+            action,
+            current_cwd,
+            session_cwd,
+            highlighted: CwdSelection::Session,
+            selection: None,
+        }
+    }
+
+    fn handle_key(&mut self, key_event: KeyEvent) {
+        if key_event.kind == KeyEventKind::Release {
+            return;
+        }
+        if key_event.modifiers.contains(KeyModifiers::CONTROL)
+            && matches!(key_event.code, KeyCode::Char('c') | KeyCode::Char('d'))
+        {
+            self.select(CwdSelection::Session);
+            return;
+        }
+        match key_event.code {
+            KeyCode::Up | KeyCode::Char('k') => self.set_highlight(self.highlighted.prev()),
+            KeyCode::Down | KeyCode::Char('j') => self.set_highlight(self.highlighted.next()),
+            KeyCode::Char('1') => self.select(CwdSelection::Session),
+            KeyCode::Char('2') => self.select(CwdSelection::Current),
+            KeyCode::Enter => self.select(self.highlighted),
+            KeyCode::Esc => self.select(CwdSelection::Session),
+            _ => {}
+        }
+    }
+
+    fn set_highlight(&mut self, highlight: CwdSelection) {
+        if self.highlighted != highlight {
+            self.highlighted = highlight;
+            self.request_frame.schedule_frame();
+        }
+    }
+
+    fn select(&mut self, selection: CwdSelection) {
+        self.highlighted = selection;
+        self.selection = Some(selection);
+        self.request_frame.schedule_frame();
+    }
+
+    fn is_done(&self) -> bool {
+        self.selection.is_some()
+    }
+
+    fn selection(&self) -> Option<CwdSelection> {
+        self.selection
+    }
+}
+
+impl WidgetRef for &CwdPromptScreen {
+    fn render_ref(&self, area: Rect, buf: &mut Buffer) {
+        Clear.render(area, buf);
+        let mut column = ColumnRenderable::new();
+
+        let action_verb = self.action.verb();
+        let action_past = self.action.past_participle();
+        let current_cwd = self.current_cwd.as_str();
+        let session_cwd = self.session_cwd.as_str();
+
+        column.push("");
+        column.push(Line::from(vec![
+            "Choose working directory to ".into(),
+            action_verb.bold(),
+            " this session".into(),
+        ]));
+        column.push("");
+        column.push(
+            Line::from(format!(
+                "Session = latest cwd recorded in the {action_past} session"
+            ))
+            .dim()
+            .inset(Insets::tlbr(0, 2, 0, 0)),
+        );
+        column.push(
+            Line::from("Current = your current working directory".dim())
+                .inset(Insets::tlbr(0, 2, 0, 0)),
+        );
+        column.push("");
+        column.push(selection_option_row(
+            0,
+            format!("Use session directory ({session_cwd})"),
+            self.highlighted == CwdSelection::Session,
+        ));
+        column.push(selection_option_row(
+            1,
+            format!("Use current directory ({current_cwd})"),
+            self.highlighted == CwdSelection::Current,
+        ));
+        column.push("");
+        column.push(
+            Line::from(vec![
+                "Press ".dim(),
+                key_hint::plain(KeyCode::Enter).into(),
+                " to continue".dim(),
+            ])
+            .inset(Insets::tlbr(0, 2, 0, 0)),
+        );
+        column.render(area, buf);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test_backend::VT100Backend;
+    use crossterm::event::KeyEvent;
+    use crossterm::event::KeyModifiers;
+    use pretty_assertions::assert_eq;
+    use ratatui::Terminal;
+
+    fn new_prompt() -> CwdPromptScreen {
+        CwdPromptScreen::new(
+            FrameRequester::test_dummy(),
+            CwdPromptAction::Resume,
+            "/Users/example/current".to_string(),
+            "/Users/example/session".to_string(),
+        )
+    }
+
+    #[test]
+    fn cwd_prompt_snapshot() {
+        let screen = new_prompt();
+        let mut terminal = Terminal::new(VT100Backend::new(80, 14)).expect("terminal");
+        terminal
+            .draw(|frame| frame.render_widget_ref(&screen, frame.area()))
+            .expect("render cwd prompt");
+        insta::assert_snapshot!("cwd_prompt_modal", terminal.backend());
+    }
+
+    #[test]
+    fn cwd_prompt_fork_snapshot() {
+        let screen = CwdPromptScreen::new(
+            FrameRequester::test_dummy(),
+            CwdPromptAction::Fork,
+            "/Users/example/current".to_string(),
+            "/Users/example/session".to_string(),
+        );
+        let mut terminal = Terminal::new(VT100Backend::new(80, 14)).expect("terminal");
+        terminal
+            .draw(|frame| frame.render_widget_ref(&screen, frame.area()))
+            .expect("render cwd prompt");
+        insta::assert_snapshot!("cwd_prompt_fork_modal", terminal.backend());
+    }
+
+    #[test]
+    fn cwd_prompt_selects_session_by_default() {
+        let mut screen = new_prompt();
+        screen.handle_key(KeyEvent::new(KeyCode::Enter, KeyModifiers::NONE));
+        assert_eq!(screen.selection(), Some(CwdSelection::Session));
+    }
+
+    #[test]
+    fn cwd_prompt_can_select_current() {
+        let mut screen = new_prompt();
+        screen.handle_key(KeyEvent::new(KeyCode::Down, KeyModifiers::NONE));
+        screen.handle_key(KeyEvent::new(KeyCode::Enter, KeyModifiers::NONE));
+        assert_eq!(screen.selection(), Some(CwdSelection::Current));
+    }
+}
diff --git a/codex-rs/tui/src/lib.rs b/codex-rs/tui/src/lib.rs
index e3ee2ed4e6..0fac506d32 100644
--- a/codex-rs/tui/src/lib.rs
+++ b/codex-rs/tui/src/lib.rs
@@ -27,13 +27,19 @@ use codex_core::config_loader::ConfigLoadError;
 use codex_core::config_loader::format_config_error_with_source;
 use codex_core::find_thread_path_by_id_str;
 use codex_core::get_platform_sandbox;
+use codex_core::path_utils;
 use codex_core::protocol::AskForApproval;
 use codex_core::read_session_meta_line;
 use codex_core::terminal::Multiplexer;
 use codex_protocol::config_types::AltScreenMode;
 use codex_protocol::config_types::SandboxMode;
+use codex_protocol::protocol::RolloutItem;
+use codex_protocol::protocol::RolloutLine;
 use codex_utils_absolute_path::AbsolutePathBuf;
+use cwd_prompt::CwdPromptAction;
+use cwd_prompt::CwdSelection;
 use std::fs::OpenOptions;
+use std::path::Path;
 use std::path::PathBuf;
 use tracing::error;
 use tracing_appender::non_blocking;
@@ -54,6 +60,7 @@ mod collab;
 mod collaboration_modes;
 mod color;
 pub mod custom_terminal;
+mod cwd_prompt;
 mod diff_render;
 mod exec_cell;
 mod exec_command;
@@ -577,25 +584,27 @@ async fn run_ratatui_app(
         resume_picker::SessionSelection::StartFresh
     };
 
