feat(maintenance): add dashboard preview and expandable event list

- Add POST /api/maintenance/preview-dboards endpoint for table-to-dashboard preview
- Extend GET /api/maintenance/events with per-event dashboard list (id+title)
- Add 'Show affected dashboards' button to StartMaintenanceForm
- Add expandable row to MaintenanceEventsTable (click count to see names)
- Resolve dashboard titles via SupersetClient.get_dashboards() lookup map
- Add i18n keys for preview feature (en/ru)

backend/src/api/routes/maintenance/_routes.py

@@ -40,6 +40,9 @@ from ._router import router
 from ._schemas import (
     MaintenanceAlreadyActiveResponse,
     MaintenanceDashboardBannerState,
+    MaintenanceDashboardInfo,
+    MaintenanceDashboardPreviewRequest,
+    MaintenanceDashboardPreviewResponse,
     MaintenanceEndResponse,
     MaintenanceEventItem,
     MaintenanceEventListResponse,
@@ -119,7 +122,7 @@ async def list_dashboard_banners(
 
 # #region list_events [C:2] [TYPE Function]
 # @ingroup Api
-# @BRIEF Get active and completed maintenance event lists with affected dashboard counts.
+# @BRIEF Get active and completed maintenance event lists with affected dashboard counts and names.
 # @RELATION DEPENDS_ON -> [EXT:code:has_permission_maintenance_READ]
 @router.get("/events", response_model=MaintenanceEventListResponse)
 async def list_events(
@@ -189,8 +192,39 @@ async def list_events(
             .all()
         )
 
+        # ── Build dashboard title lookup from Superset ──
+        dashboard_title_map: dict[int, str] = {}
+        try:
+            from ....dependencies import get_config_manager as _gcm
+            config_manager = _gcm()
+            # Collect unique environment IDs from all events
+            env_ids = {e.environment_id for e in active_events + completed_events if e.environment_id}
+            for env_id in env_ids:
+                env = next((e for e in config_manager.get_environments() if e.id == env_id), None)
+                if env:
+                    try:
+                        from ....core.superset_client import SupersetClient
+                        client = SupersetClient(env)
+                        _, dashboards = await client.get_dashboards()
+                        for d in dashboards:
+                            did = d.get("id")
+                            title = d.get("dashboard_title") or d.get("title") or str(did)
+                            if did is not None:
+                                dashboard_title_map[int(did)] = title
+                    except Exception as e:
+                        app_logger.explore(
+                            "Failed to fetch dashboards for title lookup",
+                            extra={"env_id": env_id},
+                            error=str(e),
+                        )
+        except Exception as e:
+            app_logger.explore(
+                "Failed to build dashboard title map",
+                error=str(e),
+            )
+
         def _to_item(event: MaintenanceEvent) -> MaintenanceEventItem:
-            affected_count = (
+            states = (
                 db.query(MaintenanceDashboardState)
                 .filter(
                     MaintenanceDashboardState.event_id == event.id,
@@ -199,8 +233,16 @@ async def list_events(
                         MaintenanceDashboardStateStatus.PENDING_APPLY,
                     ]),
                 )
-                .count()
+                .all()
             )
+            affected_count = len(states)
+            dashboards = [
+                MaintenanceDashboardInfo(
+                    id=state.dashboard_id,
+                    title=dashboard_title_map.get(state.dashboard_id, str(state.dashboard_id)),
+                )
+                for state in states
+            ]
             return MaintenanceEventItem(
                 id=event.id,
                 tables=list(event.tables) if event.tables else [],
@@ -209,6 +251,7 @@ async def list_events(
                 message=event.message or None,
                 status=event.status.value,
                 affected_count=affected_count,
+                dashboards=dashboards,
                 created_at=event.created_at.isoformat() if event.created_at else "",
             )
 
