fix(cron): pass agentId to runHeartbeatOnce for main-session jobs (#14140)

* fix(cron): pass agentId to runHeartbeatOnce for main-session jobs

Main-session cron jobs with agentId always ran the heartbeat under
the default agent, ignoring the job's agent binding. enqueueSystemEvent
correctly routed the system event to the bound agent's session, but
runHeartbeatOnce was called without agentId, so the heartbeat ran under
the default agent and never picked up the event.

Thread agentId from job.agentId through the CronServiceDeps type,
timer execution, and the gateway wrapper so heartbeat-runner uses the
correct agent.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* cron: add heartbeat agentId propagation regression test (#14140) (thanks @ishikawa-pro)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/gateway/server-cron.ts

@@ -69,9 +69,11 @@ export function buildGatewayCronService(params: {
     requestHeartbeatNow,
     runHeartbeatOnce: async (opts) => {
       const runtimeConfig = loadConfig();
+      const agentId = opts?.agentId ? resolveCronAgent(opts.agentId).agentId : undefined;
       return await runHeartbeatOnce({
         cfg: runtimeConfig,
         reason: opts?.reason,
+        agentId,
         deps: { ...params.deps, runtime: defaultRuntime },
       });
     },