diff --git a/codex-rs/Cargo.lock b/codex-rs/Cargo.lock
index d94daa0e8f..6e2e7d65d9 100644
--- a/codex-rs/Cargo.lock
+++ b/codex-rs/Cargo.lock
@@ -2844,6 +2844,7 @@ dependencies = [
  "codex-utils-cargo-bin",
  "codex-utils-cli",
  "codex-utils-oss",
+ "codex-utils-path-uri",
  "codex-utils-sandbox-summary",
  "core_test_support",
  "libc",
diff --git a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
index 6b37f7c45e..719abb3ce3 100644
--- a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
+++ b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
@@ -19041,7 +19041,7 @@
             "description": "Reviewer currently used for approval requests on this thread."
           },
           "cwd": {
-            "$ref": "#/definitions/v2/AbsolutePathBuf"
+            "$ref": "#/definitions/v2/ApiPathString"
           },
           "instructionSources": {
             "default": [],
diff --git a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
index f36b90fffa..508935e020 100644
--- a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
+++ b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
@@ -16849,7 +16849,7 @@
           "description": "Reviewer currently used for approval requests on this thread."
         },
         "cwd": {
-          "$ref": "#/definitions/AbsolutePathBuf"
+          "$ref": "#/definitions/ApiPathString"
         },
         "instructionSources": {
           "default": [],
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json
index 33373b9f72..5b8be8f50a 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json
@@ -28,6 +28,9 @@
     "AgentPath": {
       "type": "string"
     },
+    "ApiPathString": {
+      "type": "string"
+    },
     "ApprovalsReviewer": {
       "description": "Configures who approval requests are routed to for review. Examples include sandbox escapes, blocked network access, MCP approval prompts, and ARC escalations. Defaults to `user`. `auto_review` uses a carefully prompted subagent to gather relevant context and apply a risk-based decision framework before approving or denying the request. The legacy value `guardian_subagent` is accepted for compatibility.",
       "enum": [
@@ -2319,7 +2322,7 @@
       "description": "Reviewer currently used for approval requests on this thread."
     },
     "cwd": {
-      "$ref": "#/definitions/AbsolutePathBuf"
+      "$ref": "#/definitions/ApiPathString"
     },
     "instructionSources": {
       "default": [],
diff --git a/codex-rs/app-server-protocol/schema/typescript/v2/ThreadStartResponse.ts b/codex-rs/app-server-protocol/schema/typescript/v2/ThreadStartResponse.ts
index 38859a3805..85929eefe3 100644
--- a/codex-rs/app-server-protocol/schema/typescript/v2/ThreadStartResponse.ts
+++ b/codex-rs/app-server-protocol/schema/typescript/v2/ThreadStartResponse.ts
@@ -2,13 +2,14 @@
 
 // This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
 import type { AbsolutePathBuf } from "../AbsolutePathBuf";
+import type { ApiPathString } from "../ApiPathString";
 import type { ReasoningEffort } from "../ReasoningEffort";
 import type { ApprovalsReviewer } from "./ApprovalsReviewer";
 import type { AskForApproval } from "./AskForApproval";
 import type { SandboxPolicy } from "./SandboxPolicy";
 import type { Thread } from "./Thread";
 
-export type ThreadStartResponse = {thread: Thread, model: string, modelProvider: string, serviceTier: string | null, cwd: AbsolutePathBuf, /**
+export type ThreadStartResponse = {thread: Thread, model: string, modelProvider: string, serviceTier: string | null, cwd: ApiPathString, /**
  * Instruction source files currently loaded for this thread.
