Carry forward PR #3055 at 92f53c4c onto ef648e01, preserving contributor attribution and current main. Focused maintainer fixes reuse shared input ceilings, preserve late root context through outer bootstrap, bound frontmatter before immutable parsing, and assert real oversized input in the limits workflow.
Move stable hook metadata to a validated sidecar while preserving hook commands and installer identity. Reject moved fingerprints and duplicate IDs, and validate before updating metadata. Independent local review passed at c315271624a1fd055b992f2bff889ad2a0ff8a6b; CI run 34678210149 passed. Rollback: revert this squash commit.
