feat(chat): agent panels — named Claude panels that can hand work to each other

Committing work that was left uncommitted in the shared tree. I did not write it;
I reviewed it in full, verified it against the running system, and am landing it at
the owner's explicit request because no one currently owns it.

This REPAIRS master. `useAgentPanel.ts` shipped in dbe585f and calls
`/chat/agent-panels`, but `registerAgentPanelRoutes` existed only in the working
tree — so on master as pushed, every one of those calls 404s. The feature has been
half-landed since that commit.

What it is. A panel on a dashboard can be given a name ("frontend", "code-reviewer").
Naming it mints two things: a `sessionKey`, which is the panel's permanent continuity
(it keys the sidecar's on-disk resume map and `chat_session_events`, so the same panel
reopens the same Claude session), and a `handoffToken`, a bearer credential scoped to
exactly one verb. The agent in that panel is then addressable by name, and can pass
work to a peer on the same dashboard over `/api/agent-handoff`.

Three doors, deliberately separate:
  - `/chat/agent-panels` (browser, session-authed) — name / list / rename / forget.
    Mounted on the chat router rather than given its own prefix: these routes create
    and name Claude sessions, which is authority `chat` already grants. A second
    top-level mount would have meant a second capability entry claiming the same
    thing under a different name.
  - `/api/agent-handoff` (agent, token-authed) — peers and send. Unprotected by the
    session middleware and exempted in `capabilities/totality.ts` with its reasoning
    written down, because the caller is a subprocess with a token, not a browser with
    a cookie.
  - The transcript stays where transcripts live. DELETE forgets the address and the
    panel's claim on the session; it does not touch ~/.claude/projects.

Security, as verified rather than assumed:
  - The sender is derived from the token, never from the request body — there is no
    `from` field on the wire, so it cannot be forged.
  - Every lookup is scoped to the token's `userId` AND `dashboardId`, so an agent can
    only see and reach peers on its own dashboard.
  - `toAgentPanelView` strips `handoffToken` and `userId`, and it is the only shape
    the browser routes return. Confirmed by reading every return path.
  - Live-tested: a real token on `GET /api/agent-handoff/peers` returns 200 with
    correctly scoped peers; a bogus one returns 401.

Two judgement calls in the code worth knowing about, both already commented at their
site: the introduction turn inlines the handoff token into a runnable curl (a
single-owner MVP trade), and `agent_panels` carries no FK to `dashboards.id` because
that primary key is mid-rework to a composite.

Schema uses `uniqueIndex` throughout, never `unique().on(...)` — the rule that exists
because drizzle-kit mis-diffs named composite unique constraints and re-creates them,
which is what wiped seven tables on 2026-08-03.

NO `bun db:push` IS NEEDED. `agent_panels` is already live in Postgres with 6 rows;
the schema file is catching up to a database that already has it.

Verified: `bunx tsgo` clean, `bun test` 538 pass / 0 fail across 35 files.

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

src/servers/api/chat/chat.ts

@@ -23,6 +23,7 @@ import { listChatModels } from './list-models';
 import { logger } from './logger';
 import { readSttConfig } from '../server-settings/stt';
 import { transcribeAudio } from '../stt/transcribe';
+import { registerAgentPanelRoutes } from './agent-panels-routes';
 
 export const chatRouter = createRouter();
 
@@ -165,3 +166,8 @@ chatRouter.post('/stt', async (ctx: Context) => {
     return ctx.json({ error: err instanceof Error ? err.message : 'Failed to reach Whisper server' }, 502);
   }
 });
+
+// The agent address book — naming a chat panel so other agents on the same dashboard can reach it.
+// Lives on this router because it is the same authority `chat` already grants: creating and naming
+// Claude sessions. See servers/api/chat/agent-panels-routes.ts and docs/agent-coordination.md.
+registerAgentPanelRoutes(chatRouter);