overview: one endpoint, live projections and a response cache (m36)

PLAN.md

@@ -238,7 +238,7 @@ src/
   web/
     server.zig  router.zig  auth.zig  sse.zig  static.zig  metrics.zig  openapi.zig
     handlers/
-      auth.zig  stats.zig  queries.zig  clients.zig  groups.zig  blocklists.zig
+      auth.zig  overview.zig  queries.zig  clients.zig  groups.zig  blocklists.zig
       rules.zig  local.zig  lookup.zig  pause.zig  settings.zig
       upstream_health.zig  certs.zig  health.zig  version.zig
 
@@ -484,6 +484,8 @@ CREATE INDEX idx_query_log_client ON query_log(client_ip);
 CREATE INDEX idx_query_log_domain ON query_log(domain_id);
 ```
 
+The sketch above is the original shape; `src/storage/querylog_schema.zig` is the authority, and the provenance columns milestone 28 added are not repeated here. Beside the raw rows the file carries four projection tables — `bucket_totals`, `bucket_clients`, `bucket_types`, `bucket_routes` — on a 30-minute grain, which is what `GET /api/overview` reads for the 24h, 7d and 30d windows instead of scanning every row. They are maintained by the batch writer and by retention inside the same transaction as the raw rows, so SQLite's transaction is the whole coherence story: no second file, no backfill, no rebuild command. The 1h window is narrower than the grain and takes one raw scan.
+
 ### 11.4 Query Logger
 
 - In-memory buffer, mutex guarded, hard cap `query_log_buffer_max` (default 10000).
@@ -493,7 +495,7 @@ CREATE INDEX idx_query_log_domain ON query_log(domain_id);
 
 ### 11.5 Retention
 
-Periodic delete of rows older than `retention_days`; scheduled checkpoint/VACUUM on `querylog.db` only.
+Periodic delete of rows older than `retention_days`, dropping the projection buckets behind the cutoff and recomputing the straddling one in the same transaction; scheduled checkpoint/VACUUM on `querylog.db` only.
 
 ### 11.6 Disk Discipline (cloudflared lesson)
 
@@ -536,7 +538,7 @@ Scalars in `settings(key, value)`; ordered/structured items in dedicated tables.
 ### 13.1 Endpoints
 
 - `POST /api/auth/login`, `POST /api/auth/logout`
-- `GET /api/stats?period=…`, `GET /api/stats/timeseries?period=…`, `GET /api/stats/types?period=…`, `GET /api/stats/routes?period=…`, `GET /api/stats/clients?period=…`
+- `GET /api/overview?period=…` — every Overview panel in one response over one read transaction
 - `GET /api/queries` (filter + paginate), `GET /api/queries/live` (SSE, per-IP cap)
 - `GET/PUT /api/clients/{id}`
 - `GET/POST/PUT/DELETE /api/groups…`, `/api/blocklists…`, `/api/rules…`, `/api/local-records…`, `/api/forward-zones…`
@@ -664,7 +666,7 @@ The project publishes released binaries and container images from its own Gitea
 6. Disk-fill degrades gracefully; no silent log-flood failure mode.
 7. Web UI + API provide full admin functionality; OpenAPI contract tests green.
 8. `nxdns export` round-trips via `nxdns import`.
-9. Query logging, stats, SSE live stream work; querylog.db corruption self-heals.
+9. Query logging, the overview, SSE live stream work; querylog.db corruption self-heals.
 10. Local DoH + DoT endpoints serve LAN clients.
 11. Schema upgrade = install + restart (migration test proves it).
 12. All suites green in Gitea CI for both targets.