Enhance map functionality and API documentation

- Updated API documentation for the `rebuildZooms` endpoint to clarify its long execution time and response behavior.
- Modified MapView component to manage tile cache invalidation after rebuilding zoom levels, ensuring fresh tile display.
- Introduced a new composable for handling tile cache invalidation state after admin actions.
- Enhanced character icon creation to reflect ownership status with distinct colors.
- Improved loading state handling in various components for better user experience during data fetching.

docs/api.md

@@ -40,7 +40,7 @@ The API is available under the `/map/api/` prefix. Requests requiring authentica
 - **POST /map/api/admin/maps/:id** — update a map (name, hidden, priority).
 - **POST /map/api/admin/maps/:id/toggle-hidden** — toggle map visibility.
 - **POST /map/api/admin/wipe** — wipe grids, markers, tiles, and maps from the database.
-- **POST /map/api/admin/rebuildZooms** — rebuild tile zoom levels.
+- **POST /map/api/admin/rebuildZooms** — rebuild tile zoom levels from base tiles. The operation can take a long time (minutes) when there are many grids; the client should allow for request timeouts or show appropriate loading state. On success returns 200; on failure (e.g. store error) returns 500.
 - **GET /map/api/admin/export** — download data export (ZIP).
 - **POST /map/api/admin/merge** — upload and apply a merge (ZIP with grids and markers).
 - **GET /map/api/admin/wipeTile** — delete a tile. Query: `map`, `x`, `y`.

frontend-nuxt/components/MapView.vue

@@ -195,6 +195,8 @@ let intervalId: ReturnType<typeof setInterval> | null = null
 let autoMode = false
 let mapContainer: HTMLElement | null = null
 let contextMenuHandler: ((ev: MouseEvent) => void) | null = null
+let mounted = false
+let visibilityChangeHandler: (() => void) | null = null
 
 function toLatLng(x: number, y: number) {
   return leafletMap!.unproject([x, y], HnHMaxZoom)
@@ -264,6 +266,7 @@ function onKeydown(e: KeyboardEvent) {
 }
 
 onMounted(async () => {
+  mounted = true
   if (import.meta.client) {
     window.addEventListener('keydown', onKeydown)
   }
@@ -353,9 +356,11 @@ onMounted(async () => {
     getCurrentMapId: () => mapLogic.state.mapid.value,
     connectionStateRef: sseConnectionState,
     onMerge: (mapTo: number, shift: { x: number; y: number }) => {
+      if (!mounted) return
       const latLng = toLatLng(shift.x * 100, shift.y * 100)
       layersManager!.changeMap(mapTo)
       api.getMarkers().then((body) => {
+        if (!mounted) return
         layersManager!.updateMarkers(Array.isArray(body) ? body : [])
         questGivers.value = layersManager!.getQuestGivers()
       })
@@ -363,6 +368,17 @@ onMounted(async () => {
     },
   })
 
+  const { shouldInvalidateTileCache, clearRebuildDoneFlag } = useRebuildZoomsInvalidation()
+  if (shouldInvalidateTileCache()) {
+    mapInit.layer.cache = {}
+    mapInit.overlayLayer.cache = {}
+    clearRebuildDoneFlag()
+    nextTick(() => {
+      mapInit.layer.redraw()
+      mapInit.overlayLayer.redraw()
+    })
+  }
+
   const charsList = Array.isArray(charactersData) ? charactersData : []
   layersManager.updateCharacters(charsList)
   players.value = layersManager.getPlayers()
@@ -395,6 +411,7 @@ onMounted(async () => {
 
