[Phase 2] Extend the repo-local pinning standard to all first-party reusables #671

Story

As a maintainer,
I want broaden the mutable-ref exception in AGENTS.md and versioning.md to cover every first-party same-repo reusable, not just the two agents,
so that the channel-tag standard and its compliance-audit exemption explicitly include ci-failure-analyst, so the repin and the future test are sanctioned.

Acceptance Criteria

1. AGENTS.md §"Release channel tags & the mutable-ref exception" states the exception applies to all first-party same-repo reusables and names ci-failure-analyst as an in-scope channel namespace.
2. The doc records that the release-channel-tags ruleset must add target ci-failure-analyst/** for the exception's guarantees to hold, cross-referencing the human-gated ruleset story.
3. docs/release/versioning.md channel scheme is generalized so it reads correctly for non-agent reusables.
4. The text makes clear a compliance audit must not flag @ci-failure-analyst/stable as an unpinned action.

Tasks / Subtasks

• Edit the AGENTS.md exception section to generalize from the two agents to all first-party same-repo reusables, listing ci-failure-analyst. (AC: test issue from agent #1, Optimize review: small-PR and incremental fast paths #4)
• Add a note that the ruleset target set must include ci-failure-analyst/** (deferred to the hands_off ruleset story). (AC: Go-live improvements for PR review agent #2)
• Generalize the versioning.md channel/tag prose for non-agent reusables. (AC: Add @claude delegation, auto-merge, and rebase handling #3)

Dev Notes

• AGENTS.md exception is around lines 96-120; the ruleset currently targets only pr-review/** and dev-lead/**.
• The CANONICAL org standard lives in petry-projects/.github (cross-repo). This story updates only the repo-local AGENTS.md/docs; the org-wide promotion is the human-gated story id 8 — do not attempt cross-repo edits here.
• Keep the documented invariant that agents running as GITHUB_TOKEN cannot move/delete release tags (only admin/automation can).

Project Structure Notes

Edits AGENTS.md and docs/release/versioning.md only.

References

• AGENTS.md#release-channel-tags-the-mutable-ref-exception
• docs/release/versioning.md
• docs/initiatives/agentic-release-strategy.md

Likely target surface

• AGENTS.md
• docs/release/versioning.md

Story prepared by the BMAD Scrum Master (Bob) for epic #667. Status: ready-for-dev.