LLM Signature

LLM Signature

Provenance, not marketing. A Co-Authored-By: Claude <noreply@anthropic.com> line says an AI touched the commit and nothing else; this signature records what actually shaped the work — the exact model and the versioned tool stack — as machine-readable git trailers:

Assisted-By: claude-sonnet-5
Agent-Stack: claude-code@2.1.0; engineering-discipline@2.1.0 (craft-collection); session-workflow@0.15.0 (craft-collection)

Trailers are the native mechanism: hidden from git log --oneline, filterable with git log --format='%(trailers:key=Assisted-By)', parseable with git interpret-trailers. Full grammar and semantics: references/spec.md.

Semantics

• Assisted-By names the model that is writing and orchestrating — the one responsible for the change. One model: the orchestrator at commit time, not every subagent it delegated to. The model is never added as a commit co-author or committer; this trailer is its only appearance.
• Agent-Stack is environment-at-commit provenance: the harness and the enabled plugins, each as name@version (marketplace) — what was installed and enabled, not a claim that every item fired. The marketplace label is a lookup key (its repo or claude plugin marketplace list resolves it) — URLs stay out of commits.

Generate — always by script, never by hand

A remembered version is wrong the moment anything updates, so the signature is rendered from live sources every time:

uv run --no-project -- python "${CLAUDE_PLUGIN_ROOT}/skills/llm-signature/scripts/render_signature.py"

The model comes from the session transcript (last main-loop assistant message — subagent sidechains never sign; a discovered transcript signs only when fresh and verified against this cwd); the stack comes from claude plugin list and claude --version. --json for machine use, --plugin <name> (repeatable) to narrow the stack, --model / --transcript as explicit overrides. If the model cannot be resolved, the script fails rather than guessing — do not substitute a hand-typed signature; commit unsigned or fix the resolution.

Apply

Commits — in a project that adopts the signature (one declaration in the repo's CLAUDE.md; see references/spec.md § Adopting), run the script at commit time and append its output verbatim as the final paragraph of the commit message. Drop any Co-Authored-By line carrying the vendor's identity (an anthropic.com or claude+noreply address) and any "Generated with Claude Code" badge — the signature replaces both. Real human co-authors keep their lines, even one named Claude.

PR bodies — same block, fenced as text, at the end of the description.

Mechanical enforcement (optional) — --apply <msg-file> rewrites a commit message in place (scrub boilerplate, refresh trailers, never fail the commit), built to be wired as a git prepare-commit-msg hook; recipe in references/spec.md.