   // Markers load asynchronously after map is visible.
   api.getMarkers().then((body) => {
+    if (!mounted) return
     layersManager!.updateMarkers(Array.isArray(body) ? body : [])
     questGivers.value = layersManager!.getQuestGivers()
   })
@@ -406,6 +423,7 @@ onMounted(async () => {
     api
       .getCharacters()
       .then((body) => {
+        if (!mounted) return
         const list = Array.isArray(body) ? body : []
         layersManager!.updateCharacters(list)
         players.value = layersManager!.getPlayers()
@@ -429,17 +447,31 @@ onMounted(async () => {
 
   startCharacterPoll()
   if (import.meta.client) {
-    document.addEventListener('visibilitychange', () => {
+    visibilityChangeHandler = () => {
       startCharacterPoll()
-    })
+    }
+    document.addEventListener('visibilitychange', visibilityChangeHandler)
   }
 
   watch(mapLogic.state.showGridCoordinates, (v) => {
-    if (mapInit?.coordLayer) {
+    if (!mapInit?.coordLayer || !leafletMap) return
-      ;(mapInit.coordLayer.options as { visible?: boolean }).visible = v
+    const coordLayer = mapInit.coordLayer
-      mapInit.coordLayer.setOpacity(v ? 1 : 0)
+    const layerWithMap = coordLayer as L.GridLayer & { _map?: L.Map }
-      mapInit.coordLayer.redraw?.()
+    if (v) {
-      if (v) mapInit.coordLayer.bringToFront?.()
+      ;(coordLayer.options as { visible?: boolean }).visible = true
+      if (!layerWithMap._map) {
+        coordLayer.addTo(leafletMap)
+        coordLayer.setZIndex(500)
+        coordLayer.setOpacity(1)
+        coordLayer.bringToFront?.()
+      }
+      leafletMap.invalidateSize()
+      nextTick(() => {
+        coordLayer.redraw?.()
+      })
+    } else {
+      coordLayer.setOpacity(0)
+      coordLayer.remove()
     }
   })
 
@@ -553,8 +585,12 @@ onMounted(async () => {
 })
 
 onBeforeUnmount(() => {
+  mounted = false
   if (import.meta.client) {
     window.removeEventListener('keydown', onKeydown)
+    if (visibilityChangeHandler) {
+      document.removeEventListener('visibilitychange', visibilityChangeHandler)
+    }
   }
   mapNavigate.setGoTo(null)
   if (contextMenuHandler) {

frontend-nuxt/components/map/MapControlsContent.vue

@@ -56,7 +56,12 @@
         Display
       </h3>
       <label class="label cursor-pointer justify-start gap-2 py-0 hover:bg-base-200/50 rounded-lg px-2 -mx-2 touch-manipulation" :class="touchFriendly ? 'min-h-11' : ''">
-        <input v-model="showGridCoordinates" type="checkbox" class="checkbox checkbox-sm" />
+        <input
+          v-model="showGridCoordinates"
+          type="checkbox"
+          class="checkbox checkbox-sm"
+          data-testid="show-grid-coordinates"
+        />
         <span>Show grid coordinates</span>
       </label>
       <label class="label cursor-pointer justify-start gap-2 py-0 hover:bg-base-200/50 rounded-lg px-2 -mx-2 touch-manipulation" :class="touchFriendly ? 'min-h-11' : ''">

frontend-nuxt/composables/useMapApi.ts

@@ -117,7 +117,7 @@ export function useMapApi() {
   // Profile
   async function meTokens() {
     const data = await request<{ tokens: string[] }>('me/tokens', { method: 'POST' })
-    return data!.tokens
+    return data?.tokens ?? []
   }
 
   async function mePassword(pass: string) {

frontend-nuxt/composables/useMapInit.ts

@@ -95,6 +95,8 @@ export async function initLeafletMap(
     'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII='
   overlayLayer.addTo(map)
 
