to_constrained took the active clef from the staff instance's clef_sequence and
fell back to Clef::default() -- treble. A staff that declared its clef only on the
Staff, with no ClefChange, therefore drew a treble clef and placed every note
against it. The field was decorative in the projection.
It is the fallback. StaffContent now carries default_clef -- the clef belongs to
the Staff, the sequence to the StaffInstance, and resolving "the clef at time t"
needs both -- and active_clef_or(clefs, at, default) resolves against it.
active_clef remains as that with the treble default, for callers with no staff to
hand, so the public API is intact.
The part worth pausing on: epiphany-editor-core reads the same function for
hit-test pitch resolution. Fixing only the projection would have left a click on a
bass staff resolving its pitch as treble -- the engraved clef and the editor
disagreeing about what note is where. Both now go through active_clef_or.
Removal was rejected: the field is named for its purpose, is encoded on the wire,
and dropping it would be schema-major.
Zero golden churn: every fixture and generator declares treble, which is also
Clef::default(), so nothing that exists today moves. Locked by
a_staff_declaring_only_a_default_clef_engraves_in_it and mutation-verified by
restoring the Clef::default() fallback. Scoping that test by provenance was
necessary -- valid_score_rich has three staves and only one was re-clefed, so the
first assertion I wrote ("no gClef anywhere") failed against a correct fix.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Levi Neuwirth
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