feat(message-queue): per-conversation queue + steering injection

A per-conversation message queue (new message-queue extension) holds user
messages enqueued while a turn generates; delivered mid-turn as steering at the
tool-result boundary (or carried to a new turn if no tool call fires).

- kernel: RunTurnInput.drainSteering callback (generic; kernel stays pure)
- wire 0.7.0->0.8.0: QueuedMessage, QueuePayload, TurnSteeringEvent (additive)
- transport-contract 0.11.0->0.12.0: POST /conversations/:id/queue + chat.queue WS op
- message-queue ext: queue state + per-conversation custom surface (rendererId message-queue)
- session-orchestrator: enqueue facade + drainSteering wiring + post-seal carry
- transport-http/ws: queue endpoint + chat.queue op (fixes WsClientMessage exhaustive switch)
- host-bin: register message-queue

1043 vitest + 199 transport bun pass; tsc/biome clean; boot smoke clean.
FE courier: frontend-message-queue-handoff.md.

1 files changed, 2 insertions, 0 deletions

diff --git a/packages/host-bin/src/main.ts b/packages/host-bin/src/main.ts
index 420f12e..59ce47d 100644
--- a/packages/host-bin/src/main.ts
+++ b/packages/host-bin/src/main.ts
@@ -20,6 +20,7 @@ import {
 	type StorageNamespace,
 } from "@dispatch/kernel";
 import { extension as lspExt } from "@dispatch/lsp";
+import { extension as messageQueueExt } from "@dispatch/message-queue";
 import { extension as providerOpenaiCompatExt } from "@dispatch/provider-openai-compat";
 import { extension as sessionOrchestratorExt } from "@dispatch/session-orchestrator";
 import { extension as skillsExt } from "@dispatch/skills";
@@ -73,6 +74,7 @@ const CORE_EXTENSIONS: readonly Extension[] = [
 	toolShellExt,
 	toolWriteFileExt,
 	throughputStoreExt,
+	messageQueueExt,
 	sessionOrchestratorExt,
 	skillsExt,
 	cacheWarmingExt,