Implement HTTP timeout configurations and enhance API documentation

- Added optional HTTP server timeout configurations (`HNHMAP_READ_TIMEOUT`, `HNHMAP_WRITE_TIMEOUT`, `HNHMAP_IDLE_TIMEOUT`) to `.env.example` and updated the server initialization in `main.go` to utilize these settings.
- Enhanced API documentation for the `rebuildZooms` endpoint to clarify its background processing and polling mechanism for status updates.
- Updated `configuration.md` to include new timeout environment variables for better configuration guidance.
- Improved error handling in the client for large request bodies, ensuring appropriate responses for oversized payloads.

.env.example

@@ -1,5 +1,8 @@
 # Backend (Go)
 # HNHMAP_PORT=8080
+# HNHMAP_READ_TIMEOUT=30s   # HTTP read timeout (optional)
+# HNHMAP_WRITE_TIMEOUT=60s  # HTTP write timeout (optional)
+# HNHMAP_IDLE_TIMEOUT=120s # HTTP idle timeout (optional)
 # HNHMAP_BOOTSTRAP_PASSWORD=  # Set once for first run: login as admin with this password to create the first admin user (then unset or leave empty)
 # Grids directory (default: grids); in Docker often /map
 # HNHMAP_GRIDS=grids

cmd/hnh-map/main.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 	"strconv"
+	"time"
 
 	"github.com/andyleap/hnh-map/internal/app"
 	"github.com/andyleap/hnh-map/internal/app/handlers"
@@ -79,6 +80,32 @@ func main() {
 	publicDir := filepath.Join(workDir, "public")
 	r := a.Router(publicDir, h)
 
+	readTimeout := 30 * time.Second
+	if v := os.Getenv("HNHMAP_READ_TIMEOUT"); v != "" {
+		if d, err := time.ParseDuration(v); err == nil && d > 0 {
+			readTimeout = d
+		}
+	}
+	writeTimeout := 60 * time.Second
+	if v := os.Getenv("HNHMAP_WRITE_TIMEOUT"); v != "" {
+		if d, err := time.ParseDuration(v); err == nil && d > 0 {
+			writeTimeout = d
+		}
+	}
+	idleTimeout := 120 * time.Second
+	if v := os.Getenv("HNHMAP_IDLE_TIMEOUT"); v != "" {
+		if d, err := time.ParseDuration(v); err == nil && d > 0 {
+			idleTimeout = d
+		}
+	}
+
+	srv := &http.Server{
+		Addr:         fmt.Sprintf(":%d", *port),
+		Handler:      r,
+		ReadTimeout:  readTimeout,
+		WriteTimeout: writeTimeout,
+		IdleTimeout:  idleTimeout,
+	}
 	log.Printf("Listening on port %d", *port)
-	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", *port), r))
+	log.Fatal(srv.ListenAndServe())
 }

docs/api.md

@@ -40,7 +40,8 @@ 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 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.
+- **POST /map/api/admin/rebuildZooms** — start rebuilding tile zoom levels from base tiles in the background. Returns **202 Accepted** immediately; the operation can take minutes when there are many grids. The client may poll **GET /map/api/admin/rebuildZooms/status** until `{"running": false}` and then refresh the map.
+- **GET /map/api/admin/rebuildZooms/status** — returns `{"running": true|false}` indicating whether a rebuild started via POST rebuildZooms is still in progress.
 - **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`.

docs/configuration.md

@@ -6,6 +6,9 @@
 |-----------------|-------------|---------|
 | `HNHMAP_PORT` | HTTP server port | 8080 |
 | `-port` | Same (command-line flag) | value of `HNHMAP_PORT` or 8080 |
+| `HNHMAP_READ_TIMEOUT` | HTTP server read timeout (e.g. `30s`) | 30s |
+| `HNHMAP_WRITE_TIMEOUT` | HTTP server write timeout (e.g. `60s`) | 60s |
+| `HNHMAP_IDLE_TIMEOUT` | HTTP server idle timeout (e.g. `120s`) | 120s |
 | `HNHMAP_BOOTSTRAP_PASSWORD` | Password for initial setup: when no users exist, logging in as `admin` with this password creates the first admin user | — |
 | `HNHMAP_BASE_URL` | Full application URL for OAuth redirect_uri (e.g. `https://map.example.com`). If not set, derived from `Host` and `X-Forwarded-*` headers | — |
 | `HNHMAP_OAUTH_GOOGLE_CLIENT_ID` | Google OAuth Client ID | — |

