fix(chat): keep empty soft-swap centered until first turn

cometline/src/lib/components/ChatView.svelte

@@ -137,9 +137,8 @@
 			// loads would otherwise dock the composer and skip FirstTurnFlight.
 			return chatStore.items.length > 0;
 		}
-		// Store is still bound to a previous session (mid-switch). Before our
-		// first sync, assume visible when we do not yet know the target is empty
-		// so we don't flash EmptyChatState while switching to a full transcript.
+		// Mid-switch: no user/assistant yet stays hero (fork status notes ignored).
+		if (!chatStore.hasCachedConversationTurns(sessionId)) return false;
 		if (!snapshotSynced) return true;
 		return snapshotItems.length > 0;
 	});
@@ -203,7 +202,9 @@
 	// destination avatar/thinking indicator appear before the overlay arrives.
 	// Soft swaps (/change fork, sidebar click) keep ChatView mounted — this must
 	// be remount-equivalent so composer phase + flight flags are not stuck until Cmd+R.
-	$effect(() => {
+	// Use $effect.pre so stale awaiting/firstTurn flags clear BEFORE syncComposerPhase
+	// can dock on the previous session's mid-switch visibility.
+	$effect.pre(() => {
 		void sessionId;
 		untrack(() => {
 			flightAbortController?.abort();
@@ -212,12 +213,13 @@
 			userBubbleFlight?.dismissParticle();
 			firstTurnActive = false;
 			firstTurnHandoffPending = false;
-			const cachedCount = chatStore.getCachedItemCount(sessionId);
+			const hasTurns = chatStore.hasCachedConversationTurns(sessionId);
 			awaitingFirstAssistant = chatStore.isAwaitingFirstAssistant(sessionId);
-			// Empty session: explicitly false. Do NOT use `!awaitingFirstAssistant`
+			// No user/assistant yet: explicitly false. Do NOT use `!awaitingFirstAssistant`
 			// (true when idle) which wrongly marks flight done after soft swaps.
-			firstTurnFlightDone = cachedCount > 0;
-			if (cachedCount === 0 && !awaitingFirstAssistant) {
+			// Fork system notes are status-only and must not mark flight done.
+			firstTurnFlightDone = hasTurns;
+			if (!hasTurns && !awaitingFirstAssistant) {
 				snapshotItems = [];
 				snapshotSynced = true;
 				shellStore.centerComposer();

cometline/src/lib/conversation/conversation-controller.test.ts

@@ -9,13 +9,15 @@ import {
 import { chatStore } from '$lib/stores/chat.svelte';
 import { sessionStore } from '$lib/stores/session.svelte';
 import { shellStore } from '$lib/stores/shell.svelte';
-import { getSession } from '$lib/client/cometmind';
+import { getSession, getSessionMessages } from '$lib/client/cometmind';
 
 type FlightPayload = Parameters<ConversationFlightAdapter['onUserMessageFlight']>[0];
 type FlightContext = Parameters<ConversationFlightAdapter['onUserMessageFlight']>[1];
 
 vi.mock('$lib/client/cometmind', () => ({
-	getSession: vi.fn().mockResolvedValue({ id: 'sess-1', title: 'Updated' })
+	getSession: vi.fn().mockResolvedValue({ id: 'sess-1', title: 'Updated' }),
+	getSessionMessages: vi.fn().mockResolvedValue({ session_id: 'sess-1', items: [] }),
+	listChildSessions: vi.fn().mockResolvedValue({ sessions: [] })
 }));
 
 describe('createConversationController', () => {
@@ -25,6 +27,7 @@ describe('createConversationController', () => {
 		sessionStore.setSessions([]);
 		resetConversationTurnQueuesForTests();
 		shellStore.centerComposer();
+		vi.mocked(getSessionMessages).mockResolvedValue({ session_id: 'sess-1', items: [] });
 		vi.mocked(getSession).mockResolvedValue({
 			id: 'sess-1',
 			workspace_id: 'ws-1',
@@ -639,6 +642,62 @@ describe('createConversationController', () => {
 		centerSpy.mockRestore();
 	});
 
