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, 191 insertions, 0 deletions

diff --git a/src/features/tabs/tabs.test.ts b/src/features/tabs/tabs.test.ts
new file mode 100644
index 0000000..3034e76
--- /dev/null
+++ b/src/features/tabs/tabs.test.ts
@@ -0,0 +1,191 @@
+import { describe, expect, it } from "vitest";
+import type { Tab, TabsState } from "./tabs";
+import {
+	activeTab,
+	closeTab,
+	createTab,
+	deriveTitle,
+	initialState,
+	newDraft,
+	selectTab,
+	setModel,
+	setTitle,
+} from "./tabs";
+
+const tab = (conversationId: string, model = "default", title = "Chat"): Tab => ({
+	conversationId,
+	model,
+	title,
+});
+
+describe("initialState", () => {
+	it("returns empty draft state when no persisted state", () => {
+		const state = initialState();
+		expect(state.tabs).toEqual([]);
+		expect(state.activeConversationId).toBeNull();
+	});
+
+	it("returns persisted state when provided", () => {
+		const persisted: TabsState = {
+			tabs: [tab("c1")],
+			activeConversationId: "c1",
+		};
+		const state = initialState(persisted);
+		expect(state.tabs).toHaveLength(1);
+		expect(state.activeConversationId).toBe("c1");
+	});
+});
+
+describe("newDraft", () => {
+	it("sets activeConversationId to null", () => {
+		const state: TabsState = { tabs: [tab("c1")], activeConversationId: "c1" };
+		const next = newDraft(state);
+		expect(next.activeConversationId).toBeNull();
+	});
+
+	it("keeps existing tabs", () => {
+		const state: TabsState = { tabs: [tab("c1"), tab("c2")], activeConversationId: "c1" };
+		const next = newDraft(state);
+		expect(next.tabs).toHaveLength(2);
+	});
+});
+
+describe("createTab", () => {
+	it("appends and activates", () => {
+		const state = initialState();
+		const next = createTab(state, tab("c1"));
+		expect(next.tabs).toHaveLength(1);
+		expect(next.tabs[0]?.conversationId).toBe("c1");
+		expect(next.activeConversationId).toBe("c1");
+	});
+
+	it("does not duplicate an existing conversationId", () => {
+		const state: TabsState = { tabs: [tab("c1")], activeConversationId: "c1" };
+		const next = createTab(state, tab("c1"));
+		expect(next.tabs).toHaveLength(1);
+	});
+
+	it("activates an already-existing tab when createTab is called again", () => {
+		const state: TabsState = { tabs: [tab("c1"), tab("c2")], activeConversationId: "c2" };
+		const next = createTab(state, tab("c1"));
+		expect(next.activeConversationId).toBe("c1");
+	});
+});
+
+describe("selectTab", () => {
+	it("changes active", () => {
+		const state: TabsState = { tabs: [tab("c1"), tab("c2")], activeConversationId: "c1" };
+		const next = selectTab(state, "c2");
+		expect(next.activeConversationId).toBe("c2");
+	});
+});
+
+describe("closeTab", () => {
+	it("removes the tab", () => {
+		const state: TabsState = { tabs: [tab("c1"), tab("c2")], activeConversationId: "c1" };
+		const next = closeTab(state, "c2");
+		expect(next.tabs).toHaveLength(1);
+		expect(next.tabs[0]?.conversationId).toBe("c1");
+	});
+
+	it("closing the active tab activates a neighbour (previous preferred)", () => {
+		const state: TabsState = {
+			tabs: [tab("c1"), tab("c2"), tab("c3")],
+			activeConversationId: "c2",
+		};
+		const next = closeTab(state, "c2");
+		expect(next.activeConversationId).toBe("c1");
+	});
+
+	it("closing the first active tab activates the next", () => {
+		const state: TabsState = {
+			tabs: [tab("c1"), tab("c2"), tab("c3")],
+			activeConversationId: "c1",
+		};
+		const next = closeTab(state, "c1");
+		expect(next.activeConversationId).toBe("c2");
+	});
+
+	it("closing the last tab returns to draft (null active)", () => {
+		const state: TabsState = { tabs: [tab("c1")], activeConversationId: "c1" };
+		const next = closeTab(state, "c1");
+		expect(next.tabs).toHaveLength(0);
+		expect(next.activeConversationId).toBeNull();
+	});
+
+	it("closing a non-active tab does not change active", () => {
+		const state: TabsState = {
+			tabs: [tab("c1"), tab("c2"), tab("c3")],
+			activeConversationId: "c3",
+		};
+		const next = closeTab(state, "c1");
+		expect(next.activeConversationId).toBe("c3");
+	});
+
+	it("closing a non-existent tab is a no-op", () => {
+		const state: TabsState = { tabs: [tab("c1")], activeConversationId: "c1" };
+		const next = closeTab(state, "missing");
+		expect(next).toEqual(state);
+	});
+});
+
+describe("setModel", () => {
+	it("updates the right tab", () => {
+		const state: TabsState = { tabs: [tab("c1", "old"), tab("c2")], activeConversationId: "c1" };
+		const next = setModel(state, "c1", "new-model");
+		expect(next.tabs[0]?.model).toBe("new-model");
+		expect(next.tabs[1]?.model).toBe("default");
+	});
+});
+
+describe("setTitle", () => {
+	it("updates the right tab", () => {
+		const state: TabsState = { tabs: [tab("c1"), tab("c2")], activeConversationId: "c1" };
+		const next = setTitle(state, "c1", "Updated title");
+		expect(next.tabs[0]?.title).toBe("Updated title");
+		expect(next.tabs[1]?.title).toBe("Chat");
+	});
+});
+
+describe("activeTab", () => {
+	it("returns the active tab", () => {
+		const state: TabsState = { tabs: [tab("c1"), tab("c2")], activeConversationId: "c2" };
+		expect(activeTab(state)?.conversationId).toBe("c2");
+	});
+
+	it("returns null when activeConversationId is null", () => {
+		const state: TabsState = { tabs: [tab("c1")], activeConversationId: null };
+		expect(activeTab(state)).toBeNull();
+	});
+
+	it("returns null when active tab is not found in tabs", () => {
+		const state: TabsState = { tabs: [tab("c1")], activeConversationId: "missing" };
+		expect(activeTab(state)).toBeNull();
+	});
+});
+
+describe("deriveTitle", () => {
+	it("truncates long messages with ellipsis", () => {
+		const msg = "This is a very long message that should be truncated at some point";
+		expect(deriveTitle(msg, 20)).toBe("This is a very long \u2026");
+	});
+
+	it("returns full message when under max", () => {
+		expect(deriveTitle("Short", 40)).toBe("Short");
+	});
+
+	it("collapses whitespace", () => {
+		expect(deriveTitle("  hello   world  ")).toBe("hello world");
+	});
+
+	it("falls back to 'New chat' for empty input", () => {
+		expect(deriveTitle("")).toBe("New chat");
+		expect(deriveTitle("   ")).toBe("New chat");
+	});
+
+	it("uses default max of ~40 chars", () => {
+		const msg = "a".repeat(50);
+		const result = deriveTitle(msg);
+		expect(result).toBe(`${"a".repeat(40)}\u2026`);
+	});
+});