frontend-nuxt/components/MapView.vue

@@ -283,6 +283,7 @@ function updateSelectedMarkerForBookmark() {
   }
 }
 let intervalId: ReturnType<typeof setInterval> | null = null
+let characterPollFirstTickId: ReturnType<typeof setTimeout> | null = null
 let autoMode = false
 let mapContainer: HTMLElement | null = null
 let contextMenuHandler: ((ev: MouseEvent) => void) | null = null
@@ -554,13 +555,20 @@ onMounted(async () => {
   }
 
   function startCharacterPoll() {
+    if (characterPollFirstTickId) clearTimeout(characterPollFirstTickId)
+    characterPollFirstTickId = null
     if (intervalId) clearInterval(intervalId)
+    intervalId = null
     const ms =
       typeof document !== 'undefined' && document.visibilityState === 'hidden'
         ? CHARACTER_POLL_MS_HIDDEN
         : CHARACTER_POLL_MS
-    pollCharacters()
-    intervalId = setInterval(pollCharacters, ms)
+    // First tick after delay to avoid double-fetch with initial getCharacters() in Promise.all
+    characterPollFirstTickId = setTimeout(() => {
+      characterPollFirstTickId = null
+      pollCharacters()
+      intervalId = setInterval(pollCharacters, ms)
+    }, ms)
   }
 
   startCharacterPoll()
@@ -703,6 +711,7 @@ onBeforeUnmount(() => {
   if (contextMenuHandler) {
     document.removeEventListener('contextmenu', contextMenuHandler, true)
   }
+  if (characterPollFirstTickId) clearTimeout(characterPollFirstTickId)
   if (intervalId) clearInterval(intervalId)
   updatesHandle?.cleanup()
   if (leafletMap) leafletMap.remove()

frontend-nuxt/components/UserAvatar.vue

@@ -9,6 +9,7 @@
         :src="useGravatarUrl(email, size)"
         alt=""
         class="w-full h-full object-cover"
+        loading="lazy"
         @error="gravatarError = true"
       >
       <div

frontend-nuxt/components/map/MapSearch.vue

@@ -98,6 +98,20 @@ const recent = useRecentLocations()
 
 const inputRef = ref<HTMLInputElement | null>(null)
 const query = ref('')
+const queryDebounced = ref('')
+let queryDebounceId: ReturnType<typeof setTimeout> | null = null
+const SEARCH_DEBOUNCE_MS = 180
+watch(
+  query,
+  (v) => {
+    if (queryDebounceId) clearTimeout(queryDebounceId)
+    queryDebounceId = setTimeout(() => {
+      queryDebounced.value = v
+      queryDebounceId = null
+    }, SEARCH_DEBOUNCE_MS)
+  },
+  { immediate: true }
+)
 const showDropdown = ref(false)
 const highlightIndex = ref(0)
 let closeDropdownTimer: ReturnType<typeof setTimeout> | null = null
@@ -113,7 +127,7 @@ interface Suggestion {
 }
 
 const suggestions = computed<Suggestion[]>(() => {
-  const q = query.value.trim().toLowerCase()
+  const q = queryDebounced.value.trim().toLowerCase()
   if (!q) return []
 
   const coordMatch = q.match(/^\s*(-?\d+)\s*[,;\s]\s*(-?\d+)\s*$/)
@@ -193,10 +207,18 @@ const emit = defineEmits<{
   'jump-to-marker': [id: number]
 }>()
 
+watch(suggestions, () => {
+  highlightIndex.value = 0
+}, { flush: 'sync' })
+
 onMounted(() => {
   useMapNavigate().setFocusSearch(() => inputRef.value?.focus())
 })
 
+onBeforeUnmount(() => {
+  if (queryDebounceId) clearTimeout(queryDebounceId)
+})
+
 onBeforeUnmount(() => {
   if (closeDropdownTimer) clearTimeout(closeDropdownTimer)
   useMapNavigate().setFocusSearch(null)

frontend-nuxt/composables/useGravatarUrl.ts

@@ -1,8 +1,11 @@
 import md5 from 'md5'
 