+    let current_cwd = config.cwd.clone();
+    let allow_prompt = cli.cwd.is_none();
+    let action_and_path_if_resume_or_fork = match &session_selection {
+        resume_picker::SessionSelection::Resume(path) => Some((CwdPromptAction::Resume, path)),
+        resume_picker::SessionSelection::Fork(path) => Some((CwdPromptAction::Fork, path)),
+        _ => None,
+    };
+    let fallback_cwd = match action_and_path_if_resume_or_fork {
+        Some((action, path)) => {
+            resolve_cwd_for_resume_or_fork(&mut tui, &current_cwd, path, action, allow_prompt)
+                .await?
+        }
+        None => None,
+    };
+
     let config = match &session_selection {
-        resume_picker::SessionSelection::Resume(path)
-        | resume_picker::SessionSelection::Fork(path) => {
-            let history_cwd = match read_session_meta_line(path).await {
-                Ok(meta_line) => Some(meta_line.meta.cwd),
-                Err(err) => {
-                    let rollout_path = path.display().to_string();
-                    tracing::warn!(
-                        %rollout_path,
-                        %err,
-                        "Failed to read session metadata from rollout"
-                    );
-                    None
-                }
-            };
+        resume_picker::SessionSelection::Resume(_) | resume_picker::SessionSelection::Fork(_) => {
             load_config_or_exit_with_fallback_cwd(
                 cli_kv_overrides.clone(),
                 overrides.clone(),
-                history_cwd,
+                fallback_cwd,
             )
             .await
         }
@@ -618,6 +627,8 @@ async fn run_ratatui_app(
         &mut tui,
         auth_manager,
         config,
+        cli_kv_overrides.clone(),
+        overrides.clone(),
         active_profile,
         prompt,
         images,
@@ -635,6 +646,77 @@ async fn run_ratatui_app(
     app_result
 }
 
