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, 157 insertions, 0 deletions

diff --git a/src/features/tabs/tabs-store.test.ts b/src/features/tabs/tabs-store.test.ts
new file mode 100644
index 0000000..81ec8ad
--- /dev/null
+++ b/src/features/tabs/tabs-store.test.ts
@@ -0,0 +1,157 @@
+import { describe, expect, it } from "vitest";
+import type { TabsState } from "./tabs";
+import type { TabsStorage } from "./tabs-store.svelte";
+import { createTabsStore } from "./tabs-store.svelte";
+
+function createMemoryStorage(initial?: TabsState): TabsStorage & { data: TabsState | null } {
+	let data: TabsState | null = initial ?? null;
+	return {
+		get data() {
+			return data;
+		},
+		set data(v: TabsState | null) {
+			data = v;
+		},
+		load() {
+			return data;
+		},
+		save(state: TabsState) {
+			data = state;
+		},
+	};
+}
+
+describe("createTabsStore", () => {
+	it("loads persisted state on construct", () => {
+		const persisted: TabsState = {
+			tabs: [{ conversationId: "c1", model: "m1", title: "T1" }],
+			activeConversationId: "c1",
+		};
+		const storage = createMemoryStorage(persisted);
+		const store = createTabsStore(storage);
+
+		expect(store.tabs).toHaveLength(1);
+		expect(store.activeConversationId).toBe("c1");
+		expect(store.activeTab?.conversationId).toBe("c1");
+	});
+
+	it("starts with empty draft when no persisted state", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		expect(store.tabs).toHaveLength(0);
+		expect(store.activeConversationId).toBeNull();
+		expect(store.activeTab).toBeNull();
+	});
+
+	it("saves after every mutation", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		expect(storage.data?.tabs).toHaveLength(1);
+		expect(storage.data?.activeConversationId).toBe("c1");
+
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+		expect(storage.data?.tabs).toHaveLength(2);
+
+		store.selectTab("c1");
+		expect(storage.data?.activeConversationId).toBe("c1");
+
+		store.closeTab("c1");
+		expect(storage.data?.tabs).toHaveLength(1);
+		expect(storage.data?.activeConversationId).toBe("c2");
+
+		store.setModel("c2", "new-model");
+		expect(storage.data?.tabs[0]?.model).toBe("new-model");
+
+		store.setTitle("c2", "New Title");
+		expect(storage.data?.tabs[0]?.title).toBe("New Title");
+
+		store.newDraft();
+		expect(storage.data?.activeConversationId).toBeNull();
+	});
+
+	it("createTab appends and activates", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		expect(store.tabs).toHaveLength(1);
+		expect(store.activeConversationId).toBe("c1");
+
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+		expect(store.tabs).toHaveLength(2);
+		expect(store.activeConversationId).toBe("c2");
+	});
+
+	it("selectTab changes active", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+
+		store.selectTab("c1");
+		expect(store.activeConversationId).toBe("c1");
+	});
+
+	it("closeTab removes and activates neighbour", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+		store.createTab({ conversationId: "c3", model: "m3", title: "T3" });
+
+		store.selectTab("c2");
+		store.closeTab("c2");
+		expect(store.tabs).toHaveLength(2);
+		expect(store.activeConversationId).toBe("c1");
+	});
+
+	it("closing the last tab returns to draft", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		store.closeTab("c1");
+		expect(store.tabs).toHaveLength(0);
+		expect(store.activeConversationId).toBeNull();
+	});
+
+	it("setModel updates the right tab", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		store.createTab({ conversationId: "c1", model: "old", title: "T1" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+
+		store.setModel("c1", "new-model");
+		expect(store.tabs[0]?.model).toBe("new-model");
+		expect(store.tabs[1]?.model).toBe("m2");
+	});
+
+	it("setTitle updates the right tab", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		store.createTab({ conversationId: "c1", model: "m1", title: "Old" });
+
+		store.setTitle("c1", "New Title");
+		expect(store.tabs[0]?.title).toBe("New Title");
+	});
+
+	it("newDraft clears active but keeps tabs", () => {
+		const storage = createMemoryStorage();
+		const store = createTabsStore(storage);
+
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+
+		store.newDraft();
+		expect(store.tabs).toHaveLength(2);
+		expect(store.activeConversationId).toBeNull();
+		expect(store.activeTab).toBeNull();
+	});
+});