Add repository-scoped governance settings to basectl config #2668

Problem

The accepted Base governance design and implementation plan identify package 3 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

Implement the accepted basectl config interface for repository-scoped base_manifest.yaml governance settings after the schema work in #1613. Support separate issue/PR loop limits (default three), reviewer mode, Ready freshness and review-policy selection. Make repository scope explicit; validate schema; preserve existing machine-local config behavior; show a useful diff; fail clearly outside a repository or for unsupported settings. Migrate .github/base-review-policy.yml with a compatibility period and do not remove its reader before the replacement is released and documented.

Scope and non-goals

Scope: Implement the accepted basectl config interface for repository-scoped base_manifest.yaml governance settings after the schema work in #1613. Support separate issue/PR loop limits (default three), reviewer mode, Ready freshness and review-policy selection. Make repository scope explicit; validate schema; preserve existing machine-local config behavior; show a useful diff; fail clearly outside a repository or for unsupported settings. Migrate .github/base-review-policy.yml with a compatibility period and do not remove its reader before the replacement is released and documented.

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

• cli/bash/commands/basectl/config, manifest schema/loader, config reference and docs/review-governance.md.
• 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: Publish and test the governance-aware base manifest schema #1613
• Acceptance criteria:
• The command reads and updates only the selected repository manifest and validates all accepted governance keys against Publish and test the governance-aware base manifest schema #1613's schema.
• Issue and PR loop limits are independent, default to three, and reject values outside documented bounds.
• Dry-run/diff output is reviewable; failed validation leaves the manifest unchanged.
• Machine-local config remains intact; non-repository and unsupported-key errors are actionable.
• The old review-policy reader remains compatible until a separate documented migration gate is met.
• Validation:
• Add command tests for repository detection, valid/invalid config, independent loop limits, dry-run/diff, write preservation and machine-local compatibility.
• Add manifest-schema contract coverage and CLI help/reference checks.
• Run focused basectl config tests and git diff --check.
• Risks and rollback: A repository-scoped write could target the wrong checkout; require explicit root resolution and atomic writes. Roll back by reverting the CLI/schema PR while retaining the compatibility reader.
• 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.