fix: resolve maintenance windows race condition and N+1 query

- Add GET /api/v1/maintenance-windows bulk endpoint to eliminate N+1
  per-host API calls (1 request instead of N+1)
- Fix two-phase state update race: setHosts() was called before
  setWindowsByHost(), causing React to render hosts with empty windows
- Add AbortController to cancel stale fetch requests on unmount/re-fetch
- Batch state updates atomically (React 18 auto-batching)
- Replace silent catch{} with proper error handling
- Add refreshData() wrapper for mutation handlers and Refresh button

Backend: maintenance_windows.rs - new list_all_windows handler +
all_windows_router(), mounted in main.rs
Frontend: client.ts - new listAll() API method
Frontend: MaintenanceWindowsPage.tsx - rewritten fetchData

crates/pm-web/src/main.rs

@@ -288,6 +288,11 @@ pub fn build_router(state: AppState) -> Router {
             "/hosts/{host_id}/maintenance-windows",
             routes::maintenance_windows::router(),
         )
+        // Maintenance windows — bulk list-all endpoint
+        .nest(
+            "/maintenance-windows",
+            routes::maintenance_windows::all_windows_router(),
+        )
         // CA root certificate download
         .nest("/ca", routes::ca::ca_router())
         // Certificate list / renew / revoke

crates/pm-web/src/routes/maintenance_windows.rs

@@ -1,6 +1,7 @@
 //! Maintenance window management routes.
 //!
 //! GET    /api/v1/hosts/{id}/maintenance-windows           — list windows for host
+//! GET    /api/v1/maintenance-windows                     — list ALL windows (bulk)
 //! POST   /api/v1/hosts/{id}/maintenance-windows           — create window for host
 //! PUT    /api/v1/hosts/{id}/maintenance-windows/{win_id}  — update window
 //! DELETE /api/v1/hosts/{id}/maintenance-windows/{win_id}  — delete window
@@ -32,6 +33,41 @@ pub fn router() -> Router<AppState> {
         .route("/{win_id}", put(update_window).delete(delete_window))
 }
 
+/// Top-level router for `/api/v1/maintenance-windows` — bulk list-all endpoint.
+pub fn all_windows_router() -> Router<AppState> {
+    Router::new().route("/", get(list_all_windows))
+}
+
+// ── GET /api/v1/maintenance-windows ──────────────────────────────────────────
+
+/// Bulk endpoint: return every maintenance window across all hosts.
+/// Eliminates N+1 queries from the frontend (one request instead of one per host).
+async fn list_all_windows(
+    State(state): State<AppState>,
+    _auth: AuthUser,
+) -> Result<Json<Value>, (StatusCode, Json<Value>)> {
+    let windows: Vec<MaintenanceWindow> = sqlx::query_as(
+        r#"
+        SELECT id, host_id, label, recurrence, start_at, duration_minutes,
+               recurrence_day, enabled, auto_apply, created_at, updated_at
+        FROM   maintenance_windows
+        ORDER  BY host_id, created_at ASC
+        "#,
+    )
+    .fetch_all(&state.db)
+    .await
+    .map_err(|e| {
+        tracing::error!(error = %e, "list_all_windows: query failed");
+        err(
+            StatusCode::INTERNAL_SERVER_ERROR,
+            "internal_error",
+            "Database error",
+        )
+    })?;
+
+    Ok(Json(json!({ "windows": windows })))
+}
+
 // ── Error helper ──────────────────────────────────────────────────────────────
 
 #[inline]

frontend/src/api/client.ts

@@ -5,6 +5,7 @@ import type {
   CreateHostRequest,
   CreateJobRequest,
   CreateMaintenanceWindowRequest,
+  MaintenanceWindow,
   UpdateMaintenanceWindowRequest,
   Certificate,
   IssuedCert,
@@ -176,6 +177,10 @@ export const patchesApi = {
 
 // ── Maintenance Windows API ───────────────────────────────────────────────────
 export const maintenanceWindowsApi = {
+  /** Bulk: fetch ALL maintenance windows across every host in one request. */
+  listAll: () =>
+    apiClient.get<{ windows: MaintenanceWindow[] }>('/maintenance-windows'),
+  /** Per-host: fetch windows for a single host. */
   list: (hostId: string) =>
     apiClient.get(`/hosts/${hostId}/maintenance-windows`),
   create: (hostId: string, body: CreateMaintenanceWindowRequest) =>

frontend/src/pages/MaintenanceWindowsPage.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useState, useCallback } from 'react'
+import { useEffect, useState, useCallback, useRef } from 'react'
 import {
   Alert,
   Box,
@@ -444,35 +444,70 @@ export default function MaintenanceWindowsPage() {
   const [deleteOpen, setDeleteOpen] = useState(false)
   const [deleteWindow, setDeleteWindow] = useState<MaintenanceWindow | null>(null)
 
