If the rejection exists only in PR review comments, Keep the Why cannot magically see it from the clone.
It gets picked up when an agent with access to that review context processes the feedback - for example during review, revision, or merge work - and records the rationale into context/.
Otherwise someone has to carry it in.
That is actually the boundary I care about: PR comments are transient discussion; once a rejection matters to future work, the reasoning should become repository knowledge.
Makes sense to me. The case I'd watch is a PR a person rejects and simply closes, since no agent reviews, revises or merges it, and I suspect that's how many rejections end.