+  // Not added to map here — added in MapView when user enables "Show grid coordinates"
+  // so createTile() always runs with visible: true and labels render (no empty tiles from init).
   const coordLayer = new GridCoordLayer({
     tileSize: TileSize,
     minZoom: HnHMinZoom,
@@ -103,10 +105,8 @@ export async function initLeafletMap(
     visible: false,
     pane: 'tilePane',
     updateWhenIdle: true,
-    keepBuffer: 2,
+    keepBuffer: 4,
   } as GridCoordLayerOptions)
-  coordLayer.addTo(map)
-  coordLayer.setZIndex(500)
 
   const markerLayer = L.layerGroup()
   markerLayer.addTo(map)

frontend-nuxt/composables/useRebuildZoomsInvalidation.ts

@@ -0,0 +1,30 @@
+/**
+ * Shared state for tile cache invalidation after admin "Rebuild zooms".
+ * Admin sets the timestamp on success; MapView on mount clears tile caches
+ * when a rebuild was done recently, so the map shows fresh tiles even if
+ * SSE was missed (e.g. admin in another tab).
+ */
+const REBUILD_DONE_TTL_MS = 5 * 60 * 1000 // 5 minutes
+
+export function useRebuildZoomsInvalidation() {
+  const rebuildZoomsDoneAt = useState('rebuildZoomsDoneAt', () => 0)
+
+  function markRebuildDone() {
+    rebuildZoomsDoneAt.value = Date.now()
+  }
+
+  function shouldInvalidateTileCache(): boolean {
+    if (rebuildZoomsDoneAt.value <= 0) return false
+    return Date.now() - rebuildZoomsDoneAt.value < REBUILD_DONE_TTL_MS
+  }
+
+  function clearRebuildDoneFlag() {
+    rebuildZoomsDoneAt.value = 0
+  }
+
+  return {
+    markRebuildDone,
+    shouldInvalidateTileCache,
+    clearRebuildDoneFlag,
+  }
+}

frontend-nuxt/layouts/default.vue

@@ -85,7 +85,7 @@
                     <label class="flex cursor-pointer items-center gap-3 py-2 px-2 rounded-lg hover:bg-base-300/50 w-full min-h-0">
                       <icons-icon-sun v-if="!dark" class="size-4 shrink-0 opacity-80" />
                       <icons-icon-moon v-else class="size-4 shrink-0 opacity-80" />
-                      <span class="flex-1 text-sm">Тёмная тема</span>
+                      <span class="flex-1 text-sm">Dark theme</span>
                       <input
                         type="checkbox"
                         class="toggle toggle-sm toggle-primary shrink-0"
@@ -183,7 +183,7 @@
               <label class="flex cursor-pointer items-center gap-3 py-3 px-2 rounded-lg hover:bg-base-300/50 w-full min-h-0 touch-manipulation">
                 <icons-icon-sun v-if="!dark" class="size-4 shrink-0 opacity-80" />
                 <icons-icon-moon v-else class="size-4 shrink-0 opacity-80" />
-                <span class="flex-1 text-sm">Тёмная тема</span>
+                <span class="flex-1 text-sm">Dark theme</span>
                 <input
                   type="checkbox"
                   class="toggle toggle-sm toggle-primary shrink-0"
@@ -244,6 +244,8 @@ const { isLoginPath } = useAppPaths()
 const isLogin = computed(() => isLoginPath(route.path))
 const isAdmin = computed(() => !!me.value?.auths?.includes('admin'))
 
+let loadId = 0
+
 async function loadMe() {
   if (isLogin.value) return
   try {
@@ -253,10 +255,12 @@ async function loadMe() {
   }
 }
 
-async function loadConfig() {
+async function loadConfig(loadToken: number) {
   if (isLogin.value) return
+  if (loadToken !== loadId) return
   try {
     const config = await useMapApi().getConfig()
+    if (loadToken !== loadId) return
     if (config?.title) title.value = config.title
   } catch (_) {}
 }
@@ -269,7 +273,10 @@ onMounted(() => {
 watch(
   () => route.path,
   (path) => {
-    if (!isLoginPath(path)) loadMe().then(loadConfig)
+    if (!isLoginPath(path)) {
+      const currentLoadId = ++loadId
+      loadMe().then(() => loadConfig(currentLoadId))
+    }
   },
   { immediate: true }
 )

frontend-nuxt/lib/Character.ts

@@ -1,21 +1,21 @@
 import type L from 'leaflet'
+import { getColorForCharacterId, type CharacterColors } from '~/lib/characterColors'
 import { HnHMaxZoom } from '~/lib/LeafletCustomTypes'
 
 export type LeafletApi = typeof import('leaflet')
 
