fix: optimistic user message echo + tabs persistence

Bug 1 (sent message didn't appear until turn end): the transcript only folded
assistant AgentEvents, so the user's own message showed only after turn-sealed
resync. Add core/chunks appendUserMessage() (provisional user chunk, superseded
on history sync) and call it in chat send() — the message now renders instantly.

Bug 2 (tabs didn't persist on refresh): the app passed { storage: undefined }
to createLocalStore, which the adapter treats as a no-op store, so nothing was
saved. Default to globalThis.localStorage. Regression test exercises the
non-injected path.

Also updated app store tests for the echo (assistant-vs-user chunk filtering).
Verified: svelte-check 0/0, vitest 288 (stable x2), biome clean, build ok.

2 files changed, 60 insertions, 8 deletions

diff --git a/src/app/store.svelte.ts b/src/app/store.svelte.ts
index 07d850b..760c390 100644
--- a/src/app/store.svelte.ts
+++ b/src/app/store.svelte.ts
@@ -100,7 +100,7 @@ export function createAppStore(opts?: CreateAppStoreOptions): AppStore {
 
 	const fetchImpl = opts?.fetchImpl ?? globalThis.fetch.bind(globalThis);
 	const indexedDBFactory = opts?.indexedDB ?? globalThis.indexedDB;
-	const localStorageOpt = opts?.localStorage;
+	const localStorageOpt = opts?.localStorage ?? globalThis.localStorage;
 
 	const storageAdapter = createLocalStore<TabsState>("dispatch.tabs", {
 		storage: localStorageOpt,
diff --git a/src/app/store.test.ts b/src/app/store.test.ts
index dabc80d..86a21d6 100644
--- a/src/app/store.test.ts
+++ b/src/app/store.test.ts
@@ -388,9 +388,11 @@ describe("createAppStore", () => {
 		});
 
 		expect(store.activeChat.chunks.length).toBeGreaterThan(0);
-		const textChunks = store.activeChat.chunks.filter((c) => c.chunk.type === "text");
-		expect(textChunks).toHaveLength(1);
-		expect((textChunks[0]?.chunk as { type: "text"; text: string }).text).toBe("Hello world");
+		const assistantChunks = store.activeChat.chunks.filter(
+			(c) => c.role === "assistant" && c.chunk.type === "text",
+		);
+		expect(assistantChunks).toHaveLength(1);
+		expect((assistantChunks[0]?.chunk as { type: "text"; text: string }).text).toBe("Hello world");
 
 		store.dispose();
 	});
@@ -580,14 +582,19 @@ describe("createAppStore", () => {
 		});
 
 		store.selectTab(convId1);
-		const textChunks1 = store.activeChat.chunks.filter((c) => c.chunk.type === "text");
-		expect(textChunks1).toHaveLength(1);
-		expect((textChunks1[0]?.chunk as { type: "text"; text: string }).text).toBe(
+		const assistantChunks1 = store.activeChat.chunks.filter(
+			(c) => c.role === "assistant" && c.chunk.type === "text",
+		);
+		expect(assistantChunks1).toHaveLength(1);
+		expect((assistantChunks1[0]?.chunk as { type: "text"; text: string }).text).toBe(
 			"response to first",
 		);
 
 		store.selectTab(convId2);
-		expect(store.activeChat.chunks).toEqual([]);
+		const assistantChunks2 = store.activeChat.chunks.filter(
+			(c) => c.role === "assistant" && c.chunk.type === "text",
+		);
+		expect(assistantChunks2).toEqual([]);
 
 		store.dispose();
 	});
@@ -654,6 +661,51 @@ describe("createAppStore", () => {
 		store2.dispose();
 	});
 
+	it("tabs persist to globalThis.localStorage when no storage is injected", () => {
+		const realLs = globalThis.localStorage;
+		const memLs = createFakeStorage();
+		globalThis.localStorage = memLs;
+		try {
+			const ws1 = fakeSocket();
+			const store = createAppStore({
+				socketFactory: () => ws1,
+				fetchImpl: fakeFetchImpl(),
+			});
+			ws1.resolveOpen();
+
+			store.send("persist via default");
+			const convId = store.tabs[0]?.conversationId;
+			const title = store.tabs[0]?.title;
+			expect(convId).toBeDefined();
+			expect(title).toBeDefined();
+
+			const raw = globalThis.localStorage.getItem("dispatch.tabs");
+			expect(raw).not.toBeNull();
+			const parsed = JSON.parse(raw as string);
+			expect(parsed.tabs).toHaveLength(1);
+			expect(parsed.tabs[0].conversationId).toBe(convId);
+			expect(parsed.tabs[0].title).toBe(title);
+
+			store.dispose();
+
+			const ws2 = fakeSocket();
+			const store2 = createAppStore({
+				socketFactory: () => ws2,
+				fetchImpl: fakeFetchImpl(),
+			});
+			ws2.resolveOpen();
+
+			expect(store2.tabs).toHaveLength(1);
+			expect(store2.tabs[0]?.conversationId).toBe(convId);
+			expect(store2.tabs[0]?.title).toBe(title);
+			expect(store2.activeConversationId).toBe(convId);
+
+			store2.dispose();
+		} finally {
+			globalThis.localStorage = realLs;
+		}
+	});
+
 	it("newDraft resets to draft mode", () => {
 		const ws = fakeSocket();
 		const store = createAppStore({