t9 attributed its mutation to t2 in both the contract row and the test comment.
The sweep disproved that attribution: t9 stayed green under t2's schema_major
change, because the from-empty spine reaches a note whatever the block stamps.
A mutation borrowed from another test signs nothing unless it is observed to
kill this one.
Signed with the dispatch-arm bypass instead:
OperationKind::SetTuningContext(_) => OperationEffect::Applied
which skips tuning reduction without making the match non-exhaustive - so the
mutation isolates the reduction rather than being absorbed by a compile error.
Observed exactly as predicted: the spine operations stayed applied, the note
stayed reachable, and the test failed on the authored tuning-context
assertion, with the seeded default 440.0 surviving in place of the authored
441.0. Reversed by editing back; baseline green.
Both attribution sites now name that mutation and record why the previous one
was wrong, since a wrong mutation attribution is worse than a missing one: it
reads as signed.
Gate: 1410 tests, clippy 0, fmt clean, git diff --check clean.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QjsEnYhm1gPpf6ii2iFxFV
Levi Neuwirth
25c473314b