@@ -219,6 +262,88 @@ async def list_events(
 # #endregion list_events
 
 
+# ── POST /api/maintenance/preview-dashboards ────────────────
+# FR-015: operator, admin (NOT viewer)
+
+# #region preview_dashboards [C:3] [TYPE Function]
+# @ingroup Api
+# @BRIEF Preview which dashboards would be affected by a maintenance event for given tables.
+#   Calls find_affected_dashboards then resolves titles from Superset.
+# @RELATION DEPENDS_ON -> [EXT:code:has_permission_maintenance_READ]
+# @RELATION DEPENDS_ON -> [find_affected_dashboards]
+@router.post("/preview-dashboards", response_model=MaintenanceDashboardPreviewResponse)
+async def preview_dashboards(
+    request: MaintenanceDashboardPreviewRequest,
+    db: Session = Depends(get_db),
+    _=Depends(has_permission("maintenance", "READ")),
+):
+    with belief_scope("preview_dashboards"):
+        # Resolve environment
+        from ....dependencies import get_config_manager as _gcm
+        config_manager = _gcm()
+        env = next(
+            (e for e in config_manager.get_environments() if e.id == request.environment_id),
+            None,
+        )
+        if not env:
+            raise HTTPException(status_code=404, detail=f"Environment {request.environment_id} not found")
+
+        from ....core.superset_client import SupersetClient
+        from ....services.maintenance._dashboard_scanner import find_affected_dashboards
+
+        client = SupersetClient(env)
+
+        # Load settings for scope/excluded/forced filtering
+        settings = db.query(MaintenanceSettings).filter(
+            MaintenanceSettings.id == "default"
+        ).first()
+
+        # Find affected dashboard IDs
+        try:
+            dashboard_ids = await find_affected_dashboards(
+                request.tables,
+                client,
+                settings,
+            )
+        except Exception as e:
+            app_logger.explore(
+                "Preview failed",
+                extra={"tables": request.tables},
+                error=str(e),
+            )
+            raise HTTPException(status_code=502, detail=f"Failed to query Superset: {e}")
+
+        # Build title lookup
+        title_map: dict[int, str] = {}
+        try:
+            _, all_dashboards = await client.get_dashboards()
+            for d in all_dashboards:
+                did = d.get("id")
+                title = d.get("dashboard_title") or d.get("title") or str(did)
+                if did is not None:
+                    title_map[int(did)] = title
+        except Exception as e:
+            app_logger.explore(
+                "Failed to fetch dashboards for title resolution",
+                error=str(e),
+            )
+
+        result = [
+            MaintenanceDashboardInfo(
+                id=did,
+                title=title_map.get(did, str(did)),
+            )
+            for did in dashboard_ids
+        ]
+
+        app_logger.reflect(
+            "Preview completed",
+            extra={"tables": request.tables, "count": len(result)},
+        )
+        return MaintenanceDashboardPreviewResponse(dashboards=result)
+# #endregion preview_dashboards
+
+
 # ── POST /api/maintenance/start ──────────────────────────────
 # FR-001: Always returns 202 {task_id} after validation
 # FR-015: operator, admin (NOT viewer)

backend/src/api/routes/maintenance/_schemas.py

@@ -22,6 +22,14 @@ class MaintenanceStartRequest(BaseModel):
 # #endregion MaintenanceStartRequest
 
 
+# #region MaintenanceDashboardPreviewRequest [C:1] [TYPE Class]
+# @BRIEF POST /api/maintenance/preview-dashboards request body.
+class MaintenanceDashboardPreviewRequest(BaseModel):
+    tables: list[str] = Field(..., min_length=1, max_length=100)
+    environment_id: str = Field(..., description="Target environment for the preview")
+# #endregion MaintenanceDashboardPreviewRequest
+
+
 # #region MaintenanceSettingsUpdate [C:1] [TYPE Class]
 # @BRIEF PUT /api/maintenance/settings request body — all fields optional for partial update.
 class MaintenanceSettingsUpdate(BaseModel):
@@ -114,6 +122,14 @@ class MaintenanceSettingsResponse(BaseModel):
 # #endregion MaintenanceSettingsResponse
 
