diff --git a/desktop/src-tauri/src/managed_agents/runtime_commands.rs b/desktop/src-tauri/src/managed_agents/runtime_commands.rs
index 3349eb011..32831a6d7 100644
--- a/desktop/src-tauri/src/managed_agents/runtime_commands.rs
+++ b/desktop/src-tauri/src/managed_agents/runtime_commands.rs
@@ -79,80 +79,17 @@ fn emit_status<R: tauri::Runtime>(app: &tauri::AppHandle<R>, status: &ManagedAge
     let _ = app.emit(STATUS_EVENT, status);
 }
 
-fn observer_lifecycle_key(
-    outer_pubkey: &str,
-    payload: &super::ManagedAgentRuntimeLifecycleObserverPayload,
-) -> Result<ManagedAgentRuntimeKey, String> {
-    if !outer_pubkey.eq_ignore_ascii_case(&payload.pubkey) {
-        return Err("observer signer does not match lifecycle payload pubkey".into());
-    }
-    if matches!(
-        payload.lifecycle,
-        ManagedAgentRuntimeLifecycle::Starting | ManagedAgentRuntimeLifecycle::Stopped
-    ) {
-        return Err("observer cannot author starting or stopped lifecycle".into());
-    }
-    if payload.lifecycle == ManagedAgentRuntimeLifecycle::Failed && payload.error.is_none() {
-        return Err("failed lifecycle requires an error".into());
-    }
-    if payload.lifecycle != ManagedAgentRuntimeLifecycle::Failed && payload.error.is_some() {
-        return Err("lifecycle error is only valid for failed".into());
-    }
-    ManagedAgentRuntimeKey::new(payload.pubkey.clone(), &payload.relay_url)
-}
-
-#[tauri::command]
-pub fn put_managed_agent_runtime_lifecycle(
-    outer_pubkey: String,
-    payload: super::ManagedAgentRuntimeLifecycleObserverPayload,
-    app: AppHandle,
-) -> Result<ManagedAgentRuntimeStatus, String> {
-    put_managed_agent_runtime_lifecycle_for(outer_pubkey, payload, &app)
-}
-
-/// Runtime-generic core so the sibling capability check is testable under `MockRuntime` (§3.3a / §7).
-pub(crate) fn put_managed_agent_runtime_lifecycle_for<R: tauri::Runtime>(
-    outer_pubkey: String,
-    payload: super::ManagedAgentRuntimeLifecycleObserverPayload,
-    app: &tauri::AppHandle<R>,
-) -> Result<ManagedAgentRuntimeStatus, String> {
-    let key = observer_lifecycle_key(&outer_pubkey, &payload)?;
-    let state = app.state::<AppState>();
-    let records = load_managed_agents(app)?;
-    let record = records
-        .iter()
-        .find(|record| record.pubkey.eq_ignore_ascii_case(&key.pubkey))
-        .ok_or_else(|| format!("agent {} not found", key.pubkey))?;
-    // Capture the active scope BEFORE taking the runtime lock so a concurrent
-    // workspace switch cannot slip a stale-scope frame past the check.
-    let current_scope_id = state.capture_active_scope().map(|scope| scope.scope_id);
-    let mut runtimes = state
-        .managed_agent_processes
-        .lock()
-        .map_err(|e| e.to_string())?;
-    let runtime = runtimes
-        .get_mut(&key)
-        .ok_or_else(|| "lifecycle frame does not match a tracked runtime pair".to_string())?;
-    if runtime.start_nonce != payload.start_nonce {
-        return Err("lifecycle frame does not match the current harness generation".into());
-    }
-    if runtime.scope_id != current_scope_id {
-        return Err("lifecycle frame does not match the current workspace scope".into());
-    }
-    let exited = runtime
-        .child
-        .try_wait()
-        .map_err(|e| e.to_string())?
-        .is_some();
-    if exited {
-        return Err("lifecycle frame arrived after process exit".into());
-    }
-    runtime.lifecycle = payload.lifecycle;
-    runtime.error = payload.error;
-    let status = status_for(app, record, &key, Some(runtime), None);
-    emit_status(app, &status);
-    Ok(status)
-}
+// Observer-authored runtime-lifecycle capability command (§3.3a): extracted to
+// keep this file under the 1000-line size ratchet.
+#[path = "runtime_commands_observer.rs"]
+mod observer;
+pub use observer::put_managed_agent_runtime_lifecycle;
+// Re-exported for the capability and unit test suites only; production code
+// reaches the core through the `#[tauri::command]` wrapper inside `observer`.
