feat: workspaces shell + cwd-lsp rename + mcp/settings/system-prompt features + app wiring

- workspaces: URL-driven conversation grouping (home listing at /, routing,
  store, http adapter, WorkspaceCard) wired into the App.svelte shell
- rename features/workspace -> features/cwd-lsp (the cwd/lsp status feature)
- new features: mcp (status view), settings (chat-limit field), system-prompt
  (prompt builder), all rendered via the generic surface host
- chat: store + ChatView updates
- tabs: tabs-store updates
- app wiring: ErrorModal (full-screen error surface), app/App.svelte + store.svelte

This commit makes HEAD typecheck clean for the first time: the prior HEAD
(c95cc77) imported features/settings from app/App.svelte but never committed
the feature, so only the full working tree was green.

4 files changed, 33 insertions, 22 deletions

diff --git a/src/features/tabs/tabs-store.test.ts b/src/features/tabs/tabs-store.test.ts
index 81ec8ad..71a38dc 100644
--- a/src/features/tabs/tabs-store.test.ts
+++ b/src/features/tabs/tabs-store.test.ts
@@ -24,7 +24,7 @@ function createMemoryStorage(initial?: TabsState): TabsStorage & { data: TabsSta
 describe("createTabsStore", () => {
 	it("loads persisted state on construct", () => {
 		const persisted: TabsState = {
-			tabs: [{ conversationId: "c1", model: "m1", title: "T1" }],
+			tabs: [{ conversationId: "c1", model: "m1", title: "T1", workspaceId: "default" }],
 			activeConversationId: "c1",
 		};
 		const storage = createMemoryStorage(persisted);
@@ -48,11 +48,11 @@ describe("createTabsStore", () => {
 		const storage = createMemoryStorage();
 		const store = createTabsStore(storage);
 
-		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1", workspaceId: "default" });
 		expect(storage.data?.tabs).toHaveLength(1);
 		expect(storage.data?.activeConversationId).toBe("c1");
 
-		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2", workspaceId: "default" });
 		expect(storage.data?.tabs).toHaveLength(2);
 
 		store.selectTab("c1");
@@ -76,11 +76,11 @@ describe("createTabsStore", () => {
 		const storage = createMemoryStorage();
 		const store = createTabsStore(storage);
 
-		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1", workspaceId: "default" });
 		expect(store.tabs).toHaveLength(1);
 		expect(store.activeConversationId).toBe("c1");
 
-		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2", workspaceId: "default" });
 		expect(store.tabs).toHaveLength(2);
 		expect(store.activeConversationId).toBe("c2");
 	});
@@ -89,8 +89,8 @@ describe("createTabsStore", () => {
 		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: "c1", model: "m1", title: "T1", workspaceId: "default" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2", workspaceId: "default" });
 
 		store.selectTab("c1");
 		expect(store.activeConversationId).toBe("c1");
@@ -100,9 +100,9 @@ describe("createTabsStore", () => {
 		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.createTab({ conversationId: "c1", model: "m1", title: "T1", workspaceId: "default" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2", workspaceId: "default" });
+		store.createTab({ conversationId: "c3", model: "m3", title: "T3", workspaceId: "default" });
 
 		store.selectTab("c2");
 		store.closeTab("c2");
@@ -114,7 +114,7 @@ describe("createTabsStore", () => {
 		const storage = createMemoryStorage();
 		const store = createTabsStore(storage);
 
-		store.createTab({ conversationId: "c1", model: "m1", title: "T1" });
+		store.createTab({ conversationId: "c1", model: "m1", title: "T1", workspaceId: "default" });
 		store.closeTab("c1");
 		expect(store.tabs).toHaveLength(0);
 		expect(store.activeConversationId).toBeNull();
@@ -124,8 +124,8 @@ describe("createTabsStore", () => {
 		const storage = createMemoryStorage();
 		const store = createTabsStore(storage);
 
-		store.createTab({ conversationId: "c1", model: "old", title: "T1" });
-		store.createTab({ conversationId: "c2", model: "m2", title: "T2" });
+		store.createTab({ conversationId: "c1", model: "old", title: "T1", workspaceId: "default" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2", workspaceId: "default" });
 
 		store.setModel("c1", "new-model");
 		expect(store.tabs[0]?.model).toBe("new-model");
@@ -136,7 +136,7 @@ describe("createTabsStore", () => {
 		const storage = createMemoryStorage();
 		const store = createTabsStore(storage);
 
