epiphany/crates/epiphany-layout-ir/DECISIONS.md

epiphany-layout-ir — decisions and Pass 11 candidates

This file records (a) the implementation decisions the QUICKSTART asked each agent to make once and document, and (b) the ambiguities discovered while building epiphany-layout-ir, batched as Pass 11 candidates for the spec rather than improvised in code (QUICKSTART, Process notes: "Ambiguities go into a batch, not into code … Don't open Pass 11 until you have at least three such items batched.").

RATIFIED (Pass 11, 2026-06-21); WIRED (Pass 12, P12-I2). layout P11-2 (LayoutObjectId derivation) is ratified into core_spec.tex §"Provenance" (req:layoutir:object-id-derivation): the spec pins a MUSCLOID-tagged derivation keying multiply-manifested objects on (source, region) and synthesized objects on (source, synthesis_kind, stable_semantic_instance_key). This is now wired: epiphany-determinism exposes the reserved built-in DomainTag::LAYOUT_OBJECT_ID (MUSCLOID), and all three derivations in provenance.rs route through it (stable_layout_id, manifestation_layout_id, synthesized_layout_id — the last no longer borrows MUSCCONF). Layout ids stay non-canonical (not document state, in no content hash), so realizing the derivation changed layout-id values (and the data-prov hex in the SVG goldens) but no durable or interchanged artifact. layout P11-1 (layout→ops dependency) stays a crate-topology call for the G–K re-cut. See spec/PASS11_RATIFICATION_LOG.md.

Scope

The crate implements the Chapter 7 interface surface: all four stages, the logical composite taxonomy, overrides and cross-region objects, time-axis payloads and trait, spring slots and constraints, vertical bands, resolved pages/systems, render configuration, glyph-catalog identity, and incremental cache/dependency types. Per the QUICKSTART's prototype framing, the algorithms behind those interfaces remain simple; the constraint solver still returns validated input geometry verbatim and performs no production engraving, casting-off, quality optimization, or rendering.

The round-trip's strict stage-equality assertion (the full Provenance of every object is preserved object-for-object) reflects this prototype's 1:1 projection — one layout object per laid-out score-graph object. A later stage that flattens a composite object into multiple glyphs would relax that assertion to source-coverage (every glyph's source is a laid-out object, every laid-out object is covered); the provenance-preservation contract itself is unchanged.

Implementation decisions (QUICKSTART "Decisions you'll need to make")

1. Replica ID entropy / 2. event-arena storage / 3. chunk store — N/A to this crate (Agents B and D).
2. Async or sync — sync only. No async traits anywhere; #![forbid(unsafe_code)].
3. MSRV — workspace 1.77. No exotic features.

Local decisions

• f32 IR coordinates, quantized at serialization. IR coordinates are single-precision staff spaces (StaffSpace(f32), Chapter 7 §7.2: "Single- precision floating point MUST be used for IR coordinates"). Quantization to the canonical 1/1024 grid happens only when serializing canonical ResolvedLayoutIR output — exactly as Appendix D §"Quantized Layout Coordinates" prescribes: "Internal solvers MAY use floating point during computation; canonical serialization rounds to QuantizedCoord." [ResolvedLayoutIR::canonical_bytes] is that boundary; it round-trips f32 jitter below 1/2048 staff space to identical bytes. (An earlier draft of this crate quantized throughout the pipeline; that contradicted the explicit Chapter 7 f32 requirement and is corrected here.)

• Depend on epiphany-ops for OperationKindTag. The QUICKSTART lists Agent E's dependencies as "A and B," but also assigns Agent E the edit-barrier types with OperationKindTag-based prohibited_operation_kinds. OperationKindTag is Agent C's canonical discriminator type (Chapter 6); reproducing it here would create a second definition that could drift. We therefore take a single, narrow dependency on epiphany-ops for that one type. This is sound: epiphany-ops does not depend on this crate (no cycle), and Agent E lands after Agent C. See Pass 11 candidate 1.

• ObjectKind for edit barriers is the TypedObjectId discriminant. The spec's EditBarrier.affected_object_kinds: Vec<ObjectKind> needs a score-graph object class key. The ObjectKind in epiphany-ops is a narrow system-counter-collision kind (Voice/Pitch/Registered), semantically unrelated, so we define a local ObjectKind(pub u16) over the TypedObjectId discriminant — the natural object-class key in this codebase.

