fix: credit only a row the live item actually wrote

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

frontend/src/lib/itemStore.svelte.ts

@@ -249,6 +249,9 @@ class Entry<V> {
 	 *  each, and each row a caller says it wrote for one of them. A row left over after that is a
 	 *  row nobody here has the value of. */
 	private values = 0
+	/** Whether the last value handed in made this entry write a row of its own. Loading, it
+	 *  cannot: the caller's own row is then the only one, and is already counted. */
+	private seedWroteRow = false
 	private queue: Promise<unknown> = Promise.resolve()
 	private ports: ItemRowPort
 	private store: StoreInternals
@@ -528,18 +531,21 @@ class Entry<V> {
 	 *  rather than leaving the row to this entry: the two are one value, and counting the second
 	 *  row as unaccounted would read as someone else having written it. */
 	noteRow(): void {
-		this.values++
+		if (this.seedWroteRow) this.values++
 	}
 
 	applyExternal(value: V): number {
 		this.externals++
 		this.values++
+		this.seedWroteRow = false
 		if (this.loaded && serialize(value) === serialize(this.value)) return this.revision
 		this.edits++
 		this.pristine = false
 		this.removed = false
 		this.replaceValue(value)
+		const rowsBefore = this.ports.rowMark(this.key)
 		this.reconcile()
+		this.seedWroteRow = this.ports.rowMark(this.key) !== rowsBefore
 		return this.revision
 	}
 

frontend/src/lib/itemStore.test.ts

@@ -906,6 +906,33 @@ describe('item store: origins', () => {
 		expect(rows.writes.at(-1)).toEqual({ path: 'u/me/r', value: typed })
 	})
 
+	it('is not fooled by the chat crediting a row a loading item never wrote', async () => {
+		const rows = fakeRows()
+		const read = deferred<ItemLoad<Res>>()
+		const store = createItemStore(rows.port)
+		const key: ItemKey = { workspace: 'w', kind: 'resource', path: 'u/me/r' }
+		const { handle: item } = store.acquire(
+			key,
+			{ workspace: 'w', path: 'u/me/r' },
+			adapter(() => read.promise)
+		)
+		await settle()
+
+		// The chat seeds and persists while the first GET is out. Loading, this entry writes no
+		// row of its own, so the chat's save is the only row that value produced.
+		item.applyExternal({ ...deployedRes, description: 'from the chat' })
+		store.bridge.noteRow('w', 'resource', 'u/me/r')
+		rows.handExternally('u/me/r')
+		// The legacy agent editor then writes the same resource: a row nobody here has.
+		rows.handExternally('u/me/r')
+		read.resolve({ deployed: deployedRes })
+		await settle()
+
+		// Two rows, one of them unaccounted for. Crediting the chat twice would hide it and let
+		// this editor post over the agent editor's newer draft.
+		expect(item.canSave).toBe(false)
+	})
+
 	it('stays blocked when an unseen row follows the edit it kept', async () => {
 		const rows = fakeRows()
 		const read = deferred<ItemLoad<Res>>()