Explain a Change

Teach how one change alters the existing system. A defect review belongs to tk-review, a concept artifact to tk-explain, and researched topic learning to tk-teach; naming these owners does not invoke them. Return NotApplicable for a review-only or implementation request.

Establish the evidence

Resolve repository identity and the exact target before explaining. Pin base/head commit SHAs and comparison semantics: a PR/branch normally uses its merge base, an explicit commit range uses its requested endpoints, and a workspace diff records HEAD plus staged, unstaged and relevant untracked content hashes. If multiple targets remain plausible, ask for the missing selector; never silently substitute the current checkout for an inaccessible PR.