feat(core): remove spawn_mode from agent roles

codex-rs/app-server-protocol/src/protocol/thread_history.rs

@@ -2527,7 +2527,6 @@ mod tests {
                 prompt: "inspect the repo".into(),
                 model: "gpt-5.4-mini".into(),
                 reasoning_effort: codex_protocol::openai_models::ReasoningEffort::Medium,
-                spawn_mode: codex_protocol::protocol::AgentSpawnMode::Spawn,
                 status: AgentStatus::Running,
             }),
         ];

codex-rs/core/config.schema.json

@@ -6,13 +6,6 @@
       "description": "A path that is guaranteed to be absolute and normalized (though it is not guaranteed to be canonicalized or exist on the filesystem).\n\nIMPORTANT: When deserializing an `AbsolutePathBuf`, a base path must be set using [AbsolutePathBufGuard::new]. If no base path is set, the deserialization will fail unless the path being deserialized is already absolute.",
       "type": "string"
     },
-    "AgentRoleSpawnMode": {
-      "enum": [
-        "spawn",
-        "fork"
-      ],
-      "type": "string"
-    },
     "AgentRoleToml": {
       "additionalProperties": false,
       "properties": {
@@ -43,14 +36,6 @@
           },
           "type": "array"
         },
-        "spawn_mode": {
-          "allOf": [
-            {
-              "$ref": "#/definitions/AgentRoleSpawnMode"
-            }
-          ],
-          "description": "Optional default spawn mode when `spawn_agent` omits `spawn_mode`."
-        },
         "watchdog_interval_s": {
           "description": "Optional watchdog interval in seconds for roles that should behave as watchdogs.",
           "format": "int64",
@@ -2625,4 +2610,4 @@
   },
   "title": "ConfigToml",
   "type": "object"
-}
+}

codex-rs/core/root_agent_prompt.md

@@ -1,6 +1,6 @@
 # You are the Root Agent
 
-You are the **root agent** in a multi-agent Codex session. Until you see `# You are a Subagent`, these instructions define your role. If this thread was created from the root thread with `spawn_mode = "fork"` (a forked child), you may see both sets of instructions; apply subagent instructions as local role guidance while root instructions remain governing system-level rules.
+You are the **root agent** in a multi-agent Codex session. Until you see `# You are a Subagent`, these instructions define your role. If this thread was created from the root thread with `fork_context = true` (a forked child), you may see both sets of instructions; apply subagent instructions as local role guidance while root instructions remain governing system-level rules.
 
 ## Root Agent Responsibilities
 
@@ -36,23 +36,23 @@ Create a subagent and give it an initial task.
 Parameters:
 - `message` (required): the task description.
 - `agent_type` (optional): the role to assign (`default`, `explorer`, `fast-worker`, or `worker`).
-- `spawn_mode` (optional): one of `spawn` or `fork`.
+- `fork_context` (optional): when `true`, the child receives the current thread history.
 
 Guidance:
-- When `spawn_mode` is omitted, the default is `fork` unless the selected role overrides it.
+- When `fork_context` is omitted, the default comes from the selected role and otherwise falls back to `true`.
 - Use `agent_type = "explorer"` for specific codebase questions; it defaults to context-free `spawn`.
 - Use `agent_type = "fast-worker"` for tightly constrained execution work that can run from a self-contained prompt; it also defaults to context-free `spawn`.
 - Use `agent_type = "worker"` for broader implementation work that should inherit current-thread context; it defaults to `fork`.
-- Choose `fork` vs `spawn` by context requirements first (not by task shape).
-- Use `spawn_mode = "fork"` when the child should preserve your current conversation history and rely on current-thread context, including:
+- Choose `fork_context = true` vs `false` by context requirements first (not by task shape).
+- Use `fork_context = true` when the child should preserve your current conversation history and rely on current-thread context, including:
   - current debugging-thread relevance (for example, "summarize only failures relevant to this investigation")
   - active plan / ExecPlan branch continuation
   - recent user decisions, tradeoffs, or rejected approaches
   - parallel review work that should inherit the same context automatically
-- Use `spawn_mode = "spawn"` only when the child can do the task correctly from a fresh prompt you provide now, without needing current-thread context.
-- For `spawn`, make the task, inputs, and expected output explicit (especially for independent, output-heavy work where you want the child to distill results and keep the root thread context clean).
-- Needle-in-a-haystack searches are strong `spawn` candidates when the child can search from a precise prompt without current-thread context.
-- Do not choose `spawn` solely because work is output-heavy or command-heavy if it still depends on current-thread context.
+- Use `fork_context = false` only when the child can do the task correctly from a fresh prompt you provide now, without needing current-thread context.
+- For `fork_context = false`, make the task, inputs, and expected output explicit (especially for independent, output-heavy work where you want the child to distill results and keep the root thread context clean).
+- Needle-in-a-haystack searches are strong `fork_context = false` candidates when the child can search from a precise prompt without current-thread context.
+- Do not choose `fork_context = false` solely because work is output-heavy or command-heavy if it still depends on current-thread context.
 