+const gravatarCache = new Map<string, string>()
+
 /**
  * Returns Gravatar avatar URL for the given email, or empty string if no email.
  * Gravatar expects: trim, lowercase, then MD5 hex. Use empty string to show a placeholder (e.g. initial letter) in the UI.
+ * Results are memoized by (email, size) to avoid recomputing MD5 on every render.
  *
  * @param email - User email (optional)
  * @param size - Avatar size in pixels (default 64; navbar 32, drawer 40, profile 64–80)
@@ -10,7 +13,12 @@ import md5 from 'md5'
 export function useGravatarUrl(email: string | undefined, size?: number): string {
   const normalized = email?.trim().toLowerCase()
   if (!normalized) return ''
-  const hash = md5(normalized)
   const s = size ?? 64
-  return `https://www.gravatar.com/avatar/${hash}?s=${s}&d=identicon`
+  const key = `${normalized}\n${s}`
+  const cached = gravatarCache.get(key)
+  if (cached !== undefined) return cached
+  const hash = md5(normalized)
+  const url = `https://www.gravatar.com/avatar/${hash}?s=${s}&d=identicon`
+  gravatarCache.set(key, url)
+  return url
 }

frontend-nuxt/composables/useMapApi.ts

@@ -13,6 +13,12 @@ export type { Character, ConfigResponse, MapInfo, MapInfoAdmin, Marker, MeRespon
 // Singleton: shared by all useMapApi() callers so 401 triggers one global handler (e.g. app.vue)
 const onApiErrorCallbacks = new Map<symbol, () => void>()
 
+// In-flight dedup: one me() request at a time; concurrent callers share the same promise.
+let mePromise: Promise<MeResponse> | null = null
+
+// In-flight dedup for GET endpoints: same path + method shares one request across all callers.
+const inFlightByKey = new Map<string, Promise<unknown>>()
+
 export function useMapApi() {
   const config = useRuntimeConfig()
   const apiBase = config.public.apiBase as string
@@ -40,20 +46,31 @@ export function useMapApi() {
     return undefined as T
   }
 
+  function requestDeduped<T>(path: string, opts?: RequestInit): Promise<T> {
+    const key = path + (opts?.method ?? 'GET')
+    const existing = inFlightByKey.get(key)
+    if (existing) return existing as Promise<T>
+    const p = request<T>(path, opts).finally(() => {
+      inFlightByKey.delete(key)
+    })
+    inFlightByKey.set(key, p)
+    return p
+  }
+
   async function getConfig() {
-    return request<ConfigResponse>('config')
+    return requestDeduped<ConfigResponse>('config')
   }
 
   async function getCharacters() {
-    return request<Character[]>('v1/characters')
+    return requestDeduped<Character[]>('v1/characters')
   }
 
   async function getMarkers() {
-    return request<Marker[]>('v1/markers')
+    return requestDeduped<Marker[]>('v1/markers')
   }
 
   async function getMaps() {
-    return request<Record<string, MapInfo>>('maps')
+    return requestDeduped<Record<string, MapInfo>>('maps')
   }
 
   // Auth
@@ -92,11 +109,17 @@ export function useMapApi() {
   }
 
   async function logout() {
+    mePromise = null
+    inFlightByKey.clear()
     await fetch(`${apiBase}/logout`, { method: 'POST', credentials: 'include' })
   }
 
   async function me() {
-    return request<MeResponse>('me')
+    if (mePromise) return mePromise
+    mePromise = request<MeResponse>('me').finally(() => {
+      mePromise = null
+    })
+    return mePromise
   }
 
   async function meUpdate(body: { email?: string }) {
@@ -182,7 +205,19 @@ export function useMapApi() {
   }
 
   async function adminRebuildZooms() {
-    await request('admin/rebuildZooms', { method: 'POST' })
+    const res = await fetch(`${apiBase}/admin/rebuildZooms`, {
+      method: 'POST',
+      credentials: 'include',
+    })
+    if (res.status === 401 || res.status === 403) {
+      onApiErrorCallbacks.forEach((cb) => cb())
+      throw new Error('Unauthorized')
+    }
+    if (res.status !== 200 && res.status !== 202) throw new Error(`API ${res.status}`)
+  }
+
+  async function adminRebuildZoomsStatus(): Promise<{ running: boolean }> {
+    return request<{ running: boolean }>('admin/rebuildZooms/status')
   }
 
   function adminExportUrl() {
@@ -250,6 +285,7 @@ export function useMapApi() {
     adminMapToggleHidden,
     adminWipe,
     adminRebuildZooms,
+    adminRebuildZoomsStatus,
     adminExportUrl,
     adminMerge,
     adminWipeTile,

