#67: movePage didn't check the destination wasn't the page itself or inside its
own subtree, so MCP/REST/agent/fast-drag could persist+broadcast a cycle. Reject
before the update (self-parent, or moved page among the destination parent's
ancestors via getPageBreadCrumbs).
#64: movePage emitted PAGE_MOVED from a stale pre-read even when the row didn't
change / was concurrently deleted (phantom move). Gate the emit on
updateResult.numUpdatedRows !== 0n. Both are movePage hardening in one method.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>