Remove tracked AI context files from the Base repository after replacement release #2688

Problem

The accepted Base governance design and implementation plan identify package 14/base as a required deliverable. This issue translates that package into a reviewed, bounded issue/PR train; it does not authorize implementation before the issue reaches Ready.

Expected behavior

After package 13b is released and proven, remove the Base repository's tracked .ai-context/ files in a separate reviewed PR. Update AGENTS.md, CONTRIBUTING.md, manifest checklists and scheduled exports that refer to them. Remove only the obsolete .ai-context/ item check from the PR-body validator successor; keep every other PR contract validation rule.

Scope and non-goals

Scope: After package 13b is released and proven, remove the Base repository's tracked .ai-context/ files in a separate reviewed PR. Update AGENTS.md, CONTRIBUTING.md, manifest checklists and scheduled exports that refer to them. Remove only the obsolete .ai-context/ item check from the PR-body validator successor; keep every other PR contract validation rule.

Non-goals: Do not silently expand scope, activate unreviewed policy, mirror issue fields onto PRs, grant agents merge/release authority, or make changes outside the named affected areas. Any new product decision or materially new work gets a separate issue and decision record.

Affected areas

• Base .ai-context/, AGENTS.md, CONTRIBUTING.md, manifest checklist, scheduled exports and PR validator.
• Accepted source: governance design and implementation plan, PR #2664
• Parent tracker: #2665

Impact and evidence

1. Product intent: Implements only the accepted governance design and plan; any product-requirement change must be filed separately.
2. Architecture and contracts: Destination is the package-specific section of the merged governance design/implementation plan plus the affected canonical contract named above.
3. User guidance: The issue identifies likely guidance paths; the implementation PR must name updated user/FAQ/README paths or give a change-specific reason why none is affected.
4. CLI/API and reference: The affected-area list determines whether CLI/API/reference docs change; the implementation PR must cite the exact reference path or justify no impact.
5. Operations and safety: No privileged automation or merge authority is implied; the PR must list operational/security effects and any rollback.
6. Validation and testing: The issue lists the planned tests; the PR must report executed validation and explain any unavailable test.
7. Examples and downstream use: The implementation PR must identify affected examples/consumers or give evidence that this change has no downstream surface.
8. Governance and contributor process: This package changes or preserves the contributor/governance contract as described in Scope; links must point to the canonical rules.
9. Decision records: No new decision is accepted by this issue; any durable deviation requires a proposed decision record and explicit maintainer acceptance.
10. Release notes: The PR must include a user-facing release-note line or a reasoned none; this issue does not pre-decide that disposition.

These are issue-stage dispositions to refine during Triage. Before Ready, every category must have its exact destination or evidence-based no-impact reason; the PR repeats the ten-category evidence for actual changes.

Open questions

• None known. If implementation exposes an unresolved contract, return this issue to Triage and record the decision before implementation continues.

Plan

• S1: One focused PR for this issue. Use Fixes #N only if no additional slice is needed; if the maintainer approves multiple PRs, name each S1…Sn here before the first is opened and use Part of #N.
• Dependencies: the P13b issue, the P5a issue, the P7c issue
• Acceptance criteria:
• Package 13b release and output/privacy/failure proof are linked before cleanup begins.
• All tracked .ai-context/ files and stale references/scheduled exports in Base are removed or migrated to canonical docs.
• The PR-body validator retains issue/slice, validation, all impact categories and release-note checks while dropping only the obsolete .ai-context/ item check.
• Generated exports remain outside the repository and are not treated as canonical source documents.
• Rollback restores tracked context and schedules if the replacement is unavailable or materially regresses.
• Validation:
• Search tracked files, workflows, docs and tests for stale .ai-context/ references; classify all hits.
• Run repository context/agent instruction checks and the PR-validator contract fixtures.
• Confirm basectl export-context output remains outside the repo.
• Risks and rollback: Removing the old source too early creates an unmaintained context gap; block until package 13b is released and proven, and restore through a reviewed PR if needed.
• Decision impact: No decision is accepted merely by implementing the issue. Record the relevant accepted decision/ADR and file a superseding record if the maintainer approves a change.