MR-description completeness fallback (extension of C3)

[azevedo]

Status

Future enhancement to C3. New candidate surfaced during C3 design discussion. Not in the original 10.

Context

C3 (Plan-driven Requirements Completeness check, separate issue) uses plans as the completeness source. During design, the question was raised: "when reviewing an MR it might also make sense to do a similar check against the MR description".

MR_DESCRIPTION is already captured for MR-scope reviews and passed as context to reviewers via commands/ba/review.md:181, but C3 v1 explicitly does NOT use it as a completeness check source.

Decision

Out of scope for C3 v1. Track as a future enhancement.

Rationale for current exclusion

• SSoT principle. Checking against plan AND MR description simultaneously creates risk of conflict and duplicated coverage. If plan says "implement A, B, C" and MR description says "implements A and C (skipping B for now)", the completeness check has to pick a side.
• Trust profile differs. MR descriptions are often written after implementation to summarize what was shipped — sometimes by an author optimizing for reviewer approval. Plans are upfront contracts authored before implementation. Different trust profiles; not equivalently authoritative.
• C3 v1 keeps a single source per run to avoid the SSoT problem.

Design captured (for the future enhancement)

Position in C3's chain

Insert as a fallback after both plan sources fail:

1. --plan <path> flag
2. Existing 7-day mtime fallback (commands/ba/review.md:181)
3. NEW: MR-description fallback (this enhancement) — only triggers when both plan sources are absent AND scope is MR
4. Silent skip if all fail

This ordering preserves SSoT: only one source is ever used per run.

Confidence calibration

Verdicts produced from MR-description criteria should carry lower confidence than plan-derived verdicts. Concrete options:

• Cap all verdicts at confidence ≤ 75 when sourcing from MR description
• Or: demote each verdict by one anchor from what it would be plan-sourced

Surface the source in the section header: "Requirements check (MR-description fallback — lower confidence)".

Scope

• MR scope only. Branch/staged/recent scopes have no MR description.
• Parse MR_DESCRIPTION for structured sections matching ## Acceptance Criteria, ## Behaviors to Test, ## What this does, ## Changes, or similar markdown patterns.
• If no structured section found, fall back to bullet lists in the description body.
• If MR description is essentially empty (only an auto-generated template, or just a sentence), skip with a header note.

Conflict avoidance

If both plan AND MR description are available, use plan only. Never use both. This is the SSoT rule.

Trigger conditions for revisit

• User regularly reviews MRs that have descriptions but no corresponding committed plan — e.g., hotfixes, refactors, or exploratory work where /ba:plan wasn't used
• Desire for completeness coverage in plan-less MRs — currently those reviews skip the completeness section entirely; this enhancement would partially fill that gap

Dependencies

• C3 (separate issue) must land first. This is an extension of C3, not standalone.

References

• C3 issue (Plan-driven Requirements Completeness check)
• commands/ba/review.md:181 — existing MR_DESCRIPTION capture and context-passing
• User's own caveats during C3 design: SSoT + trust profile concerns (both legitimate; both reasons this is gated to "no plan available")