feat(concurrency): loading-ring for queued chats (CR-13 consumed)

Backend shipped "queued" ConversationStatus (additive to [email protected]): when a
request blocks on a concurrency slot, conversation.statusChanged broadcasts
"queued" (broadcast-only, never persisted); "active" on slot grant.

FE consumes it:
- WS parser (adapters/ws/logic.ts): accepts "queued" in the status set.
- Store handler: "queued" updates the status map + opens a tab for a new
  cross-device queued conversation (like "active").
- TabList: status === "queued" -> loading-ring (spinner, aria-label "Queued");
  "active" -> loading-dots (unchanged).
- Composer: status type widened to ComposerStatus (idle|running|queued|error),
  exported from features/chat. "queued" -> a loading-ring status icon +
  placeholder "Queued for a slot…"; behaves like "running" for the send
  button (steer/stop — the turn is in flight, just waiting for a slot).
- App.svelte: composerStatus derived (error > queued > running > idle) —
  conversationStatus === "queued" wins over generating so the corner shows a
  ring during the wait (turn-start fires before the slot is granted, so
  generating is already true while status === "queued").
- Re-mirrored .dispatch/wire.reference.md (ConversationStatus widened + header).

Tests: WS parser accepts queued; store handler sets status + opens a cross-device
tab + transitions queued->active->idle; TabList renders a ring for queued + dots
for active. typecheck 0/0, 925 tests green (x2), biome clean, build OK.
backend-handoff.md CR-13 marked RESOLVED.

3 files changed, 90 insertions, 8 deletions

diff --git a/src/app/App.svelte b/src/app/App.svelte
index 5aa103d..b46885c 100644
--- a/src/app/App.svelte
+++ b/src/app/App.svelte
@@ -16,6 +16,7 @@
 		ModelSelector,
 		ReasoningEffortSelector,
 		type CompactNowResult,
+		type ComposerStatus,
 		type ReasoningEffortSaveResult,
 		type SaveCompactPercentResult,
 	} from "../features/chat";
@@ -238,6 +239,19 @@
 		return tab?.title ?? NEW_TAB_TITLE;
 	});
 
+	// The composer status-bar status. Priority: error > queued > running > idle.
+	// `queued` (the turn is in flight but waiting for a concurrency slot — CR-13)
+	// wins over `running` so the corner shows a ring, not dots, during the wait.
+	// `turn-start` fires before the slot is granted, so `generating` is already
+	// true while `conversationStatus === "queued"`; the explicit queued check is
+	// what distinguishes the two.
+	const composerStatus = $derived.by<ComposerStatus>(() => {
+		if (store.activeChat.error) return "error";
+		const id = store.activeConversationId;
+		if (id !== null && store.conversationStatus(id) === "queued") return "queued";
+		return store.activeChat.generating ? "running" : "idle";
+	});
+
 	// Conversation/tab switch → snap to the bottom of the new transcript.
 	$effect(() => {
 		void store.activeConversationId;
@@ -588,11 +602,7 @@
 			onStop={handleStop}
 			contextSize={store.activeChat.currentContextSize}
 			contextWindow={store.modelInfo[store.activeModel]?.contextWindow}
-			status={store.activeChat.error
-				? "error"
-				: store.activeChat.generating
-					? "running"
-					: "idle"}
+			status={composerStatus}
 		/>
 	</div>
 
diff --git a/src/app/store.svelte.ts b/src/app/store.svelte.ts
index 8bc1080..0506f91 100644
--- a/src/app/store.svelte.ts
+++ b/src/app/store.svelte.ts
@@ -980,10 +980,14 @@ export function createAppStore(opts?: CreateAppStoreOptions): AppStore {
         }
         return;
       }
-      // active / idle — update the status map (drives the tab spinner).
+      // active / queued / idle — update the status map (drives the tab spinner).
+      // `queued` = the turn is in flight but waiting for a concurrency slot
+      // (broadcast-only, never persisted — CR-13); the tab shows a ring.
       conversationStatuses = new Map(conversationStatuses).set(conversationId, status);
-      // If this is a new active conversation we don't have a tab for, open one.
-      if (status === "active" && !chatStores.has(conversationId)) {
+      // If this is a new active OR queued conversation we don't have a tab for,
+      // open one — so a cross-device turn (incl. one waiting in the concurrency
+      // queue) is visible. `idle` never opens a tab.
+      if ((status === "active" || status === "queued") && !chatStores.has(conversationId)) {
         openConversation(conversationId, workspaceId);
       }
     },
diff --git a/src/app/store.test.ts b/src/app/store.test.ts
index 2074d9e..b47a378 100644
--- a/src/app/store.test.ts
+++ b/src/app/store.test.ts
@@ -1634,4 +1634,72 @@ describe("createAppStore", () => {
     expect(result.providers).toEqual([]);
     store.dispose();
   });
+
+  // ── Conversation status: `queued` (CR-13 — waiting for a concurrency slot) ────
+
+  it("conversation.statusChanged 'queued' sets the status (tab spinner) without opening a duplicate tab", () => {
+    const ws = fakeSocket();
+    const store = createAppStore({
+      socketFactory: () => ws,
+      fetchImpl: fakeFetchImpl(),
+      localStorage: createFakeStorage(),
+    });
+    ws.resolveOpen();
+    store.send("hello");
+    const convId = activeConversationId(store);
+    const tabsBefore = store.tabs.length;
+
+    // The backend broadcasts "queued" while the turn waits for a slot.
+    ws.feedServerMessage({
+      type: "conversation.statusChanged",
+      conversationId: convId,
+      status: "queued",
+      workspaceId: "default",
+    });
+
+    expect(store.conversationStatus(convId)).toBe("queued");
+    // The tab already exists (opened on send) — no duplicate tab is opened.
+    expect(store.tabs.length).toBe(tabsBefore);
+
+    // Granted → "active" (dots), then idle on turn seal.
+    ws.feedServerMessage({
+      type: "conversation.statusChanged",
+      conversationId: convId,
+      status: "active",
+      workspaceId: "default",
+    });
+    expect(store.conversationStatus(convId)).toBe("active");
+    ws.feedServerMessage({
+      type: "conversation.statusChanged",
+      conversationId: convId,
+      status: "idle",
+      workspaceId: "default",
+    });
+    expect(store.conversationStatus(convId)).toBe("idle");
+    store.dispose();
+  });
+
+  it("conversation.statusChanged 'queued' opens a tab for a new cross-device conversation", () => {
+    const ws = fakeSocket();
+    const store = createAppStore({
+      socketFactory: () => ws,
+      fetchImpl: fakeFetchImpl(),
+      localStorage: createFakeStorage(),
+    });
+    ws.resolveOpen();
+    expect(store.tabs.length).toBe(0);
+
+    // Another device's turn is waiting for a slot — broadcast "queued".
+    ws.feedServerMessage({
+      type: "conversation.statusChanged",
+      conversationId: "other-device-conv",
+      status: "queued",
+      workspaceId: "default",
+    });
+
+    expect(store.conversationStatus("other-device-conv")).toBe("queued");
+    // A queued conversation we had no tab for opens one (like `active`).
+    expect(store.tabs.some((t) => t.conversationId === "other-device-conv")).toBe(true);
+    store.dispose();
+  });
 });