 ### 2) `send_input`
 

codex-rs/core/src/tools/handlers/multi_agents/spawn.rs

@@ -11,7 +11,6 @@ use crate::agent::role::default_fork_context_for_role;
 use crate::agent::role::watchdog_interval_for_role;
 use crate::config::Config;
 use codex_features::Feature;
-use codex_protocol::protocol::AgentSpawnMode;
 use codex_protocol::protocol::SessionSource;
 use std::collections::HashSet;
 
@@ -198,13 +197,6 @@ impl ToolHandler for Handler {
                     prompt,
                     model: effective_model,
                     reasoning_effort: effective_reasoning_effort,
-                    spawn_mode: if is_watchdog {
-                        AgentSpawnMode::Watchdog
-                    } else if fork_context {
-                        AgentSpawnMode::Fork
-                    } else {
-                        AgentSpawnMode::Spawn
-                    },
                     status,
                 }
                 .into(),

codex-rs/core/src/tools/handlers/multi_agents_tests.rs

@@ -449,7 +449,7 @@ async fn multi_agent_v2_spawn_fork_context_ignores_child_model_overrides() {
 }
 
 #[tokio::test]
-async fn spawn_agent_watchdog_role_returns_handle_without_spawn_mode() {
+async fn spawn_agent_watchdog_role_returns_handle_with_role_defaults() {
     let (mut session, mut turn) = make_session_and_context().await;
     let manager = thread_manager();
     session.services.agent_control = manager.agent_control();

codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs

@@ -6,7 +6,6 @@ use crate::agent::role::DEFAULT_ROLE_NAME;
 use crate::agent::role::apply_role_to_config;
 use crate::agent::role::default_fork_context_for_role;
 use codex_protocol::AgentPath;
-use codex_protocol::protocol::AgentSpawnMode;
 use codex_protocol::protocol::InterAgentCommunication;
 use codex_protocol::protocol::Op;
 
@@ -178,11 +177,6 @@ impl ToolHandler for Handler {
                     prompt,
                     model: effective_model,
                     reasoning_effort: effective_reasoning_effort,
-                    spawn_mode: if fork_context {
-                        AgentSpawnMode::Fork
-                    } else {
-                        AgentSpawnMode::Spawn
-                    },
                     status,
                 }
                 .into(),

codex-rs/core/watchdog_agent_prompt.md

@@ -52,7 +52,7 @@ When you detect these, prescribe the corrective action explicitly.
 
 Use only the multi-agent tools that exist here:
 
-- `spawn_agent` (prefer `spawn_mode = "fork"` when shared context matters).
+- `spawn_agent` (prefer `fork_context = true` when shared context matters).
 - `send_input`.
 - `compact_parent_context` (watchdog-only recovery tool; see below).
 - `watchdog_self_close` (watchdog-only immediate exit tool; see below).

codex-rs/protocol/src/protocol.rs

@@ -3420,16 +3420,6 @@ pub struct CollabAgentSpawnBeginEvent {
     pub reasoning_effort: ReasoningEffortConfig,
 }
 
