SCTP teardown

[shinyoshiaki]

This pull request focuses on making the SCTP teardown process robust, ensuring that after stopping, no asynchronous handles (timers, immediates) are left open and no timer rescheduling occurs. The changes introduce explicit stopping flags, guard all timer and input paths, and add regression tests to verify handle cleanup and prevent timer leaks. The implementation is careful to maintain backward compatibility and minimal impact on other components.

SCTP teardown and timer management improvements:

• Added isStopping and isClosed flags to the SCTP class, and a unified isStopped getter to track and gate all teardown-related logic. All timer callbacks and rescheduling logic now check these flags to prevent timer regeneration after stopping. (packages/sctp/src/sctp.ts) [1] [2]
• Updated all timer expiration, scheduling, and transmission methods (timer1Expired, timer2Expired, timer3Expired, timerReconfigHandleExpired, transmit, sendSack, scheduleSack, handleData, etc.) to return early if isStopped is true, ensuring no new timers or async operations are scheduled post-stop. (packages/sctp/src/sctp.ts) [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
• Modified stop() to clear all pending timer/immediate handles, set transport.onData = undefined, and ensure idempotence and no implicit transport closing, maintaining backward compatibility. (packages/sctp/src/sctp.ts) [1] [2]

Testing and regression checks:

• Added a comprehensive regression test to api.test.ts verifying that after sending many messages and stopping, no timers are rescheduled, all handles are cleared, and transport.onData is undefined. (packages/sctp/tests/api.test.ts)
• Introduced a new test script (open-handles-check.ts) and npm script (test:open-handles) for automated open handle detection after SCTP teardown, ensuring no timer leaks in real scenarios. (packages/sctp/tests/open-handles-check.ts, packages/sctp/package.json) [1] [2]

Documentation and planning:

• Added a detailed task ticket outlining the motivation, technical approach, constraints, and completion criteria for robust SCTP teardown and open handle detection. (TICKET-ticket-d57c0b1a-bdea-41a4-8c0e-bc21983606bf.md)