-/** SVG data URL for character marker icon (teal pin, bottom-center anchor). */
+function buildCharacterIconUrl(colors: CharacterColors): string {
-const CHARACTER_ICON_URL =
+  const svg =
-  'data:image/svg+xml,' +
-  encodeURIComponent(
     '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 32" width="24" height="32">' +
-      '<path fill="#0d9488" stroke="#0f766e" stroke-width="1" d="M12 2a6 6 0 0 1 6 6c0 4-6 10-6 10s-6-6-6-10a6 6 0 0 1 6-6z"/>' +
+    `<path fill="${colors.fill}" stroke="${colors.stroke}" stroke-width="1" d="M12 2a6 6 0 0 1 6 6c0 4-6 10-6 10s-6-6-6-10a6 6 0 0 1 6-6z"/>` +
     '<circle cx="12" cy="8" r="2.5" fill="white"/>' +
     '</svg>'
-  )
+  return 'data:image/svg+xml,' + encodeURIComponent(svg)
+}
 
-function createCharacterIcon(L: LeafletApi): L.Icon {
+export function createCharacterIcon(L: LeafletApi, colors: CharacterColors): L.Icon {
   return new L.Icon({
-    iconUrl: CHARACTER_ICON_URL,
+    iconUrl: buildCharacterIconUrl(colors),
     iconSize: [24, 32],
     iconAnchor: [12, 32],
     popupAnchor: [0, -32],
@@ -28,6 +28,8 @@ export interface CharacterData {
   type: string
   id: number
   map: number
+  /** True when this character was last updated by one of the current user's tokens. */
+  ownedByMe?: boolean
 }
 
 export interface CharacterMapViewRef {
@@ -44,6 +46,7 @@ export interface MapCharacter {
   map: number
   text: string
   value: number
+  ownedByMe?: boolean
   leafletMarker: L.Marker | null
   remove: (mapview: CharacterMapViewRef) => void
   add: (mapview: CharacterMapViewRef) => void
@@ -54,7 +57,9 @@ export interface MapCharacter {
 export function createCharacter(data: CharacterData, L: LeafletApi): MapCharacter {
   let leafletMarker: L.Marker | null = null
   let onClick: ((e: L.LeafletMouseEvent) => void) | null = null
-  const characterIcon = createCharacterIcon(L)
+  let ownedByMe = data.ownedByMe ?? false
+  const colors = getColorForCharacterId(data.id, { ownedByMe })
+  let characterIcon = createCharacterIcon(L, colors)
 
   const character: MapCharacter = {
     id: data.id,
@@ -64,6 +69,12 @@ export function createCharacter(data: CharacterData, L: LeafletApi): MapCharacte
     map: data.map,
     text: data.name,
     value: data.id,
+    get ownedByMe() {
+      return ownedByMe
+    },
+    set ownedByMe(v: boolean | undefined) {
+      ownedByMe = v ?? false
+    },
 
     get leafletMarker() {
       return leafletMarker
@@ -90,6 +101,12 @@ export function createCharacter(data: CharacterData, L: LeafletApi): MapCharacte
     },
 
     update(mapview: CharacterMapViewRef, updated: CharacterData | MapCharacter): void {
+      const updatedOwnedByMe = (updated as { ownedByMe?: boolean }).ownedByMe ?? false
+      if (ownedByMe !== updatedOwnedByMe) {
+        ownedByMe = updatedOwnedByMe
+        characterIcon = createCharacterIcon(L, getColorForCharacterId(character.id, { ownedByMe }))
+        if (leafletMarker) leafletMarker.setIcon(characterIcon)
+      }
       if (character.map !== updated.map) {
         character.remove(mapview)
       }

frontend-nuxt/lib/LeafletCustomTypes.ts

@@ -11,10 +11,10 @@ export interface GridCoordLayerOptions extends L.GridLayerOptions {
 
