diff --git a/codex-rs/app-server/tests/suite/v2/multi_agent_v2_developer_instructions.rs b/codex-rs/app-server/tests/suite/v2/multi_agent_v2_developer_instructions.rs
index cab6b5253c..ca54c8dc3f 100644
--- a/codex-rs/app-server/tests/suite/v2/multi_agent_v2_developer_instructions.rs
+++ b/codex-rs/app-server/tests/suite/v2/multi_agent_v2_developer_instructions.rs
@@ -53,7 +53,6 @@ const ROLE_INSTRUCTIONS: &str = "configured role developer instructions";
 /// V2 fork modes, roles, and unset/blank overrides expose their agreed instruction precedence.
 #[test_case("no history"; "no history")]
 #[test_case("full history"; "full history")]
-#[test_case("bounded history"; "bounded history")]
 #[test_case("configured role without instructions"; "configured role without instructions")]
 #[test_case("unset override"; "unset override")]
 #[test_case("blank override"; "blank override")]
@@ -61,14 +60,12 @@ const ROLE_INSTRUCTIONS: &str = "configured role developer instructions";
 #[test_case("explicit configured role"; "explicit configured role")]
 #[test_case("full history configured role"; "full history configured role")]
 #[test_case("implicit configured default"; "implicit configured default")]
-#[test_case("bounded implicit configured default"; "bounded implicit configured default")]
 #[test_case("full fork skips default role"; "full fork skips default role")]
 #[tokio::test]
 async fn spawned_subagents_apply_configured_developer_instruction_precedence(
     case: &str,
 ) -> Result<()> {
     let fork_turns = match case {
-        "bounded history" | "bounded implicit configured default" => Some("1"),
         "no history" | "explicit configured role" | "implicit configured default" => Some("none"),
         _ => None,
     };
@@ -81,8 +78,7 @@ async fn spawned_subagents_apply_configured_developer_instruction_precedence(
     let configured_override = match case {
         "unset override"
         | "full history configured role"
-        | "configured role without instructions"
-        | "bounded implicit configured default" => None,
+        | "configured role without instructions" => None,
         "blank override" => Some("   "),
         "full history" => Some("  child-only developer instructions  "),
         _ => Some(CHILD_INSTRUCTIONS),
@@ -98,7 +94,6 @@ async fn spawned_subagents_apply_configured_developer_instruction_precedence(
             | "explicit configured role"
             | "full history configured role"
             | "implicit configured default"
-            | "bounded implicit configured default"
             | "full fork skips default role"
     );
     let role_has_instructions = matches!(
@@ -106,7 +101,6 @@ async fn spawned_subagents_apply_configured_developer_instruction_precedence(
         "explicit configured role"
             | "full history configured role"
             | "implicit configured default"
-            | "bounded implicit configured default"
             | "full fork skips default role"
     );
     let expected = match case {
@@ -114,8 +108,7 @@ async fn spawned_subagents_apply_configured_developer_instruction_precedence(
         "blank override" => None,
         "explicit configured role"
         | "full history configured role"
-        | "implicit configured default"
-        | "bounded implicit configured default" => Some(ROLE_INSTRUCTIONS),
+        | "implicit configured default" => Some(ROLE_INSTRUCTIONS),
         _ => Some(CHILD_INSTRUCTIONS),
     };
     const PARENT_PROMPT: &str = "spawn the instruction override worker";
diff --git a/codex-rs/core/src/agent/control.rs b/codex-rs/core/src/agent/control.rs
index a7af5100a8..903f178b17 100644
--- a/codex-rs/core/src/agent/control.rs
+++ b/codex-rs/core/src/agent/control.rs
@@ -19,7 +19,6 @@ use crate::thread_manager::ResumeThreadWithHistoryOptions;
 use crate::thread_manager::ThreadIdGenerator;
 use crate::thread_manager::ThreadManagerState;
 use crate::thread_manager::default_thread_id_generator;
-use crate::thread_rollout_truncation::truncate_rollout_to_last_n_fork_turns;
 use crate::turn_timing::now_unix_timestamp_ms;
 use codex_history::InitialHistory;
 use codex_history::ResumedHistory;
diff --git a/codex-rs/core/src/agent/control/spawn.rs b/codex-rs/core/src/agent/control/spawn.rs
index db563dfe90..deef223bfc 100644
--- a/codex-rs/core/src/agent/control/spawn.rs
+++ b/codex-rs/core/src/agent/control/spawn.rs
@@ -7,7 +7,6 @@ use crate::agent::child_config::build_agent_resume_config;
 use crate::agent::role::apply_role_to_config;
 use crate::agent::types::AgentMetadata;
 use crate::agent::types::LiveAgent;
-use crate::agent::types::SpawnAgentForkMode;
 use crate::agent::types::SpawnAgentOptions;
 use crate::agents_md_manager::SessionInstructions;
 use crate::codex_thread::CodexThread;
@@ -122,8 +121,7 @@ fn keep_forked_rollout_item(item: &RolloutItem, preserve_context_baselines: bool
         | RolloutItem::RetainedContext(_)
         | RolloutItem::SecurityRiskScore(_) => false,
         // Full-history forks preserve the cached prompt prefix and can keep diffing
-        // from the parent's durable baseline. Truncated forks drop part of that prompt,
-        // so they must rebuild context on their first child turn.
+        // from the parent's durable baseline unless legacy compaction requires rebuilding it.
         RolloutItem::TurnContext(_) | RolloutItem::WorldState(_) => preserve_context_baselines,
         // Child threads inherit model context, not the parent's cumulative usage state.
         RolloutItem::TokenUsageRecord(_) => false,
@@ -140,7 +138,11 @@ fn retain_forked_developer_message(item: &mut ResponseItem, usage_hint_texts: &[
         return false;
     };
     content.retain(|content_item| {
-        if content_item.kind().0 == "guardian.approved_action" {
+        // Persisted role hints can predate the current bundled wording and lack markers.
+        if matches!(
+            content_item.kind().0.as_str(),
+            "guardian.approved_action" | "multi_agent.role_instructions" | "multi_agent.usage_hint"
+        ) {
             return false;
         }
         let ContentItem::InputText { text } = content_item.content() else {
@@ -990,11 +992,11 @@ impl LocalAgentControl {
                 "spawn_agent fork requires a parent spawn call id".to_string(),
             ));
         }
-        let Some(fork_mode) = options.fork_mode.as_ref() else {
+        if options.fork_mode.is_none() {
             return Err(CodexErr::Fatal(
                 "spawn_agent fork requires a fork mode".to_string(),
             ));
-        };
+        }
         let SessionSource::SubAgent(SubAgentSource::ThreadSpawn {
             parent_thread_id, ..
         }) = &session_source
@@ -1062,10 +1064,6 @@ impl LocalAgentControl {
                 Some(meta_line.meta.selected_capability_roots.clone())
             })
             .unwrap_or_default();
-        if let SpawnAgentForkMode::LastNTurns(last_n_turns) = fork_mode {
-            forked_rollout_items =
-                truncate_rollout_to_last_n_fork_turns(forked_rollout_items, *last_n_turns);
-        }
         let multi_agent_v2_usage_hint_texts_to_filter: Vec<String> =
             if multi_agent_version == MultiAgentVersion::V2 {
                 let parent_config = parent_thread.session.get_config().await;
@@ -1082,19 +1080,17 @@ impl LocalAgentControl {
             } else {
                 Vec::new()
             };
-        let mut preserve_context_baselines = matches!(fork_mode, SpawnAgentForkMode::FullHistory);
-        if preserve_context_baselines {
-            for item in forked_rollout_items.iter().rev() {
-                let RolloutItem::Compacted(compacted) = item else {
-                    continue;
-                };
-                // Legacy checkpoints force the child to rebuild context regardless of the
-                // live parent's reference baseline; an older superseded checkpoint does not.
-                if compacted.replacement_history.is_none() {
-                    preserve_context_baselines = false;
-                }
-                break;
+        let mut preserve_context_baselines = true;
+        for item in forked_rollout_items.iter().rev() {
+            let RolloutItem::Compacted(compacted) = item else {
+                continue;
+            };
+            // Legacy checkpoints force the child to rebuild context regardless of the
+            // live parent's reference baseline; an older superseded checkpoint does not.
+            if compacted.replacement_history.is_none() {
+                preserve_context_baselines = false;
             }
+            break;
         }
         let mut replaced_parent_developer_instructions = false;
         // Scrub inherited hints and replace only the parent's developer-instruction fragment.
diff --git a/codex-rs/core/src/agent/control/spawn_telemetry.rs b/codex-rs/core/src/agent/control/spawn_telemetry.rs
index 7b681ce9c7..1501d935d2 100644
--- a/codex-rs/core/src/agent/control/spawn_telemetry.rs
+++ b/codex-rs/core/src/agent/control/spawn_telemetry.rs
@@ -28,7 +28,6 @@ pub(super) fn record_spawn_success(
     let fork_mode = match fork_mode {
         None => "none",
         Some(SpawnAgentForkMode::FullHistory) => "all",
-        Some(SpawnAgentForkMode::LastNTurns(_)) => "last_n",
     };
     let history_mode = match measurements.history_mode {
         ThreadHistoryMode::Legacy => "legacy",
diff --git a/codex-rs/core/src/agent/control/spawn_telemetry_tests.rs b/codex-rs/core/src/agent/control/spawn_telemetry_tests.rs
index 410ace28d9..2c44e6cc60 100644
--- a/codex-rs/core/src/agent/control/spawn_telemetry_tests.rs
+++ b/codex-rs/core/src/agent/control/spawn_telemetry_tests.rs
@@ -39,7 +39,7 @@ fn records_bounded_spawn_phase_metrics() {
 
