epiphany/spec/PASS12_BATCH.md

Pass 12 — Batch Tracker

Maintained by Agent F (testkit & tripwire), per spec/PHASE2_QUICKSTART.md: "Ambiguities discovered during Phase 2 implementation go into a Pass 12 batch, not into code improvisations. … Don't open Pass 12 until at least 3 items accumulate."

Status: OPEN. Agent H's landing (spelling + decomposition pre-passes) surfaced five candidates, crossing the ≥3 threshold. This file is the running collection; G ratifies (or defers/rejects) the batch when Phase 2's open questions are resolved. F collects, F does not resolve.

How an item lands here

When implementation hits a behavior the ratified spec does not determine, the responsible agent records it in their crate's DECISIONS.md with an ID (P12-<agent><n>) and a one-line rationale, then adds a row below. Improvising in code instead is the failure mode this batch exists to prevent.

Items

ID	Source	Summary	Disposition target
P12-H1	epiphany-core H	Ratify SpellingAlgorithmId::Default = Temperley line-of-fifths v1 (Pass 11 closed before H landed; the id "default" is the crate's proposal until ratified — not a byte layout, so nothing golden-locks on it).	G (algorithm-choice ratification)
P12-H2	epiphany-core H	KeySignatureChange / ClefChange are anchor-only placeholders; context-aware spelling infers tonal context from the melody (line-of-fifths centre of gravity) rather than a declared key. A real key/clef content model would let spelling/decomposition honour declared keys and place cancelling naturals. Flagged as a graph-model gap.	G (graph model)
P12-H3	epiphany-core H	Chromatic-run convention (ascending = sharps, descending = flats) is only a tiebreak in the centre-of-gravity rule, so an isolated chromatic run with no tonal context may pick the enharmonic the convention would not. Voice-leading refinement deferred.	G / Pass 12 (spelling)
P12-H4	epiphany-core H	Decomposition simplifications: single governing meter per region (multi/mid-region meter changes deferred); region origin assumed a barline (anacrusis deferred); compound-meter beat grouping beyond the dyadic default; tuplet nesting and cross-beat tuplet members; double+ augmentation dots (MAX_DOTS = 1).	G (decomposition scope)
P12-H5	epiphany-core H	Automatic spelling under aleatoric regions (the spec's open question). H spells pitches region-independently but performs no region-specific aleatoric spelling; defer if the algorithm does not generalise cleanly.	G / Pass 12 (open question)
P12-I1 RESOLVED (I-1)	epiphany-layout-ir / engrave / render-svg I	The v0 pipeline was a structural placeholder (one arbitrary glyph per object at y = 0), not real notation. Resolved by I-1 (Phase 2-3): to_constrained now builds real notation — clef-relative noteheads (by NoteValue), spelling-derived accidentals, key/time signatures, rests, barlines, and the staff-line/stem strokes — and the Engraver re-spaces it; the human visual-acceptance gate is met (goldens locked against the stub and the real Engraver). The Ch 7 engraving-boundary question resolved to: notation construction lives in to_constrained, horizontal spacing in the Engraver.	✅ done
P12-I2 RESOLVED (wired)	epiphany-determinism / epiphany-layout-ir I	Stable layout-object id derivation (MUSCLOID, Pass-11 item 2.6). Wired: epiphany-determinism now reserves the built-in DomainTag::LAYOUT_OBJECT_ID (MUSCLOID), and layout-ir's provenance derivations (single / multiply-manifested / synthesized) plus the engraving-decision id route through it (no longer borrowing MUSCCONF). Layout ids stay non-canonical, so only data-prov hex in the render goldens changed; no durable/interchanged artifact. See layout-ir/DECISIONS.md and req:layoutir:object-id-derivation.	✅ done
P12-I3 RESOLVED (I-4a)	epiphany-layout-ir I	The bundled BRAVURA_METRICS were approximations disagreeing with the renderer's genuine outlines. Resolved by I-4a: the metrics table is re-extracted from the same SHA-pinned bravura-1.392 font the outlines come from, with bboxes rounded outward so each metric box contains the drawn ink (a render-svg test proves containment); BRAVURA_VERSION = SemVer(1, 392, 0). A coupled barline-placement bug it surfaced (bottom-origin glyph floated) was fixed in the same increment.	✅ done
P12-K1	epiphany-ops K	A v0 RespellPitch carried a ContentHash fingerprint of the spelling, not the PitchSpelling. The v0→v1 migration (Operation Catalog, M1) cannot invert a fingerprint, so it recovers the spelling from the score-graph context (an explicit per-pitch spelling attachment whose canonical bytes hash to the fingerprint) and returns MigrationError::Irreversible (bundle opens read-only) when the context lacks it. Every other representative payload migrates self-contained; this is the lone exception. Confirm the read-only fallback is the intended disposition vs. requiring a v0 corpus that preserves spelling pre-images.	G / Pass 12 (migration)
P12-K2	epiphany-ops K	The Transpose op (Operation Catalog, M2 Group 1) carries a minimal chromatic_steps: i32 interval and reduce_onto applies it as a CMN alteration shift only. Faithful interval algebra (diatonic vs. chromatic intervals, octave/nominal renormalization, transposition in non-CMN pitch spaces) is the deferred Chapter 4 tuning-catalog territory. The prototype also clamps the shifted alteration to the i8 range, so an extreme transpose silently saturates instead of renormalizing — another reason the representation needs pinning. Pin the interval representation and transposition semantics when the tuning catalog lands.	G / Pass 12 (tuning)

Not yet open elsewhere

Agent I (Track A) has contributed P12-I1..I3 above. Track B's Agent K has contributed P12-K1 (Operation Catalog M1). Agent J (Binary Format companion) has not yet contributed; when it does, append rows — the batch is already open, so it joins directly (no new threshold).