frontend-nuxt/pages/admin/index.vue

@@ -60,11 +60,11 @@
             aria-label="Search users"
           />
         </div>
-          <div class="flex flex-col gap-2">
+          <div class="flex flex-col gap-2 max-h-[60vh] overflow-y-auto">
             <div
               v-for="u in filteredUsers"
               :key="u"
-              class="flex items-center justify-between gap-3 w-full p-3 rounded-lg bg-base-300/50 hover:bg-base-300/70 transition-colors"
+              class="flex items-center justify-between gap-3 w-full p-3 rounded-lg bg-base-300/50 hover:bg-base-300/70 transition-colors shrink-0"
             >
               <div class="flex items-center gap-2 min-w-0">
                 <div class="avatar avatar-placeholder">
@@ -103,7 +103,7 @@
             aria-label="Search maps"
           />
         </div>
-          <div class="overflow-x-auto">
+          <div class="overflow-x-auto max-h-[60vh] overflow-y-auto">
             <table class="table table-sm table-zebra min-w-[32rem]">
               <thead>
                 <tr>
@@ -199,7 +199,7 @@
         </h2>
           <div class="flex flex-col gap-3">
             <div>
-              <a :href="api.adminExportUrl()" target="_blank" rel="noopener" class="btn btn-sm min-h-11 touch-manipulation">
+              <a :href="exportUrl" target="_blank" rel="noopener" class="btn btn-sm min-h-11 touch-manipulation">
                 Export zip
               </a>
             </div>
@@ -284,6 +284,7 @@ definePageMeta({ middleware: 'admin' })
 useHead({ title: 'Admin – HnH Map' })
 
 const api = useMapApi()
+const exportUrl = computed(() => api.adminExportUrl())
 const toast = useToast()
 const users = ref<string[]>([])
 const maps = ref<MapInfoAdmin[]>([])
@@ -391,6 +392,15 @@ async function doRebuildZooms() {
   rebuilding.value = true
   try {
     await api.adminRebuildZooms()
+    // Rebuild runs in background; poll status until done
+    const poll = async (): Promise<void> => {
+      const { running } = await api.adminRebuildZoomsStatus()
+      if (running) {
+        await new Promise((r) => setTimeout(r, 2000))
+        return poll()
+      }
+    }
+    await poll()
     markRebuildDone()
     showRebuildModal.value = false
     toast.success('Zooms rebuilt.')

internal/app/handlers/admin.go

@@ -321,6 +321,7 @@ func (h *Handlers) APIAdminHideMarker(rw http.ResponseWriter, req *http.Request)
 }
 
 // APIAdminRebuildZooms handles POST /map/api/admin/rebuildZooms.
+// It starts the rebuild in the background and returns 202 Accepted immediately.
 func (h *Handlers) APIAdminRebuildZooms(rw http.ResponseWriter, req *http.Request) {
 	if !h.requireMethod(rw, req, http.MethodPost) {
 		return
@@ -328,11 +329,22 @@ func (h *Handlers) APIAdminRebuildZooms(rw http.ResponseWriter, req *http.Reques
 	if h.requireAdmin(rw, req) == nil {
 		return
 	}
-	if err := h.Admin.RebuildZooms(req.Context()); err != nil {
-		HandleServiceError(rw, err)
+	h.Admin.StartRebuildZooms()
+	rw.WriteHeader(http.StatusAccepted)
+}
+
+// APIAdminRebuildZoomsStatus handles GET /map/api/admin/rebuildZooms/status.
+// Returns {"running": true|false} so the client can poll until the rebuild finishes.
+func (h *Handlers) APIAdminRebuildZoomsStatus(rw http.ResponseWriter, req *http.Request) {
+	if req.Method != http.MethodGet {
+		JSONError(rw, http.StatusMethodNotAllowed, "method not allowed", "METHOD_NOT_ALLOWED")
 		return
 	}
-	rw.WriteHeader(http.StatusOK)
+	if h.requireAdmin(rw, req) == nil {
+		return
+	}
+	running := h.Admin.RebuildZoomsRunning()
+	JSON(rw, http.StatusOK, map[string]bool{"running": running})
 }
 
 // APIAdminExport handles GET /map/api/admin/export.
@@ -426,6 +438,8 @@ func (h *Handlers) APIAdminRoute(rw http.ResponseWriter, req *http.Request, path
 		h.APIAdminWipe(rw, req)
 	case path == "rebuildZooms":
 		h.APIAdminRebuildZooms(rw, req)
+	case path == "rebuildZooms/status":
+		h.APIAdminRebuildZoomsStatus(rw, req)
 	case path == "export":
 		h.APIAdminExport(rw, req)
 	case path == "merge":

internal/app/handlers/client.go

@@ -12,6 +12,9 @@ import (
 	"github.com/andyleap/hnh-map/internal/app/services"
 )
 
+// maxClientBodySize is the maximum size for position and marker update request bodies.
+const maxClientBodySize = 2 * 1024 * 1024 // 2 MB
+
 var clientPath = regexp.MustCompile(`client/([^/]+)/(.*)`)
 