+#[cfg(test)]
+use observer::observer_lifecycle_key;
+#[cfg(test)]
+pub(crate) use observer::put_managed_agent_runtime_lifecycle_for;
 
 #[tauri::command]
 pub fn list_managed_agent_runtimes(
diff --git a/desktop/src-tauri/src/managed_agents/runtime_commands_observer.rs b/desktop/src-tauri/src/managed_agents/runtime_commands_observer.rs
new file mode 100644
index 000000000..3a33b679c
--- /dev/null
+++ b/desktop/src-tauri/src/managed_agents/runtime_commands_observer.rs
@@ -0,0 +1,82 @@
+//! Observer-authored runtime-lifecycle capability command (§3.3a).
+//!
+//! Extracted here to keep `runtime_commands.rs` under the 1000-line size
+//! ratchet; `#[path]`-included from there. Behavior is identical to the inline
+//! definition — this is a mechanical move.
+
+use super::*;
+
+pub(super) fn observer_lifecycle_key(
+    outer_pubkey: &str,
+    payload: &crate::managed_agents::ManagedAgentRuntimeLifecycleObserverPayload,
+) -> Result<ManagedAgentRuntimeKey, String> {
+    if !outer_pubkey.eq_ignore_ascii_case(&payload.pubkey) {
+        return Err("observer signer does not match lifecycle payload pubkey".into());
+    }
+    if matches!(
+        payload.lifecycle,
+        ManagedAgentRuntimeLifecycle::Starting | ManagedAgentRuntimeLifecycle::Stopped
+    ) {
+        return Err("observer cannot author starting or stopped lifecycle".into());
+    }
+    if payload.lifecycle == ManagedAgentRuntimeLifecycle::Failed && payload.error.is_none() {
+        return Err("failed lifecycle requires an error".into());
+    }
+    if payload.lifecycle != ManagedAgentRuntimeLifecycle::Failed && payload.error.is_some() {
+        return Err("lifecycle error is only valid for failed".into());
+    }
+    ManagedAgentRuntimeKey::new(payload.pubkey.clone(), &payload.relay_url)
+}
+
+#[tauri::command]
+pub fn put_managed_agent_runtime_lifecycle(
+    outer_pubkey: String,
+    payload: crate::managed_agents::ManagedAgentRuntimeLifecycleObserverPayload,
+    app: AppHandle,
+) -> Result<ManagedAgentRuntimeStatus, String> {
+    put_managed_agent_runtime_lifecycle_for(outer_pubkey, payload, &app)
+}
+
+/// Runtime-generic core so the sibling capability check is testable under `MockRuntime` (§3.3a / §7).
+pub(crate) fn put_managed_agent_runtime_lifecycle_for<R: tauri::Runtime>(
+    outer_pubkey: String,
+    payload: crate::managed_agents::ManagedAgentRuntimeLifecycleObserverPayload,
+    app: &tauri::AppHandle<R>,
+) -> Result<ManagedAgentRuntimeStatus, String> {
+    let key = observer_lifecycle_key(&outer_pubkey, &payload)?;
+    let state = app.state::<AppState>();
+    let records = load_managed_agents(app)?;
+    let record = records
+        .iter()
+        .find(|record| record.pubkey.eq_ignore_ascii_case(&key.pubkey))
+        .ok_or_else(|| format!("agent {} not found", key.pubkey))?;
+    // Capture the active scope BEFORE taking the runtime lock so a concurrent
+    // workspace switch cannot slip a stale-scope frame past the check.
+    let current_scope_id = state.capture_active_scope().map(|scope| scope.scope_id);
+    let mut runtimes = state
+        .managed_agent_processes
+        .lock()
+        .map_err(|e| e.to_string())?;
+    let runtime = runtimes
+        .get_mut(&key)
+        .ok_or_else(|| "lifecycle frame does not match a tracked runtime pair".to_string())?;
+    if runtime.start_nonce != payload.start_nonce {
+        return Err("lifecycle frame does not match the current harness generation".into());
+    }
+    if runtime.scope_id != current_scope_id {
+        return Err("lifecycle frame does not match the current workspace scope".into());
+    }
+    let exited = runtime
+        .child
+        .try_wait()
+        .map_err(|e| e.to_string())?
+        .is_some();
+    if exited {
+        return Err("lifecycle frame arrived after process exit".into());
+    }
+    runtime.lifecycle = payload.lifecycle;
+    runtime.error = payload.error;
+    let status = status_for(app, record, &key, Some(runtime), None);
+    emit_status(app, &status);
+    Ok(status)
+}