+pub(crate) async fn read_session_cwd(path: &Path) -> Option<PathBuf> {
+    // Prefer the latest TurnContext cwd so resume/fork reflects the most recent
+    // session directory (for the changed-cwd prompt). The alternative would be
+    // mutating the SessionMeta line when the session cwd changes, but the rollout
+    // is an append-only JSONL log and rewriting the head would be error-prone.
+    // When rollouts move to SQLite, we can drop this scan.
+    if let Some(cwd) = parse_latest_turn_context_cwd(path).await {
+        return Some(cwd);
+    }
+    match read_session_meta_line(path).await {
+        Ok(meta_line) => Some(meta_line.meta.cwd),
+        Err(err) => {
+            let rollout_path = path.display().to_string();
+            tracing::warn!(
+                %rollout_path,
+                %err,
+                "Failed to read session metadata from rollout"
+            );
+            None
+        }
+    }
+}
+
+async fn parse_latest_turn_context_cwd(path: &Path) -> Option<PathBuf> {
+    let text = tokio::fs::read_to_string(path).await.ok()?;
+    for line in text.lines().rev() {
+        let trimmed = line.trim();
+        if trimmed.is_empty() {
+            continue;
+        }
+        let Ok(rollout_line) = serde_json::from_str::<RolloutLine>(trimmed) else {
+            continue;
+        };
+        if let RolloutItem::TurnContext(item) = rollout_line.item {
+            return Some(item.cwd);
+        }
+    }
+    None
+}
+
+pub(crate) fn cwds_differ(current_cwd: &Path, session_cwd: &Path) -> bool {
+    match (
+        path_utils::normalize_for_path_comparison(current_cwd),
+        path_utils::normalize_for_path_comparison(session_cwd),
+    ) {
+        (Ok(current), Ok(session)) => current != session,
+        _ => current_cwd != session_cwd,
+    }
+}
+
+pub(crate) async fn resolve_cwd_for_resume_or_fork(
+    tui: &mut Tui,
+    current_cwd: &Path,
+    path: &Path,
+    action: CwdPromptAction,
+    allow_prompt: bool,
+) -> color_eyre::Result<Option<PathBuf>> {
+    let Some(history_cwd) = read_session_cwd(path).await else {
+        return Ok(None);
+    };
+    if allow_prompt && cwds_differ(current_cwd, &history_cwd) {
+        let selection =
+            cwd_prompt::run_cwd_selection_prompt(tui, action, current_cwd, &history_cwd).await?;
+        return Ok(Some(match selection {
+            CwdSelection::Current => current_cwd.to_path_buf(),
+            CwdSelection::Session => history_cwd,
+        }));
+    }
+    Ok(Some(history_cwd))
+}
+
 #[expect(
     clippy::print_stderr,
     reason = "TUI should no longer be displayed, so we can write to stderr."
@@ -772,7 +854,14 @@ fn should_show_login_screen(login_status: LoginStatus, config: &Config) -> bool
 mod tests {
     use super::*;
     use codex_core::config::ConfigBuilder;
+    use codex_core::config::ConfigOverrides;
     use codex_core::config::ProjectConfig;
+    use codex_core::protocol::AskForApproval;
+    use codex_protocol::protocol::RolloutItem;
+    use codex_protocol::protocol::RolloutLine;
+    use codex_protocol::protocol::SessionMeta;
+    use codex_protocol::protocol::SessionMetaLine;
+    use codex_protocol::protocol::TurnContextItem;
     use serial_test::serial;
     use tempfile::TempDir;
 