     record_spawn_success(
         &telemetry,
-        Some(&SpawnAgentForkMode::LastNTurns(3)),
+        Some(&SpawnAgentForkMode::FullHistory),
         MultiAgentVersion::V2,
         SpawnMeasurements {
             history_mode: ThreadHistoryMode::Paginated,
@@ -74,7 +74,7 @@ fn records_bounded_spawn_phase_metrics() {
                 })
                 .collect::<BTreeMap<_, _>>();
             assert_eq!(attributes.len(), 5);
-            assert_eq!(attributes["fork_mode"], "last_n");
+            assert_eq!(attributes["fork_mode"], "all");
             assert_eq!(attributes["history_mode"], "paginated");
             assert_eq!(attributes["multi_agent_version"], "v2");
             assert_eq!(attributes["product_sku"], "codex");
diff --git a/codex-rs/core/src/agent/control_tests.rs b/codex-rs/core/src/agent/control_tests.rs
index 81846759f8..a0a1df5458 100644
--- a/codex-rs/core/src/agent/control_tests.rs
+++ b/codex-rs/core/src/agent/control_tests.rs
@@ -31,7 +31,6 @@ use crate::thread_manager::ForkSnapshot;
 use crate::thread_manager::StartThreadOptions;
 use crate::tools::handlers::multi_agents_common::thread_spawn_source;
 use assert_matches::assert_matches;
-use codex_extension_api::ExtensionDataInit;
 use codex_extension_api::Instructions;
 use codex_extension_api::LoadInstructionsFuture;
 use codex_extension_api::LoadedUserInstructions;
@@ -46,8 +45,6 @@ use codex_login::AuthManager;
 use codex_login::CodexAuth;
 use codex_protocol::AgentPath;
 use codex_protocol::ResponseItemId;
-use codex_protocol::capabilities::CapabilityRootLocation;
-use codex_protocol::capabilities::SelectedCapabilityRoot;
 use codex_protocol::config_types::ApprovalsReviewer;
 use codex_protocol::config_types::CollaborationMode;
 use codex_protocol::config_types::ModeKind;
@@ -2243,88 +2240,6 @@ async fn spawn_agent_fork_sanitizes_inherited_compaction_metadata() {
     );
 }
 
-#[tokio::test]
-async fn spawn_agent_numeric_fork_from_compacted_paginated_parent_clamps_to_provable_turns() {
-    let harness = AgentControlHarness::new().await;
-    let (parent_thread_id, parent_thread) = harness.start_paginated_thread().await;
-    let parent_spawn_call_id = "spawn-call-paginated-numeric".to_string();
-    parent_thread
-        .session
-        .persist_rollout_items(&[
-            RolloutItem::Compacted(CompactedItem {
-                message: String::new(),
-                replacement_history: Some(vec![
-                    ResponseItem::Message {
-                        id: None,
-                        role: "user".to_string(),
-                        content: vec![ContentItem::InputText {
-                            text: "compacted summary".to_string(),
-                        }],
-                        phase: None,
-                        internal_chat_message_metadata_passthrough: None,
-                    }
-                    .into(),
-                ]),
-                retained_context: None,
-                guardian_history: None,
-                mcp_resource_origins: None,
-                window_number: None,
-                first_window_id: None,
-                previous_window_id: None,
-                window_id: None,
-                compaction_response_id: None,
-                latest_token_usage_record: None,
-                resume_metadata: None,
-            }),
-            rollout_response_item(ResponseItem::Message {
-                id: None,
-                role: "user".to_string(),
-                content: vec![ContentItem::InputText {
-                    text: "recent parent turn".to_string(),
-                }],
-                phase: None,
-                internal_chat_message_metadata_passthrough: None,
-            }),
-            rollout_response_item(spawn_agent_call(&parent_spawn_call_id)),
-        ])
-        .await;
-
-    let clamped_child_thread_id = harness
-        .spawn_anonymous_child(
-            parent_thread_id,
-            SpawnAgentOptions {
-                fork_parent_spawn_call_id: Some(parent_spawn_call_id),
-                fork_mode: Some(SpawnAgentForkMode::LastNTurns(2)),
-                ..Default::default()
-            },
-        )
-        .await;
-    let clamped_child_thread = harness
-        .manager
-        .get_thread(clamped_child_thread_id)
-        .await
-        .expect("clamped child thread should be registered");
-    let clamped_history = clamped_child_thread.session.clone_history().await;
-    assert!(
-        history_contains_text(clamped_history.raw_items(), "recent parent turn"),
-        "clamped numeric fork should keep the provable recent turn"
-    );
-    assert!(
-        !history_contains_text(clamped_history.raw_items(), "compacted summary"),
-        "clamped numeric fork should not expand into compacted parent context"
-    );
-
-    let _ = harness
-        .control
-        .shutdown_live_agent(clamped_child_thread_id)
-        .await
-        .expect("clamped child shutdown should submit");
-    let _ = parent_thread
-        .submit(Op::Shutdown {})
-        .await
-        .expect("parent shutdown should submit");
-}
-
 #[tokio::test]
 async fn spawn_agent_can_fork_parent_thread_history_with_sanitized_items() {
     let managed_fragment = "<managed_developer_instructions>\nParent developer instructions.\n</managed_developer_instructions>";
@@ -2708,8 +2623,10 @@ async fn spawn_agent_can_fork_parent_thread_history_with_sanitized_items() {
         .expect("parent shutdown should submit");
 }
 
+#[test_case::test_case(true; "marked catalog hints")]
+#[test_case::test_case(false; "unmarked bundled hints")]
 #[tokio::test]
-async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history() {
+async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history(marked: bool) {
     let harness = AgentControlHarness::new().await;
     let mut parent_config = harness.config.clone();
     let _ = parent_config.features.enable(Feature::MultiAgentV2);
@@ -2738,7 +2655,7 @@ async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history() {
     let parent_spawn_call_id = "spawn-call-compacted-usage-hints".to_string();
     let catalog_role = |base: &str| MultiAgentRoleInstructions::Composed {
         base: base.to_string(),
-        marked: true,
+        marked,
         omit_update_plan_instructions: false,
         max_concurrency: 2,
         wait_agent_enabled: false,
@@ -2768,10 +2685,15 @@ async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history() {
             id: None,
             role: "developer".to_string(),
             content: vec![ContentItem::InputText {
-                text: "Parent root guidance.".to_string(),
+                text: "Previous parent root guidance.".to_string(),
             }],
             phase: None,
-            internal_chat_message_metadata_passthrough: None,
+            internal_chat_message_metadata_passthrough: Some(
+                InternalChatMessageMetadataPassthrough {
+                    content_item_kinds: Some(vec![ContentItemKind("multi_agent.usage_hint".to_string())]),
+                    ..Default::default()
+                },
+            ),
         },
         ResponseItem::Message {
             id: None,
@@ -2922,7 +2844,7 @@ async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history() {
         "forked child history should not inherit compacted parent agent messages"
     );
     assert!(
-        !history_contains_text(history.raw_items(), "Parent root guidance."),
+        !history_contains_text(history.raw_items(), "Previous parent root guidance."),
         "forked child history should strip stale parent hints from compacted replacement history"
     );
     assert!(
@@ -3529,443 +3451,6 @@ async fn spawn_agent_fork_flushes_parent_rollout_before_loading_history() {
         .expect("parent shutdown should submit");
 }
 