• Edit-barrier scopes and conditions are evaluated precisely. A Region/StaffInstance/AnalysisLayer/PitchSpace barrier prohibits only objects within that scope; the editor (which holds the score) supplies the candidate object's structural location via EditContext. The known conditions ObjectExists and ObjectHasExtensionData are evaluated via an EditOracle the editor implements, not hardcoded to true. Only genuinely unknown narrowing — a Registered scope or an unknown Registered condition — is treated conservatively (as matching), per Chapter 8 §"Behavior Under Unknown Extensions". This avoids over-prohibiting edits to objects demonstrably outside a known scope or to objects a known condition excludes.

• stable_layout_id and the engraving-decision id are MUSCLOID-tagged (P12-I2 wired). A layout object's stable id is a pure function of its source (and, for manifestations/synthesized objects, the region or the synthesis kind+instance key), so it is invariant under insertion/removal/reordering of other objects (Chapter 7 §"Provenance"). Both ids are now domain-separated under the reserved built-in DomainTag::LAYOUT_OBJECT_ID (MUSCLOID), the spec's non-canonical layout namespace (req:layoutir:object-id-derivation); the engraving-decision id keeps its literal engraving-decision discriminator prefix so it cannot alias a layout-object id within that namespace. Neither borrows MUSCCONF any longer. See the header note for the realization details.

• Repeated manifestations get per-(source, region) ids. A score-graph object manifested within a region is laid out per manifestation: its stable id derives from (source, region) via manifestation_layout_id / Provenance::manifested. A staff manifested in two time-disjoint regions (Chapter 5 §"Region Overlap and Concurrency") therefore yields two distinct layout objects — both visual staves are preserved, neither dropped — and the ids do not collide. The id is still independent of traversal position (it depends on region identity, not order), so it stays stable across relayouts. Score-level cross-cutting objects, which have a single manifestation, keep a source-only id (Provenance::projected).

• GlyphObjectId/VerticalBandId reuse the provenance hash. A glyph's GlyphObjectId is its provenance stable_id (already manifestation-aware); a staff band's VerticalBandId is the staff layout object's manifestation id (VerticalBand::staff_manifestation), so two manifestations of a staff get two distinct bands. Both are stable across relayouts.

• Bundled Bravura metrics are a representative slice. BRAVURA_METRICS holds ~two dozen real-Bravura glyphs (noteheads, clefs, accidentals, rests, flags, time signatures, barlines, dynamics) with advance, bounding box, and named anchors, in 1/1024-staff-space units, tracking the BRAVURA_VERSION release. Enough to exercise the MUSCFNTM catalog identity and the GlyphCatalog metric-lookup interface end to end without shipping a font file; render-data lookup and a full catalog are out-of-core concerns (Chapter 7 §"Glyph Catalog Interface").

• Glyph identity flows to the resolved/render stages. ResolvedGlyph and RenderPrimitive carry an owned-or-borrowed GlyphReference, so the renderer knows what symbol to draw and the canonical encoding is injective in glyph identity — swapping two glyphs' names (even with the consulted-name set, and so the metrics hash, unchanged) changes the bytes.

• The render-to-hit-test contract lives at the RenderIR boundary, in world coordinates. RenderIR::hit_test_map (hittest.rs) turns the provenance the spec calls "the basis of hit-testing, selection, and back-reference navigation" (Chapter 7 §"RenderIR") into a structured map an editor can use directly: one HitRegion per glyph/stroke carrying the full chain — rendered primitive → layout object (stable_id) → score object (source) — plus a selectable HitShape (a glyph's placed bounding_box, or a stroke's segment + half-width) with contains/aabb and hit/within queries. Two deliberate boundaries: (1) shapes are in staff-space world coords (the same frame as RenderPrimitive.position, before any renderer's world→screen transform), so the contract is renderer-independent and a GUI applies the inverse of the same transform its renderer uses; (2) a glyph's region is its IR bounding_box (the boundary's granularity, which I-4a made contain the drawn ink), not the render-only outline. Tested against the real pipeline, not guessed by the GUI.

• Comprehensive, rejecting canonical encoding for ResolvedLayoutIR. The canonical output (ResolvedLayoutIR::canonical_bytes, via CanonicalEncode) covers the full resolved layout — every glyph's provenance (source, stable id, synthesis kind, sorted/deduped dependencies), glyph name, and quantized position, every engraving decision, and the complete catalog identity — so any change that distinguishes two layouts (a swapped glyph, an altered engraving decision, a different manifestation id, a different font version) changes the bytes. A non-finite or out-of-range coordinate is rejected with a panic (faulting in every build), never normalized to the origin (Appendix D: invalid geometry is rejected).

