[gjermundgaraba]

Summary

• add an optional commit-msg hook that rejects non-merge commits without the committer's DCO sign-off
• install only the DCO hook so existing hooks, including Git LFS, remain intact
• document intentional sign-off and recovery for an existing commit
• run the hook regression script in the existing license-header workflow

Why

The repository's DCO check reports missing sign-offs after a push. This hook gives contributors the same feedback before creating a commit without automatically making the legal attestation for them.

Verification

• .githooks/test-commit-msg
• real Git commits with a --- divider and custom trailer.separators
• unsigned local merge commit
• shellcheck .githooks/commit-msg .githooks/test-commit-msg
• make check-license-headers
• git diff --check

[linear-code]

FOU-1168

[greptile-apps]

Greptile Summary

The PR adds an optional local DCO commit hook, regression coverage in CI, and contributor installation and recovery instructions.

• Adds commit-message validation for author or committer sign-off while exempting merge commits.
• Adds a shell regression script and runs it in the license-header workflow.
• Documents manual hook installation and commit repair.

Confidence Score: 4/5

The PR is not yet safe to merge because the documented installation can silently leave the DCO hook inactive for contributors using core.hooksPath.

The updated command fixes the linked-worktree case but still copies into the common Git directory even when Git is configured to execute hooks from another path.

Files Needing Attention: spec/CONTRIBUTING.md

Important Files Changed

Filename	Overview
.githooks/commit-msg	Adds the DCO trailer check and merge-commit exemption without an identified blocking defect.
.githooks/test-commit-msg	Covers accepted author and committer trailers, unrelated and absent trailers, dividers, custom separators, and merges.
.github/workflows/license-headers.yml	Runs the new hook regression script in the existing workflow.
spec/CONTRIBUTING.md	Updates installation to support linked worktrees, but the command still ignores a configured core.hooksPath and can leave the hook inactive.

_{Reviews (2): Last reviewed commit: "docs: support worktrees when installing ..." | Re-trigger Greptile}