+	it('syncComposerPhase keeps empty session centered even when hasVisibleConversation is true', () => {
+		chatStore.bindSession('sess-1');
+		const { controller } = createDeps({ hasVisibleConversation: true });
+		controller.bindSession();
+		shellStore.centerComposer();
+
+		controller.syncComposerPhase({
+			hasVisibleConversation: true,
+			firstTurnActive: false,
+			awaitingFirstAssistant: false
+		});
+
+		expect(shellStore.composerPhase).toBe('centered');
+		expect(chatStore.getCachedItemCount('sess-1')).toBe(0);
+	});
+
+	it('treats fork status-only transcript as firstTurn and keeps composer centered', async () => {
+		vi.mocked(getSessionMessages).mockResolvedValue({
+			session_id: 'sess-1',
+			items: [
+				{
+					type: 'system',
+					text: 'Forked from a session in /old. File tools now operate under /new.'
+				}
+			]
+		});
+		chatStore.bindSession('sess-1');
+		await chatStore.loadTranscript('sess-1');
+		expect(chatStore.getCachedItemCount('sess-1')).toBe(1);
+		expect(chatStore.hasCachedConversationTurns('sess-1')).toBe(false);
+
+		const onUserMessageFlight = vi.fn().mockImplementation((_, ctx: FlightContext) => {
+			ctx.stageUser('hello', undefined);
+		});
+		const { controller, send } = createDeps({
+			hasVisibleConversation: true,
+			flight: { onUserMessageFlight }
+		});
+		controller.bindSession();
+		expect(shellStore.composerPhase).toBe('centered');
+
+		controller.syncComposerPhase({
+			hasVisibleConversation: true,
+			firstTurnActive: false,
+			awaitingFirstAssistant: false
+		});
+		expect(shellStore.composerPhase).toBe('centered');
+
+		await controller.enqueue('hello');
+		expect(onUserMessageFlight).toHaveBeenCalledWith(
+			'hello',
+			expect.objectContaining({ firstTurn: true, sessionId: 'sess-1' })
+		);
+		expect(send).toHaveBeenCalledWith('sess-1', { text: 'hello' }, { skipUser: true });
+	});
+
 	it('runs FirstTurnFlight when hasVisibleConversation is true only due to loading and cache is empty', async () => {
 		chatStore.bindSession('sess-1');
 		const onUserMessageFlight = vi.fn().mockImplementation((_, ctx: FlightContext) => {

cometline/src/lib/conversation/conversation-controller.ts

@@ -82,9 +82,9 @@ async function runTurn(
 	const userDisplay = payload.displayText ?? payload.text;
 	const usesFlight = Boolean(deps.flight?.onUserMessageFlight);
 	const isViewing = deps.getSessionId() === turnSessionId;
-	// Content emptiness — not hasVisibleConversation(). Loading makes the latter
-	// true on an empty fork/soft swap and would skip FirstTurnFlight.
-	const firstTurn = chatStore.getCachedItemCount(turnSessionId) === 0;
+	// No user/assistant yet — not hasVisibleConversation() / raw item count.
+	// Fork AppendSystemMessage becomes a status row and must not skip FirstTurnFlight.
+	const firstTurn = !chatStore.hasCachedConversationTurns(turnSessionId);
 	const flightPayload = payload.images?.length ? payload : userDisplay;
 	const contexts = messageContextRefsFromWebContexts(payload.webContexts);
 	let stagedUserId: string | undefined;
@@ -211,7 +211,7 @@ export function createConversationController(
 			// content/in-flight dock. Do not dock solely because isLoading — that
 			// leaves the composer stuck docked after /change → empty fork.
 			if (
-				chatStore.getCachedItemCount(sessionId) > 0 ||
+				chatStore.hasCachedConversationTurns(sessionId) ||
 				chatStore.hasInFlightTurn(sessionId)
 			) {
 				shellStore.dockComposer();
@@ -267,6 +267,16 @@ export function createConversationController(
 			if (chatStore.sessionID !== deps.getSessionId()) return;
 			if (firstTurnActive) return;
 
+			const sessionId = deps.getSessionId();
+			const empty = !chatStore.hasCachedConversationTurns(sessionId);
+			// Soft /change into an empty fork (status-only system note counts as empty):
+			// mid-switch visibility flags must not dock after we just centered —
+			// emptiness wins until real user/assistant content or first-turn prepare.
+			if (empty && !awaitingFirstAssistant) {
+				shellStore.centerComposer();
+				return;
+			}
+
 			if (hasVisibleConversation) {
 				shellStore.dockComposer();
 			} else if (!awaitingFirstAssistant) {

cometline/src/lib/stores/chat.svelte.ts

@@ -92,6 +92,14 @@ function createChatStore() {
 		return cachedItemCount(targetSessionID);
 	}
 
+	/** User/assistant turns only — fork system notes map to `status` and must not
+	 *  count as a real conversation for first-turn / composer dock. */
+	function hasCachedConversationTurns(targetSessionID: string) {
+		return getCachedItems(targetSessionID).some(
+			(item) => item.type === 'user' || item.type === 'assistant'
+		);
+	}
+
 	function getCachedItems(targetSessionID: string) {
 		return sessionCache.get(targetSessionID) ?? [];
 	}
@@ -927,6 +935,7 @@ function createChatStore() {
 		hasInFlightTurn,
 		isAwaitingFirstAssistant,
 		getCachedItemCount,
+		hasCachedConversationTurns,
 		clear,
 		resetTranscript,
 		detachActiveSession,