Generate AI context outside the repository through basectl #2687

Problem

The accepted Base governance design and implementation plan identify package 13b 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 reviewed basectl export-context contract by invoking a user-selected installed AI CLI to summarize canonical repository documents and write the generated artifact to an export location outside the repo. Do not add a maintained .ai-context/ source tree or remove existing tracked context in this issue.

Scope and non-goals

Scope: Implement the reviewed basectl export-context contract by invoking a user-selected installed AI CLI to summarize canonical repository documents and write the generated artifact to an export location outside the repo. Do not add a maintained .ai-context/ source tree or remove existing tracked context in this issue.

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

• basectl export-context command, CLI reference, tests and user/privacy guidance.
• 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 P13a issue
• Acceptance criteria:
• The command invokes only a selected, supported installed CLI using a noninteractive, bounded invocation.
• Output is written outside the repository, is attributable to source paths/revision/date and never overwrites tracked files.
• Provider absence, nonzero exit, timeout, cancellation and partial output fail clearly and leave no misleading success artifact.
• Privacy notice, redaction and prompt-injection boundaries match package 13a; no secrets are passed by Base.
• CLI help/reference and tests document output and cleanup behavior.
• Validation:
• Use fake CLI executables to test provider selection, arguments, timeouts, output path, errors and secret redaction.
• Verify repository status stays unchanged and exported artifact records source provenance.
• Run focused CLI tests and security fixtures.
• Risks and rollback: A provider may transmit repository content externally; require explicit selection/consent, disclose source data, and keep export outside the repo. Disable the command if privacy or output guarantees fail.
• 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.