  */
 instructionSources: Array<AbsolutePathBuf>, approvalPolicy: AskForApproval, /**
diff --git a/codex-rs/app-server-protocol/src/protocol/common.rs b/codex-rs/app-server-protocol/src/protocol/common.rs
index 7611c27ff1..49a5b5671e 100644
--- a/codex-rs/app-server-protocol/src/protocol/common.rs
+++ b/codex-rs/app-server-protocol/src/protocol/common.rs
@@ -2516,7 +2516,10 @@ mod tests {
                 model: "gpt-5".to_string(),
                 model_provider: "openai".to_string(),
                 service_tier: None,
-                cwd,
+                cwd: codex_utils_path_uri::ApiPathString::from_abs_path(
+                    &cwd,
+                    codex_utils_path_uri::PathConvention::native(),
+                )?,
                 runtime_workspace_roots: Vec::new(),
                 instruction_sources: vec![absolute_path("/tmp/AGENTS.md")],
                 approval_policy: v2::AskForApproval::OnFailure,
diff --git a/codex-rs/app-server-protocol/src/protocol/v2/thread.rs b/codex-rs/app-server-protocol/src/protocol/v2/thread.rs
index 0252c4b048..b990662349 100644
--- a/codex-rs/app-server-protocol/src/protocol/v2/thread.rs
+++ b/codex-rs/app-server-protocol/src/protocol/v2/thread.rs
@@ -26,6 +26,7 @@ use codex_protocol::protocol::ThreadGoalStatus as CoreThreadGoalStatus;
 use codex_protocol::protocol::TokenUsage as CoreTokenUsage;
 use codex_protocol::protocol::TokenUsageInfo as CoreTokenUsageInfo;
 use codex_utils_absolute_path::AbsolutePathBuf;
+use codex_utils_path_uri::ApiPathString;
 use schemars::JsonSchema;
 use serde::Deserialize;
 use serde::Serialize;
@@ -155,7 +156,7 @@ pub struct ThreadStartResponse {
     pub model: String,
     pub model_provider: String,
     pub service_tier: Option<String>,
-    pub cwd: AbsolutePathBuf,
+    pub cwd: ApiPathString,
     /// Thread-scoped runtime workspace roots used to materialize
     /// `:workspace_roots`.
     #[experimental("thread/start.runtimeWorkspaceRoots")]
diff --git a/codex-rs/app-server/src/request_processors/thread_processor.rs b/codex-rs/app-server/src/request_processors/thread_processor.rs
index 747e1a091b..ff9ae13947 100644
--- a/codex-rs/app-server/src/request_processors/thread_processor.rs
+++ b/codex-rs/app-server/src/request_processors/thread_processor.rs
@@ -4,6 +4,8 @@ use codex_app_server_protocol::SelectedCapabilityRoot;
 use codex_extension_api::ExtensionDataInit;
 use codex_protocol::models::BUILT_IN_PERMISSION_PROFILE_DANGER_FULL_ACCESS;
 use codex_protocol::models::BUILT_IN_PERMISSION_PROFILE_WORKSPACE;
+use codex_utils_path_uri::ApiPathString;
+use codex_utils_path_uri::PathUri;
 
 const THREAD_LIST_DEFAULT_LIMIT: usize = 25;
 const THREAD_LIST_MAX_LIMIT: usize = 100;
@@ -1230,7 +1232,21 @@ impl ThreadRequestProcessor {
             &config_snapshot.permission_profile,
             config_snapshot.cwd().as_path(),
         );
-        let cwd = config_snapshot.cwd().clone();
+        let cwd_uri = config_snapshot
+            .environment_selections()
+            .first()
+            .map(|environment| environment.cwd.clone())
+            .unwrap_or_else(|| PathUri::from_abs_path(config_snapshot.cwd()));
+        let cwd_convention = cwd_uri.infer_path_convention().ok_or_else(|| {
+            internal_error(format!(
+                "could not infer the path convention for thread cwd `{cwd_uri}`"
+            ))
+        })?;
+        let cwd = ApiPathString::from_path_uri(&cwd_uri, cwd_convention).map_err(|err| {
+            internal_error(format!(
+                "could not render thread cwd `{cwd_uri}` using {cwd_convention}: {err}"
+            ))
+        })?;
         let active_permission_profile =
             thread_response_active_permission_profile(config_snapshot.active_permission_profile);
 
diff --git a/codex-rs/app-server/tests/suite/v2/thread_start.rs b/codex-rs/app-server/tests/suite/v2/thread_start.rs
index c0946ba679..75a093850a 100644
--- a/codex-rs/app-server/tests/suite/v2/thread_start.rs
+++ b/codex-rs/app-server/tests/suite/v2/thread_start.rs
@@ -232,7 +232,7 @@ async fn thread_start_accepts_absolute_runtime_workspace_roots() -> Result<()> {
         ..
