Add comprehensive edge case tests for transport lifecycle

[groupsky]

Priority: MEDIUM

Description

PR #292 adds basic test for stop() during initialization, but several critical edge cases remain untested. These edge cases were identified during code review and represent real race conditions that could occur in production.

Missing Test Scenarios

High Priority

1. Multiple stop() calls during initialization - Verify idempotency
2. stop() racing with timeout - Verify timeout is cleared
3. stop() racing with error event - Verify no double-rejection
4. Concurrent start() during stop() - Verify no server orphaning

Medium Priority

5. 'initialized' event firing after stop() - Verify handler doesn't set started=true
6. Error event firing after stop() clears listeners - Verify defensive handling
7. Rapid start/stop/start cycles - Stress test for state consistency

Example Test Structure

describe('edge cases', () => {
  it('should handle multiple stop() calls during initialization', async () => {
    const startPromise = transport.start()
    await Promise.all([
      transport.stop(),
      transport.stop(),
      transport.stop()
    ])
    await expect(startPromise).rejects.toThrow()
  })

  it('should clear timeout when stop() interrupts initialization', async () => {
    jest.useFakeTimers()
    const startPromise = transport.start()
    await transport.stop()
    jest.advanceTimersByTime(11000)
    // Verify no additional cleanup or errors occurred
  })
})

Benefits

• Catches regression bugs
• Documents expected behavior in edge cases
• Validates all code paths are reachable and correct
• Improves confidence in concurrent operation safety

Related

• PR fix(emulator): prevent race condition when stop() called during TCP initialization #292 (basic test)
• Issue bug: calling stop() during TCP transport initialization causes race condition #275 (original race condition)
• Issue feat(emulator): add concurrent operation protection to TCP transport #278 (concurrent operation protection)

[groupsky]

✅ VERIFIED FIXED: Both TCP transport (tcp.test.ts lines 89-159, 812-827) and RTU transport (rtu.test.ts lines 74-152, 708-724) have comprehensive lifecycle edge case tests covering: stop during initialization, repeated start/stop cycles, event listener leaks, stop when not initialized, and multiple stop calls.