-  // ── Fetch all hosts + their windows ──────────────────────────────────────
-  const fetchData = useCallback(async () => {
+  // ── AbortController ref for cancelling stale fetches ──────────────────────
+  const abortRef = useRef<AbortController | null>(null)
+
+  // ── Fetch hosts + all maintenance windows in 2 parallel requests ─────────
+  // Uses bulk /maintenance-windows endpoint instead of N+1 per-host calls.
+  // State updates are batched atomically so React never renders hosts without
+  // their windows (the root cause of the "randomly missing data" bug).
+  const fetchData = useCallback(async (signal?: AbortSignal) => {
     setLoading(true)
     setError(null)
     try {
-      const hostsRes = await hostsApi.list({ limit: 500 })
-      const fetchedHosts: Host[] = hostsRes.data?.hosts ?? hostsRes.data ?? []
-      setHosts(fetchedHosts)
+      // Fetch hosts and ALL windows in parallel — 2 requests, not N+1.
+      const [hostsRes, windowsRes] = await Promise.all([
+        hostsApi.list({ limit: 500 }),
+        maintenanceWindowsApi.listAll(),
+      ])
 
+      // If the request was aborted (e.g. component unmounted or new fetch
+      // started), discard the results silently.
+      if (signal?.aborted) return
+
+      const fetchedHosts: Host[] = hostsRes.data?.hosts ?? hostsRes.data ?? []
+      const allWindows: MaintenanceWindow[] = windowsRes.data?.windows ?? []
+
+      // Group windows by host_id for O(N) lookup.
       const windowMap: Record<string, MaintenanceWindow[]> = {}
-      await Promise.all(
-        fetchedHosts.map(async (h) => {
-          try {
-            const res = await maintenanceWindowsApi.list(h.id)
-            windowMap[h.id] = res.data?.windows ?? []
-          } catch {
-            windowMap[h.id] = []
+      for (const w of allWindows) {
+        if (!windowMap[w.host_id]) windowMap[w.host_id] = []
+        windowMap[w.host_id].push(w)
       }
-        })
-      )
+
+      // Batch both state updates together — React 18+ auto-batches these
+      // into a single render, eliminating the race condition where hosts
+      // rendered with stale/empty windows.
+      setHosts(fetchedHosts)
       setWindowsByHost(windowMap)
-    } catch {
+    } catch (err: unknown) {
+      if (signal?.aborted) return // stale request — ignore silently
+      // Only log real errors, not cancellations.
+      if (err instanceof DOMException && err.name === 'AbortError') return
       setError('Failed to load hosts or maintenance windows.')
     } finally {
+      if (!signal?.aborted) {
         setLoading(false)
       }
+    }
   }, [])
 
-  useEffect(() => { fetchData() }, [fetchData])
+  useEffect(() => {
+    // Cancel any in-flight fetch from a previous render.
+    abortRef.current?.abort()
+    const controller = new AbortController()
+    abortRef.current = controller
+    fetchData(controller.signal)
+    return () => { controller.abort() }
+  }, [fetchData])
+
+  // ── Refresh helper: cancels any in-flight fetch, starts a new one ────────
+  const refreshData = useCallback(() => {
+    abortRef.current?.abort()
+    const controller = new AbortController()
+    abortRef.current = controller
+    fetchData(controller.signal)
+  }, [fetchData])
 
   // ── Helpers ───────────────────────────────────────────────────────────────
   const showSnackbar = (message: string, severity: 'success' | 'error') =>
@@ -498,7 +533,7 @@ export default function MaintenanceWindowsPage() {
     })
     setCreateOpen(false)
     showSnackbar('Maintenance window created', 'success')
-    await fetchData()
+    refreshData()
   }
 
   // ── Edit window ───────────────────────────────────────────────────────────
@@ -529,7 +564,7 @@ export default function MaintenanceWindowsPage() {
     })
     setEditOpen(false)
     showSnackbar('Maintenance window updated', 'success')
-    await fetchData()
+    refreshData()
   }
 
   // ── Delete window ─────────────────────────────────────────────────────────
@@ -544,7 +579,7 @@ export default function MaintenanceWindowsPage() {
       await maintenanceWindowsApi.remove(deleteWindow.host_id, deleteWindow.id)
       setDeleteOpen(false)
       showSnackbar('Maintenance window deleted', 'success')
-      await fetchData()
+      refreshData()
     } catch {
       showSnackbar('Failed to delete maintenance window', 'error')
     }
@@ -561,7 +596,7 @@ export default function MaintenanceWindowsPage() {
         </Typography>
         <Button
           startIcon={<RefreshIcon />}
-          onClick={fetchData}
+          onClick={refreshData}
           disabled={loading}
         >
           Refresh