fix(agent-inbox): review round 1

- codeman agent post: accept text that starts with "-" (markdown from a
  file), --json and -h stay options.
- DELETE /api/sessions/:id on a persisted-only row drops the inbox a detach
  kept.
- inbox --wait: wait.ended is exit 3 only when the session list no longer has
  the session; a restart or detach ending the wait is exit 2 (wait again).
- A read whose client hung up during ?wait= marks nothing seen.
- InboxPostSchema bound is 4x the byte cap, so every oversize message gets
  the store's "post a file path" answer.
- Store: restore sorts oldest first; the TTL sweep checks every message,
  not only the first.
- Docs: admins can act as any session of the receiver's owner (now tested
  for admin and non-admin); a peek with ?wait= does not block; exit codes.
- Tests: partial PUT /api/settings keeps persistence on.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/server.ts

@@ -1691,8 +1691,9 @@ export class WebServer extends EventEmitter {
     // detached a few lines above, before `session.stop()`, so on a delete the
     // session's own exit event never reaches the registry.
     // The agent inbox goes with a DELETED session only. killMux=false is shutdown or
-    // detach, and a detached session comes back to the mail posted while it was away.
-    // Before cancelAll, so a reader released by it reads an empty inbox.
+    // detach: mail posted before that is still there when the session is re-attached
+    // (while detached, the routes answer 404, so nothing new arrives). Before
+    // cancelAll, so a reader released by it reads an empty inbox.
     if (killMux) agentInbox.drop(sessionId);
     sessionWaits.notifySignal(sessionId, 'exit');
     sessionWaits.cancelAll(sessionId);