@@ -846,4 +935,180 @@ mod tests {
         );
         Ok(())
     }
+
+    fn build_turn_context(config: &Config, cwd: PathBuf) -> TurnContextItem {
+        let model = config
+            .model
+            .clone()
+            .unwrap_or_else(|| "gpt-5.1".to_string());
+        TurnContextItem {
+            cwd,
+            approval_policy: config.approval_policy.value(),
+            sandbox_policy: config.sandbox_policy.get().clone(),
+            model,
+            personality: None,
+            collaboration_mode: None,
+            effort: config.model_reasoning_effort,
+            summary: config.model_reasoning_summary,
+            user_instructions: None,
+            developer_instructions: None,
+            final_output_json_schema: None,
+            truncation_policy: None,
+        }
+    }
+
+    #[tokio::test]
+    async fn read_session_cwd_prefers_latest_turn_context() -> std::io::Result<()> {
+        let temp_dir = TempDir::new()?;
+        let config = build_config(&temp_dir).await?;
+        let first = temp_dir.path().join("first");
+        let second = temp_dir.path().join("second");
+        std::fs::create_dir_all(&first)?;
+        std::fs::create_dir_all(&second)?;
+
+        let rollout_path = temp_dir.path().join("rollout.jsonl");
+        let lines = vec![
+            RolloutLine {
+                timestamp: "t0".to_string(),
+                item: RolloutItem::TurnContext(build_turn_context(&config, first)),
+            },
+            RolloutLine {
+                timestamp: "t1".to_string(),
+                item: RolloutItem::TurnContext(build_turn_context(&config, second.clone())),
+            },
+        ];
+        let mut text = String::new();
+        for line in lines {
+            text.push_str(&serde_json::to_string(&line).expect("serialize rollout"));
+            text.push('\n');
+        }
+        std::fs::write(&rollout_path, text)?;
+
+        let cwd = read_session_cwd(&rollout_path).await.expect("expected cwd");
+        assert_eq!(cwd, second);
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn should_prompt_when_meta_matches_current_but_latest_turn_differs() -> std::io::Result<()>
+    {
+        let temp_dir = TempDir::new()?;
+        let config = build_config(&temp_dir).await?;
+        let current = temp_dir.path().join("current");
+        let latest = temp_dir.path().join("latest");
+        std::fs::create_dir_all(&current)?;
+        std::fs::create_dir_all(&latest)?;
+
+        let rollout_path = temp_dir.path().join("rollout.jsonl");
+        let session_meta = SessionMeta {
+            cwd: current.clone(),
+            ..SessionMeta::default()
+        };
+        let lines = vec![
+            RolloutLine {
+                timestamp: "t0".to_string(),
+                item: RolloutItem::SessionMeta(SessionMetaLine {
+                    meta: session_meta,
+                    git: None,
+                }),
+            },
+            RolloutLine {
+                timestamp: "t1".to_string(),
+                item: RolloutItem::TurnContext(build_turn_context(&config, latest.clone())),
+            },
+        ];
+        let mut text = String::new();
+        for line in lines {
+            text.push_str(&serde_json::to_string(&line).expect("serialize rollout"));
+            text.push('\n');
+        }
+        std::fs::write(&rollout_path, text)?;
+
+        let session_cwd = read_session_cwd(&rollout_path).await.expect("expected cwd");
+        assert_eq!(session_cwd, latest);
+        assert!(cwds_differ(&current, &session_cwd));
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn config_rebuild_changes_trust_defaults_with_cwd() -> std::io::Result<()> {
+        let temp_dir = TempDir::new()?;
+        let codex_home = temp_dir.path().to_path_buf();