 /**
  * Grid layer that draws one coordinate label per Leaflet tile in the top-left corner.
- * coords.(x,y,z) are Leaflet tile indices and zoom; they map to game tiles as:
+ * Uses only coords.z (do not use map.getZoom()) so labels stay in sync with tiles.
- *   scaleFactor = 2^(HnHMaxZoom - coords.z),
+ * SmartTileLayer has zoomReverse: true, so URL z = 6 - coords.z; backend maps z=6 → storageZ=0.
- *   topLeft = (coords.x * scaleFactor, coords.y * scaleFactor).
+ * Game tile for this Leaflet tile: scaleFactor = 2^(HnHMaxZoom - coords.z),
- * This matches backend tile URL {mapid}/{z}/{x}_{y}.png (storageZ: z=6→0, Coord = tile index).
+ * topLeft = (coords.x * scaleFactor, coords.y * scaleFactor) — same (x,y) as backend tile.
  */
 export const GridCoordLayer = L.GridLayer.extend({
   options: {

frontend-nuxt/lib/__tests__/Character.test.ts

@@ -5,10 +5,15 @@ vi.mock('leaflet', () => {
     on: vi.fn().mockReturnThis(),
     addTo: vi.fn().mockReturnThis(),
     setLatLng: vi.fn().mockReturnThis(),
+    setIcon: vi.fn().mockReturnThis(),
   }
   return {
-    default: { marker: vi.fn(() => markerMock) },
+    default: {
       marker: vi.fn(() => markerMock),
+      Icon: vi.fn().mockImplementation(() => ({})),
+    },
+    marker: vi.fn(() => markerMock),
+    Icon: vi.fn().mockImplementation(() => ({})),
   }
 })
 
@@ -16,8 +21,13 @@ vi.mock('~/lib/LeafletCustomTypes', () => ({
   HnHMaxZoom: 6,
 }))
 
+import type L from 'leaflet'
 import { createCharacter, type CharacterData, type CharacterMapViewRef } from '../Character'
 
+function getL(): L {
+  return require('leaflet').default
+}
+
 function makeCharData(overrides: Partial<CharacterData> = {}): CharacterData {
   return {
     name: 'Hero',
@@ -49,7 +59,7 @@ describe('createCharacter', () => {
   })
 
   it('creates character with correct properties', () => {
-    const char = createCharacter(makeCharData())
+    const char = createCharacter(makeCharData(), getL())
     expect(char.id).toBe(1)
     expect(char.name).toBe('Hero')
     expect(char.position).toEqual({ x: 100, y: 200 })
@@ -60,26 +70,26 @@ describe('createCharacter', () => {
   })
 
   it('starts with null leaflet marker', () => {
-    const char = createCharacter(makeCharData())
+    const char = createCharacter(makeCharData(), getL())
     expect(char.leafletMarker).toBeNull()
   })
 
   it('add creates marker when character is on correct map', () => {
-    const char = createCharacter(makeCharData())
+    const char = createCharacter(makeCharData(), getL())
     const mapview = makeMapViewRef(1)
     char.add(mapview)
     expect(mapview.map.unproject).toHaveBeenCalled()
   })
 
   it('add does not create marker for different map', () => {
-    const char = createCharacter(makeCharData({ map: 2 }))
+    const char = createCharacter(makeCharData({ map: 2 }), getL())
     const mapview = makeMapViewRef(1)
     char.add(mapview)
     expect(mapview.map.unproject).not.toHaveBeenCalled()
   })
 
   it('update changes position and map', () => {
-    const char = createCharacter(makeCharData())
+    const char = createCharacter(makeCharData(), getL())
     const mapview = makeMapViewRef(1)
 
     char.update(mapview, {
@@ -93,15 +103,25 @@ describe('createCharacter', () => {
   })
 