 // ClientRouter handles /client/* requests with token-based auth.
@@ -112,12 +115,16 @@ func (h *Handlers) clientGridUpload(rw http.ResponseWriter, req *http.Request) {
 
 func (h *Handlers) clientPositionUpdate(rw http.ResponseWriter, req *http.Request) {
 	defer req.Body.Close()
-	buf, err := io.ReadAll(req.Body)
+	buf, err := io.ReadAll(io.LimitReader(req.Body, maxClientBodySize+1))
 	if err != nil {
 		slog.Error("error reading position update", "error", err)
 		JSONError(rw, http.StatusBadRequest, "failed to read body", "BAD_REQUEST")
 		return
 	}
+	if len(buf) > maxClientBodySize {
+		JSONError(rw, http.StatusRequestEntityTooLarge, "request body too large", "PAYLOAD_TOO_LARGE")
+		return
+	}
 	if err := h.Client.UpdatePositions(req.Context(), buf); err != nil {
 		slog.Error("position update failed", "error", err)
 		HandleServiceError(rw, err)
@@ -126,12 +133,16 @@ func (h *Handlers) clientPositionUpdate(rw http.ResponseWriter, req *http.Reques
 
 func (h *Handlers) clientMarkerUpdate(rw http.ResponseWriter, req *http.Request) {
 	defer req.Body.Close()
-	buf, err := io.ReadAll(req.Body)
+	buf, err := io.ReadAll(io.LimitReader(req.Body, maxClientBodySize+1))
 	if err != nil {
 		slog.Error("error reading marker update", "error", err)
 		JSONError(rw, http.StatusBadRequest, "failed to read body", "BAD_REQUEST")
 		return
 	}
+	if len(buf) > maxClientBodySize {
+		JSONError(rw, http.StatusRequestEntityTooLarge, "request body too large", "PAYLOAD_TOO_LARGE")
+		return
+	}
 	if err := h.Client.UploadMarkers(req.Context(), buf); err != nil {
 		slog.Error("marker update failed", "error", err)
 		HandleServiceError(rw, err)

internal/app/handlers/handlers_test.go

@@ -1,6 +1,7 @@
 package handlers_test
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
@@ -677,3 +678,38 @@ func TestClientRouter_InvalidToken(t *testing.T) {
 		t.Fatalf("expected 401, got %d", rr.Code)
 	}
 }
+
+func TestClientRouter_PositionUpdate_BodyTooLarge(t *testing.T) {
+	env := newTestEnv(t)
+	env.createUser(t, "alice", "pass", app.Auths{app.AUTH_UPLOAD})
+	tokens := env.auth.GenerateTokenForUser(context.Background(), "alice")
+	if len(tokens) == 0 {
+		t.Fatal("expected token")
+	}
+	// Body larger than maxClientBodySize (2MB)
+	bigBody := bytes.Repeat([]byte("x"), 2*1024*1024+1)
+	req := httptest.NewRequest(http.MethodPost, "/client/"+tokens[0]+"/positionUpdate", bytes.NewReader(bigBody))
+	req.Header.Set("Content-Type", "application/json")
+	rr := httptest.NewRecorder()
+	env.h.ClientRouter(rr, req)
+	if rr.Code != http.StatusRequestEntityTooLarge {
+		t.Fatalf("expected 413, got %d: %s", rr.Code, rr.Body.String())
+	}
+}
+
+func TestClientRouter_MarkerUpdate_BodyTooLarge(t *testing.T) {
+	env := newTestEnv(t)
+	env.createUser(t, "alice", "pass", app.Auths{app.AUTH_UPLOAD})
+	tokens := env.auth.GenerateTokenForUser(context.Background(), "alice")
+	if len(tokens) == 0 {
+		t.Fatal("expected token")
+	}
+	bigBody := bytes.Repeat([]byte("x"), 2*1024*1024+1)
+	req := httptest.NewRequest(http.MethodPost, "/client/"+tokens[0]+"/markerUpdate", bytes.NewReader(bigBody))
+	req.Header.Set("Content-Type", "application/json")
+	rr := httptest.NewRecorder()
+	env.h.ClientRouter(rr, req)
+	if rr.Code != http.StatusRequestEntityTooLarge {
+		t.Fatalf("expected 413, got %d: %s", rr.Code, rr.Body.String())
+	}
+}

internal/app/services/admin.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log/slog"
 	"strconv"
+	"sync"
 
