test: prove unsigned contribution is rejected

[enoreyes]

Problem

DCO must reject a contribution whose newly introduced commit lacks a Signed-off-by trailer.

Scope

One harmless disposable Markdown file and one deliberately unsigned commit.

Non-goals

No merge, production change, ruleset change, protection weakening, or persistent branch.

Acceptance

DCO / signoff fails with missing_dco_signoff while all other applicable checks remain intact; this pull request is then closed and its branch deleted.

Validation

Inspect the DCO annotation for commit 2d1d1c7 and the stable remediation command git commit --amend --signoff.

Dependencies

Protected main merge 738bfd7 and active ruleset 21212019.

Risk

The branch contains no executable content and is never merged.

Rollout

Close without merge after observing the required failure, then delete the branch.

Observability

GitHub preserves the pull request and failed DCO check URL.

Documentation

The disposable file is test evidence only and will not reach main.

Compatibility

No compatibility impact.

Generated artifacts

None.

Agent authorship

Factory Droid created this authorized negative test under @enoreyes authority; the commit intentionally omits DCO signoff.

[enoreyes]

Validation complete: DCO / signoff rejected commit 2d1d1c7 with missing_dco_signoff and git commit --amend --signoff remediation; Metadata, Quality, CodeQL, and dependency review passed. This contribution is intentionally not merged.