-#[tokio::test]
-async fn spawn_agent_fork_last_n_turns_keeps_only_recent_turns() {
-    let harness = AgentControlHarness::new().await;
-    let (parent_thread_id, parent_thread) = harness.start_thread().await;
-    let old_turn_context = parent_thread.session.new_default_turn().await;
-    parent_thread
-        .session
-        .record_conversation_items(
-            old_turn_context.as_ref(),
-            old_turn_context.model_info(),
-            &[user_message("old parent context")],
-        )
-        .await;
-    let source = McpAttributionSource {
-        connector_id: None,
-        plugin_id: None,
-        server_name: "example".to_string(),
-        tool_name: "search".to_string(),
-        first_turn_id: old_turn_context.sub_id.clone(),
-    };
-    parent_thread
-        .session
-        .services
-        .executed_tool_calls
-        .record_mcp_source(source.clone());
-    parent_thread
-        .session
-        .record_conversation_items(
-            old_turn_context.as_ref(),
-            old_turn_context.model_info(),
-            &[assistant_message("old MCP result", /*phase*/ None)],
-        )
-        .await;
-    let queued_communication = InterAgentCommunication::new(
-        AgentPath::root(),
-        AgentPath::try_from("/root/worker").expect("agent path"),
-        Vec::new(),
-        "queued message".to_string(),
-        /*trigger_turn*/ false,
-    );
-    let queued_turn_context = parent_thread.session.new_default_turn().await;
-    parent_thread
-        .session
-        .record_conversation_items(
-            queued_turn_context.as_ref(),
-            queued_turn_context.model_info(),
-            &[queued_communication.to_response_input_item().into()],
-        )
-        .await;
-
-    let triggered_communication = InterAgentCommunication::new(
-        AgentPath::root(),
-        AgentPath::try_from("/root/worker").expect("agent path"),
-        Vec::new(),
-        "triggered context".to_string(),
-        /*trigger_turn*/ true,
-    );
-    let triggered_turn_context = parent_thread.session.new_default_turn().await;
-    parent_thread
-        .session
-        .record_conversation_items(
-            triggered_turn_context.as_ref(),
-            triggered_turn_context.model_info(),
-            &[triggered_communication.to_response_input_item().into()],
-        )
-        .await;
-    parent_thread
-        .inject_response_items(vec![user_message("current parent task")])
-        .await
-        .expect("inject current parent task");
-    let spawn_turn_context = parent_thread.session.new_default_turn().await;
-    let parent_spawn_call_id = "spawn-call-last-n".to_string();
-    parent_thread
-        .session
-        .record_conversation_items(
-            spawn_turn_context.as_ref(),
-            spawn_turn_context.model_info(),
-            &[spawn_agent_call(&parent_spawn_call_id)],
-        )
-        .await;
-    parent_thread
-        .session
-        .persist_rollout_items(&[RolloutItem::TurnContext(
-            spawn_turn_context.to_turn_context_item(),
-        )])
-        .await;
-    parent_thread
-        .session
-        .ensure_rollout_materialized(PersistContext::Standard)
-        .await;
-    parent_thread
-        .session
-        .flush_rollout()
-        .await
-        .expect("parent rollout should flush");
-
-    let child_thread_id = harness
-        .control
-        .spawn_agent_with_metadata(
-            harness.config.clone(),
-            text_input("child task"),
-            SessionSource::SubAgent(SubAgentSource::ThreadSpawn {
-                parent_thread_id,
-                depth: 1,
-                agent_path: None,
-                agent_nickname: None,
-                agent_role: None,
-            }),
-            SpawnAgentOptions {
-                fork_parent_spawn_call_id: Some(parent_spawn_call_id.clone()),
-                fork_mode: Some(SpawnAgentForkMode::LastNTurns(2)),
-                ..Default::default()
-            },
-        )
-        .await
-        .expect("forked spawn should keep only the last two turns")
-        .thread_id;
-
-    let child_thread = harness
-        .manager
-        .get_thread(child_thread_id)
-        .await
-        .expect("child thread should be registered");
-    let history = child_thread.session.clone_history().await;
-
-    assert!(
-        !history_contains_text(history.raw_items(), "old parent context"),
-        "forked child history should drop parent context outside the requested last-N turn window"
-    );
-    assert!(
-        !history_contains_text(history.raw_items(), "old MCP result"),
-        "forked child history should drop the old result while retaining its attribution"
-    );
-    assert!(
-        !history_contains_text(history.raw_items(), "queued message"),
-        "forked child history should drop queued inter-agent messages outside the requested last-N turn window"
-    );
-    assert!(
-        !history_contains_text(history.raw_items(), "triggered context"),
-        "forked child history should filter assistant inter-agent messages even when they fall inside the requested last-N turn window"
-    );
-    assert!(
-        history_contains_text(history.raw_items(), "current parent task"),
-        "forked child history should keep the parent user message from the requested last-N turn window"
-    );
-    assert!(
-        child_thread
-            .session
-            .reference_context_item()
-            .await
-            .is_none(),
-        "last-N forked child should rebuild context after truncating the cached prefix"
-    );
-    assert_eq!(
-        mcp_attribution_in_constructed_request(&child_thread).await,
-        McpAttribution {
-            status: McpAttributionStatus::Complete,
-            error_reason: None,
-            sources: vec![source],
-        }
-    );
-
-    let _ = harness
-        .control
-        .shutdown_live_agent(child_thread_id)
-        .await
-        .expect("child shutdown should submit");
-    let _ = parent_thread
-        .submit(Op::Shutdown {})
-        .await
-        .expect("parent shutdown should submit");
-}
-
-#[tokio::test]
-async fn spawn_agent_fork_last_n_turns_drops_parent_startup_prefix_when_under_limit() {
-    let harness = AgentControlHarness::new().await;
-    let selected_capability_roots = vec![SelectedCapabilityRoot {
-        id: "demo@1".to_string(),
-        location: CapabilityRootLocation::Environment {
-            environment_id: "build".to_string(),
-            path: PathUri::parse("file:///plugins/demo").expect("plugin root URI"),
-        },
-    }];
-    let mut thread_extension_init = ExtensionDataInit::new();
-    thread_extension_init.insert(selected_capability_roots.clone());
-    let parent = harness
-        .manager
-        .start_thread(StartThreadOptions {
-            environments: Some(Vec::new()),
-            thread_extension_init,
-            ..StartThreadOptions::new(harness.config.clone())
-        })
-        .await
-        .expect("start parent thread");
-    let parent_thread_id = parent.thread_id;
-    let parent_thread = parent.thread;
-    let startup_turn_context = parent_thread.session.new_default_turn().await;
-    parent_thread
-        .session
-        .record_conversation_items(
-            startup_turn_context.as_ref(),
-            startup_turn_context.model_info(),
-            &[ResponseItem::Message {
-                id: None,
-                role: "developer".to_string(),
-                content: vec![ContentItem::InputText {
-                    text: "parent startup developer context".to_string(),
-                }],
-                phase: None,
-                internal_chat_message_metadata_passthrough: None,
-            }],
-        )
-        .await;
-    parent_thread
-        .inject_response_items(vec![user_message("current parent task")])
-        .await
-        .expect("inject current parent task");
-    let spawn_turn_context = parent_thread.session.new_default_turn().await;
-    let parent_spawn_call_id = "spawn-call-last-n-under-limit".to_string();
-    parent_thread
-        .session
-        .record_conversation_items(
-            spawn_turn_context.as_ref(),
-            spawn_turn_context.model_info(),
-            &[spawn_agent_call(&parent_spawn_call_id)],
-        )
-        .await;
-    parent_thread
-        .session
-        .ensure_rollout_materialized(PersistContext::Standard)
-        .await;
-    parent_thread
-        .session
-        .flush_rollout()
-        .await
-        .expect("parent rollout should flush");
-
-    let child_thread_id = harness
-        .control
-        .spawn_agent_with_metadata(
-            harness.config.clone(),
-            text_input("child task"),
-            SessionSource::SubAgent(SubAgentSource::ThreadSpawn {
-                parent_thread_id,
-                depth: 1,
-                agent_path: None,
-                agent_nickname: None,
-                agent_role: None,
-            }),
-            SpawnAgentOptions {
-                fork_parent_spawn_call_id: Some(parent_spawn_call_id),
-                fork_mode: Some(SpawnAgentForkMode::LastNTurns(2)),
-                ..Default::default()
-            },
-        )
-        .await
-        .expect("bounded forked spawn should drop startup prefix")
-        .thread_id;
-
-    let child_thread = harness
-        .manager
-        .get_thread(child_thread_id)
-        .await
-        .expect("child thread should be registered");
-    let history = child_thread.session.clone_history().await;
-    assert!(
-        history_contains_text(history.raw_items(), "current parent task"),
-        "bounded fork should retain the requested recent parent turn"
-    );
-    assert!(
-        !history_contains_text(history.raw_items(), "parent startup developer context"),
-        "bounded fork should drop parent startup context even when fewer turns exist than requested"
-    );
-    assert_eq!(
-        &child_thread.session.services.selected_capability_roots,
-        &selected_capability_roots
-    );
-    assert!(
-        child_thread
-            .session
-            .reference_context_item()
-            .await
-            .is_none(),
-        "bounded forked child should still rebuild context after truncating the cached prefix"
-    );
-
-    let _ = harness
-        .control
-        .shutdown_live_agent(child_thread_id)
-        .await
-        .expect("child shutdown should submit");
-    let _ = parent_thread
-        .submit(Op::Shutdown {})
-        .await
-        .expect("parent shutdown should submit");
-}
-
-#[tokio::test]
-async fn spawn_agent_fork_last_n_turns_strips_parent_usage_hints() {
-    let persistent_fragment =
-        "<persistent_mode>\nParent persistent instructions.\n</persistent_mode>";
-    let harness = AgentControlHarness::new().await;
-    let mut parent_config = harness.config.clone();
-    let _ = parent_config.features.enable(Feature::MultiAgentV2);
-    parent_config.developer_instructions = Some("Parent developer instructions.".to_string());
-    parent_config.multi_agent_v2.root_agent_usage_hint_text =
-        Some("Parent root guidance.".to_string());
-    let mut child_config = harness.config.clone();
-    let _ = child_config.features.enable(Feature::MultiAgentV2);
-    child_config.developer_instructions = Some("Child developer instructions.".to_string());
-    child_config.multi_agent_v2.subagent_developer_instructions =
-        Some("Child developer instructions.".to_string());
-    child_config.multi_agent_v2.subagent_usage_hint_text =
-        Some("Child subagent guidance.".to_string());
-    let new_thread = harness
-        .manager
-        .start_thread(StartThreadOptions::new(parent_config))
-        .await
-        .expect("start parent thread");
-    let parent_thread_id = new_thread.thread_id;
-    let parent_thread = new_thread.thread;
-    parent_thread
-        .inject_response_items(vec![user_message("parent task")])
-        .await
-        .expect("inject parent task");
-    let turn_context = parent_thread.session.new_default_turn().await;
-    let parent_spawn_call_id = "spawn-call-last-n-usage-hints".to_string();
-    parent_thread
-        .session
-        .record_conversation_items(
-            turn_context.as_ref(),
-            turn_context.model_info(),
-            &[
-                ResponseItem::Message {
-                    id: None,
-                    role: "developer".to_string(),
-                    content: vec![ContentItem::InputText {
-                        text: "Parent root guidance.".to_string(),
-                    }],
-                    phase: None,
-                    internal_chat_message_metadata_passthrough: None,
-                },
-                ResponseItem::Message {
-                    id: None,
-                    role: "developer".to_string(),
-                    content: vec![
-                        ContentItem::InputText {
-                            text: "Parent developer instructions.".to_string(),
-                        },
-                        ContentItem::InputText {
-                            text: "Preserved bounded developer context.".to_string(),
-                        },
-                        ContentItem::InputText {
-                            text: persistent_fragment.to_string(),
-                        },
-                    ],
-                    phase: None,
-                    internal_chat_message_metadata_passthrough: None,
-                },
-                spawn_agent_call(&parent_spawn_call_id),
-            ],
-        )
-        .await;
-    parent_thread
-        .session
-        .ensure_rollout_materialized(PersistContext::Standard)
-        .await;
-    parent_thread
-        .session
-        .flush_rollout()
-        .await
-        .expect("parent rollout should flush");
-
-    let child_thread_id = harness
-        .control
-        .spawn_agent_with_metadata(
-            child_config,
-            text_input("child task"),
-            SessionSource::SubAgent(SubAgentSource::ThreadSpawn {
-                parent_thread_id,
-                depth: 1,
-                agent_path: None,
-                agent_nickname: None,
-                agent_role: None,
-            }),
-            SpawnAgentOptions {
-                fork_parent_spawn_call_id: Some(parent_spawn_call_id),
-                fork_mode: Some(SpawnAgentForkMode::LastNTurns(2)),
-                ..Default::default()
-            },
-        )
-        .await
-        .expect("bounded forked spawn should sanitize parent usage hints")
-        .thread_id;
-
-    let child_thread = harness
-        .manager
-        .get_thread(child_thread_id)
-        .await
-        .expect("child thread should be registered");
-    let history = child_thread.session.clone_history().await;
-    assert!(
-        history_contains_text(history.raw_items(), "parent task"),
-        "bounded fork should retain the requested recent parent turn"
-    );
-    assert!(
-        !history_contains_text(history.raw_items(), "Parent root guidance."),
-        "bounded fork should strip stale parent root hints before the child rebuilds startup context"
-    );
-    assert!(
-        !history_contains_text(history.raw_items(), "Parent developer instructions."),
-        "bounded fork should remove parent instructions before the child rebuilds startup context"
-    );
-    assert!(
-        !history_contains_text(history.raw_items(), "Child developer instructions."),
-        "bounded fork should not inject child instructions before its canonical context rebuild"
-    );
-    assert!(
-        !history_contains_text(history.raw_items(), persistent_fragment),
-        "bounded fork should remove persistent instructions before rebuilding context for the child's effort"
-    );
-    assert!(
-        history_contains_text(history.raw_items(), "Preserved bounded developer context."),
-        "bounded fork should preserve unrelated developer fragments"
-    );
-
-    let _ = harness
-        .control
-        .shutdown_live_agent(child_thread_id)
-        .await
-        .expect("child shutdown should submit");
-    let _ = parent_thread
-        .submit(Op::Shutdown {})
-        .await
-        .expect("parent shutdown should submit");
-}
-
 #[tokio::test]
 async fn spawn_agent_respects_legacy_max_threads_alias() {
     let max_threads = 1usize;
@@ -4537,7 +4022,7 @@ async fn spawn_thread_subagent_gets_random_nickname_in_session_source() {
 }
 
