docs(devlog): record release train 4 provider-compat lane

[lidge-jun]

Summary

Records the release-train 4 provider-compatibility lane in devlog/_plan/260927_release_train_4/provider-compat/: the per-phase plans, audits and results for the #5927 and #5497 carries (#6097, #6112), the #4213 trial-prompt fix (#6117), the issue and deferred-PR dispositions, and the merge receipts. It also fixes a formatting error in 010_images.md that landed with #6097, where a note was appended with literal \n sequences. Documentation only; no source, test or docs-site change.

Verification

• git diff --name-only origin/dev lists only the seven files under this unit's directory.
• bun run privacy:scan and bun run structure:check passed; bun test tests/ci-workflows/repo-hygiene.test.ts ran 15 pass, 0 fail on the exact head 0c8c50a8f8.
• Unpublished security analysis stays in ignored scratch; these notes describe only fixes that are already public on dev.

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed.
• Security-sensitive changes were reviewed for secrets, auth, and unsafe defaults.

[github-actions]

✅ Deterministic PR hygiene checks passed.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-27T19:49:59.516498Z	0c8c50a	PR opened

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📥 Commits

Reviewing files that changed from the base of the PR and between 296f0ce and 0c8c50a.

📒 Files selected for processing (7)

• devlog/_plan/260927_release_train_4/provider-compat/000_plan.md
• devlog/_plan/260927_release_train_4/provider-compat/010_images.md
• devlog/_plan/260927_release_train_4/provider-compat/020_response_tier.md
• devlog/_plan/260927_release_train_4/provider-compat/030_issues.md
• devlog/_plan/260927_release_train_4/provider-compat/040_integration.md
• devlog/_plan/260927_release_train_4/provider-compat/050_trial_nux.md
• devlog/_plan/260927_release_train_4/provider-compat/060_merge.md

 __________________________________________________________________________________
< Controlling complexity is the essence of computer programming. - Brian Kernighan >
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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 0c8c50a8f8

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[chatgpt-codex-connector]

Require CI on #6117's final head before completion

Do not treat the earlier 36bd4f2847 run and local focused checks as a substitute for required CI on the rebased #6117 head: the rebase changed the union to resolve a test-layout overlap, yet 890eb6d660 was merged before its required checks—or even the promised final dev run—completed. The lane therefore records a merge that bypassed the repository's exact-head gate; obtain successful required CI for the final head and do not mark this phase complete on older-head evidence.

AGENTS.md reference: AGENTS.md:L238-L240

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