fix(#2732): detect crashed subagent sessions with shorter timeout

When a subagent session disappears from the status registry (process
crashed), the main agent was waiting the full stale timeout before
acting. Fix:

- Add sessionGoneTimeoutMs config option (default 60s, vs 30min normal)
- task-poller: use shorter timeout when session is gone from status
- manager: verify session existence when gone, fail crashed tasks
  immediately with descriptive error
- Add legacy-plugin-toast hook for #2823 migration warnings
- Update schema with new config option

src/plugin/event.ts

@@ -195,6 +195,7 @@ export function createEventHandler(args: {
 
   const dispatchToHooks = async (input: EventInput): Promise<void> => {
     await Promise.resolve(hooks.autoUpdateChecker?.event?.(input));
+    await Promise.resolve(hooks.legacyPluginToast?.event?.(input));
     await Promise.resolve(hooks.claudeCodeHooks?.event?.(input));
     await Promise.resolve(hooks.backgroundNotificationHook?.event?.(input));
     await Promise.resolve(hooks.sessionNotification?.(input));

src/plugin/hooks/create-session-hooks.ts

@@ -25,6 +25,7 @@ import {
   createQuestionLabelTruncatorHook,
   createPreemptiveCompactionHook,
   createRuntimeFallbackHook,
+  createLegacyPluginToastHook,
 } from "../../hooks"
 import { createAnthropicEffortHook } from "../../hooks/anthropic-effort"
 import {
@@ -60,6 +61,7 @@ export type SessionHooks = {
   taskResumeInfo: ReturnType<typeof createTaskResumeInfoHook> | null
   anthropicEffort: ReturnType<typeof createAnthropicEffortHook> | null
   runtimeFallback: ReturnType<typeof createRuntimeFallbackHook> | null
+  legacyPluginToast: ReturnType<typeof createLegacyPluginToastHook> | null
 }
 
 export function createSessionHooks(args: {
@@ -262,6 +264,11 @@ export function createSessionHooks(args: {
           pluginConfig,
         }))
     : null
+
+  const legacyPluginToast = isHookEnabled("legacy-plugin-toast")
+    ? safeHook("legacy-plugin-toast", () => createLegacyPluginToastHook(ctx))
+    : null
+
   return {
     contextWindowMonitor,
     preemptiveCompaction,
@@ -286,5 +293,6 @@ export function createSessionHooks(args: {
     taskResumeInfo,
     anthropicEffort,
     runtimeFallback,
+    legacyPluginToast,
   }
 }