epiphany/spikes/editor-toolkit/FIXTURE_RECIPE.md

T4 spike fixture recipe (pin 7)

Approved 2026-07-28 at the recipe level; moved here from spec/DRAFT_T4_FIXTURE_RECIPE.md. Revision 1 asserted three things about the pipeline that reading it disproves (ties as curves, two rest glyphs from eighth-density, multi-subpath coverage from 4/4). Revision 2 fixed those and introduced three of its own: a command census that skipped H/V, barlines filed as strokes, and ledger quotas expressed in "positions" that can mean zero ink. This revision corrects those and drops ties to zero.

CONTRACT_EDITOR_T4_SPIKE.md pin 7 requires this recipe to be committed and user-reviewed before any candidate-specific implementation begins, because staff × measure dimensions do not pin the workload and the workload is what gets tessellated. That review is discharged; the generator's census (below) is a separate, still-open gate.

One recipe, scaled across rungs by dimension only. F1 1 staff × 10 measures, F2 4 × 32, F3 12 × 100, F4 24 × 200. Every rate is an integral per-measure quota under one fixed cadence, so scale is the only thing that moves between rungs — up to bounded edge effects where a rung's measure count does not divide the cadence, which the census reports rather than the recipe glossing.

---

What the pipeline actually draws

Verified in epiphany-layout-ir and epiphany-engrave before choosing any rate, because a recipe that asks for ink the pipeline does not emit silently under-delivers.

• Curves are slurs, and only slurs. Curve's own doc: "Slurs engrave to one of these; ties and other span curves will follow" (constrained.rs:109-111) — future tense. constrained.rs has a TypedObjectId::Slur arm and no Tie arm; ties fall through with the other structures, which "are carried as zero-extent traced [anchors]" (constrained.rs:734). Revision 1 counted ties as curves and inflated every curve figure by 50%. The casting lines I cited only transform curves already produced upstream — they were evidence of nothing.
• Rest glyph follows note value exactly — rest_glyph (engrave_theory.rs:112): Whole→restWhole, Half→restHalf, Quarter→restQuarter, Eighth→rest8th, and None for anything shorter, deliberately, so missing coverage surfaces instead of misrendering. An all-eighths recipe therefore yields rest8th only; revision 1 claimed both quarter and eighth rests from a rhythm that cannot produce them.
• timeSig4 is single-subpath (measured: 1 subpath, 34 commands). Revision 1's claim that 4/4 brings multi-subpath coverage "free" was simply false. timeSig8 is the multi-subpath digit (3 subpaths) and 4/4 does not use it.
• Beams are NOT drawn. beam_slope_penalty is "vacuous 0.0: no beam geometry is drawn yet (beams exist logically, not visually)" (quality.rs:40-41). Eighth density here is an event-count choice, not a beam-ink claim. When beams land, the stroke mix changes and this is revisited.
• Strokes — staff lines, stems, ledger lines, plus zero-extent traced anchors (casting.rs:1081, lib.rs:119). Barlines are glyphs, not strokes (constrained.rs:1455) — revision 2 listed them wrongly.
• Ledger lines are emitted per staff step, not per off-staff note (ledger_steps, constrained.rs:2642-2659): the even steps strictly outside the staff, from the staff out to the note. By absolute staff step: −1 and +9 emit 0 ledgers; −2, −3, +10 and +11 emit 1; −4 and +12 emit 2. The recipe therefore pins off-staff pitches by exact staff step; "±1 and ±2 ledger positions" (revision 2) would have produced roughly half the ledger ink it implied.
• Clefs are emitted per staff instance, not per system (no restatement on later systems — editor-gui/DECISIONS.md), which holds given the topology pinned below.

Measured glyph cost, since accidental rate does not control complexity

The census definition is BravuraGlyphCatalog::render_data(name).outline.len() — the typed Vec<PathCommand> candidates actually consume. Revision 2 counted M/L/C/Z tokens in the source d string and was wrong for it: the parser converts each H and V to a PathCommand::LineTo (glyphs/src/path.rs:92), so those are real commands in the tessellator's input, not serialization shorthand. Recounted with them:

glyph	subpaths	commands
accidentalSharp	2	71
accidentalDoubleSharp	1	37
accidentalNatural	2	29
accidentalFlat	2	24
noteheadBlack	1	6
restQuarter	1	38
rest8th	1	19
gClef	4	59
fClef	3	28
timeSig4	1	34

A sharp costs 2.4× a flat. So the accidental mix must be pinned, not just the rate.

---

The recipe

Nothing is sampled. Every quantity below is an integral per-measure quota placed by a fixed rule, so the content is identical run to run, machine to machine, with no rounding policy needed. The generator still takes a seed, but its only role is replica/identity minting as in the testkit fixtures — it does not influence content. That is strictly stronger than revision 1's "fixed seed", which left the selection algorithm free.

Topology

• One region, containing one staff instance per staff. No nested or parallel regions.
• Staves take gClef on even indices, fClef on odd — both complex multi-subpath clefs, in a mix a real keyboard/orchestral score would have.
• 4/4 throughout: timeSig4 twice per staff (numerator + denominator).
• Single-pitch note events only — no chords. Chord cardinality would change notehead-per-slot density and stem sharing, and is not a variable this comparison needs.
• One voice per staff instance (see the limitation below).