 	"github.com/andyleap/hnh-map/internal/app"
 	"github.com/andyleap/hnh-map/internal/app/store"
@@ -17,6 +18,9 @@ import (
 type AdminService struct {
 	st     *store.Store
 	mapSvc *MapService
+
+	rebuildMu    sync.Mutex
+	rebuildRunning bool
 }
 
 // NewAdminService creates an AdminService with the given store and map service.
@@ -372,3 +376,32 @@ func (s *AdminService) HideMarker(ctx context.Context, markerID string) error {
 func (s *AdminService) RebuildZooms(ctx context.Context) error {
 	return s.mapSvc.RebuildZooms(ctx)
 }
+
+// StartRebuildZooms starts RebuildZooms in a goroutine and returns immediately.
+// RebuildZoomsRunning returns true while the rebuild is in progress.
+func (s *AdminService) StartRebuildZooms() {
+	s.rebuildMu.Lock()
+	if s.rebuildRunning {
+		s.rebuildMu.Unlock()
+		return
+	}
+	s.rebuildRunning = true
+	s.rebuildMu.Unlock()
+	go func() {
+		defer func() {
+			s.rebuildMu.Lock()
+			s.rebuildRunning = false
+			s.rebuildMu.Unlock()
+		}()
+		if err := s.mapSvc.RebuildZooms(context.Background()); err != nil {
+			slog.Error("RebuildZooms background failed", "error", err)
+		}
+	}()
+}
+
+// RebuildZoomsRunning returns true if a rebuild is currently in progress.
+func (s *AdminService) RebuildZoomsRunning() bool {
+	s.rebuildMu.Lock()
+	defer s.rebuildMu.Unlock()
+	return s.rebuildRunning
+}

internal/app/services/export.go

@@ -35,14 +35,23 @@ func NewExportService(st *store.Store, mapSvc *MapService) *ExportService {
 	return &ExportService{st: st, mapSvc: mapSvc}
 }
 
-// Export writes all map data as a ZIP archive to the given writer.
-func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
-	zw := zip.NewWriter(w)
-	defer zw.Close()
+// exportEntry describes a single grid PNG to copy into the ZIP (collected inside a read-only View).
+type exportEntry struct {
+	ZipPath  string // e.g. "1/grid1.png"
+	FilePath string // absolute path on disk
+}
 
-	return s.st.Update(ctx, func(tx *bbolt.Tx) error {
-		maps := map[int]mapData{}
-		gridMap := map[string]int{}
+// Export writes all map data as a ZIP archive to the given writer.
+// It uses a read-only View to collect data, then builds the ZIP outside the transaction
+// so that the write lock is not held during file I/O.
+func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
+	var maps map[int]mapData
+	var gridMap map[string]int
+	var filesToCopy []exportEntry
+
+	if err := s.st.View(ctx, func(tx *bbolt.Tx) error {
+		maps = map[int]mapData{}
+		gridMap = map[string]int{}
 
 		grids := tx.Bucket(store.BucketGrids)
 		if grids == nil {
@@ -54,6 +63,11 @@ func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
 		}
 
 		if err := grids.ForEach(func(k, v []byte) error {
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
 			gd := app.GridData{}
 			if err := json.Unmarshal(v, &gd); err != nil {
 				return err
@@ -84,17 +98,11 @@ func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
 			if err := json.Unmarshal(tdraw, &td); err != nil {
 				return err
 			}
-			fw, err := zw.Create(fmt.Sprintf("%d/%s.png", gd.Map, gd.ID))
-			if err != nil {
-				return err
-			}
-			f, err := os.Open(filepath.Join(s.mapSvc.GridStorage(), td.File))
-			if err != nil {
-				return err
-			}
-			_, err = io.Copy(fw, f)
-			f.Close()
-			return err
+			filesToCopy = append(filesToCopy, exportEntry{
+				ZipPath:  fmt.Sprintf("%d/%s.png", gd.Map, gd.ID),
+				FilePath: filepath.Join(s.mapSvc.GridStorage(), td.File),
+			})
+			return nil
 		}); err != nil {
 			return err
 		}
@@ -104,6 +112,11 @@ func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
 			markersgrid := markersb.Bucket(store.BucketMarkersGrid)
 			if markersgrid != nil {
 				markersgrid.ForEach(func(k, v []byte) error {
+					select {
+					case <-ctx.Done():
+						return ctx.Err()
+					default:
+					}
 					marker := app.Marker{}
 					if json.Unmarshal(v, &marker) != nil {
 						return nil
@@ -115,16 +128,41 @@ func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
 				})
 			}
 		}
-
-		for mapid, md := range maps {
-			fw, err := zw.Create(fmt.Sprintf("%d/grids.json", mapid))
-			if err != nil {
-				return err
-			}
-			json.NewEncoder(fw).Encode(md)
-		}
 		return nil
-	})
+	}); err != nil {
+		return err
+	}
+
+	// Build ZIP outside the transaction so the write lock is not held during file I/O.
+	zw := zip.NewWriter(w)
+	defer zw.Close()
+
+	for _, e := range filesToCopy {
+		fw, err := zw.Create(e.ZipPath)
+		if err != nil {
+			return err
+		}
+		f, err := os.Open(e.FilePath)
+		if err != nil {
+			return err
+		}
+		_, err = io.Copy(fw, f)
+		f.Close()
+		if err != nil {
+			return err
+		}
+	}
+
+	for mapid, md := range maps {
+		fw, err := zw.Create(fmt.Sprintf("%d/grids.json", mapid))
+		if err != nil {
+			return err
+		}
+		if err := json.NewEncoder(fw).Encode(md); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 // Merge imports map data from a ZIP file.

