feat(chat): message queue + steering — mid-turn injection at tool-result boundaries

Consume the message-queue + steering handoff ([email protected], [email protected]).
Re-pinned file: deps + re-mirrored .dispatch/*.reference.md.

- fold steering AgentEvent into the transcript as a provisional user bubble
  (after the tool-result it followed; no de-dup — the queue surface carried it)
- add rendererId: "message-queue" custom renderer (pure parser + MessageQueueList)
  rendered as a compact panel above the Composer (hidden when queue is empty)
- add ChatStore.queueMessage / AppStore.queueMessage — sends chat.queue WS op
  (trim/validate non-empty; auto-starts a turn if idle)
- Composer switches to chat.queue while generating (button → Queue, placeholder
  → Steer the conversation...)
- exhaustiveness guards updated for steering + chat.queue
- carry-to-new-turn needs no special handling (normal new turn)

664 tests green.

2 files changed, 25 insertions, 0 deletions

diff --git a/src/features/surface-host/ui/MessageQueueList.svelte b/src/features/surface-host/ui/MessageQueueList.svelte
new file mode 100644
index 0000000..12de970
--- /dev/null
+++ b/src/features/surface-host/ui/MessageQueueList.svelte
@@ -0,0 +1,22 @@
+<script lang="ts">
+	import { parseMessageQueuePayload } from "../logic/message-queue";
+
+	let { payload }: { readonly payload: unknown } = $props();
+
+	// Parse defensively; an unparseable payload yields null → render nothing
+	// (graceful skip, per the custom-field contract).
+	const data = $derived(parseMessageQueuePayload(payload));
+</script>
+
+{#if data !== null && data.messages.length > 0}
+	<ul class="flex flex-col gap-1 text-sm">
+		{#each data.messages as msg (msg.id)}
+			<li class="rounded-box bg-base-200 px-3 py-2">
+				<p class="whitespace-pre-wrap">{msg.text}</p>
+				<time class="text-xs opacity-50" datetime={new Date(msg.queuedAt).toISOString()}>
+					{new Date(msg.queuedAt).toLocaleTimeString()}
+				</time>
+			</li>
+		{/each}
+	</ul>
+{/if}
diff --git a/src/features/surface-host/ui/SurfaceView.svelte b/src/features/surface-host/ui/SurfaceView.svelte
index 24be8b8..e5f807a 100644
--- a/src/features/surface-host/ui/SurfaceView.svelte
+++ b/src/features/surface-host/ui/SurfaceView.svelte
@@ -2,6 +2,7 @@
 	import type { InvokeMessage, SurfaceSpec } from "@dispatch/ui-contract";
 	import { groupRenderFields, planSurface } from "../logic/plan";
 	import Button from "./Button.svelte";
+	import MessageQueueList from "./MessageQueueList.svelte";
 	import Number from "./Number.svelte";
 	import Progress from "./Progress.svelte";
 	import Selector from "./Selector.svelte";
@@ -40,6 +41,8 @@
 			     unknown ids gracefully render nothing. -->
 			{#if group.field.rendererId === "table"}
 				<SurfaceTable payload={group.field.payload} />
+			{:else if group.field.rendererId === "message-queue"}
+				<MessageQueueList payload={group.field.payload} />
 			{/if}
 		{/if}
 	{/each}