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	epiphany-layout-ir / engrave / render-svg I	The v0 to_logical/to_constrained pipeline is a structural placeholder: each layout object becomes one arbitrary glyph (BRAVURA_METRICS[discriminant % N]) at y = 0, not real notation. Chapter 7 says the logical stage has "engraving decisions made"; the spec should clarify which engraving decisions (glyph-by-duration selection, pitch→staff-position, clef/key/meter/barline realization, stems/beams) are core-IR construction versus solver work, so the real-notation engraving has a defined home before it is built next phase. Consequence: the QUICKSTART human visual-acceptance gate ("the SVG visually parses as standard notation") is a next-phase gate, not met by stub output — this phase's gate is renderer correctness/faithfulness.	G / Pass 12 (Ch 7 engraving boundary)
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	epiphany-layout-ir I	The bundled BRAVURA_METRICS are approximations that disagree with the genuine Bravura outlines the renderer now extracts from the font (e.g. timeSig4: metrics bbox [40,0,1240,2048] vs real outline ≈ [0.08,-1.0,1.8,1.004] staff spaces). Real spacing needs exact metrics; regenerate the metrics table from the font or reconcile it with the outline source.	G / Pass 12 (glyph metrics)
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).