internal/app/services/map.go

@@ -184,6 +184,38 @@ func (s *MapService) GetTile(ctx context.Context, mapID int, c app.Coord, zoom i
 	return td
 }
 
+// getSubTiles returns up to 4 tile data for the given parent coord at zoom z-1 (sub-tiles at z).
+// Order: (0,0), (1,0), (0,1), (1,1) to match the 2x2 loop in UpdateZoomLevel.
+func (s *MapService) getSubTiles(ctx context.Context, mapid int, c app.Coord, z int) []*app.TileData {
+	coords := []app.Coord{
+		{X: c.X*2 + 0, Y: c.Y*2 + 0},
+		{X: c.X*2 + 1, Y: c.Y*2 + 0},
+		{X: c.X*2 + 0, Y: c.Y*2 + 1},
+		{X: c.X*2 + 1, Y: c.Y*2 + 1},
+	}
+	keys := make([]string, len(coords))
+	for i := range coords {
+		keys[i] = coords[i].Name()
+	}
+	var rawMap map[string][]byte
+	if err := s.st.View(ctx, func(tx *bbolt.Tx) error {
+		rawMap = s.st.GetTiles(tx, mapid, z-1, keys)
+		return nil
+	}); err != nil {
+		return nil
+	}
+	result := make([]*app.TileData, 4)
+	for i, k := range keys {
+		if raw, ok := rawMap[k]; ok && len(raw) > 0 {
+			td := &app.TileData{}
+			if json.Unmarshal(raw, td) == nil {
+				result[i] = td
+			}
+		}
+	}
+	return result
+}
+
 // SaveTile persists a tile and broadcasts the update.
 func (s *MapService) SaveTile(ctx context.Context, mapid int, c app.Coord, z int, f string, t int64) {
 	s.st.Update(ctx, func(tx *bbolt.Tx) error {
@@ -203,32 +235,28 @@ func (s *MapService) SaveTile(ctx context.Context, mapid int, c app.Coord, z int
 	})
 }
 
-// UpdateZoomLevel composes a zoom tile from 4 sub-tiles.
+// UpdateZoomLevel composes a zoom tile from 4 sub-tiles (one View for all 4 tile reads).
 func (s *MapService) UpdateZoomLevel(ctx context.Context, mapid int, c app.Coord, z int) {
+	subTiles := s.getSubTiles(ctx, mapid, c, z)
 	img := image.NewNRGBA(image.Rect(0, 0, app.GridSize, app.GridSize))
 	draw.Draw(img, img.Bounds(), image.Transparent, image.Point{}, draw.Src)
-	for x := 0; x <= 1; x++ {
-		for y := 0; y <= 1; y++ {
-			subC := c
-			subC.X *= 2
-			subC.Y *= 2
-			subC.X += x
-			subC.Y += y
-			td := s.GetTile(ctx, mapid, subC, z-1)
-			if td == nil || td.File == "" {
-				continue
-			}
-			subf, err := os.Open(filepath.Join(s.gridStorage, td.File))
-			if err != nil {
-				continue
-			}
-			subimg, _, err := image.Decode(subf)
-			subf.Close()
-			if err != nil {
-				continue
-			}
-			draw.BiLinear.Scale(img, image.Rect(50*x, 50*y, 50*x+50, 50*y+50), subimg, subimg.Bounds(), draw.Src, nil)
+	for i := 0; i < 4; i++ {
+		td := subTiles[i]
+		if td == nil || td.File == "" {
+			continue
 		}
+		x := i % 2
+		y := i / 2
+		subf, err := os.Open(filepath.Join(s.gridStorage, td.File))
+		if err != nil {
+			continue
+		}
+		subimg, _, err := image.Decode(subf)
+		subf.Close()
+		if err != nil {
+			continue
+		}
+		draw.BiLinear.Scale(img, image.Rect(50*x, 50*y, 50*x+50, 50*y+50), subimg, subimg.Bounds(), draw.Src, nil)
 	}
 	if err := os.MkdirAll(fmt.Sprintf("%s/%d/%d", s.gridStorage, mapid, z), 0755); err != nil {
 		slog.Error("failed to create zoom dir", "error", err)
@@ -266,6 +294,11 @@ func (s *MapService) RebuildZooms(ctx context.Context) error {
 			return nil
 		}
 		b.ForEach(func(k, v []byte) error {
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
 			grid := app.GridData{}
 			if err := json.Unmarshal(v, &grid); err != nil {
 				return err
@@ -282,6 +315,9 @@ func (s *MapService) RebuildZooms(ctx context.Context) error {
 	}
 