+        let trusted = temp_dir.path().join("trusted");
+        let untrusted = temp_dir.path().join("untrusted");
+        std::fs::create_dir_all(&trusted)?;
+        std::fs::create_dir_all(&untrusted)?;
+
+        // TOML keys need escaped backslashes on Windows paths.
+        let trusted_display = trusted.display().to_string().replace('\\', "\\\\");
+        let untrusted_display = untrusted.display().to_string().replace('\\', "\\\\");
+        let config_toml = format!(
+            r#"[projects."{trusted_display}"]
+trust_level = "trusted"
+
+[projects."{untrusted_display}"]
+trust_level = "untrusted"
+"#
+        );
+        std::fs::write(temp_dir.path().join("config.toml"), config_toml)?;
+
+        let trusted_overrides = ConfigOverrides {
+            cwd: Some(trusted.clone()),
+            ..Default::default()
+        };
+        let trusted_config = ConfigBuilder::default()
+            .codex_home(codex_home.clone())
+            .harness_overrides(trusted_overrides.clone())
+            .build()
+            .await?;
+        assert_eq!(
+            trusted_config.approval_policy.value(),
+            AskForApproval::OnRequest
+        );
+
+        let untrusted_overrides = ConfigOverrides {
+            cwd: Some(untrusted),
+            ..trusted_overrides
+        };
+        let untrusted_config = ConfigBuilder::default()
+            .codex_home(codex_home)
+            .harness_overrides(untrusted_overrides)
+            .build()
+            .await?;
+        assert_eq!(
+            untrusted_config.approval_policy.value(),
+            AskForApproval::UnlessTrusted
+        );
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn read_session_cwd_falls_back_to_session_meta() -> std::io::Result<()> {
+        let temp_dir = TempDir::new()?;
+        let _config = build_config(&temp_dir).await?;
+        let session_cwd = temp_dir.path().join("session");
+        std::fs::create_dir_all(&session_cwd)?;
+
+        let rollout_path = temp_dir.path().join("rollout.jsonl");
+        let session_meta = SessionMeta {
+            cwd: session_cwd.clone(),
+            ..SessionMeta::default()
+        };
+        let meta_line = RolloutLine {
+            timestamp: "t0".to_string(),
+            item: RolloutItem::SessionMeta(SessionMetaLine {
+                meta: session_meta,
+                git: None,
+            }),
+        };
+        let text = format!(
+            "{}\n",
+            serde_json::to_string(&meta_line).expect("serialize meta")
+        );
+        std::fs::write(&rollout_path, text)?;
+
+        let cwd = read_session_cwd(&rollout_path).await.expect("expected cwd");
+        assert_eq!(cwd, session_cwd);
+        Ok(())
+    }
 }
diff --git a/codex-rs/tui/src/onboarding/onboarding_screen.rs b/codex-rs/tui/src/onboarding/onboarding_screen.rs
index 7e076ae160..78a7f0ce85 100644
--- a/codex-rs/tui/src/onboarding/onboarding_screen.rs
+++ b/codex-rs/tui/src/onboarding/onboarding_screen.rs
@@ -311,6 +311,9 @@ impl WidgetRef for &OnboardingScreen {
             }
             let scratch_area = Rect::new(0, 0, width, max_h);
             let mut scratch = Buffer::empty(scratch_area);
+            if let Step::Welcome(widget) = step {
+                widget.update_layout_area(scratch_area);
+            }
             step.render_ref(scratch_area, &mut scratch);
             let h = used_rows(&scratch, width, max_h).min(max_h);
             if h > 0 {
diff --git a/codex-rs/tui/src/onboarding/welcome.rs b/codex-rs/tui/src/onboarding/welcome.rs
index 8ff5e81982..bdf4f91408 100644
--- a/codex-rs/tui/src/onboarding/welcome.rs
+++ b/codex-rs/tui/src/onboarding/welcome.rs
@@ -11,6 +11,7 @@ use ratatui::widgets::Clear;
 use ratatui::widgets::Paragraph;
 use ratatui::widgets::WidgetRef;
 use ratatui::widgets::Wrap;
+use std::cell::Cell;
 
