[fjtrujy]

Problem

The IOP-side TCP file-I/O client could retain a stale socket after driver teardown or malformed replies. Wrong reply types/lengths leave unread bytes on the stream; zero-progress and oversized write counts were not consistently rejected.

Fix

• Centralize descriptor detachment and disconnect for shutdown, reconnect and thread teardown; treat socket descriptor 0 as valid.
• Reject mismatched packet types and sizes and close desynchronized TCP streams rather than attempting to continue.
• Reject impossible read counts and zero/oversized successful write counts, while retaining valid short transfers and remote negative errors.
• Add portable plain-C regression checks for descriptor invalidation, header validation and read/write bounds.
• Keep the new CI job in its own workflow, independent of the exception-report fixes in ps2link: Fix IOP exception-report packet overflow #67. Either PR can merge first without conflicts.

Validation

• Native C unit tests: passed.
• PS2SDK IOP/EE default and LOADHIGH=1 ZEROCOPY=1 cross-builds: passed locally.
• GitHub builds and native-C checks run on each push and PR.
• git diff --check: passed.
• Real PS2 reconnect/transfer testing is still recommended before merging.

This PR does not require any changes from #67 and does not alter the existing release job. The new check is independent and can be made a required status check in branch protection.