   it('remove on a character without leaflet marker does nothing', () => {
-    const char = createCharacter(makeCharData())
+    const char = createCharacter(makeCharData(), getL())
     const mapview = makeMapViewRef(1)
     char.remove(mapview) // should not throw
     expect(char.leafletMarker).toBeNull()
   })
 
   it('setClickCallback works', () => {
-    const char = createCharacter(makeCharData())
+    const char = createCharacter(makeCharData(), getL())
     const cb = vi.fn()
     char.setClickCallback(cb)
   })
+
+  it('update with changed ownedByMe updates marker icon', () => {
+    const char = createCharacter(makeCharData({ ownedByMe: false }), getL())
+    const mapview = makeMapViewRef(1)
+    char.add(mapview)
+    const marker = char.leafletMarker as { setIcon: ReturnType<typeof vi.fn> }
+    expect(marker.setIcon).not.toHaveBeenCalled()
+    char.update(mapview, makeCharData({ ownedByMe: true }))
+    expect(marker.setIcon).toHaveBeenCalledTimes(1)
+  })
 })

frontend-nuxt/lib/characterColors.ts

@@ -0,0 +1,48 @@
+/**
+ * Palette of distinguishable colors for character markers (readable on typical map tiles).
+ * Same character id always maps to the same color via id % palette.length.
+ */
+const CHARACTER_PALETTE_FILL: string[] = [
+  '#0d9488', // teal
+  '#dc2626', // red
+  '#2563eb', // blue
+  '#16a34a', // green
+  '#ea580c', // orange
+  '#7c3aed', // violet
+  '#db2777', // pink
+  '#ca8a04', // yellow/amber
+  '#0891b2', // cyan
+  '#65a30d', // lime
+  '#4f46e5', // indigo
+  '#b45309', // brown/amber-dark
+]
+
+/** Darken a hex color by a factor (0–1). Used for stroke. */
+function darkenHex(hex: string, factor: number): string {
+  const n = hex.slice(1)
+  const r = Math.max(0, parseInt(n.slice(0, 2), 16) * (1 - factor))
+  const g = Math.max(0, parseInt(n.slice(2, 4), 16) * (1 - factor))
+  const b = Math.max(0, parseInt(n.slice(4, 6), 16) * (1 - factor))
+  return '#' + [r, g, b].map((x) => Math.round(x).toString(16).padStart(2, '0')).join('')
+}
+
+export interface CharacterColors {
+  fill: string
+  stroke: string
+}
+
+/**
+ * Returns stable fill and stroke colors for a character by id.
+ * Optionally use a distinct style for "owned by me" (e.g. brighter stroke).
+ */
+export function getColorForCharacterId(
+  id: number,
+  options?: { ownedByMe?: boolean }
+): CharacterColors {
+  const fill = CHARACTER_PALETTE_FILL[Math.abs(id) % CHARACTER_PALETTE_FILL.length]
+  const stroke = darkenHex(fill, 0.25)
+  if (options?.ownedByMe) {
+    return { fill, stroke: '#1e293b' }
+  }
+  return { fill, stroke }
+}

frontend-nuxt/pages/admin/index.vue

@@ -389,11 +389,14 @@ function confirmRebuildZooms() {
   rebuildModalRef.value?.showModal()
 }
 
+const { markRebuildDone } = useRebuildZoomsInvalidation()
+
 async function doRebuildZooms() {
   rebuildModalRef.value?.close()
   rebuilding.value = true
   try {
     await api.adminRebuildZooms()
+    markRebuildDone()
     toast.success('Zooms rebuilt.')
   } catch (e) {
     toast.error((e as Error)?.message ?? 'Failed to rebuild zooms.')

internal/app/handlers/admin.go

@@ -334,7 +334,10 @@ func (h *Handlers) APIAdminRebuildZooms(rw http.ResponseWriter, req *http.Reques
 	if h.requireAdmin(rw, req) == nil {
 		return
 	}
-	h.Admin.RebuildZooms(req.Context())
+	if err := h.Admin.RebuildZooms(req.Context()); err != nil {
+		HandleServiceError(rw, err)
+		return
+	}
 	rw.WriteHeader(http.StatusOK)
 }
 

internal/app/services/admin.go

@@ -349,6 +349,6 @@ func (s *AdminService) HideMarker(ctx context.Context, markerID string) error {
 }
 