-		store.createTab({ conversationId: "c1", model: "m1", title: "Old" });
+		store.createTab({ conversationId: "c1", model: "m1", title: "Old", workspaceId: "default" });
 
 		store.setTitle("c1", "New Title");
 		expect(store.tabs[0]?.title).toBe("New Title");
@@ -146,8 +146,8 @@ describe("createTabsStore", () => {
 		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: "c1", model: "m1", title: "T1", workspaceId: "default" });
+		store.createTab({ conversationId: "c2", model: "m2", title: "T2", workspaceId: "default" });
 
 		store.newDraft();
 		expect(store.tabs).toHaveLength(2);
diff --git a/src/features/tabs/tabs.test.ts b/src/features/tabs/tabs.test.ts
index 3c2a8c2..e3ca4fa 100644
--- a/src/features/tabs/tabs.test.ts
+++ b/src/features/tabs/tabs.test.ts
@@ -19,6 +19,7 @@ const tab = (conversationId: string, model = "default", title = "Chat"): Tab =>
 	conversationId,
 	model,
 	title,
+	workspaceId: "default",
 });
 
 describe("initialState", () => {
diff --git a/src/features/tabs/tabs.ts b/src/features/tabs/tabs.ts
index 3360d3f..53eda78 100644
--- a/src/features/tabs/tabs.ts
+++ b/src/features/tabs/tabs.ts
@@ -2,6 +2,8 @@ export interface Tab {
 	readonly conversationId: string;
 	readonly model: string;
 	readonly title: string;
+	/** The workspace this tab belongs to (the workspace's URL slug). */
+	readonly workspaceId: string;
 }
 
 export interface TabsState {
@@ -13,7 +15,15 @@ const DEFAULT_TITLE = "New chat";
 const DEFAULT_MAX_TITLE_LENGTH = 40;
 
 export function initialState(persisted?: TabsState): TabsState {
-	if (persisted !== undefined) return persisted;
+	if (persisted !== undefined) {
+		// Migrate tabs persisted before workspaces: assign them to the "default"
+		// workspace (the fallback for conversations with no workspace).
+		const tabs = persisted.tabs.map((t) => {
+			const wid = (t as { workspaceId?: string }).workspaceId;
+			return { ...t, workspaceId: wid ?? "default" };
+		});
+		return { tabs, activeConversationId: persisted.activeConversationId };
+	}
 	return { tabs: [], activeConversationId: null };
 }
 
diff --git a/src/features/tabs/ui.test.ts b/src/features/tabs/ui.test.ts
index 6cd66bd..a46b692 100644
--- a/src/features/tabs/ui.test.ts
+++ b/src/features/tabs/ui.test.ts
@@ -5,9 +5,9 @@ import type { Tab } from "./tabs";
 import TabBar from "./ui/TabBar.svelte";
 
 const sampleTabs: readonly Tab[] = [
-	{ conversationId: "c1", model: "openai/gpt-4", title: "First" },
-	{ conversationId: "c2", model: "anthropic/claude-3", title: "Second" },
-	{ conversationId: "c3", model: "google/gemini", title: "Third" },
+	{ conversationId: "c1", model: "openai/gpt-4", title: "First", workspaceId: "default" },
+	{ conversationId: "c2", model: "anthropic/claude-3", title: "Second", workspaceId: "default" },
+	{ conversationId: "c3", model: "google/gemini", title: "Third", workspaceId: "default" },
 ];
 
 describe("TabBar", () => {
@@ -178,8 +178,8 @@ describe("TabBar", () => {
 
 	it("renders a short-handle tab ID badge (shortest unique prefix) per tab", () => {
 		const tabs: readonly Tab[] = [
-			{ conversationId: "3f9a1b2c-1111", model: "m", title: "Alpha" },
-			{ conversationId: "7c2db4e5-2222", model: "m", title: "Beta" },
+			{ conversationId: "3f9a1b2c-1111", model: "m", title: "Alpha", workspaceId: "default" },
+			{ conversationId: "7c2db4e5-2222", model: "m", title: "Beta", workspaceId: "default" },
 		];
 		render(TabBar, {
 			props: {