Stroke and Curve gain `vertical_band: VerticalBandId`, the field GlyphObject has
always carried. Curve's own doc comment used to call it "a *free* primitive (no
vertical band, no spring slot)" -- but the projection computed each primitive's
band, used it for the glyphs, and threw it away for the strokes and curves.
The engraver then reconstructed it geometrically, and got it wrong twice: nearest
glyph by x handed a lower-staff stem to the upper staff (4132a7a), and nearest
glyph to a slur's start endpoint handed a bottom-staff slur to the top staff
(b1bfe04). Both tore primitives off their own notes, both reached a committed
golden, both were caught by review rather than by the gate. A slur is the proof
the inference can never be made safe: its endpoints are deliberately lifted clear
of its own staff, into the zone where the nearest notehead belongs to the
neighbour. No distance metric recovers the owner.
Both fixes were correct and both were the wrong shape -- reconstructing by
inference a fact the projection had in hand and discarded. So: the projection
declares it (a slur's staff is its notes' staff), the engraver's attribution
becomes three map lookups, and ~60 lines of geometric rules, epsilons, and
fallbacks are deleted.
Two bands had to become unconditional, since strokes could otherwise name bands
that no glyph had caused to exist -- validation now rejects that as UnknownBand:
- a staff band per staff of the region, in the region's own staff order (the
order y_origin stacks by), not only for staves that emitted a glyph. A staff
whose clef is unbundled engraves to an anchor *stroke* and no glyph.
- the margin band unconditionally, because a region's own traced anchor is a
stroke that names it whether or not a margin glyph puts a member in it.
Both may carry zero members, as an inter-staff gap band already did: membership
realizes the spring solve over glyphs; existence is what attribution needs.
Strokes and curves are deliberately NOT added to VerticalBand::members -- their
band reference is one-way.
vertical_band is not part of ResolvedLayoutIR::canonical_bytes (primitives are
encoded field-by-field), so this is layout metadata outside the canonical
encoding: no companion-version bump, and ENGRAVER_VERSION stays at 11 because the
output is unchanged. Zero goldens churn -- which is the evidence that the declared
owner agrees with the inferred one across the entire corpus.
Locked by every_stroke_and_curve_names_a_band_that_exists, verified by mutation:
making the margin band conditional again fails it on valid_score_rich. The two
tear-off regressions are kept -- they now assert an outcome the data model
guarantees, which is where a dropped declaration would surface.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Levi Neuwirth
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