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 Add core/chunks appendUserMessage() (provisional user chunk, superseded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, 0 deletions

diff --git a/src/features/chat/store.svelte.ts b/src/features/chat/store.svelte.ts
index e997f49..1d8ab17 100644
--- a/src/features/chat/store.svelte.ts
+++ b/src/features/chat/store.svelte.ts
@@ -6,6 +6,7 @@ import type {
 import type { ChatMessage } from "@dispatch/wire";
 import type { RenderedChunk, TranscriptState } from "../../core/chunks";
 import {
+	appendUserMessage,
 	applyHistory,
 	foldEvent,
 	initialState,
@@ -94,6 +95,7 @@ export function createChatStore(deps: ChatStoreDependencies): ChatStore {
 		},
 
 		send(text: string): void {
+			transcript = appendUserMessage(transcript, text);
 			const msg: ChatSendMessage = {
 				type: "chat.send",
 				conversationId: deps.conversationId,
diff --git a/src/features/chat/store.test.ts b/src/features/chat/store.test.ts
index 4ec40a9..de60b14 100644
--- a/src/features/chat/store.test.ts
+++ b/src/features/chat/store.test.ts
@@ -436,4 +436,62 @@ describe("createChatStore", () => {
 
 		store.dispose();
 	});
+
+	it("send optimistically shows the user message immediately", () => {
+		const transport = createFakeTransport();
+		const historySync = createFakeHistorySync();
+		const cache = createFakeCache();
+		const store = createChatStore({
+			conversationId: CONV_ID,
+			transport: transport.impl,
+			historySync: historySync.impl,
+			cache: cache.impl,
+		});
+
+		store.send("hi");
+
+		expect(store.messages).toHaveLength(1);
+		expect(store.messages[0]?.role).toBe("user");
+		expect(store.messages[0]?.chunks).toHaveLength(1);
+		expect(store.messages[0]?.chunks[0]?.type).toBe("text");
+		expect((store.messages[0]?.chunks[0] as { type: "text"; text: string }).text).toBe("hi");
+
+		store.dispose();
+	});
+
+	it("the optimistic user message is replaced after turn-sealed + history sync", async () => {
+		const transport = createFakeTransport();
+		const historySync = createFakeHistorySync();
+		const cache = createFakeCache();
+		const store = createChatStore({
+			conversationId: CONV_ID,
+			transport: transport.impl,
+			historySync: historySync.impl,
+			cache: cache.impl,
+		});
+
+		historySync.returnChunks = [
+			{ seq: 1, role: "user", chunk: { type: "text", text: "hi" } },
+			{ seq: 2, role: "assistant", chunk: { type: "text", text: "hello!" } },
+		];
+
+		store.send("hi");
+		expect(store.messages).toHaveLength(1);
+		expect(store.messages[0]?.role).toBe("user");
+
+		store.handleDelta(deltaEvent({ type: "turn-start", conversationId: CONV_ID, turnId: "t1" }));
+		store.handleDelta(
+			deltaEvent({ type: "text-delta", conversationId: CONV_ID, turnId: "t1", delta: "hello!" }),
+		);
+		store.handleDelta(deltaEvent({ type: "turn-sealed", conversationId: CONV_ID, turnId: "t1" }));
+
+		await vi.waitFor(() => {
+			expect(store.messages.length).toBe(2);
+		});
+
+		expect(store.messages[0]?.role).toBe("user");
+		expect(store.messages[1]?.role).toBe("assistant");
+
+		store.dispose();
+	});
 });