a spawned session says who started it

The other half of making a spawned agent visible. The commander's pane now lists
its children; opening one gave no way back — no link to the conversation that owns
it, and nothing to tell it apart from a chat somebody had started themselves and
forgotten.

`parentCommanderOf` is the row `ingestSpawnedChildren` already writes, read from
the other end. So this needed no table and no write path: a commander's children
were recorded because deleting one has to take them with it, and that record
answers "who is my parent" for free. Nothing had asked.

`GET /chat/sessions/:id` carries `spawnedBy`, and the chat panel renders one line
above the transcript linking back to the commander. Null for almost every session,
which is the normal case rather than a miss — a chat somebody opened has no parent
— so the bar renders nothing at all rather than saying so. Never fatal: a session
must open when this lookup will not.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/api/chat/chat.ts

@@ -13,6 +13,7 @@ import {
   getChatNotifyPreferences,
   setChatNotifyPreference,
   forgetChatSessions,
+  parentCommanderOf,
 } from 'officerdb';
 import type { NotifyPreference } from 'officerdb/types';
 import { setNudge, getNudge, cancelNudge } from 'officerdb';
@@ -273,6 +274,15 @@ chatRouter.get('/sessions/:id', async (ctx) => {
       travels with the conversation.
     */
     isCommander: (await listCommandHqSessionIds(user.id)).has(id),
+    /*
+      Which commander spawned this, if any — the row `ingestSpawnedChildren` writes, read from the other
+      end. A spawned agent has always been fully readable here; what it could never say was who started
+      it, so opening one gave no way back to the conversation that owns it.
+    
+      Null for almost every session and that is the normal case, not a miss: a chat somebody opened
+      themselves has no parent. Never fatal — a session must render when this lookup will not.
+    */
+    spawnedBy: await parentCommanderOf(id).catch(() => null),
   });
 });