perf: hourly update check only with a browser open; opt-in retention, incremental auto-vacuum and Compact

- update-scheduler: default interval 1 h (DASHBOARD_UPDATE_CHECK_INTERVAL_MS and its 60 s floor kept);
  a scheduled tick with no /ws client is skipped, and the next browser to connect gets one catch-up
  check when the last one is stale (websocket.js onConnection). Manual check unchanged.
- db-retention.js: shared session purge (used by POST /api/settings/cleanup too), opt-in
  AGENTHUB_RETENTION_DAYS applied by the hourly maintenance in 25-session transactions with yields
  (max 5000/run), bounded incremental_vacuum when the freelist is large, and a manual Compact
  (VACUUM in a worker, converting to auto_vacuum=INCREMENTAL).
- db.js: new databases are INCREMENTAL; an existing one up to 32 MB is converted at startup.
- GET/PUT /api/settings/retention, POST /api/settings/compact (confirm: true); Settings → Data →
  Session cleanup gets the Automatic cleanup control and Compact now (en + vi).

server/openapi-extra/misc.js

@@ -11,6 +11,9 @@
  *   - GET    /api/settings/backup              (Settings)
  *   - PUT    /api/settings/backup              (Settings)
  *   - POST   /api/settings/backup/run          (Settings)
+ *   - GET    /api/settings/retention           (Settings)
+ *   - PUT    /api/settings/retention           (Settings)
+ *   - POST   /api/settings/compact             (Settings)
  *   - GET    /api/workflows/runs               (Workflows)
  *   - GET    /api/workflows/runs/{runId}       (Workflows)
  *   - GET    /api/remote-sources               (Remote Sources)
@@ -1225,6 +1228,117 @@ const paths = {
     },
   },
 
+  "/api/settings/retention": (() => {
+    const state = {
+      description: "Automatic retention setting, database space and the last Compact",
+      content: {
+        "application/json": {
+          schema: {
+            type: "object",
+            required: ["days", "max_days", "env_owned", "compacting"],
+            properties: {
+              days: {
+                type: "integer",
+                minimum: 0,
+                maximum: 3650,
+                description:
+                  "Finished sessions older than this many days are purged by the hourly maintenance; 0 = off (the default)",
+              },
+              max_days: { type: "integer" },
+              env_owned: { type: "object", properties: { days: { type: "boolean" } } },
+              last_run: {
+                type: "object",
+                nullable: true,
+                description:
+                  "This process's last hourly maintenance: {at, retention?: {purged_sessions, purged_events, purged_agents, error?}, reclaim: {reclaimed_pages, error?}, ms}",
+              },
+              space: {
+                type: "object",
+                nullable: true,
+                properties: {
+                  auto_vacuum: { type: "string", enum: ["none", "full", "incremental"] },
+                  page_size: { type: "integer" },
+                  page_count: { type: "integer" },
+                  freelist_pages: { type: "integer" },
+                  free_bytes: { type: "integer" },
+                },
+              },
+              db_size: { type: "integer", description: "Database file size in bytes" },
+              compacting: { type: "boolean" },
+              last_compact: {
+                type: "object",
+                nullable: true,
+                description:
+                  "This process's last Compact: {at, ok, size_before?, size_after?, ms?, error?}",
+              },
+            },
+          },
+        },
+      },
+    };
+    return {
+      get: {
+        tags: ["Settings"],
+        summary: "Automatic retention and database space",
+        operationId: "getRetention",
+        responses: { 200: state },
+      },
+      put: {
+        tags: ["Settings"],
+        summary: "Set the automatic retention",
+        description:
+          "Persisted to the settings file as AGENTHUB_RETENTION_DAYS. 0 turns it off. Same-origin only; in server mode an admin's.",
+        operationId: "setRetention",
+        requestBody: {
+          required: true,
+          content: {
+            "application/json": {
+              schema: {
+                type: "object",
+                required: ["days"],
+                properties: { days: { type: "integer", minimum: 0, maximum: 3650 } },
+              },
+            },
+          },
+        },
+        responses: {
+          200: { ...state, description: "The new state" },
+          400: { description: "INVALID_INPUT: days is not a whole number from 0 to 3650" },
+          403: { description: "EBADORIGIN: another site asked" },
+          409: { description: "EENVOWNED: the environment set AGENTHUB_RETENTION_DAYS" },
+          500: { description: "ESAVE: the settings file could not be written" },
+        },
+      },
+    };
+  })(),
+
+  "/api/settings/compact": {
+    post: {
+      tags: ["Settings"],
+      summary: "Compact the database now (full VACUUM)",
+      description:
+        "Rewrites the database in a worker thread, switching it to incremental auto_vacuum, then truncates the WAL. Hook writes wait while it runs. Answers at once; poll GET /api/settings/retention while `compacting`. Same-origin only; in server mode an admin's.",
+      operationId: "compactDatabase",
+      requestBody: {
+        required: true,
+        content: {
+          "application/json": {
+            schema: {
+              type: "object",
+              required: ["confirm"],
+              properties: { confirm: { type: "boolean", enum: [true] } },
+            },
+          },
+        },
+      },
+      responses: {
+        202: { description: "Started (or already running); the retention state" },
+        400: { description: "ECONFIRM: confirm: true is missing" },
+        403: { description: "EBADORIGIN: another site asked" },
+      },
+    },
+  },
+
   "/api/settings/codex-hooks": (() => {
     const status = {
       description: "Where AgentHub's Codex hooks stand",