 
+# #region MaintenanceDashboardInfo [C:1] [TYPE Class]
+# @BRIEF Dashboard ID + title pair for event detail and preview responses.
+class MaintenanceDashboardInfo(BaseModel):
+    id: int
+    title: str
+# #endregion MaintenanceDashboardInfo
+
+
 # #region MaintenanceEventItem [C:1] [TYPE Class]
 # @BRIEF Single maintenance event summary for GET /api/maintenance/events.
 class MaintenanceEventItem(BaseModel):
@@ -124,6 +140,7 @@ class MaintenanceEventItem(BaseModel):
     message: str | None = None
     status: str
     affected_count: int
+    dashboards: list[MaintenanceDashboardInfo] = []
     created_at: str
 # #endregion MaintenanceEventItem
 
@@ -154,4 +171,11 @@ class MaintenanceAlreadyActiveResponse(BaseModel):
     status: str = "already_active"
 # #endregion MaintenanceAlreadyActiveResponse
 
+
+# #region MaintenanceDashboardPreviewResponse [C:1] [TYPE Class]
+# @BRIEF Response for POST /api/maintenance/preview-dashboards.
+class MaintenanceDashboardPreviewResponse(BaseModel):
+    dashboards: list[MaintenanceDashboardInfo]
+# #endregion MaintenanceDashboardPreviewResponse
+
 # #endregion MaintenanceSchemasModule

frontend/src/lib/api/maintenance.ts

@@ -80,4 +80,14 @@ export async function listDashboardBanners<T = unknown>(): Promise<T> {
 	return requestApi<T>(`${BASE}/dashboard-banners`, 'GET');
 }
 // #endregion listDashboardBanners
+
+// #region previewDashboards [C:2] [TYPE Function] [SEMANTICS maintenance, preview, dashboards]
+// @BRIEF Preview which dashboards would be affected by maintenance for given tables.
+// @PRE params contains { tables: string[], environment_id: string }.
+// @POST Returns { dashboards: [{ id, title }] }.
+// @RELATION DEPENDS_ON -> [requestApi]
+export async function previewDashboards<T = unknown>(params: Record<string, unknown>): Promise<T> {
+	return requestApi<T>(`${BASE}/preview-dashboards`, 'POST', params);
+}
+// #endregion previewDashboards
 // #endregion MaintenanceApi

frontend/src/lib/components/MaintenanceEventsTable.svelte

@@ -1,6 +1,6 @@
-<!-- #region MaintenanceEventsTable [C:3] [TYPE Component] [SEMANTICS maintenance, table, events, active, completed, remove] -->
+<!-- #region MaintenanceEventsTable [C:3] [TYPE Component] [SEMANTICS maintenance, table, events, active, completed, remove, expandable] -->
 <!-- @ingroup Components -->
-<!-- @BRIEF Active/completed maintenance events table with removal actions. Uses inline table, skeleton rows, empty state, and status badges. -->
+<!-- @BRIEF Active/completed maintenance events table with removal actions and expandable dashboard list per event. -->
 <!-- @LAYER Component -->
 <!-- @RELATION DEPENDS_ON -> [MaintenanceStore] -->
 <!-- @RELATION DEPENDS_ON -> [MaintenanceApi] -->
@@ -10,9 +10,10 @@
 <!-- @UX_STATE empty -> No active events: dashed border placeholder. -->
 <!-- @UX_STATE loading -> Skeleton rows displayed. -->
 <!-- @UX_STATE error -> Toast shown on removal failure. -->
+<!-- @UX_STATE expanded -> Dashboard list visible in sub-row for clicked event. -->
 <!-- @UX_FEEDBACK Toast success/error on removal. -->
 <!-- @UX_RECOVERY Retry via individual or bulk remove. -->
-<!-- @UX_REACTIVITY Props -> $props(), LocalState -> $state(removingEventId, isRemovingAll) -->
+<!-- @UX_REACTIVITY Props -> $props(), LocalState -> $state(removingEventId, isRemovingAll, expandedEventIds) -->
 <script lang="ts">
   import { maintenanceStore } from "$lib/stores/maintenance.svelte.js";
   import Button from "$lib/ui/Button.svelte";
@@ -25,6 +26,19 @@
   let showRemoveAllConfirm = $state(false);
   let removeTarget = $state(null);
 
