[BUG] Persisted idle signal can starve the event loop before an immediate same-thread run

Describe the Bug

An idle agent signal sent with ifIdle: { behavior: 'persist' }, followed immediately by a new run on the same memory thread, can starve the Node.js event loop indefinitely.

The synthetic persisted-signal run resolves its completion promise before its timer-based active-run cleanup executes. waitForCrossAgentThreadRun can then repeatedly await that already-resolved promise, creating an unbounded microtask loop. Timers and HTTP requests stop progressing while one CPU core remains saturated.

Steps To Reproduce

1. Clone the reproduction branch:
   bash复制

   git clone --branch repro/persisted-signal-starvation https://github.com/juanmaagd/mastra.git
   cd mastra

2. Install dependencies with Node 22 and pnpm:
   bash复制

   pnpm install --frozen-lockfile

3. Run the bounded regression:
   bash复制

   pnpm --filter @mastra/core exec vitest run src/agent/__tests__/agent-signals.test.ts -t "allows a run immediately after persisting an idle signal"

4. Observe that the child process does not exit. The parent watchdog terminates it with SIGKILL after 5 seconds.

The fixture subscribes to a thread, persists an idle signal, waits for persistence, and immediately starts a competing run on the same resource/thread pair. It does not call any external model or service.

Link to Minimal Reproducible Example

https://github.com/juanmaagd/mastra/tree/repro/persisted-signal-starvation/reproductions/persisted-signal-starvation

Expected Behavior

The completed synthetic persisted-signal run should release the thread without starving the event loop. The immediate same-thread run should proceed, timers and HTTP requests should remain responsive, and the process should exit normally.

Environment Information

System:
  OS: macOS 26.6.2
  CPU: arm64 Apple M5 Pro
  Memory: 48 GB
  Shell: zsh 5.9
Binaries:
  Node: 22.23.0
  npm: 10.9.8
  pnpm: 11.22.0
npmPackages:
  @mastra/core: 1.66.0
  @mastra/factory: 0.14.0
  @mastra/memory: 1.29.0
  @mastra/libsql: 1.22.5
LLM Provider: None; deterministic local LanguageModelV2 test double
Browser: Not applicable

Verification

• I have searched the existing issues to make sure this is not a duplicate
• I have included sufficient information for the team to reproduce and understand the issue