Document explicit upstream proxy port fix in runner-doctor B2 catalog

[Copilot]

The self-hosted runner doctor knowledge base's B2 entry (mandatory corporate proxy) only covered the PROXY_ENV_VARS allowlist fix from #6267. It did not capture the explicit-port parsing bug (#8877) fixed in #8887, where a corporate proxy genuinely listening on port 80 was silently rewritten to Squid's 3128 default, breaking all cache_peer chaining.

Changes

• .github/workflows/shared/self-hosted-failure-modes.md — extended the B2 row across three columns:
  • Fix / flag: parseProxyUrl() (src/upstream-proxy.ts) lost explicitly-supplied default ports because URL normalization strips :80. The fix reads the raw authority port via getExplicitProxyPort() before normalization, keeps the 3128 fallback only when no port was supplied, and rejects explicitly-empty ports. Applies to both host https_proxy/http_proxy auto-detection and --upstream-proxy.
  • Probe: set https_proxy=http://proxy.corp.example.com:80 and check the generated squid.conf — a cache_peer port of 3128 instead of 80 confirms the unpatched bug.
  • Citations: appended #8877, #8887.
• .github/agents/self-hosted-runner-doctor.md — mirrored the identical row edit in the embedded catalog table.
• scripts/ci/self-hosted-runner-doctor-workflow.test.ts — assertions pinning the new B2 text and citation suffix in both catalog copies, consistent with the existing alignment checks.

No playbook paragraph or error-string lookup entry exists for B2 in either file, so the catalog row is the sole entry point. self-hosted-runner-doctor.md transcludes the shared file via {{#runtime-import}}, so no lock recompile is needed.

Behavior being documented

https_proxy=http://proxy.corp.example.com:80

# before #8887
cache_peer proxy.corp.example.com parent 3128 0 no-query ...

# after #8887
cache_peer proxy.corp.example.com parent 80 0 no-query ...

Documentation and test-only; no production code is modified.

• Fixes 🩺 Runner Doctor UpdateUpdate B2 (corporate proxy) with the explicit-port proxy-parsing fix (#8877, #8887) #8921

[Copilot]

Copilot review overview

🟢 Approval recommended

The documentation accurately reflects the implemented proxy-port behavior and remains synchronized with focused regression coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Documents the upstream proxy explicit-port fix in the runner-doctor B2 catalog and keeps both catalog copies aligned.

Changes:

• Adds B2 diagnosis, remediation, probe, and citations for #8877/#8887.
• Adds regression assertions for both catalog copies.

File	Description
.github/​workflows/​shared/​self-hosted-failure-modes.md	Expands the canonical B2 entry.
.github/​agents/​self-hosted-runner-doctor.md	Mirrors the updated B2 guidance.
scripts/​ci/​self-hosted-runner-doctor-workflow.test.ts	Verifies the new guidance and citations.

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[github-actions]

✅ Copilot review passed with no inline comments.

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