 use crate::ascii_animation::AsciiAnimation;
 use crate::onboarding::onboarding_screen::KeyboardHandler;
@@ -19,13 +20,14 @@ use crate::tui::FrameRequester;
 
 use super::onboarding_screen::StepState;
 
-const MIN_ANIMATION_HEIGHT: u16 = 20;
+const MIN_ANIMATION_HEIGHT: u16 = 37;
 const MIN_ANIMATION_WIDTH: u16 = 60;
 
 pub(crate) struct WelcomeWidget {
     pub is_logged_in: bool,
     animation: AsciiAnimation,
     animations_enabled: bool,
+    layout_area: Cell<Option<Rect>>,
 }
 
 impl KeyboardHandler for WelcomeWidget {
@@ -53,8 +55,13 @@ impl WelcomeWidget {
             is_logged_in,
             animation: AsciiAnimation::new(request_frame),
             animations_enabled,
+            layout_area: Cell::new(None),
         }
     }
+
+    pub(crate) fn update_layout_area(&self, area: Rect) {
+        self.layout_area.set(Some(area));
+    }
 }
 
 impl WidgetRef for &WelcomeWidget {
@@ -64,12 +71,14 @@ impl WidgetRef for &WelcomeWidget {
             self.animation.schedule_next_frame();
         }
 
+        let layout_area = self.layout_area.get().unwrap_or(area);
         // Skip the animation entirely when the viewport is too small so we don't clip frames.
-        let show_animation =
-            area.height >= MIN_ANIMATION_HEIGHT && area.width >= MIN_ANIMATION_WIDTH;
+        let show_animation = self.animations_enabled
+            && layout_area.height >= MIN_ANIMATION_HEIGHT
+            && layout_area.width >= MIN_ANIMATION_WIDTH;
 
         let mut lines: Vec<Line> = Vec::new();
-        if show_animation && self.animations_enabled {
+        if show_animation {
             let frame = self.animation.current_frame();
             lines.extend(frame.lines().map(Into::into));
             lines.push("".into());
@@ -99,6 +108,7 @@ impl StepStateProvider for WelcomeWidget {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use pretty_assertions::assert_eq;
     use ratatui::buffer::Buffer;
     use ratatui::layout::Rect;
 
@@ -106,31 +116,37 @@ mod tests {
     static VARIANT_B: [&str; 1] = ["frame-b"];
     static VARIANTS: [&[&str]; 2] = [&VARIANT_A, &VARIANT_B];
 
+    fn row_containing(buf: &Buffer, needle: &str) -> Option<u16> {
+        (0..buf.area.height).find(|&y| {
+            let mut row = String::new();
+            for x in 0..buf.area.width {
+                row.push_str(buf[(x, y)].symbol());
+            }
+            row.contains(needle)
+        })
+    }
+
     #[test]
     fn welcome_renders_animation_on_first_draw() {
         let widget = WelcomeWidget::new(false, FrameRequester::test_dummy(), true);
         let area = Rect::new(0, 0, MIN_ANIMATION_WIDTH, MIN_ANIMATION_HEIGHT);
         let mut buf = Buffer::empty(area);
+        let frame_lines = widget.animation.current_frame().lines().count() as u16;
         (&widget).render(area, &mut buf);
 
-        let mut found = false;
-        let mut last_non_empty: Option<u16> = None;
-        for y in 0..area.height {
-            for x in 0..area.width {
-                if !buf[(x, y)].symbol().trim().is_empty() {
-                    found = true;
-                    last_non_empty = Some(y);
-                    break;
-                }
-            }
-        }
+        let welcome_row = row_containing(&buf, "Welcome");
+        assert_eq!(welcome_row, Some(frame_lines + 1));
+    }
 
-        assert!(found, "expected welcome animation to render characters");
-        let measured_rows = last_non_empty.map(|v| v + 2).unwrap_or(0);
-        assert!(
-            measured_rows >= MIN_ANIMATION_HEIGHT,
-            "expected measurement to report at least {MIN_ANIMATION_HEIGHT} rows, got {measured_rows}"
-        );
+    #[test]
+    fn welcome_skips_animation_below_height_breakpoint() {
+        let widget = WelcomeWidget::new(false, FrameRequester::test_dummy(), true);
+        let area = Rect::new(0, 0, MIN_ANIMATION_WIDTH, MIN_ANIMATION_HEIGHT - 1);
+        let mut buf = Buffer::empty(area);
+        (&widget).render(area, &mut buf);
+
+        let welcome_row = row_containing(&buf, "Welcome");
+        assert_eq!(welcome_row, Some(0));
     }
 
