* fix(#3025): refuse cross-runtime skill sync in sync-skills
Skill content and directory layout are runtime-specific — the installer
applies per-runtime converters, adapter headers, brand swaps, and layout
rules at install time, and grok/gemini resolve to ANOTHER runtime's skills
root. A verbatim cross-runtime cp -r therefore produces content the installer
would never have written for the destination, and can damage a runtime the
user never named. #3024 (closed) un-masked this, making the corruption live.
Fix (option b, user decision): add a functional Step 1 guard that refuses
any --to != --from with an actionable installer pointer, before any
resolution or copy. Identity sync (--from == --to) remains a no-op. The
non-functional Step 5 comment is replaced; Arguments/Limitations updated.
Regression: tests/sync-skills-cross-runtime-refuse.test.cjs (source-text-
is-the-product) asserts the guard exits non-zero for cross-runtime, points
at the installer, precedes the cp -r copy, and preserves identity.
* docs(#3025): backfill changeset PR number (#3404)
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Co-authored-by: sim <sim@local>
622c10b2c6