fix(ai-sessions): release the staged prompt when a send is refused

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/lib/components/copilot/chat/AIChatManager.svelte.ts

@@ -2005,6 +2005,10 @@ export class AIChatManager {
 				options.files
 			)
 		}
+		// Handed off, so this manager no longer holds it. Only sendRequestImpl clears
+		// the field and a refusal never reaches it; left set, it reads to the
+		// auto-resume guard and the sidebar's draft cue as text the user is writing.
+		this.instructions = ''
 	}
 
 	/** Send the queued message, if there is one, as its own turn. The queue only

frontend/src/lib/components/copilot/chat/AIChatManager.test.ts

@@ -265,9 +265,10 @@ describe('AIChatManager cross-tab run guard', () => {
 		expect(mocks.runChatLoop).not.toHaveBeenCalled()
 		expect(manager.displayMessages).toHaveLength(2)
 		expect(manager.messages).toHaveLength(2)
-		// The prompt is handed back rather than lost, so the retry is still the
-		// user's to run once the other tab finishes.
-		expect(manager.instructions).toBe('first')
+		// Handed back rather than lost — and off the manager, which reports a
+		// non-empty `instructions` to the sidebar as text the user is writing.
+		expect(manager.queuedMessage).toBe('first')
+		expect(manager.instructions).toBe('')
 	})
 
 	// A turn flushes its queued message by re-entering sendRequest, and the lock

frontend/src/lib/components/sessions/sessionRunOwner.svelte.ts

@@ -187,8 +187,8 @@ export async function withSessionRunLock<T>(
 	}
 }
 
-/** What exclusion amounts to with no lock to take: refuse while another tab's run
- *  is visibly on screen, and otherwise go.
+/** What exclusion amounts to with no lock to take: nothing beyond the refusal
+ *  `withSessionRunLock` already made on a visibly running turn.
  *
  *  Not mutual exclusion, and cannot be made into it — a throttled hidden driver
  *  goes silent before its turn ends and is reaped as dead, and no probe tells a

frontend/src/lib/components/sessions/sessionStateIndexedDb.test.ts

@@ -278,8 +278,6 @@ describe('sessionState IndexedDB persistence', () => {
 		await vi.waitFor(() => expect(sessionState.sessions.map((s) => s.id)).toEqual(['keep']))
 	})
 
-	// A mirrored delete that announced itself would be mirrored straight back, and
-	// the two tabs would trade the same message and transaction without end.
 	it('removes a mirrored delete without announcing it', async () => {
 		const user = freshUser()
 		await login(user)
@@ -289,8 +287,7 @@ describe('sessionState IndexedDB persistence', () => {
 		await deleteSessionRecord('mirrored', false)
 		expect(deleteBroadcasts).toEqual([])
 
-		// Still genuinely removed — silence is not a no-op, it is what collects the
-		// row a write racing the other tab's delete left behind.
+		// Silence is not a no-op: the row still goes.
 		await rehydrate(user)
 		await vi.waitFor(() => expect(sessionState.sessions).toEqual([]))
 	})