maintenance: update v5.1 stable status

[edsiper]

Summary

• identify v5.1 on master as the current stable release series
• move v5.0 to maintenance-only status and update its backport guidance
• mark v4.2 and earlier release lines as End-of-Life
• add v5.1 to the security support table without inventing an unannounced EOM date

Why

The repository documentation still described v5.1 as under development and v5.0 as the current stable release after v5.1 became stable. Related maintenance, backport, and security guidance had become inconsistent.

Impact

Users and contributors now see consistent release lifecycle and backport guidance across README.md, MAINTENANCE.md, and SECURITY.md.

Validation

• git diff --check origin/master...HEAD
• python3 .github/scripts/commit_prefix_check.py
• GITHUB_EVENT_NAME=pull_request GITHUB_BASE_REF=master python3 .github/scripts/commit_prefix_check.py

Both commit-prefix checks passed. No runtime tests were run because this change only updates documentation.

Summary by CodeRabbit

• Documentation
  • Updated maintenance guidance to identify v5.1 as stable and v5.0 as receiving maintenance through November 30, 2026.
  • Marked v4.1 and v4.2 as end-of-life.
  • Updated contribution and security-reporting guidance.
  • Revised the README and security policy to reflect the current v5.1 release series and support status.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 8bcbb7e1-f14d-4835-acc4-b5abece57743

📥 Commits

Reviewing files that changed from the base of the PR and between 138886f and 9cb00a9.

📒 Files selected for processing (1)

• MAINTENANCE.md

🚧 Files skipped from review as they are similar to previous changes (1)

• MAINTENANCE.md

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📝 Walkthrough

Walkthrough

The documentation updates align maintenance, security, and repository status information with the v5.1 stable release and v5.0 maintenance period.

Changes

Release lifecycle documentation

Layer / File(s)	Summary
Support and maintenance policy MAINTENANCE.md, SECURITY.md	The policies identify v5.1 as active and stable, place v5.0 in maintenance through November 30, 2026, mark older releases as EOL, update backport guidance, and add the v5.1 EOM notice.
Repository release status README.md	The README states that master tracks stable v5.1.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to 9cb00

This documentation-only update aligns release, maintenance, and security guidance, with no actionable merge-blocking risk remaining after normal checks and review.

Possibly related PRs

• fluent/fluent-bit#12066: Updates project documentation for the v5.1 release status.
• fluent/fluent-bit#11339: Revises maintenance and security lifecycle documentation.
• fluent/fluent-bit#11818: Updates supported-version and EOL/EOM policy in SECURITY.md.

Suggested reviewers: cosmo0920

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the primary change: updating v5.1 to stable status.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch readme-update

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[chatgpt-codex-connector]

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Reviewed commit: 138886fb48

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[chatgpt-codex-connector]

Limit v5.0 to the documented maintenance fixes

For contributors deciding whether a change qualifies for a v5.0 backport, this row now says that the maintenance-only branch accepts unrestricted “Bug fixes,” while the policy at lines 23–25 limits maintenance branches to security patches, critical bug fixes, and selected low-risk enhancements. The same broad wording is repeated in the v5.0 section, so the document gives conflicting guidance about which fixes maintainers will accept; qualify this as critical bug fixes to match the stated maintenance policy.

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