feat(cleanup): hide and prune stale mailboxes

Mailbox listings grew unbounded as old sessions ended without
unregistering. This adds two layers of cleanup, configurable via
mailbox.json or `serve` flags:

- Lazy filter: list responses (REST /v1/list, MCP list_mailboxes)
  drop mailboxes idle longer than hideAfterMinutes (default 24h),
  while always keeping the caller and any sender with messages
  pending for them.
- Background sweep: startServer runs an initial prune on boot and
  schedules an unref'd interval timer that hard-deletes mailboxes
  idle longer than deleteAfterMinutes (default 7d) which have no
  pending messages, and wipes their delivered history.

node/src/server.ts

@@ -93,11 +93,13 @@ export async function buildServer(cfg: DaemonConfig, store: MailboxStore): Promi
 
   app.get("/v1/list", async (req) => {
     const name = req.mailboxName;
-    return store.listMailboxes(name).map((m) => ({
-      name: m.name,
-      lastSeenAt: m.lastSeenAt.toISOString(),
-      pendingForYou: m.pendingForYou,
-    }));
+    return store
+      .listMailboxes(name, { hideAfterMinutes: cfg.hideAfterMinutes })
+      .map((m) => ({
+        name: m.name,
+        lastSeenAt: m.lastSeenAt.toISOString(),
+        pendingForYou: m.pendingForYou,
+      }));
   });
 
   app.post<{ Body: { to?: string } }>("/v1/rename", async (req, reply) => {
@@ -119,14 +121,45 @@ export async function buildServer(cfg: DaemonConfig, store: MailboxStore): Promi
     }
   });
 
-  await registerMcp(app, store);
+  await registerMcp(app, store, cfg.hideAfterMinutes);
 
   return app;
 }
 
-export async function startServer(cfg: DaemonConfig): Promise<{ app: FastifyInstance; store: MailboxStore }> {
+function startSweep(
+  store: MailboxStore,
+  cfg: DaemonConfig,
+  log: FastifyInstance["log"],
+): NodeJS.Timeout | null {
+  if (cfg.sweepIntervalMinutes <= 0 || cfg.deleteAfterMinutes <= 0) return null;
+  const runOnce = (): void => {
+    try {
+      const r = store.pruneStale(cfg.deleteAfterMinutes);
+      if (r.deletedMailboxes > 0 || r.deletedMessages > 0) {
+        log.info(
+          r,
+          `Pruned ${r.deletedMailboxes} stale mailbox(es) and ${r.deletedMessages} delivered message(s)`,
+        );
+      }
+    } catch (err) {
+      log.error({ err }, "Stale-mailbox sweep failed");
+    }
+  };
+  runOnce();
+  const timer = setInterval(runOnce, cfg.sweepIntervalMinutes * 60_000);
+  timer.unref?.();
+  return timer;
+}
+
+export async function startServer(
+  cfg: DaemonConfig,
+): Promise<{ app: FastifyInstance; store: MailboxStore; sweepTimer: NodeJS.Timeout | null }> {
   const store = new MailboxStore(cfg.dbPath);
   const app = await buildServer(cfg, store);
   await app.listen({ host: cfg.bind, port: cfg.port });
-  return { app, store };
+  const sweepTimer = startSweep(store, cfg, app.log);
+  app.addHook("onClose", async () => {
+    if (sweepTimer) clearInterval(sweepTimer);
+  });
+  return { app, store, sweepTimer };
 }