 #[tokio::test]
-async fn spawn_thread_subagents_persist_parent_originator_across_new_and_truncated_fork() {
+async fn spawn_thread_subagents_persist_parent_originator_across_new_and_full_fork() {
     let harness = AgentControlHarness::new().await;
     let parent = harness
         .manager
@@ -4588,8 +4073,8 @@ async fn spawn_thread_subagents_persist_parent_originator_across_new_and_truncat
                 agent_role: Some("explorer".to_string()),
             }),
             SpawnAgentOptions {
-                fork_parent_spawn_call_id: Some("spawn-call-last-n".to_string()),
-                fork_mode: Some(SpawnAgentForkMode::LastNTurns(1)),
+                fork_parent_spawn_call_id: Some("spawn-call-full-history".to_string()),
+                fork_mode: Some(SpawnAgentForkMode::FullHistory),
                 ..Default::default()
             },
         )
diff --git a/codex-rs/core/src/agent/types.rs b/codex-rs/core/src/agent/types.rs
index 8d612d6beb..852a516713 100644
--- a/codex-rs/core/src/agent/types.rs
+++ b/codex-rs/core/src/agent/types.rs
@@ -21,7 +21,6 @@ pub struct AgentMetadata {
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum SpawnAgentForkMode {
     FullHistory,
-    LastNTurns(usize),
 }
 
 #[derive(Clone, Debug, Default)]
diff --git a/codex-rs/core/src/thread_rollout_truncation.rs b/codex-rs/core/src/thread_rollout_truncation.rs
index 16f67a47b8..5dde1d139d 100644
--- a/codex-rs/core/src/thread_rollout_truncation.rs
+++ b/codex-rs/core/src/thread_rollout_truncation.rs
@@ -14,7 +14,6 @@ use codex_protocol::error::Result as CodexResult;
 use codex_protocol::items::TurnItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::protocol::EventMsg;
-use codex_protocol::protocol::InterAgentCommunication;
 
 pub(crate) fn initial_history_has_prior_user_turns(conversation_history: &InitialHistory) -> bool {
     conversation_history.scan_rollout_items(rollout_item_is_user_turn_boundary)
@@ -65,72 +64,6 @@ pub(crate) fn user_message_positions_in_rollout(items: &[RolloutItem]) -> Vec<us
     user_positions
 }
 
-/// Return the indices of fork-turn boundaries in a rollout.
-///
-/// A fork-turn boundary is either:
-/// - a real user message boundary, or
-/// - an inter-agent communication whose `trigger_turn` is `true`, or
-/// - a legacy assistant inter-agent envelope with the same flag.
-///
-/// Like `user_message_positions_in_rollout`, this applies `ThreadRolledBack` markers so indexing
-/// reflects the effective post-rollback history. Rollback counts instruction turns, so a rollback
-/// removes the stale suffix starting at the earliest rolled-back instruction-turn boundary instead
-/// of simply truncating the mixed fork-boundary list.
-pub(crate) fn fork_turn_positions_in_rollout(items: &[RolloutItem]) -> Vec<usize> {
-    let mut rollback_turn_positions = Vec::new();
-    let mut fork_turn_positions = Vec::new();
-    for (idx, item) in items.iter().enumerate() {
-        match item {
-            RolloutItem::ResponseItem(item) => {
-                let has_delivery_metadata = matches!(&item.item, ResponseItem::AgentMessage { .. })
-                    && idx.checked_sub(1).is_some_and(|previous_idx| {
-                        matches!(
-                            items.get(previous_idx),
-                            Some(RolloutItem::InterAgentCommunicationMetadata { .. })
-                        )
-                    });
-                if is_user_turn_boundary(item) && !has_delivery_metadata {
-                    rollback_turn_positions.push(idx);
-                }
-                if is_real_user_message_boundary(item) || is_trigger_turn_boundary(item) {
-                    fork_turn_positions.push(idx);
-                }
-            }
-            RolloutItem::InterAgentCommunication(communication) => {
-                rollback_turn_positions.push(idx);
-                if communication.trigger_turn {
-                    fork_turn_positions.push(idx);
-                }
-            }
-            RolloutItem::InterAgentCommunicationMetadata { trigger_turn } => {
-                rollback_turn_positions.push(idx);
-                if *trigger_turn {
-                    fork_turn_positions.push(idx);
-                }
-            }
-            RolloutItem::EventMsg(EventMsg::ThreadRolledBack(rollback)) => {
-                let num_turns = usize::try_from(rollback.num_turns).unwrap_or(usize::MAX);
-                if num_turns == 0 {
-                    continue;
-                }
-                let Some(rollback_start_idx) = rollback_turn_positions
-                    .len()
-                    .checked_sub(num_turns)
-                    .map(|rollback_start| rollback_turn_positions[rollback_start])
-                    .or_else(|| rollback_turn_positions.first().copied())
-                else {
-                    continue;
-                };
-                let new_rollback_len = rollback_turn_positions.len().saturating_sub(num_turns);
-                rollback_turn_positions.truncate(new_rollback_len);
-                fork_turn_positions.retain(|position| *position < rollback_start_idx);
-            }
-            _ => {}
-        }
-    }
-    fork_turn_positions
-}
-
 /// Return a prefix of `items` obtained by cutting strictly before the nth user message.
 ///
 /// The boundary index is 0-based from the start of `items` (so `n_from_start = 0` returns
@@ -259,47 +192,6 @@ pub fn truncate_rollout_before_turn_id(
     Ok(items)
 }
 
-/// Return a suffix of `items` that keeps the last `n_from_end` fork turns.
-///
-/// If fewer than or equal to `n_from_end` fork turns exist, this keeps from the first fork-turn
-/// boundary and still drops pre-turn startup context.
-pub(crate) fn truncate_rollout_to_last_n_fork_turns(
-    mut items: Vec<RolloutItem>,
-    n_from_end: usize,
-) -> Vec<RolloutItem> {
-    if n_from_end == 0 {
-        return Vec::new();
-    }
-
-    let fork_turn_positions = fork_turn_positions_in_rollout(&items);
-    let Some(keep_idx) = fork_turn_positions
-        .len()
-        .checked_sub(n_from_end)
-        .map(|position| fork_turn_positions[position])
-        .or_else(|| fork_turn_positions.first().copied())
-    else {
-        return Vec::new();
-    };
-    items.split_off(keep_idx)
-}
-
-fn is_real_user_message_boundary(item: &ResponseItem) -> bool {
-    matches!(
-        event_mapping::parse_turn_item(item),
-        Some(TurnItem::UserMessage(_))
-    )
-}
-
-fn is_trigger_turn_boundary(item: &ResponseItem) -> bool {
-    let ResponseItem::Message { role, content, .. } = item else {
-        return false;
-    };
-
-    role == "assistant"
-        && InterAgentCommunication::from_message_content(content)
-            .is_some_and(|communication| communication.trigger_turn)
-}
-
 #[cfg(test)]
 #[path = "thread_rollout_truncation_tests.rs"]
 mod tests;
diff --git a/codex-rs/core/src/thread_rollout_truncation_tests.rs b/codex-rs/core/src/thread_rollout_truncation_tests.rs
index 68ec36cc48..9625f74677 100644
--- a/codex-rs/core/src/thread_rollout_truncation_tests.rs
+++ b/codex-rs/core/src/thread_rollout_truncation_tests.rs
@@ -2,12 +2,10 @@ use super::*;
 use crate::session::step_context::StepContext;
 use crate::session::tests::build_world_state_from_turn_context;
 use crate::session::tests::make_session_and_context;
-use codex_protocol::AgentPath;
 use codex_protocol::ResponseItemId;
 use codex_protocol::error::CodexErrorDetails;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ReasoningItemReasoningSummary;
-use codex_protocol::protocol::InterAgentCommunication;
 use codex_protocol::protocol::ThreadRolledBackEvent;
 use codex_protocol::protocol::TurnCompleteEvent;
 use codex_protocol::protocol::TurnStartedEvent;
@@ -43,39 +41,6 @@ fn assistant_msg(text: &str) -> ResponseItem {
     }
 }
 
