fix(subagent): preserve Codex fatal and grace semantics

packages/subagent/subagent-codex/src/run.ts

@@ -24,6 +24,47 @@ import { CodexAppServerWire } from './wire.ts'
 /** Default POSIX grace between subprocess termination tiers. */
 export const DEFAULT_DISPOSE_GRACE_MS = 3_000
 
+/** Largest delay Node schedules without collapsing it to one millisecond. */
+const MAX_TIMER_DELAY_MS = 2_147_483_647n
+
+/**
+ * Bound final exit observation at twice a positive finite grace without
+ * narrowing the public config to Node's single-timer integer range.
+ */
+function doubledGraceWindow(graceMs: number): {
+  readonly signal: AbortSignal
+  readonly cancel: () => void
+} {
+  const whole = Math.floor(graceMs)
+  let remaining = BigInt(whole) * 2n
+    + BigInt(Math.ceil((graceMs - whole) * 2))
+  const controller = new AbortController()
+  let timer: ReturnType<typeof setTimeout> | undefined
+  const arm = (): void => {
+    const chunk = remaining > MAX_TIMER_DELAY_MS
+      ? MAX_TIMER_DELAY_MS
+      : remaining
+    remaining -= chunk
+    timer = setTimeout(() => {
+      timer = undefined
+      if (remaining === 0n) {
+        controller.abort()
+      } else {
+        arm()
+      }
+    }, Number(chunk))
+  }
+  arm()
+  return {
+    signal: controller.signal,
+    cancel: () => {
+      if (timer === undefined) return
+      clearTimeout(timer)
+      timer = undefined
+    },
+  }
+}
+
 /** Fully resolved inputs for one Codex app-server run. */
 export interface CodexRunSpec {
   /** Parent Session workspace, also supplied to `thread/start`. */
@@ -88,8 +129,13 @@ export async function disposeCodexChild(
     // A concurrently closed stdin does not change tree ownership below.
   }
   child.terminate()
-  if (!(await child.waitForExit(AbortSignal.timeout(graceMs * 2)))) {
-    throw new Error('subagent-codex: app-server process tree did not exit within its dispose window')
+  const exitWindow = doubledGraceWindow(graceMs)
+  try {
+    if (!(await child.waitForExit(exitWindow.signal))) {
+      throw new Error('subagent-codex: app-server process tree did not exit within its dispose window')
+    }
+  } finally {
+    exitWindow.cancel()
   }
   await child.done
 }

packages/subagent/subagent-codex/src/wire.ts

@@ -17,12 +17,17 @@ type JsonObject = Record<string, unknown>
 interface Deferred<T> {
   readonly promise: Promise<T>
   readonly resolve: (value: T) => void
+  readonly reject: (reason?: unknown) => void
 }
 
 function deferred<T>(): Deferred<T> {
   let resolve!: (value: T) => void
-  const promise = new Promise<T>((settle) => { resolve = settle })
-  return { promise, resolve }
+  let reject!: (reason?: unknown) => void
+  const promise = new Promise<T>((settle, fail) => {
+    resolve = settle
+    reject = fail
+  })
+  return { promise, resolve, reject }
 }
 
 function object(value: unknown, label: string): JsonObject {
@@ -93,7 +98,7 @@ async function raceAbort<T>(pending: Promise<T>, signal: AbortSignal): Promise<T
  */
 export class CodexAppServerWire {
   private readonly transport: JsonRpcLineTransport
-  private readonly fatal = deferred<Error>()
+  private readonly fatal = deferred<never>()
   private threadId: string | undefined
   private turnId: string | undefined
   private pendingTurnId: string | undefined
@@ -111,6 +116,10 @@ export class CodexAppServerWire {
     output: Writable,
   ) {
     this.transport = new JsonRpcLineTransport(input, output)
+    // Fatal protocol state can arrive after the current guarded operation has
+    // already settled. Keep the shared rejection observed without inserting
+    // another promise-adoption hop into active races.
+    void this.fatal.promise.catch(() => {})
     this.transport.onRequest((method, params) => this.handleServerRequest(method, params))
     this.transport.onNotification((method, params) => {
       try {
@@ -157,9 +166,8 @@ export class CodexAppServerWire {
    * Create the run's private ephemeral thread and retain its identity.
    * @param cwd - parent Session workspace.
    * @param signal - unpublished-start cancellation.
-   * @returns the app-server thread id.
    */
-  async startThread(cwd: string, signal: AbortSignal): Promise<string> {
+  async startThread(cwd: string, signal: AbortSignal): Promise<void> {
     const response = object(await this.guarded(this.transport.request('thread/start', {
       cwd,
       ephemeral: true,
@@ -170,7 +178,6 @@ export class CodexAppServerWire {
       throw new Error('subagent-codex: app-server did not create an ephemeral thread')
     }
     this.threadId = id
-    return id
   }
 
   /**
@@ -249,15 +256,12 @@ export class CodexAppServerWire {
   }
 
   private async guarded<T>(pending: Promise<T>, signal: AbortSignal): Promise<T> {
-    const withFatal = Promise.race([
-      pending,
-      this.fatal.promise.then((error): Promise<never> => Promise.reject(error)),
-    ])
+    const withFatal = Promise.race([pending, this.fatal.promise])
     return raceAbort(withFatal, signal)
   }
 
   private fail(error: Error): void {
-    this.fatal.resolve(error)
+    this.fatal.reject(error)
   }
 
   private readonly onInputError = (error: Error): void => {