+  // ── Expandable rows ─────────────────────────────────────────
+  let expandedEventIds = $state<Set<string>>(new Set());
+
+  function toggleExpanded(eventId: string) {
+    const next = new Set(expandedEventIds);
+    if (next.has(eventId)) {
+      next.delete(eventId);
+    } else {
+      next.add(eventId);
+    }
+    expandedEventIds = next;
+  }
+
   let isLoading = $derived(maintenanceStore.isLoading);
   let activeEvents = $derived(maintenanceStore.activeEvents);
   let completedEvents = $derived(maintenanceStore.completedEvents);
@@ -207,8 +221,24 @@
                 <td class="px-4 py-3 text-sm text-text-muted max-w-[200px] truncate" title={(event.tables || []).join(", ")}>
                   {(event.tables || []).join(", ") || "-"}
                 </td>
-                <td class="px-4 py-3 text-sm text-text">
+                <td class="px-4 py-3 text-sm">
-                  {event.affected_count ?? "-"}
+                  {#if event.dashboards && event.dashboards.length > 0}
+                    <button
+                      type="button"
+                      onclick={() => toggleExpanded(event.id)}
+                      class="inline-flex items-center gap-1 text-text hover:text-primary transition-colors cursor-pointer"
+                    >
+                      <svg
+                        class="w-3.5 h-3.5 transition-transform {expandedEventIds.has(event.id) ? 'rotate-90' : ''}"
+                        fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="2"
+                      >
+                        <path stroke-linecap="round" stroke-linejoin="round" d="M9 5l7 7-7 7" />
+                      </svg>
+                      <span class="font-medium">{event.affected_count ?? "-"}</span>
+                    </button>
+                  {:else}
+                    <span class="text-text">{event.affected_count ?? "-"}</span>
+                  {/if}
                 </td>
                 <td class="px-4 py-3 text-sm text-text-muted">
                   {formatTime(event.start_time)}
@@ -233,6 +263,26 @@
                   </Button>
                 </td>
               </tr>
+              {#if expandedEventIds.has(event.id) && event.dashboards && event.dashboards.length > 0}
+                <tr>
+                  <td colspan="7" class="px-4 py-2 bg-surface-muted">
+                    <div class="pl-6">
+                      <p class="text-xs font-medium text-text-muted mb-1">
+                        {$t.maintenance?.affected_dashboards_list || "Affected dashboards"}:
+                      </p>
+                      <ul class="space-y-0.5">
+                        {#each event.dashboards as dash (dash.id)}
+                          <li class="text-xs text-text flex items-center gap-1.5">
+                            <span class="inline-block w-1.5 h-1.5 rounded-full bg-warning-DEFAULT flex-shrink-0"></span>
+                            <span class="truncate">{dash.title}</span>
+                            <span class="text-text-subtle flex-shrink-0">#{dash.id}</span>
+                          </li>
+                        {/each}
+                      </ul>
+                    </div>
+                  </td>
+                </tr>
+              {/if}
             {/each}
           </tbody>
         </table>