-fn developer_msg(text: &str) -> ResponseItem {
-    ResponseItem::Message {
-        id: None,
-        role: "developer".to_string(),
-        content: vec![ContentItem::InputText {
-            text: text.to_string(),
-        }],
-        phase: None,
-        internal_chat_message_metadata_passthrough: None,
-    }
-}
-
-fn inter_agent_msg(text: &str, trigger_turn: bool) -> ResponseItem {
-    let communication = InterAgentCommunication::new(
-        AgentPath::root(),
-        AgentPath::try_from("/root/worker").expect("agent path"),
-        Vec::new(),
-        text.to_string(),
-        trigger_turn,
-    );
-    communication.to_response_input_item().into()
-}
-
-fn inter_agent_communication(text: &str, trigger_turn: bool) -> RolloutItem {
-    RolloutItem::InterAgentCommunication(InterAgentCommunication::new(
-        AgentPath::root(),
-        AgentPath::try_from("/root/worker").expect("agent path"),
-        Vec::new(),
-        text.to_string(),
-        trigger_turn,
-    ))
-}
-
 fn turn_started(turn_id: &str) -> RolloutItem {
     RolloutItem::EventMsg(EventMsg::TurnStarted(TurnStartedEvent {
         turn_id: turn_id.to_string(),
@@ -393,220 +358,3 @@ async fn ignores_session_prefix_messages_when_truncating_rollout_from_start() {
         serde_json::to_value(&expected).unwrap()
     );
 }
-
-#[test]
-fn truncates_rollout_to_last_n_fork_turns_counts_trigger_turn_messages() {
-    let rollout = vec![
-        response_item(user_msg("u1")),
-        response_item(assistant_msg("a1")),
-        response_item(inter_agent_msg(
-            "queued message",
-            /*trigger_turn*/ false,
-        )),
-        response_item(assistant_msg("a2")),
-        response_item(inter_agent_msg(
-            "triggered task",
-            /*trigger_turn*/ true,
-        )),
-        response_item(assistant_msg("a3")),
-        response_item(user_msg("u2")),
-        response_item(assistant_msg("a4")),
-    ];
-
-    let truncated = truncate_rollout_to_last_n_fork_turns(rollout.clone(), /*n_from_end*/ 2);
-    let expected = rollout[4..].to_vec();
-
-    assert_eq!(
-        serde_json::to_value(&truncated).unwrap(),
-        serde_json::to_value(&expected).unwrap()
-    );
-}
-
-#[test]
-fn fork_turn_positions_use_inter_agent_delivery_metadata() {
-    let rollout = vec![
-        response_item(user_msg("user task")),
-        inter_agent_communication("queued during user turn", /*trigger_turn*/ false),
-        response_item(assistant_msg("first answer")),
-        inter_agent_communication("follow-up task", /*trigger_turn*/ true),
-        response_item(assistant_msg("second answer")),
-        response_item(user_msg("next user task")),
-    ];
-
-    assert_eq!(fork_turn_positions_in_rollout(&rollout), vec![0, 3, 5]);
-}
-
-#[test]
-fn fork_turn_positions_use_canonical_agent_messages_and_delivery_metadata() {
-    let queued = InterAgentCommunication::new(
-        AgentPath::root(),
-        AgentPath::try_from("/root/worker").expect("agent path"),
-        Vec::new(),
-        "queued during user turn".to_string(),
-        /*trigger_turn*/ false,
-    );
-    let triggered = InterAgentCommunication::new(
-        AgentPath::root(),
-        AgentPath::try_from("/root/worker").expect("agent path"),
-        Vec::new(),
-        "follow-up task".to_string(),
-        /*trigger_turn*/ true,
-    );
-    let mut rollout = vec![
-        response_item(user_msg("user task")),
-        RolloutItem::InterAgentCommunicationMetadata {
-            trigger_turn: false,
-        },
-        response_item(queued.to_model_input_item()),
-        response_item(assistant_msg("first answer")),
-        RolloutItem::InterAgentCommunicationMetadata { trigger_turn: true },
-        response_item(triggered.to_model_input_item()),
-        response_item(assistant_msg("second answer")),
-        response_item(user_msg("next user task")),
-    ];
-
-    assert_eq!(fork_turn_positions_in_rollout(&rollout), vec![0, 4, 7]);
-
-    rollout.insert(
-        7,
-        RolloutItem::EventMsg(EventMsg::ThreadRolledBack(ThreadRolledBackEvent {
-            num_turns: 1,
-        })),
-    );
-    assert_eq!(fork_turn_positions_in_rollout(&rollout), vec![0, 8]);
-}
-
-#[test]
-fn truncates_rollout_to_last_n_fork_turns_drops_startup_prefix_even_when_under_limit() {
-    let rollout = vec![
-        response_item(developer_msg("startup developer context")),
-        response_item(user_msg("current task")),
-        response_item(assistant_msg("answer")),
-    ];
-
-    let truncated = truncate_rollout_to_last_n_fork_turns(rollout.clone(), /*n_from_end*/ 2);
-    let expected = rollout[1..].to_vec();
-
-    assert_eq!(
-        serde_json::to_value(&truncated).unwrap(),
-        serde_json::to_value(&expected).unwrap()
-    );
-}
-
-#[test]
-fn truncates_rollout_to_last_n_fork_turns_applies_thread_rollback_markers() {
-    let rollout = vec![
-        response_item(user_msg("u1")),
-        response_item(assistant_msg("a1")),
-        response_item(inter_agent_msg(
-            "triggered task",
-            /*trigger_turn*/ true,
-        )),
-        response_item(assistant_msg("a2")),
-        RolloutItem::EventMsg(EventMsg::ThreadRolledBack(ThreadRolledBackEvent {
-            num_turns: 1,
-        })),
-        response_item(user_msg("u2")),
-        response_item(assistant_msg("a3")),
-    ];
-
-    let truncated = truncate_rollout_to_last_n_fork_turns(rollout.clone(), /*n_from_end*/ 2);
-
-    assert_eq!(
-        serde_json::to_value(&truncated).unwrap(),
-        serde_json::to_value(&rollout).unwrap()
-    );
-}
-
-#[test]
-fn fork_turn_positions_ignore_zero_turn_rollback_markers() {
-    let rollout = vec![
-        response_item(user_msg("u1")),
-        response_item(inter_agent_msg(
-            "triggered task",
-            /*trigger_turn*/ true,
-        )),
-        RolloutItem::EventMsg(EventMsg::ThreadRolledBack(ThreadRolledBackEvent {
-            num_turns: 0,
-        })),
-        response_item(user_msg("u2")),
-    ];
-
-    assert_eq!(fork_turn_positions_in_rollout(&rollout), vec![0, 1, 3]);
-}
-
-#[test]
-fn truncates_rollout_to_last_n_fork_turns_discards_trigger_boundaries_in_rolled_back_suffix() {
-    let rollout = vec![
-        response_item(user_msg("u1")),
-        response_item(user_msg("u2")),
-        response_item(inter_agent_msg(
-            "triggered task",
-            /*trigger_turn*/ true,
-        )),
-        response_item(assistant_msg("a1")),
-        RolloutItem::EventMsg(EventMsg::ThreadRolledBack(ThreadRolledBackEvent {
-            num_turns: 1,
-        })),
-        response_item(user_msg("u3")),
-        response_item(assistant_msg("a2")),
-    ];
-
-    let truncated = truncate_rollout_to_last_n_fork_turns(rollout.clone(), /*n_from_end*/ 2);
-
-    let expected = rollout[1..].to_vec();
-
-    assert_eq!(
-        serde_json::to_value(&truncated).unwrap(),
-        serde_json::to_value(&expected).unwrap()
-    );
-}
-
-#[test]
-fn truncates_rollout_to_last_n_fork_turns_discards_rolled_back_assistant_instruction_turns() {
-    let rollout = vec![
-        response_item(user_msg("u1")),
-        response_item(assistant_msg("a1")),
-        response_item(inter_agent_msg(
-            "triggered task 1",
-            /*trigger_turn*/ true,
-        )),
-        response_item(assistant_msg("a2")),
-        RolloutItem::EventMsg(EventMsg::ThreadRolledBack(ThreadRolledBackEvent {
-            num_turns: 1,
-        })),
-        response_item(inter_agent_msg(
-            "triggered task 2",
-            /*trigger_turn*/ true,
-        )),
-        response_item(assistant_msg("a3")),
-    ];
-
-    let truncated = truncate_rollout_to_last_n_fork_turns(rollout.clone(), /*n_from_end*/ 1);
-    let expected = rollout[5..].to_vec();
-
-    assert_eq!(
-        serde_json::to_value(&truncated).unwrap(),
-        serde_json::to_value(&expected).unwrap()
-    );
-}
-
-#[test]
-fn truncates_rollout_to_last_n_fork_turns_keeps_full_rollout_when_n_is_large() {
-    let rollout = vec![
-        response_item(user_msg("u1")),
-        response_item(assistant_msg("a1")),
-        response_item(inter_agent_msg(
-            "triggered task",
-            /*trigger_turn*/ true,
-        )),
-        response_item(assistant_msg("a2")),
-    ];
-
-    let truncated = truncate_rollout_to_last_n_fork_turns(rollout.clone(), /*n_from_end*/ 10);
-
-    assert_eq!(
-        serde_json::to_value(&truncated).unwrap(),
-        serde_json::to_value(&rollout).unwrap()
-    );
-}
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_common.rs b/codex-rs/core/src/tools/handlers/multi_agents_common.rs
index be17be61b3..2146fdf84c 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_common.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_common.rs
@@ -92,7 +92,6 @@ pub(crate) fn record_collab_spawn_failure(
     let fork_mode = match fork_mode {
         None => "none",
         Some(SpawnAgentForkMode::FullHistory) => "all",
-        Some(SpawnAgentForkMode::LastNTurns(_)) => "last_n",
     };
     let multi_agent_version = match multi_agent_version {
         MultiAgentVersion::Disabled => "disabled",
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_spec.rs b/codex-rs/core/src/tools/handlers/multi_agents_spec.rs
index 92bae000c5..edc9467b4d 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_spec.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_spec.rs
@@ -664,8 +664,7 @@ fn spawn_agent_common_properties_v2(agent_type_description: &str) -> BTreeMap<St
         (
             "fork_turns".to_string(),
             JsonSchema::string(Some(
-                "Optional number of turns to fork. Defaults to `all`. Use `none`, `all`, or a positive integer string such as `3` to fork only the most recent turns."
-                    .to_string(),
+                "Parent history to inherit. Defaults to `all`; use `none` to start without parent history. Only `all` and `none` are supported.".to_string(),
             )),
         ),
         (
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
index 1667105ab8..31cd68a9f2 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
@@ -924,7 +924,7 @@ async fn multi_agent_v2_full_history_fork_inherits_root_service_tier() {
 }
 
 #[tokio::test]
-async fn multi_agent_v2_spawn_partial_fork_turns_allows_agent_type_override() {
+async fn multi_agent_v2_spawn_without_history_allows_agent_type_override() {
     let (mut session, mut turn) = make_session_and_context().await;
     let role_name = install_role_with_model_override(&mut turn).await;
     let manager = thread_manager();
@@ -951,17 +951,17 @@ async fn multi_agent_v2_spawn_partial_fork_turns_allows_agent_type_override() {
             "spawn_agent",
             function_payload(json!({
                 "message": "inspect this repo",
-                "task_name": "partial_fork",
+                "task_name": "fresh_agent",
                 "agent_type": role_name,
-                "fork_turns": "1"
+                "fork_turns": "none"
             })),
         ))
         .await
-        .expect("partial fork should allow agent_type overrides");
+        .expect("fresh agent should allow agent_type overrides");
     let (content, _) = expect_text_output(output);
     let result: serde_json::Value =
         serde_json::from_str(&content).expect("spawn_agent result should be json");
-    assert_eq!(result["task_name"], "/root/partial_fork");
+    assert_eq!(result["task_name"], "/root/fresh_agent");
     let agent_id = manager
         .captured_ops()
         .into_iter()
@@ -1254,8 +1254,10 @@ async fn multi_agent_v2_spawn_rejects_legacy_fork_context() {
     );
 }
 
