fix(athena): harden council members — compaction recovery, block TodoWrite, analysis mode

- Add session.compacted handler in BackgroundManager to prevent premature
  task completion after compaction (defer first post-compaction idle)
- Explicitly block TodoWrite/TodoRead for council members in all sync
  points (AgentConfig permission + session tools + prompt instructions)
- Add council member prefix check to todo-continuation-enforcer skip list
  to prevent infinite continuation loops on completed council members
- Add optional analysis mode (solo/delegation) question to Athena setup:
  solo = thorough but heavier, delegation = fast via explore/librarian
- Allow call_omo_agent in council member allow-list for delegation mode
- Update COUNCIL_MEMBER_PROMPT with TodoWrite prohibition and delegation
  addendum for when delegation mode is selected
- Update prepare_council_prompt tool with mode parameter

src/features/background-agent/session-idle-event-handler.ts

@@ -11,6 +11,7 @@ export function handleSessionIdleBackgroundEvent(args: {
   properties: Record<string, unknown>
   findBySession: (sessionID: string) => BackgroundTask | undefined
   idleDeferralTimers: Map<string, ReturnType<typeof setTimeout>>
+  recentlyCompactedSessions?: Set<string>
   validateSessionHasOutput: (sessionID: string) => Promise<boolean>
   checkSessionTodos: (sessionID: string) => Promise<boolean>
   tryCompleteTask: (task: BackgroundTask, source: string) => Promise<boolean>
@@ -20,6 +21,7 @@ export function handleSessionIdleBackgroundEvent(args: {
     properties,
     findBySession,
     idleDeferralTimers,
+    recentlyCompactedSessions,
     validateSessionHasOutput,
     checkSessionTodos,
     tryCompleteTask,
@@ -32,6 +34,12 @@ export function handleSessionIdleBackgroundEvent(args: {
   const task = findBySession(sessionID)
   if (!task || task.status !== "running") return
 
+  if (recentlyCompactedSessions?.has(sessionID)) {
+    recentlyCompactedSessions.delete(sessionID)
+    log("[background-agent] Skipping post-compaction session.idle:", { taskId: task.id, sessionID })
+    return
+  }
+
   const startedAt = task.startedAt
   if (!startedAt) return