frontend/src/lib/components/StartMaintenanceForm.svelte

@@ -1,6 +1,6 @@
-<!-- #region StartMaintenanceForm [C:3] [TYPE Component] [SEMANTICS maintenance, start, form, template, presets] -->
+<!-- #region StartMaintenanceForm [C:3] [TYPE Component] [SEMANTICS maintenance, start, form, template, presets, preview] -->
 <!-- @ingroup Components -->
-<!-- @BRIEF Start maintenance form with template presets, table name input, and datetime pickers. -->
+<!-- @BRIEF Start maintenance form with template presets, table name input, datetime pickers, and dashboard preview. -->
 <!-- @LAYER Component -->
 <!-- @RELATION DEPENDS_ON -> [MaintenanceApi] -->
 <!-- @RELATION DEPENDS_ON -> [EXT:frontend:addToast] -->
@@ -8,11 +8,14 @@
 <!-- @UX_STATE submitting -> Submit button shows spinner, fields disabled. -->
 <!-- @UX_STATE success -> Toast shown, form resets. -->
 <!-- @UX_STATE error -> Error toast with message. -->
+<!-- @UX_STATE preview_loading -> Preview button shows spinner, results hidden. -->
+<!-- @UX_STATE preview_loaded -> Dashboard list shown below table input. -->
+<!-- @UX_STATE preview_empty -> "No dashboards found" message shown. -->
 <!-- @UX_FEEDBACK Toast on start/success/error. -->
 <!-- @UX_RECOVERY Retry via re-submit. -->
 <script lang="ts">
 import { SvelteDate } from "svelte/reactivity";
-  import { startMaintenance } from "$lib/api/maintenance.js";
+  import { startMaintenance, previewDashboards } from "$lib/api/maintenance.js";
   import { addToast } from "$lib/toasts.svelte.js";
   import { t } from "$lib/i18n/index.svelte.js";
   import HelpTooltip from "$lib/ui/HelpTooltip.svelte";
@@ -69,6 +72,12 @@ import { SvelteDate } from "svelte/reactivity";
   // Validation
   let tableError = $state("");
 
+  // ── Preview state ──────────────────────────────────────────
+  let previewLoading = $state(false);
+  let previewDashboardsList = $state<Array<{ id: number; title: string }>>([]);
+  let previewError = $state("");
+  let previewShown = $state(false);
+
   // Initialize startTime to current datetime-local
   function initStartTime() {
     const now = new SvelteDate();
@@ -94,6 +103,39 @@ import { SvelteDate } from "svelte/reactivity";
     }
   }
 