+#[test_case::test_case("banana"; "invalid string")]
+#[test_case::test_case("0"; "zero turns")]
 #[tokio::test]
-async fn multi_agent_v2_spawn_rejects_invalid_fork_turns_string() {
+async fn multi_agent_v2_spawn_rejects_invalid_fork_turns_string(fork_turns: &str) {
     let (mut session, mut turn) = make_session_and_context().await;
     let manager = thread_manager();
     let root = manager
@@ -1279,7 +1281,7 @@ async fn multi_agent_v2_spawn_rejects_invalid_fork_turns_string() {
             function_payload(json!({
                 "message": "inspect this repo",
                 "task_name": "worker",
-                "fork_turns": "banana"
+                "fork_turns": fork_turns
             })),
         ))
         .await
@@ -1288,49 +1290,7 @@ async fn multi_agent_v2_spawn_rejects_invalid_fork_turns_string() {
 
     assert_eq!(
         err,
-        FunctionCallError::RespondToModel(
-            "fork_turns must be `none`, `all`, or a positive integer string".to_string()
-        )
-    );
-}
-
-#[tokio::test]
-async fn multi_agent_v2_spawn_rejects_zero_fork_turns() {
-    let (mut session, mut turn) = make_session_and_context().await;
-    let manager = thread_manager();
-    let root = manager
-        .start_thread(StartThreadOptions::new((*turn.config).clone()))
-        .await
-        .expect("root thread should start");
-    set_agent_control(&mut session, manager.agent_control());
-    session.thread_id = root.thread_id;
-    let mut config = (*turn.config).clone();
-    config
-        .features
-        .enable(Feature::MultiAgentV2)
-        .expect("test config should allow feature update");
-    set_turn_config(&mut turn, config);
-
-    let err = SpawnAgentHandlerV2::default()
-        .handle(invocation(
-            Arc::new(session),
-            Arc::new(turn),
-            "spawn_agent",
-            function_payload(json!({
-                "message": "inspect this repo",
-                "task_name": "worker",
-                "fork_turns": "0"
-            })),
-        ))
-        .await
-        .err()
-        .expect("zero turn count should be rejected");
-
-    assert_eq!(
-        err,
-        FunctionCallError::RespondToModel(
-            "fork_turns must be `none`, `all`, or a positive integer string".to_string()
-        )
+        FunctionCallError::RespondToModel("fork_turns must be `none` or `all`".to_string())
     );
 }
 
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs b/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
index 4562cc4ebc..3267d42aef 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
@@ -20,6 +20,7 @@ use codex_prompts::ResolvedModelMessages;
 use codex_protocol::ThreadId;
 use codex_protocol::protocol::MultiAgentVersion;
 use codex_tools::ToolSpec;
+use std::num::NonZeroUsize;
 
 #[derive(Default)]
 pub(crate) struct Handler {
@@ -288,22 +289,14 @@ impl SpawnAgentArgs {
         if fork_turns.eq_ignore_ascii_case("none") {
             return Ok(None);
         }
-        if fork_turns.eq_ignore_ascii_case("all") {
+        // Accept legacy turn counts without limiting the inherited history.
+        if fork_turns.eq_ignore_ascii_case("all") || fork_turns.parse::<NonZeroUsize>().is_ok() {
             return Ok(Some(SpawnAgentForkMode::FullHistory));
         }
 
-        let last_n_turns = fork_turns.parse::<usize>().map_err(|_| {
-            FunctionCallError::RespondToModel(
-                "fork_turns must be `none`, `all`, or a positive integer string".to_string(),
-            )
-        })?;
-        if last_n_turns == 0 {
-            return Err(FunctionCallError::RespondToModel(
-                "fork_turns must be `none`, `all`, or a positive integer string".to_string(),
-            ));
-        }
-
-        Ok(Some(SpawnAgentForkMode::LastNTurns(last_n_turns)))
+        Err(FunctionCallError::RespondToModel(
+            "fork_turns must be `none` or `all`".to_string(),
+        ))
     }
 }
 
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__compact__compaction_cold_resume_after_completion.snap b/codex-rs/core/tests/suite/snapshots/all__suite__compact__compaction_cold_resume_after_completion.snap
index c836a85c94..2477eb2974 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__compact__compaction_cold_resume_after_completion.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__compact__compaction_cold_resume_after_completion.snap
@@ -28,7 +28,7 @@ Scenario: Real paginated mid-turn compaction and cold resume from the bounded su
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...fork_turns` to `"none"` or a positive integer string. [hash=db3545796947884f]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...uctions; when doing so, set `fork_turns` to `"none"`. [hash=18ccf7e93ecabab9]
 03:message/developer:
     <MULTI_AGENT_MODE>
 04:message/user:
@@ -58,7 +58,7 @@ Scenario: Real paginated mid-turn compaction and cold resume from the bounded su
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...fork_turns` to `"none"` or a positive integer string. [hash=db3545796947884f]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...uctions; when doing so, set `fork_turns` to `"none"`. [hash=18ccf7e93ecabab9]
 03:message/developer:
     <MULTI_AGENT_MODE>
 04:message/user:
@@ -92,7 +92,7 @@ Scenario: Real paginated mid-turn compaction and cold resume from the bounded su
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...fork_turns` to `"none"` or a positive integer string. [hash=db3545796947884f]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...uctions; when doing so, set `fork_turns` to `"none"`. [hash=18ccf7e93ecabab9]
 03:message/developer:
     <MULTI_AGENT_MODE>
 04:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__agent_message_board__agent_message_board_context.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__agent_message_board__agent_message_board_context.snap
index 6360883eb4..a3a28e2414 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__agent_message_board__agent_message_board_context.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__agent_message_board__agent_message_board_context.snap
@@ -27,7 +27,7 @@ Scenario: An active agent posts a shared decision and fetches the text without a
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...fork_turns` to `"none"` or a positive integer string. [hash=db3545796947884f]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...uctions; when doing so, set `fork_turns` to `"none"`. [hash=18ccf7e93ecabab9]
 03:message/developer:
     <MULTI_AGENT_MODE>
 04:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__agent_message_board__remote__remote_board_tools.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__agent_message_board__remote__remote_board_tools.snap
index c088fe3860..f9c80a8425 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__agent_message_board__remote__remote_board_tools.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__agent_message_board__remote__remote_board_tools.snap
@@ -33,7 +33,7 @@ Scenario: Remote board tools and active-turn notifications share the existing se
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...fork_turns` to `"none"` or a positive integer string. [hash=db3545796947884f]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...uctions; when doing so, set `fork_turns` to `"none"`. [hash=18ccf7e93ecabab9]
 05:message/developer:
     <MULTI_AGENT_MODE>
 06:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_active_environment_selection.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_active_environment_selection.snap
index 795fc65bbb..2c899e4a82 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_active_environment_selection.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_active_environment_selection.snap
@@ -6,7 +6,7 @@ Scenario: Astra starts in one workspace, switches for the next step of the activ
 
 ## Window 1
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=6517f5ceb3554929):
+00:additional_tools/developer (3; hash=62160ed28e692c35):
         - namespace/functions; hash=4261ffb241688b3d
           - custom/exec
           - function/wait
@@ -14,7 +14,7 @@ Scenario: Astra starts in one workspace, switches for the next step of the activ
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -90,7 +90,7 @@ Scenario: Astra starts in one workspace, switches for the next step of the activ
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_async_question_and_answer.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_async_question_and_answer.snap
index b9999f419a..815d076e4f 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_async_question_and_answer.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_async_question_and_answer.snap
@@ -7,7 +7,7 @@ Scenario: Astra uses the catalog question schema to ask who a launch update is f
 
 ## Window 1
 -- request 1 (request) --
-00:additional_tools/developer (3; hash=2b6cdd8f97e8814b):
+00:additional_tools/developer (3; hash=f181967456befa67):
         - namespace/functions; hash=7e611b8ddd5621cf
           - custom/exec
           - function/wait
@@ -15,7 +15,7 @@ Scenario: Astra uses the catalog question schema to ask who a launch update is f
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_code_mode_call_timing.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_code_mode_call_timing.snap
index cc57f4f811..63afb9950a 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_code_mode_call_timing.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_code_mode_call_timing.snap
@@ -6,7 +6,7 @@ Scenario: Astra receives host and handler timings on completed and failed code-m
 
 ## Window 1
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -14,7 +14,7 @@ Scenario: Astra receives host and handler timings on completed and failed code-m
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -77,7 +77,7 @@ Scenario: Astra receives host and handler timings on completed and failed code-m
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_disabled_executor_skills.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_disabled_executor_skills.snap
index 12ae7112ba..ce4690a6d0 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_disabled_executor_skills.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_disabled_executor_skills.snap
@@ -16,7 +16,7 @@ Settings:
   text: {"verbosity":"low"}
   tool_choice: "auto"
 -- request 1 (request) --
-00:additional_tools/developer (3; hash=91d402a1b9d55c34):
+00:additional_tools/developer (3; hash=5e8370540461db70):
         - namespace/functions; hash=7d26e086c1dbba28
           - custom/exec
           - function/wait
@@ -24,7 +24,7 @@ Settings:
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -109,7 +109,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_input_interrupts_response.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_input_interrupts_response.snap
index 548b77a10d..b81315dda0 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_input_interrupts_response.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_input_interrupts_response.snap
@@ -6,7 +6,7 @@ Scenario: Astra receives new user input after its unfinished response is interru
 
 ## Window 1
 -- request 1 (request) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -14,7 +14,7 @@ Scenario: Astra receives new user input after its unfinished response is interru
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_input_yields_code_mode_cell.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_input_yields_code_mode_cell.snap
index 4574331821..cb8ed17bf8 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_input_yields_code_mode_cell.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_input_yields_code_mode_cell.snap
@@ -6,7 +6,7 @@ Scenario: Astra continues after new user input yields a running code cell, then
 
