feat: add re-521 (Clang AVX10.1 -march=native) + fix re-018 (macOS 14 deprecation active)

[htekdev]

New Entries

re-521 — Clang -march=native "invalid feature combination: +avx10.1-256" on ubuntu-24.04 Runners

• File: errors/runner-environment/re-521.yml
• Category: runner-environment
• Severity: warning
• Source: runner-images #14296 (filed June 27, 2026 — confirmed by runner-images team, assigned for investigation)
• Root cause: Some ubuntu-24.04 runner VMs run on Azure hosts with AVX10.1-512 CPUs. When -march=native is passed to Clang 18, it detects AVX10.1-256 from CPUID but the host promotes this to AVX10.1-512, causing [-Winvalid-feature-combination]. With -Werror, this becomes a fatal build error. Intermittent (~1% of runs) because most VMs don't land on AVX10.1-capable hosts.
• Fix: Add -Wno-invalid-feature-combination, or replace -march=native with explicit ISA target (-march=x86-64-v3).

Entry Corrections

re-018 (macos-14-sonoma-eol.yml) — Deprecation now ACTIVE

• Updated title: "macOS 14 Sonoma Runner Deprecation — NOW ACTIVE (Full EOL November 2026)"
• Updated root_cause to note deprecation is ACTIVE as of July 6, 2026 (today)
• Queue delays begin today; brownout failures begin October 5; full retirement November 2.
• Severity remains warning (jobs don't fail outright until brownouts start October 5).

Cycle 285 — July 6, 2026 (2:00 PM CT)

Phase 1: Merge Check

• PR feat: add 1 new error entry (runner-environment) #438 (re-517), feat: add 1 new error entry (runner-environment) #439 (re-518), feat: add 2 new error entries (runner-environment) #440 (re-519, re-520) — all CI green, all CLEAN. Queued via agent_merge for Hector approval ✅

Phase 2: Recent Findings (June 29 – July 6 window)

• runner-images #14337 (TODAY): SSH throughput regression in Packer/azure-arm — single reporter, unconfirmed, niche. Skip.
• runner-images #14326 (Jul 2): Windows Defender Tamper Protection unverified speculation. Skip.
• runner-images #14296 (Jun 27): Clang -march=native AVX10.1 error on ubuntu-24.04. Confirmed by team. → NEW re-521 ✅
• GitHub Changelog (Jul 2): Copilot CLI GITHUB_TOKEN + copilot-requests: write requirement. No user error reports yet — note for next cycle.
• macOS 14 Sonoma deprecation ACTIVE TODAY — re-018 updated ✅

Phase 3: Validation Pass (6 entries)

• re-018 → UPDATED (deprecation active)
• pa-124 (OIDC sub claim pull_request.closed) ✅ accurate
• ca-154 (CodeQL TRAP caching quota) ✅ accurate
• re-431, sf-089 (macos-14 workarounds) ✅ already corrected in PRs fix: update sf-089 — macos-14 pin replaced with macos-15 (deprecation July 6 2026) #433/fix: update re-431 — remove macos-14 workaround (deprecated July 6 2026), recommend macos-26 #434
• workflow-run-head-branch null on schedule (ct-105 equivalent) ✅ accurate

[htekdev]

✅ Approved by Hector for agent merge at 2026-07-07T20:24:58.841Z

The Rocha merge-agent will rebase this PR onto the latest main, wait for CI, and merge when green. This approval persists across rebases.