 // RebuildZooms delegates to MapService.
-func (s *AdminService) RebuildZooms(ctx context.Context) {
+func (s *AdminService) RebuildZooms(ctx context.Context) error {
-	s.mapSvc.RebuildZooms(ctx)
+	return s.mapSvc.RebuildZooms(ctx)
 }

internal/app/services/export.go

@@ -207,8 +207,7 @@ func (s *ExportService) Merge(ctx context.Context, zr *zip.Reader) error {
 	for _, op := range ops {
 		s.mapSvc.SaveTile(ctx, op.MapID, app.Coord{X: op.X, Y: op.Y}, 0, op.File, time.Now().UnixNano())
 	}
-	s.mapSvc.RebuildZooms(ctx)
+	return s.mapSvc.RebuildZooms(ctx)
-	return nil
 }
 
 func (s *ExportService) processMergeJSON(

internal/app/services/map.go

@@ -226,21 +226,33 @@ func (s *MapService) UpdateZoomLevel(ctx context.Context, mapid int, c app.Coord
 		slog.Error("failed to create zoom dir", "error", err)
 		return
 	}
-	f, err := os.Create(fmt.Sprintf("%s/%d/%d/%s.png", s.gridStorage, mapid, z, c.Name()))
+	path := fmt.Sprintf("%s/%d/%d/%s.png", s.gridStorage, mapid, z, c.Name())
-	s.SaveTile(ctx, mapid, c, z, fmt.Sprintf("%d/%d/%s.png", mapid, z, c.Name()), time.Now().UnixNano())
+	relPath := fmt.Sprintf("%d/%d/%s.png", mapid, z, c.Name())
+	f, err := os.Create(path)
 	if err != nil {
+		slog.Error("failed to create tile file", "path", path, "error", err)
 		return
 	}
-	defer f.Close()
+	if err := png.Encode(f, img); err != nil {
-	png.Encode(f, img)
+		f.Close()
+		os.Remove(path)
+		slog.Error("failed to encode tile PNG", "path", path, "error", err)
+		return
+	}
+	if err := f.Close(); err != nil {
+		slog.Error("failed to close tile file", "path", path, "error", err)
+		return
+	}
+	s.SaveTile(ctx, mapid, c, z, relPath, time.Now().UnixNano())
 }
 
 // RebuildZooms rebuilds all zoom levels from base tiles.
-func (s *MapService) RebuildZooms(ctx context.Context) {
+// It can take a long time for many grids; the client should account for request timeouts.
+func (s *MapService) RebuildZooms(ctx context.Context) error {
 	needProcess := map[zoomproc]struct{}{}
 	saveGrid := map[zoomproc]string{}
 
-	s.st.Update(ctx, func(tx *bbolt.Tx) error {
+	if err := s.st.Update(ctx, func(tx *bbolt.Tx) error {
 		b := tx.Bucket(store.BucketGrids)
 		if b == nil {
 			return nil
@@ -254,7 +266,10 @@ func (s *MapService) RebuildZooms(ctx context.Context) {
 		})
 		tx.DeleteBucket(store.BucketTiles)
 		return nil
-	})
+	}); err != nil {
+		slog.Error("RebuildZooms: failed to update store", "error", err)
+		return err
+	}
 
 	for g, id := range saveGrid {
 		f := fmt.Sprintf("%s/grids/%s.png", s.gridStorage, id)
@@ -271,6 +286,7 @@ func (s *MapService) RebuildZooms(ctx context.Context) {
 			needProcess[zoomproc{p.c.Parent(), p.m}] = struct{}{}
 		}
 	}
+	return nil
 }
 
 // ReportMerge sends a merge event.