 ## Window 1
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=42b12a95deaea38e):
+00:additional_tools/developer (3; hash=69c8f596545517aa):
         - namespace/functions; hash=13a36c9bc9ada856
           - custom/exec
           - function/wait
@@ -14,7 +14,7 @@ Scenario: Astra continues after new user input yields a running code cell, then
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -90,7 +90,7 @@ Scenario: Astra continues after new user input yields a running code cell, then
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_kickoff_remote_compaction_windows.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_kickoff_remote_compaction_windows.snap
index 877c62c5bf..29a6122a39 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_kickoff_remote_compaction_windows.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_kickoff_remote_compaction_windows.snap
@@ -16,7 +16,7 @@ Settings:
   text: {"verbosity":"low"}
   tool_choice: "auto"
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -24,7 +24,7 @@ Settings:
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -112,7 +112,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user[2]:
@@ -187,7 +187,7 @@ Settings:
 ## Window 2 (after request 3: input diverged at item 02)
 Settings: same as window 1
 -- request 4 (turn) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -195,7 +195,7 @@ Settings: same as window 1
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -285,7 +285,7 @@ Settings: same as window 1
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 05:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 06:message/user[2]:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_plugin_refresh.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_plugin_refresh.snap
index 878f9c13e3..5f76c13704 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_plugin_refresh.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_plugin_refresh.snap
@@ -16,7 +16,7 @@ Settings:
   text: {"verbosity":"low"}
   tool_choice: "auto"
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -24,7 +24,7 @@ Settings:
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -87,7 +87,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_settings_release_check_tool_shapes.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_settings_release_check_tool_shapes.snap
index 755867034a..ed6a215e26 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_settings_release_check_tool_shapes.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__astra_settings_release_check_tool_shapes.snap
@@ -16,7 +16,7 @@ Settings:
   text: {"verbosity":"low"}
   tool_choice: "auto"
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -24,7 +24,7 @@ Settings:
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -87,7 +87,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__code_mode_catalog_messages.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__code_mode_catalog_messages.snap
index 9eeace188a..bcf207e89d 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__code_mode_catalog_messages.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__code_mode_catalog_messages.snap
@@ -15,14 +15,14 @@ Settings:
   stream: true
   text: {"verbosity":"low"}
   tool_choice: "auto"
-  tools (7; hash=7a45a45148e7ea6a):
+  tools (7; hash=7916dd640b46ec6e):
     - custom/exec: Catalog exec instructions. Default yield: 1234 ms. `image(imageUrlOrItem: string | { image_url: s...; hash=a49b91fd82908e18
     - function/wait: Catalog wait instructions: resume the yielded cell.; args=[cell_id, max_tokens, terminate, yield_time_ms]; hash=67bc0f04da3505b3
     - function/request_user_input: Request user input for one to three short questions and wait for the response. This tool is only ...; args=[questions]; hash=64a729b25c424fc6
     - function/request_user_input_async: Ask the user one or more questions during ongoing work. Use this tool only to request missing inf...; args=[questions]; hash=d6d74f33db330162
     - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
       - function/sleep
-    - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+    - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
       - function/followup_task
       - function/interrupt_agent
       - function/list_agents
@@ -87,7 +87,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 03:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 04:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__code_mode_settled_helpers__code_mode_settled_helpers.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__code_mode_settled_helpers__code_mode_settled_helpers.snap
index d33a16adea..f72b39e0b5 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__code_mode_settled_helpers__code_mode_settled_helpers.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__code_mode_settled_helpers__code_mode_settled_helpers.snap
@@ -6,7 +6,7 @@ Scenario: Settlement helpers deliver fulfilled and rejected records with input i
 
 ## Window 1
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -14,7 +14,7 @@ Scenario: Settlement helpers deliver fulfilled and rejected records with input i
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__compaction__remote_slash_compact.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__compaction__remote_slash_compact.snap
index 00d8b90f33..4e78cadff5 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__compaction__remote_slash_compact.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__compaction__remote_slash_compact.snap
@@ -16,7 +16,7 @@ Settings:
   text: {"verbosity":"low"}
   tool_choice: "auto"
 -- request 1 (turn; Before /compact) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -24,7 +24,7 @@ Settings:
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -87,7 +87,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
@@ -146,7 +146,7 @@ Settings: unavailable (items only)
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 02:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 03:message/user:
@@ -164,7 +164,7 @@ Settings: unavailable (items only)
 ## Window 3 (after request 3: input diverged at item 00)
 Settings: same as window 1
 -- request 4 (turn; First turn after /compact) --
-00:additional_tools/developer (3; hash=2c5a5b48dbcfce9b):
+00:additional_tools/developer (3; hash=bf2e30605ff5dc17):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -172,7 +172,7 @@ Settings: same as window 1
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -235,7 +235,7 @@ Settings: same as window 1
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__guardian_code_mode_messaging.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__guardian_code_mode_messaging.snap
index 5eea74ae35..0cbd8d0890 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__guardian_code_mode_messaging.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__guardian_code_mode_messaging.snap
@@ -28,7 +28,7 @@ Scenario: A root uses Code Mode to send a confirmation and receives a real user
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...fork_turns` to `"none"` or a positive integer string. [hash=db3545796947884f]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...uctions; when doing so, set `fork_turns` to `"none"`. [hash=18ccf7e93ecabab9]
 03:message/developer:
     <MULTI_AGENT_MODE>
 04:message/user:
@@ -76,7 +76,7 @@ Scenario: A root uses Code Mode to send a confirmation and receives a real user
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...fork_turns` to `"none"` or a positive integer string. [hash=db3545796947884f]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...uctions; when doing so, set `fork_turns` to `"none"`. [hash=18ccf7e93ecabab9]
 05:message/developer:
     <MULTI_AGENT_MODE>
 06:agent_message
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__indirect_namespace_prefixes__catalog_indirect_namespace_prefixes.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__indirect_namespace_prefixes__catalog_indirect_namespace_prefixes.snap
index 6cacd42d3d..c7761cf293 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__indirect_namespace_prefixes__catalog_indirect_namespace_prefixes.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__indirect_namespace_prefixes__catalog_indirect_namespace_prefixes.snap
@@ -15,8 +15,8 @@ Settings:
   stream: true
   text: {"verbosity":"low"}
   tool_choice: "auto"
-  tools (4; hash=a9bf6ab2694395ea):
-    - custom/exec: Run JavaScript code to orchestrate/compose tool calls - Evaluates the provided JavaScript code in...; hash=046e4cb99a803db9
+  tools (4; hash=7707adf4d5cde816):
+    - custom/exec: Run JavaScript code to orchestrate/compose tool calls - Evaluates the provided JavaScript code in...; hash=66e0c24dd8b9010d
     - function/wait: Waits on a yielded `exec` cell and returns new output or completion. - Use `wait` only after `exe...; args=[cell_id, max_tokens, terminate, yield_time_ms]; hash=6692d8f6c55be489
     - function/request_user_input: Request user input for one to three short questions and wait for the response. This tool is only ...; args=[questions]; hash=64a729b25c424fc6
     - web_search; hash=e214d4db1bc49e89
@@ -49,8 +49,8 @@ Settings:
 ## Window 2 (after request 2)
 Settings: relative to window 1
   model: "prefixes-cleared"
-  tools (4; hash=5aa602f8d0ed5702):
-    ~ custom/exec: Run JavaScript code to orchestrate/compose tool calls - Evaluates the provided JavaScript code in...; hash=b1c19da7942f5c47
+  tools (4; hash=d878b195101dccae):
+    ~ custom/exec: Run JavaScript code to orchestrate/compose tool calls - Evaluates the provided JavaScript code in...; hash=881b443f5068d3fb
 -- request 3 (turn) --
 00:message/developer:
     <MODEL_INSTRUCTIONS>
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__mcp_resource_messages__mcp_resource_messages.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__mcp_resource_messages__mcp_resource_messages.snap
index e3384c1269..2ec353f71d 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__mcp_resource_messages__mcp_resource_messages.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__mcp_resource_messages__mcp_resource_messages.snap
@@ -15,14 +15,14 @@ Settings:
   stream: true
   text: {"verbosity":"low"}
   tool_choice: "auto"
-  tools (7; hash=221a8b190f48eeef):
+  tools (7; hash=dac6a853a6177003):
     - custom/exec: Run JavaScript code to orchestrate/compose tool calls - Evaluates the provided JavaScript code in...; hash=9ad48dbb5eac1f9b
     - function/wait: Waits on a yielded `exec` cell and returns new output or completion. - Use `wait` only after `exe...; args=[cell_id, max_tokens, terminate, yield_time_ms]; hash=6692d8f6c55be489
     - function/request_user_input: Request user input for one to three short questions and wait for the response. This tool is only ...; args=[questions]; hash=64a729b25c424fc6
     - function/request_user_input_async: Ask the user one or more questions during ongoing work. Use this tool only to request missing inf...; args=[questions]; hash=d6d74f33db330162
     - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
       - function/sleep
-    - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+    - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
       - function/followup_task
       - function/interrupt_agent
       - function/list_agents
@@ -87,7 +87,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 03:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 04:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__multi_agent_catalog_parameters.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__multi_agent_catalog_parameters.snap
index 76ab79bd27..5fb3ec889e 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__multi_agent_catalog_parameters.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__multi_agent_catalog_parameters.snap
@@ -16,7 +16,7 @@ Settings:
   text: {"verbosity":"low"}
   tool_choice: "auto"
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=cc5df79824bafc21):
+00:additional_tools/developer (3; hash=2b84850bc279e5ed):
         - namespace/functions; hash=fada4a476a3754dd
           - custom/exec
           - function/wait
@@ -24,7 +24,7 @@ Settings:
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=170baa4086bfe3cb
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=7e156cf57f85af87
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -87,7 +87,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__provider_capabilities__custom_provider_capabilities.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__provider_capabilities__custom_provider_capabilities.snap
index fd2c3135b2..ade1be5bcf 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__provider_capabilities__custom_provider_capabilities.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__provider_capabilities__custom_provider_capabilities.snap
@@ -15,12 +15,12 @@ Settings:
   stream: true
   text: {"verbosity":"low"}
   tool_choice: "auto"
-  tools (6; hash=3b8fa9a9ca9788e3):
+  tools (6; hash=dde875513b2c7cff):
     - function/exec_command: Runs a command in a PTY, returning output or a session ID for ongoing interaction.; args=[cmd, justification, login, max_output_tokens, prefix_rule, sandbox_permissions, shell, tty, workdir, yield_time_ms]; hash=c04108e51a8548c5
     - function/write_stdin: Writes characters to an existing unified exec session and returns recent output.; args=[chars, max_output_tokens, session_id, yield_time_ms]; hash=7fb62d8a3e2df4e2
     - function/request_user_input: Request user input for one to three short questions and wait for the response. This tool is only ...; args=[questions]; hash=64a729b25c424fc6
     - function/view_image: View a local image file from the filesystem when visual inspection is needed. Use this for images...; args=[detail, path]; hash=3b766d5bdec5d50e
-    - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=3b8ac3e34b9c55bb
+    - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=3cbf715dc154e1b7
       - function/followup_task
       - function/interrupt_agent
       - function/list_agents
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__skill_catalog_dedup__dedup_before_budgeting.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__skill_catalog_dedup__dedup_before_budgeting.snap
index 449e2a34b6..3dcc2d2c8a 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__skill_catalog_dedup__dedup_before_budgeting.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__skill_catalog_dedup__dedup_before_budgeting.snap
@@ -16,7 +16,7 @@ Settings:
   text: {"verbosity":"low"}
   tool_choice: "auto"
 -- request 1 (turn) --
-00:additional_tools/developer (3; hash=b6ebf543280ec271):
+00:additional_tools/developer (3; hash=e80da11342c6e6dd):
         - namespace/functions; hash=bd9e182b4235cdc1
           - custom/exec
           - function/wait
@@ -24,7 +24,7 @@ Settings:
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
@@ -108,7 +108,7 @@ Settings:
 
