zat covered the consume/verify half of a repo commit (verifyCommitCar, verifyCommitDiff, loadCommitFromCAR) but not the produce half. downstream PDS-shaped consumers (zds, zlay) each hand-rolled the canonical did/version:3/data/rev/prev commit, signed it, and computed the CID. signCommit(allocator, CommitParams, *Keypair) -> SignedCommit is the mirror of verifyCommitCar: it builds the canonical unsigned commit, signs the DAG-CBOR bytes, and returns the signed block plus its CID. a round-trip test signs a real MST-backed commit and verifies it through verifyCommitCar. rename internal/repo/repo_verifier.zig -> repo.zig now that the file holds both the produce and verify sides; public export names are unchanged. add a commit-sign-bench build target for the PDS write hot path. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>