Slice 3 wave A: tabs model, model selector, cache delete, localStorage

- features/tabs: pure tab-workspace reducer (create/select/close/setModel/
  setTitle/deriveTitle, draft=null active) + injected-persistence runes store
- features/chat: mutable per-tab model (setModel) + delta routing guard
  (ignore foreign conversationId) + ModelSelector.svelte + DaisyUI chat bubbles
  / composer (keeps streaming <details> keying fix)
- features/conversation-cache: surface delete(conversationId) on the wrapper
  for tab-close local-forget
- adapters/local-storage: generic injected JSON localStore<T> (quota/corrupt-safe)

Verified: svelte-check 0/0, vitest 273, biome clean, build ok.

1 files changed, 89 insertions, 0 deletions

diff --git a/src/features/chat/store.test.ts b/src/features/chat/store.test.ts
index 77a53c9..4ec40a9 100644
--- a/src/features/chat/store.test.ts
+++ b/src/features/chat/store.test.ts
@@ -347,4 +347,93 @@ describe("createChatStore", () => {
 
 		store.dispose();
 	});
+
+	it("setModel changes the model used by the next send", () => {
+		const transport = createFakeTransport();
+		const historySync = createFakeHistorySync();
+		const cache = createFakeCache();
+		const store = createChatStore({
+			conversationId: CONV_ID,
+			model: "openai/gpt-4",
+			transport: transport.impl,
+			historySync: historySync.impl,
+			cache: cache.impl,
+		});
+
+		store.send("First");
+		expect(transport.sent[0]?.model).toBe("openai/gpt-4");
+
+		store.setModel("anthropic/claude-3");
+		store.send("Second");
+		expect(transport.sent[1]?.model).toBe("anthropic/claude-3");
+
+		store.dispose();
+	});
+
+	it("setModel from undefined to a model", () => {
+		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("First");
+		expect(transport.sent[0]).not.toHaveProperty("model");
+
+		store.setModel("openai/gpt-4o");
+		store.send("Second");
+		expect(transport.sent[1]?.model).toBe("openai/gpt-4o");
+
+		store.dispose();
+	});
+
+	it("handleDelta ignores a chat.delta for a different conversationId", () => {
+		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.handleDelta(
+			deltaEvent({ type: "turn-start", conversationId: "other-conv", turnId: "t1" }),
+		);
+		store.handleDelta(
+			deltaEvent({
+				type: "text-delta",
+				conversationId: "other-conv",
+				turnId: "t1",
+				delta: "Should be ignored",
+			}),
+		);
+
+		expect(store.messages).toHaveLength(0);
+
+		store.dispose();
+	});
+
+	it("handleDelta ignores a chat.error for a different conversationId", () => {
+		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.handleDelta({ type: "chat.error", conversationId: "other-conv", message: "Wrong conv" });
+
+		expect(store.error).toBeNull();
+
+		store.dispose();
+	});
 });