     There are 4 available concurrency slots, meaning that up to 4 agents can be active at once, including you.
 
-    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d...ne"` or a positive integer string.</multi_agent_role> [hash=c7f52e90688299ce]
+    Full-history forks (`fork_turns` omitted or `"all"`) inherit the parent model and reasoning effort and d... so, set `fork_turns` to `"none"`.</multi_agent_role> [hash=d5928243dc643bcc]
 04:message/developer:
     <multi_agent_mode>Any earlier instruction enabling proactive multi-agent delegation no longer applies. D...elegation, or parallel agent work.</multi_agent_mode> [hash=2b6e037067b4390c]
 05:message/user:
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__strict_3p_cache__strict_3p_mcp_catalog_cache.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__strict_3p_cache__strict_3p_mcp_catalog_cache.snap
index b6de242b41..a4dc574b7d 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__strict_3p_cache__strict_3p_mcp_catalog_cache.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__strict_3p_cache__strict_3p_mcp_catalog_cache.snap
@@ -24,7 +24,7 @@ Settings:
           - function/request_user_input_async
         - namespace/clock: Tools for reading and waiting on time.; hash=f402e8c5e9b5e317
           - function/sleep
-        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=b263e3c84ad07c37
+        - namespace/collaboration: Tools for spawning and managing sub-agents.; hash=2c8d6295978dbe63
           - function/followup_task
           - function/interrupt_agent
           - function/list_agents
diff --git a/codex-rs/core/tests/suite/subagent_notifications.rs b/codex-rs/core/tests/suite/subagent_notifications.rs
index 89deaae707..04b3026a50 100644
--- a/codex-rs/core/tests/suite/subagent_notifications.rs
+++ b/codex-rs/core/tests/suite/subagent_notifications.rs
@@ -1200,16 +1200,13 @@ async fn submit_turn_with_trigger(test: &TestCodex, prompt: &str, trigger: &str)
 #[derive(Clone, Copy, Debug)]
 enum GrandchildParentContext {
     FullHistory,
-    LastTurn,
     NoHistory,
     Compacted,
 }
 
 #[test_case(GrandchildParentContext::FullHistory, ThreadHistoryMode::Legacy; "legacy full history")]
-#[test_case(GrandchildParentContext::LastTurn, ThreadHistoryMode::Legacy; "legacy last turn")]
 #[test_case(GrandchildParentContext::NoHistory, ThreadHistoryMode::Legacy; "legacy no history")]
 #[test_case(GrandchildParentContext::FullHistory, ThreadHistoryMode::Paginated; "paginated full history")]
-#[test_case(GrandchildParentContext::LastTurn, ThreadHistoryMode::Paginated; "paginated last turn")]
 #[test_case(GrandchildParentContext::NoHistory, ThreadHistoryMode::Paginated; "paginated no history")]
 #[test_case(GrandchildParentContext::Compacted, ThreadHistoryMode::Legacy; "legacy full history after compaction")]
 #[test_case(GrandchildParentContext::Compacted, ThreadHistoryMode::Paginated; "paginated full history after compaction")]
@@ -1233,7 +1230,6 @@ async fn grandchild_full_fork_preserves_context_baseline(
     let server = start_mock_server().await;
     let (parent_fork_turns, compact_parent) = match parent_context {
         GrandchildParentContext::FullHistory => ("all", false),
-        GrandchildParentContext::LastTurn => ("1", false),
         GrandchildParentContext::NoHistory => ("none", false),
         GrandchildParentContext::Compacted => ("all", true),
     };
@@ -1457,7 +1453,7 @@ async fn grandchild_full_fork_preserves_context_baseline(
 #[derive(Clone, Copy)]
 enum FullHistoryV2ModelSelection {
     ConfiguredDefault,
-    ExplicitOverride,
+    ExplicitOverride(&'static str),
     WorldStateIdentity,
     CurrentTimeReminders,
     MultiAgentModeInstructions,
@@ -1465,7 +1461,9 @@ enum FullHistoryV2ModelSelection {
 }
 
 #[test_case(FullHistoryV2ModelSelection::ConfiguredDefault; "configured default with omitted fork_turns")]
-#[test_case(FullHistoryV2ModelSelection::ExplicitOverride; "explicit override with fork_turns all")]
+#[test_case(FullHistoryV2ModelSelection::ExplicitOverride("all"); "explicit override with fork_turns all")]
+#[test_case(FullHistoryV2ModelSelection::ExplicitOverride("1"); "legacy one turn forks full history with explicit override")]
+#[test_case(FullHistoryV2ModelSelection::ExplicitOverride("3"); "legacy three turns forks full history with explicit override")]
 #[test_case(FullHistoryV2ModelSelection::WorldStateIdentity; "world state appends context window when agent identity changes")]
 #[test_case(FullHistoryV2ModelSelection::CurrentTimeReminders; "full fork drops inherited current-time reminders")]
 #[test_case(FullHistoryV2ModelSelection::MultiAgentModeInstructions; "full fork drops inherited multi-agent mode instructions")]
@@ -1500,11 +1498,11 @@ async fn spawned_full_history_v2_child_uses_model_precedence_without_dropping_co
             V2_DEFAULT_MODEL,
             V2_DEFAULT_REASONING_EFFORT,
         ),
-        FullHistoryV2ModelSelection::ExplicitOverride => (
+        FullHistoryV2ModelSelection::ExplicitOverride(fork_turns) => (
             json!({
                 "message": CHILD_PROMPT,
                 "task_name": "worker",
-                "fork_turns": "all",
+                "fork_turns": fork_turns,
                 "model": V2_REQUESTED_MODEL,
                 "reasoning_effort": V2_REQUESTED_REASONING_EFFORT,
             }),
@@ -1700,7 +1698,7 @@ async fn spawned_full_history_v2_child_uses_model_precedence_without_dropping_co
         builder =
             builder.with_external_time_provider(std::sync::Arc::new(FailFirstClockRead::default()));
     }
-    let test = builder.build(&server).await?;
+    let test = builder.build_with_auto_env(&server).await?;
     if matches!(selection, FullHistoryV2ModelSelection::WorldStateIdentity) {
         test.codex.submit(Op::Compact).await?;
         wait_for_event(&test.codex, |event| {
diff --git a/codex-rs/prompts/src/multi_agent_instructions.rs b/codex-rs/prompts/src/multi_agent_instructions.rs
index fea9405f26..415f52dd2a 100644
--- a/codex-rs/prompts/src/multi_agent_instructions.rs
+++ b/codex-rs/prompts/src/multi_agent_instructions.rs
@@ -5,7 +5,7 @@ use crate::without_update_plan_instructions;
 use codex_context_fragments::ContextualUserFragment;
 use codex_protocol::models::ContentItemKind;
 
-const DEFAULT_MULTI_AGENT_V2_MODEL_OVERRIDE_USAGE_HINT_TEXT: &str = "Full-history forks (`fork_turns` omitted or `\"all\"`) inherit the parent model and reasoning effort and do not accept overrides. Only set `model` or `reasoning_effort` when explicitly requested by the user, applicable `AGENTS.md` instructions, or skill instructions; when doing so, set `fork_turns` to `\"none\"` or a positive integer string.";
+const DEFAULT_MULTI_AGENT_V2_MODEL_OVERRIDE_USAGE_HINT_TEXT: &str = "Full-history forks (`fork_turns` omitted or `\"all\"`) inherit the parent model and reasoning effort and do not accept overrides. Only set `model` or `reasoning_effort` when explicitly requested by the user, applicable `AGENTS.md` instructions, or skill instructions; when doing so, set `fork_turns` to `\"none\"`.";
 const DEFAULT_MULTI_AGENT_V2_WAIT_AGENT_USAGE_HINT_TEXT: &str =
     "When calling `wait_agent`, prefer longer waits (minutes) to avoid busy polling.";
 const DEFAULT_MULTI_AGENT_V2_SHARED_USAGE_HINT_TEXT: &str = r#"Note that collaboration tools cannot be called from inside `functions.exec`. Call `spawn_agent`, `send_message`, `followup_task`, `wait_agent`, `interrupt_agent`, and `list_agents` only as direct tool calls using the recipient shown in their tool definitions, such as `to=functions.collaboration.spawn_agent`, since they are intentionally absent from the `functions.exec` `tools.*` namespace. Available tools in `functions.exec` are explicitly described with a `tools` namespace in the developer message.