feat: add localStorage persistence to focus store

Wraps the focus store with zustand/middleware persist to maintain
queue state across page refreshes and app restarts.

Persists:
- current: The currently focused item
- queue: Remaining items in the work queue

Not persisted (transient state):
- isLoading: Reset on mount
- error: Reset on mount

Storage key: "mc-focus-store"

This prevents losing your place in the queue when the app restarts
or the page refreshes during development.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/stores/focus-store.ts

@@ -6,6 +6,7 @@
  */
 
 import { create } from "zustand";
+import { persist } from "zustand/middleware";
 import type { FocusAction, FocusItem } from "@/lib/types";
 
 export interface FocusState {
@@ -34,72 +35,83 @@ export interface FocusState {
   setError: (error: string | null) => void;
 }
 
-export const useFocusStore = create<FocusState>((set, get) => ({
-  current: null,
-  queue: [],
-  isLoading: false,
-  error: null,
-
-  setItems: (items) => {
-    const [first, ...rest] = items;
-    set({
-      current: first ?? null,
-      queue: rest,
+export const useFocusStore = create<FocusState>()(
+  persist(
+    (set, get) => ({
+      current: null,
+      queue: [],
       isLoading: false,
       error: null,
-    });
-  },
 
-  act: (action, _reason) => {
-    const { current, queue } = get();
-    const [next, ...rest] = queue;
+      setItems: (items) => {
+        const [first, ...rest] = items;
+        set({
+          current: first ?? null,
+          queue: rest,
+          isLoading: false,
+          error: null,
+        });
+      },
 
-    // Log the decision (will be wired to backend decision log in Phase 7)
-    console.debug("[focus] act:", action, "on:", current?.id);
+      act: (action, _reason) => {
+        const { current, queue } = get();
+        const [next, ...rest] = queue;
 
-    const nextItem = next ?? null;
-    set({
-      current: nextItem,
-      queue: rest,
-    });
+        // Log the decision (will be wired to backend decision log in Phase 7)
+        console.debug("[focus] act:", action, "on:", current?.id);
 
-    return nextItem;
-  },
+        const nextItem = next ?? null;
+        set({
+          current: nextItem,
+          queue: rest,
+        });
 
-  setFocus: (itemId) => {
-    const { current, queue } = get();
-    const allItems = current ? [current, ...queue] : [...queue];
-    const target = allItems.find((item) => item.id === itemId);
+        return nextItem;
+      },
 
-    if (!target) return;
+      setFocus: (itemId) => {
+        const { current, queue } = get();
+        const allItems = current ? [current, ...queue] : [...queue];
+        const target = allItems.find((item) => item.id === itemId);
 
-    const remaining = allItems.filter((item) => item.id !== itemId);
-    set({
-      current: target,
-      queue: remaining,
-    });
-  },
+        if (!target) return;
 
-  reorderQueue: (fromIndex, toIndex) => {
-    const { queue } = get();
-    if (
-      fromIndex < 0 ||
-      fromIndex >= queue.length ||
-      toIndex < 0 ||
-      toIndex >= queue.length ||
-      fromIndex === toIndex
-    ) {
-      return;
+        const remaining = allItems.filter((item) => item.id !== itemId);
+        set({
+          current: target,
+          queue: remaining,
+        });
+      },
+
+      reorderQueue: (fromIndex, toIndex) => {
+        const { queue } = get();
+        if (
+          fromIndex < 0 ||
+          fromIndex >= queue.length ||
+          toIndex < 0 ||
+          toIndex >= queue.length ||
+          fromIndex === toIndex
+        ) {
+          return;
+        }
+
+        const updated = [...queue];
+        const [moved] = updated.splice(fromIndex, 1);
+        updated.splice(toIndex, 0, moved);
+
+        console.debug("[focus] reorder:", moved.id, "from", fromIndex, "to", toIndex);
+        set({ queue: updated });
+      },
+
+      setLoading: (loading) => set({ isLoading: loading }),
+      setError: (error) => set({ error }),
+    }),
+    {
+      name: "mc-focus-store",
+      partialize: (state) => ({
+        current: state.current,
+        queue: state.queue,
+      }),
     }
-
-    const updated = [...queue];
-    const [moved] = updated.splice(fromIndex, 1);
-    updated.splice(toIndex, 0, moved);
-
-    console.debug("[focus] reorder:", moved.id, "from", fromIndex, "to", toIndex);
-    set({ queue: updated });
-  },
-
-  setLoading: (loading) => set({ isLoading: loading }),
-  setError: (error) => set({ error }),
-}));
+  )
+);