fix: do not let a clean editor acknowledge a row it never knew of

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

frontend/src/lib/itemStore.svelte.ts

@@ -522,15 +522,19 @@ class Entry<V> {
 	 *  item, so the row is the caller's. `failed`: has it, on a baseline it cannot refresh. */
 	async discarded(): Promise<'done' | 'absent' | 'failed'> {
 		const asked = this.asOf()
+		// A row this entry has none of is not one it can discard: it does nothing, and the caller
+		// would read that as the row being gone while another tab's is still there.
+		let knewRow = this.row !== null
 		await this.discard(asked)
 		if (this.retired || !this.loaded) return 'absent'
-		if (!this.stale) return 'done'
+		if (!this.stale) return knewRow ? 'done' : 'absent'
 		// Stale refused it. A reload is what clears that, and with a baseline it can trust the
 		// discard means something again — so the one thing worth trying before giving up. The
 		// retry carries the state as of the request, so an edit typed during that reload stands.
 		if (!this.adapter || !(await this.load(this.adapter)).ok) return 'failed'
+		knewRow = this.row !== null
 		await this.discard(asked)
-		return this.stale ? 'failed' : 'done'
+		return this.stale ? 'failed' : knewRow ? 'done' : 'absent'
 	}
 
 	/**

frontend/src/lib/itemStore.test.ts

@@ -1127,6 +1127,27 @@ describe('item store: origins', () => {
 		})
 	})
 
+	it('says a row it never knew of is not its to discard', async () => {
+		const rows = fakeRows()
+		const store = createItemStore(rows.port)
+		// Loaded clean: no draft existed when this editor read the item.
+		const { handle: item } = store.acquire(
+			{ workspace: 'w', kind: 'resource', path: 'u/me/r' },
+			{ workspace: 'w', path: 'u/me/r' },
+			adapter({ deployed: deployedRes })
+		)
+		await settle()
+		expect(item.dirty).toBe(false)
+
+		// Another tab creates the draft afterwards. This editor knows nothing of it.
+		rows.sent.set('u/me/r', { ...deployedRes, description: 'the other tab' })
+		rows.handExternally('u/me/r')
+
+		// Its discard does nothing, so answering `done` would have the caller skip the delete and
+		// report a draft gone that is still on the server.
+		expect(await store.bridge.discard('w', 'resource', 'u/me/r')).toBe('absent')
+	})
+
 	it('says it did not deal with the row when its own first read never arrived', async () => {
 		const rows = fakeRows()
 		const store = createItemStore(rows.port)