Per measure, per staff — a fixed 7-event bar

Rhythm: six eighths + one quarter = 6/8 + 2/8 = 4/4 exactly. Seven events, metrically valid, and it makes both rest glyphs reachable.

Quota	Value	Placement rule
Events	7	positions 1–6 eighths, position 7 quarter
Rests	1	even measures: the quarter (→ restQuarter); odd measures: eighth position 3 (→ rest8th) — an exact 50/50 split of the two bundled rest glyphs
Accidentals	1 (of 6 pitched events = 16.7%, the integral replacement for revision 1's 15%)	on pitched event position 2; glyph cycles sharp → flat → natural by measure index mod 3. accidentalDoubleSharp excluded: rare in real music and single-subpath, so it adds cost without adding hole coverage
Ledger-bearing notes	1	on pitched event position 5; staff step cycles −2 → −4 → +10 → +12 by measure index mod 4, giving ledger-stroke counts 1, 2, 1, 2 — an average of 1.5 ledger strokes per measure, pinned by step rather than by a "ledger position" that can mean zero ink
Slurs	1	spanning positions 1→4, within the measure — never crossing a barline or system break, since a slur whose endpoints do not resolve to one staff traces instead of producing a curve (constrained.rs:1605)
Ties	0	see below

Ties are zero for the primary ladder, on the review's reasoning, which is better than my revision-2 argument for keeping them. Two independent grounds: the rule I wrote tied positions 6→7 while position 7 is the rest on even measures, which is an invalid tie pairing (epiphany-core/src/invariants.rs:2101); and — decisively — every structural tie anchor is emitted at the default x, which is the clef column (constrained.rs:1155, default_x = region_x + CLEF_X), so casting assigns them all to the first system regardless of their musical measure. At F4 that would pile 2,400 anchors into the most likely damage target and distort per-system rebuild timing — corrupting the measurement the whole spike turns on. Revisit when ties draw real geometry.

Pitch placement is deterministic and quota-respecting: two ordered pitch lists — on-staff (the staff's own span) and off-staff (the four steps listed above) — each advanced cyclically. The designated ledger event draws from the off-staff list; every other pitched event draws from the on-staff list. Pitch never depends on the seed.

One fixed cadence, with bounded edge imbalance — not exact thirds. 10, 32, 100, and 200 are none of them divisible by 3, so the sharp/flat/natural cycle leaves at most one extra of one or two glyph types per staff; and F1 has a single staff, so it is gClef only while every larger rung alternates clefs. The cadence is identical and deterministic at every rung; the resulting counts differ slightly at the edges, and the census reports what they are rather than the recipe claiming they are equal.

---

What that produces

Events and quotas are exact. Primitive counts are estimates to be replaced by the generator's measured census (below) — pin 7 requires glyphs / strokes / curves separately plus total path-command count.

Rung	staves × measures	events	pitched	curves (slurs)	accidentals	ledger strokes
F1	1 × 10	70	60	10	10	15
F2	4 × 32	896	768	128	128	192
F3	12 × 100	8,400	7,200	1,200	1,200	1,800
F4	24 × 200	33,600	28,800	4,800	4,800	7,200

Plus stems (≈ one per notehead), staff lines (5 × staves × systems), and barline glyphs.

---

Approve the generator, not just the recipe

Per the review, and I agree it is the right gate: the generator lands before any candidate code, and emits a per-rung census — per-type primitive counts, total path commands, and a glyph-name histogram — plus a SHA-256 hash of each rung's ResolvedLayoutIR canonical bytes, the algorithm named here rather than left to the implementation. That census is what you approve; the numbers above are my arithmetic, and the census is the measurement. The hash then makes every later round's fixture provably the one that was approved.

This is the standing gate: no candidate code exists until that output is approved. Recipe approval is not generator approval.

F4's engrave time is measured in that same preflight, against the corrected generator — not now, and not against an underspecified recipe, where a timing could not settle anything. If F4 exceeds pin 7's ten-minute wall it is dropped and the deciding rung becomes the largest remaining engraving-valid rung — expected to be F3, but not unconditionally F3.

---

Stated limitation: one voice

Corrected from revision 1, which overstated the gap. Two-voice engraving is not unproven: rs4_two_voice_counterpoint_passes_minimal (testkit/tests/reference_suite.rs:89) exercises it against the real engraver and passes, and logical projection iterates every voice. Revision 1 inferred a gap from casting tests that happen to read voices[0] — evidence about those tests, not about the engraver, which is the same reading-a-path-for-the-path error that has bitten this track before.

What is genuinely unverified is narrower: collision handling between voices, rest displacement, and deliberate stem-direction separation. The deciding ladder stays at one voice as an isolation choice — a spike measuring tessellation should not also be exercising the engraver's least-proven geometry — and a multi-voice engraving check belongs on its own, later.

What this recipe deliberately does not vary

Dynamics, articulations, text, tuplets, grace notes, repeats. Several are unengraved today (§3.7's registry), and the rest add model surface without adding a distinct primitive type — the tessellator sees glyphs, strokes, and curves, and this recipe's job is to load those three in a realistic ratio. Text is the exception and is covered by round 2's synthetic SpikeResolvedText fixtures, where it belongs.