Add: Skill lifecycle events for MCP startup debugging

[FL4TLiN3]

Summary

• Add skillStarting event emitted when MCP skill initialization begins
• Add skillStderr event to capture child process stderr output
• Add connectDurationMs and totalDurationMs fields to skillConnected event

Background

initializeRuntime to skillConnected takes approximately 7 seconds. These structured events help identify the bottleneck (binary startup time vs MCP handshake time).

New Events

skillStarting

{
  skillName: string
  command: string
  args: string[]
}

skillStderr

{
  skillName: string
  message: string
}

skillConnected (updated)

{
  skillName: string
  serverInfo?: { name: string; version: string }
  connectDurationMs?: number  // NEW
  totalDurationMs?: number    // NEW
}

Test plan

• TypeScript compiles without errors
• All unit tests pass
• Biome lint passes

Closes #49

---

Note

Introduce skillStarting and skillStderr events and add connection timing fields to skillConnected, wiring them into MCP stdio initialization.

• Runtime observability:
  • packages/core/src/schemas/runtime.ts:
    • Add skillStarting and skillStderr runtime events.
    • Extend skillConnected with connectDurationMs and totalDurationMs.
  • packages/runtime/src/skill-manager/mcp.ts:
    • Emit skillStarting before launching MCP stdio skill (with command and args).
    • Pipe stderr to skillStderr events.
    • Emit skillConnected including connection timing metrics.
• Changeset: Patch releases for @perstack/core and @perstack/runtime.

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
perstack	Ignored	Preview		Dec 4, 2025 10:59pm

[cursor]

Bug: Stderr listener attached before process spawn fails silently

The transport.stderr listener is attached before calling connect(), but StdioClientTransport.stderr only becomes available after the child process is spawned during the start() method (called internally by connect()). At this point, transport.stderr is undefined, so the if (transport.stderr) check fails silently and the listener is never attached. The skillStderr events will never be emitted. The listener needs to be attached after connect() returns, though this may miss early stderr output.

 

[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
packages/runtime/src/skill-manager/mcp.ts	0.00%	6 Missing ⚠️

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