     #[test]
@@ -139,6 +155,7 @@ mod tests {
             is_logged_in: false,
             animation: AsciiAnimation::with_variants(FrameRequester::test_dummy(), &VARIANTS, 0),
             animations_enabled: true,
+            layout_area: Cell::new(None),
         };
 
         let before = widget.animation.current_frame();
diff --git a/codex-rs/tui/src/snapshots/codex_tui__cwd_prompt__tests__cwd_prompt_fork_modal.snap b/codex-rs/tui/src/snapshots/codex_tui__cwd_prompt__tests__cwd_prompt_fork_modal.snap
new file mode 100644
index 0000000000..38b712e872
--- /dev/null
+++ b/codex-rs/tui/src/snapshots/codex_tui__cwd_prompt__tests__cwd_prompt_fork_modal.snap
@@ -0,0 +1,14 @@
+---
+source: tui/src/cwd_prompt.rs
+expression: terminal.backend()
+---
+
+Choose working directory to fork this session
+
+  Session = latest cwd recorded in the forked session                           
+  Current = your current working directory
+
+› 1. Use session directory (/Users/example/session)                             
+  2. Use current directory (/Users/example/current)
+
+  Press enter to continue
diff --git a/codex-rs/tui/src/snapshots/codex_tui__cwd_prompt__tests__cwd_prompt_modal.snap b/codex-rs/tui/src/snapshots/codex_tui__cwd_prompt__tests__cwd_prompt_modal.snap
new file mode 100644
index 0000000000..4e87cfdfc7
--- /dev/null
+++ b/codex-rs/tui/src/snapshots/codex_tui__cwd_prompt__tests__cwd_prompt_modal.snap
@@ -0,0 +1,14 @@
+---
+source: tui/src/cwd_prompt.rs
+expression: terminal.backend()
+---
+
+Choose working directory to resume this session
+
+  Session = latest cwd recorded in the resumed session                          
+  Current = your current working directory
+
+› 1. Use session directory (/Users/example/session)                             
+  2. Use current directory (/Users/example/current)
+
+  Press enter to continue
diff --git a/codex-rs/windows-sandbox-rs/src/command_runner_win.rs b/codex-rs/windows-sandbox-rs/src/command_runner_win.rs
index 1739399901..a016c00c75 100644
--- a/codex-rs/windows-sandbox-rs/src/command_runner_win.rs
+++ b/codex-rs/windows-sandbox-rs/src/command_runner_win.rs
@@ -16,6 +16,7 @@ use codex_windows_sandbox::SandboxPolicy;
 use serde::Deserialize;
 use std::collections::HashMap;
 use std::ffi::c_void;
+use std::path::Path;
 use std::path::PathBuf;
 use windows_sys::Win32::Foundation::CloseHandle;
 use windows_sys::Win32::Foundation::GetLastError;
@@ -78,13 +79,20 @@ unsafe fn create_job_kill_on_close() -> Result<HANDLE> {
     Ok(h)
 }
 
+fn read_request_file(req_path: &Path) -> Result<String> {
+    let content = std::fs::read_to_string(req_path)
+        .with_context(|| format!("read request file {}", req_path.display()));
+    let _ = std::fs::remove_file(req_path);
+    content
+}
+
 pub fn main() -> Result<()> {
     let mut input = String::new();
     let mut args = std::env::args().skip(1);
     if let Some(first) = args.next() {
         if let Some(rest) = first.strip_prefix("--request-file=") {
             let req_path = PathBuf::from(rest);
-            input = std::fs::read_to_string(&req_path).context("read request file")?;
+            input = read_request_file(&req_path)?;
         }
     }
     if input.is_empty() {
@@ -265,3 +273,21 @@ pub fn main() -> Result<()> {
     }
     std::process::exit(exit_code);
 }
+
+#[cfg(test)]
+mod tests {
+    use super::read_request_file;
+    use pretty_assertions::assert_eq;
+    use std::fs;
+
+    #[test]
+    fn removes_request_file_after_read() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let req_path = dir.path().join("request.json");
+        fs::write(&req_path, "{\"ok\":true}").expect("write request");
+
+        let content = read_request_file(&req_path).expect("read request");
+        assert_eq!(content, "{\"ok\":true}");
+        assert!(!req_path.exists(), "request file should be removed");
+    }
+}