 	for g, id := range saveGrid {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
 		f := fmt.Sprintf("%s/grids/%s.png", s.gridStorage, id)
 		if _, err := os.Stat(f); err != nil {
 			continue
@@ -289,6 +325,9 @@ func (s *MapService) RebuildZooms(ctx context.Context) error {
 		s.SaveTile(ctx, g.m, g.c, 0, fmt.Sprintf("grids/%s.png", id), time.Now().UnixNano())
 	}
 	for z := 1; z <= app.MaxZoomLevel; z++ {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
 		process := needProcess
 		needProcess = map[zoomproc]struct{}{}
 		for p := range process {
@@ -327,6 +366,11 @@ func (s *MapService) GetAllTileCache(ctx context.Context) []TileCache {
 	var cache []TileCache
 	s.st.View(ctx, func(tx *bbolt.Tx) error {
 		return s.st.ForEachTile(tx, func(mapK, zoomK, coordK, v []byte) error {
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
 			td := app.TileData{}
 			if err := json.Unmarshal(v, &td); err != nil {
 				return err

internal/app/store/db.go

@@ -17,7 +17,9 @@ func New(db *bbolt.DB) *Store {
 	return &Store{db: db}
 }
 
-// View runs fn in a read-only transaction. Checks context before starting.
+// View runs fn in a read-only transaction. It checks context before starting.
+// Long-running callbacks (e.g. large ForEach or ForEachTile) should check ctx.Done()
+// periodically and return ctx.Err() to abort early when the context is cancelled.
 func (s *Store) View(ctx context.Context, fn func(tx *bbolt.Tx) error) error {
 	select {
 	case <-ctx.Done():
@@ -27,7 +29,8 @@ func (s *Store) View(ctx context.Context, fn func(tx *bbolt.Tx) error) error {
 	}
 }
 
-// Update runs fn in a read-write transaction. Checks context before starting.
+// Update runs fn in a read-write transaction. It checks context before starting.
+// Long-running callbacks should check ctx.Done() periodically and return ctx.Err() to abort.
 func (s *Store) Update(ctx context.Context, fn func(tx *bbolt.Tx) error) error {
 	select {
 	case <-ctx.Done():
@@ -284,6 +287,30 @@ func (s *Store) GetTile(tx *bbolt.Tx, mapID, zoom int, coordKey string) []byte {
 	return zoomB.Get([]byte(coordKey))
 }
 
+// GetTiles returns raw JSON for multiple tiles in the same map/zoom in one transaction.
+// Keys that are not found are omitted from the result. Coord keys are in the form "x_y".
+func (s *Store) GetTiles(tx *bbolt.Tx, mapID, zoom int, coordKeys []string) map[string][]byte {
+	out := make(map[string][]byte, len(coordKeys))
+	tiles := tx.Bucket(BucketTiles)
+	if tiles == nil {
+		return out
+	}
+	mapB := tiles.Bucket([]byte(strconv.Itoa(mapID)))
+	if mapB == nil {
+		return out
+	}
+	zoomB := mapB.Bucket([]byte(strconv.Itoa(zoom)))
+	if zoomB == nil {
+		return out
+	}
+	for _, k := range coordKeys {
+		if v := zoomB.Get([]byte(k)); v != nil {
+			out[k] = v
+		}
+	}
+	return out
+}
+
 // PutTile stores a tile entry (creates nested buckets as needed).
 func (s *Store) PutTile(tx *bbolt.Tx, mapID, zoom int, coordKey string, raw []byte) error {
 	tiles, err := tx.CreateBucketIfNotExists(BucketTiles)