Fix service map nodes disappearing on page reload

Root cause: Zustand store resets to activeMap=null on every page load.
fetchMaps() only loaded the summary list — nodes were never reloaded
because the user had to manually re-select their map each time.

Fixes:
1. Persist last active map ID in localStorage (key: rackmapper:lastMapId)
   - loadMap() saves the ID on successful load
   - setActiveMap() saves/clears the ID
   - deleteMap() clears the ID if the deleted map was active

2. Auto-restore on mount inside fetchMaps():
   - If the saved map ID is still in the list, auto-load it
   - If there is exactly one map, auto-load it as a convenience

3. Block spurious position saves during map load (blockSaveRef):
   - fitView fires position NodeChanges for all nodes after load
   - Without a guard these would overwrite stored positions with
     React Flow's fitted coordinates immediately on every reload
   - blockSaveRef is set true on activeMap change, cleared after 800ms

4. Tighten the position-change filter:
   - Require dragging === false (strict equality, not just falsy)
   - Require position != null before saving
   - Both conditions must be true to queue a save

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/store/useMapStore.ts

@@ -2,6 +2,17 @@ import { create } from 'zustand';
 import type { ServiceMap, ServiceMapSummary } from '../types';
 import { apiClient } from '../api/client';
 
+const LAST_MAP_KEY = 'rackmapper:lastMapId';
+
+function saveLastMapId(id: string | null) {
+  if (id) localStorage.setItem(LAST_MAP_KEY, id);
+  else localStorage.removeItem(LAST_MAP_KEY);
+}
+
+function getLastMapId(): string | null {
+  return localStorage.getItem(LAST_MAP_KEY);
+}
+
 interface MapState {
   maps: ServiceMapSummary[];
   activeMap: ServiceMap | null;
@@ -13,7 +24,7 @@ interface MapState {
   setActiveMap: (map: ServiceMap | null) => void;
 }
 
-export const useMapStore = create<MapState>((set) => ({
+export const useMapStore = create<MapState>((set, get) => ({
   maps: [],
   activeMap: null,
   loading: false,
@@ -23,6 +34,15 @@ export const useMapStore = create<MapState>((set) => ({
     try {
       const maps = await apiClient.maps.list();
       set({ maps, loading: false });
+
+      // Auto-restore the last active map after loading the list
+      const lastId = getLastMapId();
+      if (lastId && maps.some((m) => m.id === lastId)) {
+        await get().loadMap(lastId);
+      } else if (maps.length === 1) {
+        // Convenience: auto-load if there's only one map
+        await get().loadMap(maps[0].id);
+      }
     } catch {
       set({ loading: false });
       throw new Error('Failed to load maps');
@@ -33,6 +53,7 @@ export const useMapStore = create<MapState>((set) => ({
     set({ loading: true });
     try {
       const map = await apiClient.maps.get(id);
+      saveLastMapId(id);
       set({ activeMap: map, loading: false });
     } catch {
       set({ loading: false });
@@ -42,17 +63,26 @@ export const useMapStore = create<MapState>((set) => ({
 
   createMap: async (name, description) => {
     const map = await apiClient.maps.create({ name, description });
-    set((s) => ({ maps: [{ id: map.id, name: map.name, description: map.description, createdAt: map.createdAt, updatedAt: map.updatedAt }, ...s.maps] }));
+    set((s) => ({
+      maps: [
+        { id: map.id, name: map.name, description: map.description, createdAt: map.createdAt, updatedAt: map.updatedAt },
+        ...s.maps,
+      ],
+    }));
     return map;
   },
 
   deleteMap: async (id) => {
     await apiClient.maps.delete(id);
+    if (getLastMapId() === id) saveLastMapId(null);
     set((s) => ({
       maps: s.maps.filter((m) => m.id !== id),
       activeMap: s.activeMap?.id === id ? null : s.activeMap,
     }));
   },
 
-  setActiveMap: (map) => set({ activeMap: map }),
+  setActiveMap: (map) => {
+    saveLastMapId(map?.id ?? null);
+    set({ activeMap: map });
+  },
 }));