     } = to_response::<ThreadStartResponse>(resp)?;
 
-    assert_eq!(response_cwd, cwd.abs());
+    assert_eq!(response_cwd.as_str(), cwd.to_string_lossy());
     assert_eq!(runtime_workspace_roots, vec![extra_root.abs()]);
 
     Ok(())
diff --git a/codex-rs/core/tests/remote_env_windows/remote_env_windows_test.rs b/codex-rs/core/tests/remote_env_windows/remote_env_windows_test.rs
index 5f73e468ed..a68ee42486 100644
--- a/codex-rs/core/tests/remote_env_windows/remote_env_windows_test.rs
+++ b/codex-rs/core/tests/remote_env_windows/remote_env_windows_test.rs
@@ -268,8 +268,7 @@ async fn app_server_starts_thread_with_windows_environment_native_cwd() -> Resul
             let response: ThreadStartResponse = to_response(response)?;
             assert!(!response.thread.id.is_empty());
             let host_cwd = codex_home.path().to_path_buf().abs();
-            // TODO(anp): Return the selected environment's native cwd from thread/start.
-            assert_eq!(response.cwd, host_cwd);
+            assert_eq!(response.cwd.as_str(), NATIVE_CWD);
             // TODO(anp): Derive runtime workspace roots from the selected remote environment.
             assert_eq!(response.runtime_workspace_roots, vec![host_cwd]);
             // TODO(anp): Discover and report instruction sources from the remote filesystem.
diff --git a/codex-rs/exec/Cargo.toml b/codex-rs/exec/Cargo.toml
index cdfc569b68..d78d9edf0d 100644
--- a/codex-rs/exec/Cargo.toml
+++ b/codex-rs/exec/Cargo.toml
@@ -39,6 +39,7 @@ codex-protocol = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
 codex-utils-cli = { workspace = true }
 codex-utils-oss = { workspace = true }
+codex-utils-path-uri = { workspace = true }
 codex-utils-sandbox-summary = { workspace = true }
 owo-colors = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
diff --git a/codex-rs/exec/src/lib.rs b/codex-rs/exec/src/lib.rs
index f8ac851bf9..d01258768c 100644
--- a/codex-rs/exec/src/lib.rs
+++ b/codex-rs/exec/src/lib.rs
@@ -100,6 +100,8 @@ use codex_utils_absolute_path::canonicalize_existing_preserving_symlinks;
 use codex_utils_cli::SharedCliOptions;
 use codex_utils_oss::ensure_oss_provider_ready;
 use codex_utils_oss::get_default_model_for_oss_provider;
+use codex_utils_path_uri::ApiPathString;
+use codex_utils_path_uri::PathConvention;
 use event_processor_with_human_output::EventProcessorWithHumanOutput;
 pub use event_processor_with_jsonl_output::CodexStatus;
 pub use event_processor_with_jsonl_output::CollectedThreadEvents;
@@ -1154,6 +1156,18 @@ fn session_configured_from_thread_start_response(
     response: &ThreadStartResponse,
     config: &Config,
 ) -> Result<SessionConfiguredEvent, String> {
+    let cwd_convention = response
+        .cwd
+        .infer_absolute_path_convention()
+        .ok_or_else(|| format!("thread cwd `{}` is not absolute", response.cwd.as_str()))?;
+    let cwd_uri = response
+        .cwd
+        .to_path_uri(cwd_convention)
+        .map_err(|err| format!("thread cwd is invalid: {err}"))?;
+    let cwd = ApiPathString::from_path_uri(&cwd_uri, PathConvention::native())
+        .map_err(|err| format!("thread cwd cannot be represented on this host: {err}"))?;
+    let cwd = AbsolutePathBuf::try_from(cwd.into_string())
+        .map_err(|err| format!("thread cwd is invalid on this host: {err}"))?;
     session_configured_from_thread_response(
         &response.thread.session_id,
         &response.thread.id,
@@ -1168,7 +1182,7 @@ fn session_configured_from_thread_start_response(
         response.approvals_reviewer.to_core(),
