check-impl-against-spec

name	check-impl-against-spec
description	Compare a pull request's implementation against spec context in spec_context.md and feed any material mismatches into review.json. Use during PR review when approved or repository spec context is available.

Check implementation against spec

Use this skill only when spec_context.md exists during PR review.

Goal

Determine whether the implementation in the checked-out PR materially matches the approved spec context. This is a supplement to the normal code review, not a separate output.

Inputs

• spec_context.md contains the spec context to compare against. It may include both product spec content (intended behavior, acceptance criteria) and tech spec content (implementation details, file changes).
• pr_diff.txt contains the annotated diff for the PR.
• pr_description.md may contain additional scope or rationale.
• The working tree contains the PR branch contents.

Process

1. Read spec_context.md and extract the concrete commitments it makes:
   • required behaviors (from the product spec)
   • required files or subsystems to change (from the tech spec)
   • stated constraints
   • required follow-up steps, validation, or migrations
2. Compare those commitments against the actual implementation in pr_diff.txt and the checked-out files.
3. Treat small implementation-level adjustments as acceptable when they preserve the spec's intent. Do not flag harmless differences in naming, structure, or low-level technique.
4. Flag a mismatch only when it is material, such as:
   • required behavior in the product spec is missing
   • the implementation contradicts a spec decision
   • the change introduces significant unplanned scope
   • a required validation, migration, or compatibility step from the tech spec is absent

Outputs

• Do not create a separate report file.
• Fold spec-alignment findings into review.json.
• Put broad spec-drift concerns in the review summary.
• Add inline comments only when the mismatch can be tied to changed lines in the diff.
• Treat material spec drift as at least an important concern.
• If the implementation matches the spec closely enough, do not add comments just to mention alignment.

Boundaries

• Do not require literal one-to-one implementation of the spec when the PR achieves the same outcome safely.
• Do not speculate about spec details that are not actually present in spec_context.md.
• Do not post to GitHub directly.