feat(server): add GET /v1/watch long-poll endpoint with abort + rename handling

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

node/src/server.ts

@@ -121,6 +121,53 @@ export async function buildServer(cfg: DaemonConfig, store: MailboxStore): Promi
     }
   });
 
+  const WATCH_DEFAULT_TIMEOUT_S = 25;
+  const WATCH_MAX_TIMEOUT_S = 300;
+
+  app.get<{ Querystring: { name?: string; timeout?: string } }>(
+    "/v1/watch",
+    async (req, reply) => {
+      const name = (req.query.name ?? "").trim();
+      if (!name) {
+        reply.code(400);
+        return { error: "name is required" };
+      }
+      if (name !== req.mailboxName) {
+        reply.code(403);
+        return { error: "X-Mailbox header must match name." };
+      }
+
+      const rawTimeout = req.query.timeout;
+      const timeoutS = rawTimeout != null ? parseInt(rawTimeout, 10) : WATCH_DEFAULT_TIMEOUT_S;
+      if (!Number.isFinite(timeoutS) || timeoutS <= 0 || timeoutS > WATCH_MAX_TIMEOUT_S) {
+        reply.code(400);
+        return { error: `timeout must be 1..${WATCH_MAX_TIMEOUT_S} seconds` };
+      }
+
+      const ac = new AbortController();
+      req.raw.on("close", () => ac.abort());
+
+      const result = await store.waitForMessage(name, timeoutS * 1000, ac.signal);
+
+      if (result.kind === "message") {
+        const msg = rowToMessage(result.message);
+        reply.code(200);
+        return { ...msg, sentAt: msg.sentAt.toISOString() };
+      }
+      if (result.kind === "renamed") {
+        reply.code(409);
+        return { reason: "renamed", to: result.to };
+      }
+      if (result.kind === "timeout") {
+        reply.code(204);
+        return reply.send();
+      }
+      // aborted — client gone, no response needed (Fastify will swallow).
+      reply.code(499);
+      return reply.send();
+    },
+  );
+
   await registerMcp(app, store, cfg.hideAfterMinutes);
 
   return app;