+  // ── Preview dashboards ────────────────────────────────────
+  async function handlePreview() {
+    const trimmedTable = tableName.trim();
+    if (!trimmedTable) {
+      tableError = $t.maintenance?.table_required || "Table name is required";
+      return;
+    }
+    tableError = "";
+
+    const envId = environmentContextStore.value?.selectedEnvId;
+    if (!envId) {
+      addToast($t.maintenance?.no_environment || "No environment selected.", "error");
+      return;
+    }
+
+    previewLoading = true;
+    previewError = "";
+    previewShown = true;
+    previewDashboardsList = [];
+
+    try {
+      const result = await previewDashboards({
+        tables: [trimmedTable],
+        environment_id: envId,
+      });
+      previewDashboardsList = result?.dashboards || [];
+    } catch (e) {
+      previewError = e?.message || $t.maintenance?.preview_error || "Failed to preview dashboards";
+    } finally {
+      previewLoading = false;
+    }
+  }
+
   // ── Submit ─────────────────────────────────────────────────
   async function handleSubmit() {
     // Validate
@@ -137,6 +179,9 @@ import { SvelteDate } from "svelte/reactivity";
       endTime = "";
       message = "";
       selectedTemplate = "custom";
+      previewShown = false;
+      previewDashboardsList = [];
+      previewError = "";
       initStartTime();
       onSuccess();
     } catch (e) {
@@ -209,6 +254,65 @@ import { SvelteDate } from "svelte/reactivity";
       {#if tableError}
         <p class="mt-1 text-xs text-destructive">{tableError}</p>
       {/if}
+
+      <!-- Preview Button -->
+      <div class="mt-2">
+        <button
+          type="button"
+          onclick={handlePreview}
+          disabled={previewLoading || !tableName.trim()}
+          class="inline-flex items-center gap-1.5 rounded-md border border-border-strong bg-surface-card px-3 py-1.5 text-xs font-medium text-text
+            transition-colors hover:bg-surface-muted disabled:opacity-50 disabled:cursor-not-allowed"
+        >
+          {#if previewLoading}
+            <svg class="w-3.5 h-3.5 animate-spin" fill="none" viewBox="0 0 24 24">
+              <circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4" />
+              <path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4z" />
+            </svg>
+            {$t.maintenance?.loading_dashboards || "Loading..."}
+          {:else}
+            <svg class="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="2">
+              <path stroke-linecap="round" stroke-linejoin="round" d="M15 12a3 3 0 11-6 0 3 3 0 016 0z" />
+              <path stroke-linecap="round" stroke-linejoin="round" d="M2.458 12C3.732 7.943 7.523 5 12 5c4.478 0 8.268 2.943 9.542 7-1.274 4.057-5.064 7-9.542 7-4.477 0-8.268-2.943-9.542-7z" />
+            </svg>
+            {$t.maintenance?.show_dashboards || "Show affected dashboards"}
+          {/if}
+        </button>
+      </div>
+
+      <!-- Preview Results -->
+      {#if previewShown}
+        <div class="mt-2 rounded-md border border-border bg-surface-muted px-3 py-2">
+          {#if previewLoading}
+            <div class="flex items-center gap-2 text-xs text-text-muted">
+              <svg class="w-3.5 h-3.5 animate-spin" fill="none" viewBox="0 0 24 24">
+                <circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4" />
+                <path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4z" />
+              </svg>
+              {$t.maintenance?.loading_dashboards || "Loading dashboards..."}
+            </div>
+          {:else if previewError}
+            <p class="text-xs text-destructive">{previewError}</p>
+          {:else if previewDashboardsList.length === 0}
+            <p class="text-xs text-text-muted">
+              {$t.maintenance?.no_dashboards_found || "No dashboards found for this table."}
+            </p>
+          {:else}
+            <p class="text-xs font-medium text-text mb-1.5">
+              {$t.maintenance?.affected_dashboards_list || "Affected dashboards"} ({previewDashboardsList.length}):
+            </p>
+            <ul class="space-y-0.5">
+              {#each previewDashboardsList as dash (dash.id)}
+                <li class="text-xs text-text-muted flex items-center gap-1.5">
+                  <span class="inline-block w-1.5 h-1.5 rounded-full bg-warning-DEFAULT flex-shrink-0"></span>
+                  <span class="truncate">{dash.title}</span>
+                  <span class="text-text-subtle flex-shrink-0">#{dash.id}</span>
+                </li>
+              {/each}
+            </ul>
+          {/if}
+        </div>
+      {/if}
     </div>
 
     <!-- Start / End Time -->

frontend/src/lib/i18n/locales/en/maintenance.json

@@ -86,5 +86,11 @@
   "banner_dark": "Dark theme",
   "banner_dark_desc": "Red/dark banner for urgent alerts",
   "banner_time_only": "Time only",
-  "banner_time_only_desc": "Just start and end time"
+  "banner_time_only_desc": "Just start and end time",
+
+  "show_dashboards": "Show affected dashboards",
+  "loading_dashboards": "Loading dashboards...",
+  "no_dashboards_found": "No dashboards found for this table.",
+  "affected_dashboards_list": "Affected dashboards",
+  "preview_error": "Failed to preview dashboards"
 }

frontend/src/lib/i18n/locales/ru/maintenance.json

@@ -86,5 +86,11 @@
   "banner_dark": "Тёмная тема",
   "banner_dark_desc": "Красный баннер для срочных уведомлений",
   "banner_time_only": "Только время",
-  "banner_time_only_desc": "Только время начала и окончания"
+  "banner_time_only_desc": "Только время начала и окончания",
+
+  "show_dashboards": "Показать затронутые дашборды",
+  "loading_dashboards": "Загрузка дашбордов...",
+  "no_dashboards_found": "Дашборды для этой таблицы не найдены.",
+  "affected_dashboards_list": "Затронутые дашборды",
+  "preview_error": "Не удалось загрузить предпросмотр дашбордов"
 }