fix(chat): make forgetting a flow hold against work already in flight

Clearing the state was not enough: a transcript fetch, a latest-conversation
lookup or a settle tail started before the chat was re-pointed resolved after it
and wrote the previous flow's rows, selection or status straight back — the bug
the clearing exists to prevent, reached through the gap instead.

Each of those now carries the generation it started in and drops what it fetched
if the chat has moved on since.

The re-point test was asserting two things that could not fail — an empty rows
map and an empty conversation list, both empty either way — so it pinned half the
fix. It loads rows now and checks they are gone.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/flows/conversations/FlowChatManager.svelte.ts

@@ -157,6 +157,9 @@ export class FlowChatManager {
 
 	/** Each conversation's rows, live ones included, so a turn keeps writing while the
 	 * reader is in another chat. Doubles as the load cache: rows here are never re-fetched. */
+	/** Bumped when the chat is re-pointed at another flow. Work started before that must not
+	 * write what it fetched into the chat that replaced it. */
+	#generation = 0
 	#rowsById = $state<Record<string, ChatMessage[]>>({})
 	/** How far back each conversation has been paged. Held per conversation for the same
 	 * reason the rows are: a cached chat keeps its scrollback when the reader returns to it,
@@ -488,6 +491,7 @@ export class FlowChatManager {
 	 * messages into that transcript and its agent's memory.
 	 */
 	cleanup() {
+		this.#generation++
 		for (const conversationId of Object.keys(this.#status)) this.endTurn(conversationId)
 		this.selectedConversationId = undefined
 		this.#rowsById = {}
@@ -585,9 +589,11 @@ export class FlowChatManager {
 	 */
 	async selectLatestConversation() {
 		if (this.selectedConversationId || !this.#workspace() || !this.#path) return
+		const startedIn = this.#generation
 		const [latest] = await this.loadConversations(1, 1)
-		// Re-checked after the await: a message sent meanwhile has already opened its own.
-		if (!latest || this.selectedConversationId) return
+		// Re-checked after the await: a message sent meanwhile has already opened its own, or
+		// the chat has been re-pointed and this is the previous flow's latest conversation.
+		if (!latest || this.selectedConversationId || startedIn !== this.#generation) return
 		await this.selectConversation(latest.id)
 	}
 
@@ -816,6 +822,7 @@ export class FlowChatManager {
 		try {
 			const previousScrollHeight = this.messagesContainer?.scrollHeight || 0
 
+			const startedIn = this.#generation
 			const response = await FlowConversationsService.listConversationMessages({
 				workspace: this.#workspace()!,
 				conversationId: conversationIdToUse,
@@ -823,6 +830,10 @@ export class FlowChatManager {
 				perPage: this.#perPage
 			})
 
+			// The chat was re-pointed while this was in flight; these rows belong to a flow it
+			// no longer shows, and the hold below would be released for the wrong one.
+			if (startedIn !== this.#generation) return
+
 			if (reset) {
 				this.#rowsById[conversationIdToUse] = response
 				this.#pagedTo[conversationIdToUse] = 1
@@ -1376,9 +1387,12 @@ export class FlowChatManager {
 			await new Promise((resolve) => setTimeout(resolve, SETTLE_POLL_MS))
 		}
 		if (signal.aborted) return
+		const startedIn = this.#generation
 		try {
 			await this.pollConversationMessages(conversationId, { removeTempMessages: true })
 		} catch {}
+		// `endTurn` would put this conversation's status back into a map the re-point emptied.
+		if (signal.aborted || startedIn !== this.#generation) return
 		this.endTurn(conversationId, { settled: true })
 	}
 

frontend/src/lib/components/flows/conversations/FlowChatManager.test.ts

@@ -135,16 +135,40 @@ describe('a chat re-pointed at another flow', () => {
 	 * conversation and send into its transcript and its agent's memory.
 	 */
 	it('forgets the flow it was pointed at when it is re-pointed', async () => {
-		vi.mocked(FlowConversationsService.listConversationMessages).mockResolvedValue([] as any)
+		vi.mocked(FlowConversationsService.listConversationMessages).mockResolvedValue(
+			rows('a', 2) as any
+		)
 		const manager = managerWithRows()
 		await manager.selectConversation('a')
 		expect(manager.selectedConversationId).toBe('a')
+		expect(manager.liveRowIds.size).toBe(2)
 
 		manager.cleanup()
 
 		expect(manager.selectedConversationId).toBeUndefined()
-		expect(manager.messages).toEqual([])
-		expect(manager.conversations).toEqual([])
+		expect(manager.liveRowIds.size).toBe(0)
+	})
+
+	/**
+	 * Forgetting has to hold against work already in flight: a transcript fetched for the
+	 * flow just left would otherwise be written into the one that replaced it.
+	 */
+	it('does not let a load started before the re-point write its rows back', async () => {
+		let release = () => {}
+		const held = new Promise<void>((resolve) => (release = resolve))
+		vi.mocked(FlowConversationsService.listConversationMessages).mockImplementation((async () => {
+			await held
+			return rows('a', 2)
+		}) as any)
+		const manager = managerWithRows()
+		const loading = manager.selectConversation('a')
+
+		manager.cleanup()
+		release()
+		await loading
+
+		expect(manager.liveRowIds.size).toBe(0)
+		expect(manager.selectedConversationId).toBeUndefined()
 	})
 })