         config.permissions.effective_permission_profile(),
         response.active_permission_profile.clone().map(Into::into),
-        response.cwd.clone(),
+        cwd,
         response.reasoning_effort.clone(),
     )
 }
diff --git a/codex-rs/exec/src/lib_tests.rs b/codex-rs/exec/src/lib_tests.rs
index 6b27d01116..ff541e276f 100644
--- a/codex-rs/exec/src/lib_tests.rs
+++ b/codex-rs/exec/src/lib_tests.rs
@@ -775,7 +775,8 @@ fn sample_thread_start_response() -> ThreadStartResponse {
         model: "gpt-5.4".to_string(),
         model_provider: "openai".to_string(),
         service_tier: None,
-        cwd: test_path_buf("/tmp").abs(),
+        cwd: ApiPathString::from_abs_path(&test_path_buf("/tmp").abs(), PathConvention::native())
+            .expect("API cwd"),
         runtime_workspace_roots: Vec::new(),
         instruction_sources: Vec::new(),
         approval_policy: codex_app_server_protocol::AskForApproval::OnRequest,
diff --git a/codex-rs/tui/Cargo.toml b/codex-rs/tui/Cargo.toml
index b000cba124..6af093286d 100644
--- a/codex-rs/tui/Cargo.toml
+++ b/codex-rs/tui/Cargo.toml
@@ -62,6 +62,7 @@ codex-utils-fuzzy-match = { workspace = true }
 codex-utils-home-dir = { workspace = true }
 codex-utils-oss = { workspace = true }
 codex-utils-path = { workspace = true }
+codex-utils-path-uri = { workspace = true }
 codex-utils-plugins = { workspace = true }
 codex-utils-sandbox-summary = { workspace = true }
 codex-utils-sleep-inhibitor = { workspace = true }
diff --git a/codex-rs/tui/src/app_server_session.rs b/codex-rs/tui/src/app_server_session.rs
index 5e36fb1c9d..eecdf73cf0 100644
--- a/codex-rs/tui/src/app_server_session.rs
+++ b/codex-rs/tui/src/app_server_session.rs
@@ -120,6 +120,8 @@ use codex_protocol::openai_models::ModelServiceTier;
 use codex_protocol::openai_models::ModelUpgrade;
 use codex_protocol::openai_models::ReasoningEffortPreset;
 use codex_utils_absolute_path::AbsolutePathBuf;
+use codex_utils_path_uri::ApiPathString;
+use codex_utils_path_uri::PathConvention;
 use color_eyre::eyre::ContextCompat;
 use color_eyre::eyre::Result;
 use color_eyre::eyre::WrapErr;
@@ -1538,9 +1540,21 @@ async fn thread_session_state_from_thread_start_response(
     config: &Config,
     thread_params_mode: ThreadParamsMode,
 ) -> Result<ThreadSessionState, String> {
+    let cwd_convention = response
+        .cwd
+        .infer_absolute_path_convention()
+        .ok_or_else(|| format!("thread cwd `{}` is not absolute", response.cwd.as_str()))?;
+    let cwd_uri = response
+        .cwd
+        .to_path_uri(cwd_convention)
+        .map_err(|err| format!("thread cwd is invalid: {err}"))?;
+    let cwd = ApiPathString::from_path_uri(&cwd_uri, PathConvention::native())
+        .map_err(|err| format!("thread cwd cannot be represented on this host: {err}"))?;
+    let cwd = AbsolutePathBuf::try_from(cwd.into_string())
+        .map_err(|err| format!("thread cwd is invalid on this host: {err}"))?;
     let permission_profile = display_permission_profile_from_thread_response(
         &response.sandbox,
-        response.cwd.as_path(),
+        cwd.as_path(),
         config,
         thread_params_mode,
     );
@@ -1556,7 +1570,7 @@ async fn thread_session_state_from_thread_start_response(
         response.approvals_reviewer.to_core(),
         permission_profile,
         response.active_permission_profile.clone().map(Into::into),
-        response.cwd.clone(),
+        cwd,
         response.runtime_workspace_roots.clone(),
         response.instruction_sources.clone(),
         response.reasoning_effort.clone(),