Reading the trailer

AI-Attribution: v=2; status=assisted; method=intersected; agent=claude-code; agent_version=2.1.228; ratio=0.62; model=claude-opus-5; session=a3f9e21c

A plain git trailer. Readable by git log, by git interpret-trailers, and by anything else that reads a commit message — the format is a specification first and this tool's output second.

The keys

v — format version

First, so it is read before the values it qualifies.

It exists because ratio=0.62 is well-formed under any definition of ratio. Change the rule for computing it and every trailer already written silently means something else, with no error to notice. Trailers live in commit messages, so that ambiguity would be permanent: a migration can rewrite a database column, nothing can rewrite pushed history.

A trailer with no v is version 1, permanently — that is every trailer written before the key existed.

The version is bumped only when the meaning of a value changes, never when a key is added. A parser that meets an unknown key keeps it and re-emits it unchanged, so additions are backward compatible on their own.

status — whether an agent contributed, and if not, why not

Value	Meaning
assisted	There is evidence an agent contributed
unassisted	The hooks were watching and saw no agent — a human wrote it
unmatched	An agent was active, but touched none of these files
uninstrumented	The commit predates the hooks, so AI use is unknown
degraded	Attribution itself failed — a fault, not a finding
undetermined	v=1 only: one of the four above, unrecorded

Only assisted means an agent contributed. The rest say why there is no such claim, and they are not interchangeable: unassisted is a finding, degraded is a bug, and uninstrumented is neither.

unassisted is a positive claim and the only one here that can be wrong in a flattering direction, so it is stamped only where the journal was actually read. Absence of evidence is uninstrumented, never unassisted — see Empty is not zero and the six states.

undetermined was the only one of these in v=1, where it covered all four situations at once. It is still read, because it is written into every commit stamped before v=2 and those trailers cannot be rewritten.

method — how much to trust it

The confidence ladder, weakest to strongest:

Method	What it means	Evidence
undetermined	No evidence either way	none
declared	Someone stated it	assertion
inferred	Derived from surrounding signals	circumstantial
observed	An agent edited these files in a recent session	file-level
intersected	The exact lines the agent produced were staged	line-level

intersected is the only level that proves the agent's output survived into the commit. observed means the agent touched the file, but the text may have been rewritten before it was staged.

agent / agent_version

Which tool, and which version of it. Read from the transcript, not configured.

model

Which model produced the work, where the agent reports one.

Taken from the most recent relevant session entry rather than the first. A commit can contain edits from more than one model — a session that escalated part-way, or two sessions touching the same files — and the turn that finished the work is the one worth attributing.

Omitted entirely when no entry recorded one, rather than emitted as unknown. A commit attributed by declared or inferred has no session to read a model from.

ratio

The fraction of the commit's changed lines that match lines the agent produced.

The denominator is lines added + lines removed in the staged diff, and the numerator counts distinct matching lines — a file that legitimately repeats a line does not let one agent-written line claim several.

Omitted rather than guessed when the commit's line counts are unknown.

session

An opaque token. It groups edits that happened together; it does not identify a person, and it is not derived from anything that does.

Checking coverage in CI

Local hooks are advisory — --no-verify bypasses them. The CI check is what makes coverage real:

- run: dun check --base "origin/${{ github.base_ref }}"

dun check fails if any commit since --base lacks a valid trailer. It does not fail on status=undetermined, because that is a legitimate verdict rather than a missing one.