-#[derive(Debug, Clone, Copy, Deserialize, Serialize, PartialEq, Eq, JsonSchema, TS, Default)]
-#[serde(rename_all = "snake_case")]
-#[ts(rename_all = "snake_case")]
-pub enum AgentSpawnMode {
-    #[default]
-    Spawn,
-    Fork,
-    Watchdog,
-}
-
 #[derive(Debug, Clone, Deserialize, Serialize, PartialEq, Eq, JsonSchema, TS)]
 pub struct CollabAgentRef {
     /// Thread ID of the receiver/new agent.
@@ -3477,9 +3467,6 @@ pub struct CollabAgentSpawnEndEvent {
     pub model: String,
     /// Effective reasoning effort used by the spawned agent after inheritance and role overrides.
     pub reasoning_effort: ReasoningEffortConfig,
-    /// Spawn mode used for this agent.
-    #[serde(default)]
-    pub spawn_mode: AgentSpawnMode,
     /// Last known status of the new agent reported to the sender agent.
     pub status: AgentStatus,
 }

codex-rs/tui/src/chatwidget.rs

@@ -139,7 +139,6 @@ use codex_protocol::protocol::AgentReasoningEvent;
 use codex_protocol::protocol::AgentReasoningRawContentDeltaEvent;
 #[cfg(test)]
 use codex_protocol::protocol::AgentReasoningRawContentEvent;
-use codex_protocol::protocol::AgentSpawnMode;
 use codex_protocol::protocol::AgentStatus;
 use codex_protocol::protocol::ApplyPatchApprovalRequestEvent;
 #[cfg(test)]
@@ -3666,10 +3665,6 @@ impl ChatWidget {
                             prompt: prompt.unwrap_or_default(),
                             model: String::new(),
                             reasoning_effort: ReasoningEffortConfig::Medium,
-                            // Thread history items do not carry spawn_mode yet, so the
-                            // replay path must choose an explicit fallback for reconstructed
-                            // spawn rows. Plain spawn is the least surprising default.
-                            spawn_mode: AgentSpawnMode::Spawn,
                             status: first_receiver
                                 .as_ref()
                                 .and_then(|thread_id| agents_states.get(&thread_id.to_string()))

codex-rs/tui/src/chatwidget/tests.rs

@@ -2341,7 +2341,6 @@ async fn collab_spawn_end_shows_requested_model_and_effort() {
             new_agent_nickname: Some("Robie".to_string()),
             new_agent_role: Some("explorer".to_string()),
             prompt: "Explore the repo".to_string(),
-            spawn_mode: codex_protocol::protocol::AgentSpawnMode::Spawn,
             model: "gpt-5".to_string(),
             reasoning_effort: ReasoningEffortConfig::High,
             status: AgentStatus::PendingInit,

codex-rs/tui/src/multi_agents.rs

@@ -583,7 +583,6 @@ fn status_summary_spans(status: &AgentStatus) -> Vec<Span<'static>> {
 mod tests {
     use super::*;
     use crate::history_cell::HistoryCell;
-    use codex_protocol::protocol::AgentSpawnMode;
     #[cfg(target_os = "macos")]
     use crossterm::event::KeyEvent;
     #[cfg(target_os = "macos")]
@@ -610,7 +609,6 @@ mod tests {
                 new_agent_nickname: Some("Robie".to_string()),
                 new_agent_role: Some("explorer".to_string()),
                 prompt: "Compute 11! and reply with just the integer result.".to_string(),
-                spawn_mode: AgentSpawnMode::Spawn,
                 model: "gpt-5".to_string(),
                 reasoning_effort: ReasoningEffortConfig::High,
                 status: AgentStatus::PendingInit,
@@ -749,7 +747,6 @@ mod tests {
                 new_agent_nickname: Some("Robie".to_string()),
                 new_agent_role: Some("explorer".to_string()),
                 prompt: String::new(),
-                spawn_mode: AgentSpawnMode::Spawn,
                 model: "gpt-5".to_string(),
                 reasoning_effort: ReasoningEffortConfig::High,
                 status: AgentStatus::PendingInit,