Gateway hub: text adapters on SessionManager + serve as interactive adapter (from #114 items 2–3)

Summary

Part of #113. Promoted from #114 items 2 and 3 now that #136 (P1, #134) put serve's run queue on SessionManager. This is the next step of decision wiki/decisions/0001-gateway-as-hub.md: the gateway owns sessions, queues and policy (Hermes-style), and every surface connects through it as an adapter.

Why now

Future: deferred architecture work & revisit triggers (from #113) #114 item 3's revisit trigger is met: serve's session/run code runs on SessionManager (src/serve/prompts.ts, src/session/manager.ts).
Lich now has two session-queue implementations: the gateway's src/gateway/bus.ts and serve's SessionManager. That is the drift 0001 was meant to prevent.
Ossuary sends every session over one WebSocket, and serve serializes frames per connection until each prompt.submit finishes, so Ossuary sessions still queue behind each other despite feat: event envelope + SessionManager (P1 / #134) #136. (Found by code reading on main@4718fb4; not yet reproduced.)

Scope

A. Text adapters on the gateway core (#114 item 2)

Move GatewayBus conversation queueing onto SessionManager (one queue implementation) — fix(gateway): one session queue, LRU eviction, telegram-only /start, awaited shutdown, webhook usage/502 #174
Profiles + Policy evolved from src/gateway/access.ts — Policy in feat(gateway): GatewayPolicy and declared adapter capabilities #178 (per-chat profiles: follow-up)
Rebuild telegram, discord, twitch and webhook as "text" adapters that declare their capabilities — feat(gateway): GatewayPolicy and declared adapter capabilities #178
Also fixes: G-10 (/start rewrite, eviction by insertion order, shutdown not awaited); webhook usage: null; webhook returning HTTP 200 on agent errors — fix(gateway): one session queue, LRU eviction, telegram-only /start, awaited shutdown, webhook usage/502 #174

B. Serve as the interactive adapter (#114 item 3)

lich serve becomes the gateway's WebSocket JSON-RPC adapter
Per-connection frame handling lets different sessions on one connection run concurrently (see Ossuary note above; overlaps draft fix(serve): cancel a prompt.submit still queued behind another frame #140) — feat(serve): queue frames per session on each connection #183
Client-executed tools (tool.invoke / tool.result)
text_delta streaming
deadline_ms and fallback actions
Protocol version and capabilities in health
JSON Schema export of the protocol

Out of scope

Retiring the orders.jsonl file bus / persona orchestrator (Future: deferred architecture work & revisit triggers (from #113) #114 item 4; needs B's client-executed tools first)
Runtime/Profile/Session split and Global agent identity & hermes-style profiles (unify on ~/.lich/**) #117 (P2)
Cron / world-tick scheduler (Future: deferred architecture work & revisit triggers (from #113) #114 item 8)

Open question

Gateway persistence (history survives a restart) and per-chat profiles were the other half of item 2's trigger. Decide whether they're in A or a follow-up.