test: handle Windows UDP fixture port reuse

[cppla]

Summary

• Follow up on the late review of test: cover native UDP continuity after closed destinations #26: classify reused UDP fixture ports through the existing platform-aware test helper instead of POSIX errno alone.
• Add a bounded Windows runner job that parses Go JSON test events and requires exactly five actual passes and zero skips for both the native UDP continuity regression and bind-error classifier. Preserve native test failures and reject malformed or missing events.
• No production/runtime, protocol or dependency changes.

Validation

• Local targeted race tests, five repetitions: passed.

• Windows amd64 test-binary cross-compilation: passed (not Windows runtime evidence).

• Formatting, diff checks and independent review: passed.

• Exact final head 55a52ae20a26a74e09ba20d96b34c56b3a034ee7: CI 35809975977 (all 11 jobs including container integration and OCI), CodeQL 35809975945 and Linux netem 35809975965 succeeded.

• Windows job 107019143907 successfully ran the JSON gate and explicitly verified five actual passes and zero skips for each top-level test. Review request addressed and resolved.

• Merged main 83c97e384cefe25520868ab6a049216f0a1a1f7f matches the tested tree. CI 35810196873 (all 11 jobs including Docker/OCI), CodeQL 35810196849 and Linux netem 35810196857 succeeded. Windows merge job 107019834706 again explicitly verified five passes and zero skips for both tests.

Evidence boundary

The regression checks default-socket continuity. It does not assert reception or recovery of a particular ICMP/socket error; the Windows job is a targeted runtime check, not the full Windows suite. No release/tag.

[Copilot]

Copilot review overview

🟡 Changes recommended

The Windows job can pass while the regression test skips; it must verify exactly five passes and zero skips.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1

Open (1)

• Ensure QUIC continuity job fails when all repeated tests are skipped · New

What changed in this PR

Test-only update making UDP fixture handling Windows-aware and adding repeated Windows regression coverage.

Changes:

• Uses platform-aware bind-error classification.
• Adds a five-run Windows UDP test job.
• The job must reject skipped tests and verify five actual passes.

File	Description
internal/​tunnel/​datagram_icmp_recovery_test.go	Classifies reused fixture ports across platforms.
.github/​workflows/​ci.yml	Adds targeted Windows UDP testing.

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