• Each glyph is routed to its own staff's band. GlyphObject.vertical_band (Chapter 7 §"Glyph-Level Objects") points at the band of the staff the glyph belongs to — LayoutObject carries that staff association, so a region manifesting two staves gets a staff band per staff with each glyph in exactly one (no cross-staff contamination). Region-level glyphs (the region object, cross-cutting, free-graphic) go to a margin band; multi-staff regions also carry empty InterStaffGap spring bands between staves. Staff-band ids are the staff layout object's manifestation id (distinct per region).

• Free-graphic and hybrid graphic objects are projected. to_logical and laid_out_object_ids project region.content.graphic_objects() (Chapter 5 §"Graphic Content"), so free-graphic and hybrid regions are not silently dropped.

• Synthesized-object ids include kind and a stable semantic key. Provenance::synthesized(source, kind, instance_key, deps) derives its id from (source, synthesis_kind, instance_key). The key describes the object's role and never traversal order, so insertion or reordering cannot renumber existing synthesized objects.

• Glyph-catalog interface: Send + Sync, metrics + render data, SemVer version, anchors as a map. GlyphCatalog is Send + Sync (shareable across parallel re-engraving) with both metrics and render_data. The in-tree Bravura catalog bundles metrics but no outlines/bitmaps, so its render_data honestly returns None (reporting Some would claim data that does not exist). font_version is Option<SemVer>, set to the SHA-pinned bravura-1.392 release the in-tree metrics are extracted from — the same font the renderer's outlines come from, so reserved metrics and drawn ink agree. The font declares a single decimal version ("Version 1.392"), recorded verbatim as SemVer { major: 1, minor: 392, patch: 0 }; see BRAVURA_VERSION for the canonical mapping rule. Glyph anchors are a map keyed by name: the catalog hash sorts them by name and rejects a duplicate name (a panic), so the hash never depends on anchor slice order (Appendix D §"Ordered Iteration"). every catalog method, including identity, is object-safe; owned font, glyph, and anchor names support a runtime-loaded dyn GlyphCatalog without leaking strings.

• Chapter 9 interface in full shape; no quality-metric computation. The ConstraintSolver interface is implemented as the spec defines it: Send + Sync, solve/solve_incremental, a SolverConfig with profile/budget/tie_breaking, a SolveReport with unsatisfied_constraints/warnings/metric_vector/budget_used/state (and the warning kinds, including QualityFloorApproached/ExtensionWarning), and an InvalidationSet with slots/bands/constraints/glyphs. The render boundary's RenderIRProducer::produce(resolved, scale, config) takes the spec's ScaleContext/RenderConfiguration. The quality-metric/tie-breaking types exist; what the QUICKSTART defers is normalization computation. The exact non-optional interface is preserved: the stub reports the non-conformance SolverTier::Stub rung (M5 follow-up — not Minimal, since a passthrough that evaluates no constraints and computes no quality metrics must not claim the lowest conformance tier; Stub orders below Minimal), an all-worst QualityMetricVector, and rejects explicit constraints it cannot evaluate rather than claiming them satisfied.

• Constraint references are validated (M5 follow-up). ConstrainedLayoutIR::validate() now also checks the LayoutConstraint vector: NoCollision/Align/PositionWithin must name glyphs in the set, SystemBreakAt/PageBreakAt must name existing spring slots, and a PositionWithin region must be finite/non-negative. Dangling constraint references are rejected (UnknownConstraintGlyph/UnknownConstraintSlot/ InvalidConstraintRegion) rather than silently accepted. Registered (extension) constraints stay opaque/conservative. Score-graph source validation (that a Provenance::source names a real graph object) still belongs at the to_logical boundary, which holds the Score.

• ScoreVersion is content-sensitive (M5 follow-up). It is now derived from the whole score's canonical bytes (Agent B's whole-score codec) rather than the layout projection's object identities, so a pure content edit (a respelling, a duration change) that changes no identifier still changes the version — required for correct incremental-layout cache invalidation (Chapter 7 §"Incremental Layout").

• The time axis has real behavior (M5 follow-up). Previously the TimeAxisModel carried bare Vec<SpringSlotId> and project/affected_slots ignored their arguments (returning the first slot / all slots) — inert payload. Each axis now holds ordered SlotPlacement { time, slot } entries: project(time) returns the slot covering a time (the greatest placement at or before it), affected_slots(range) returns the slots in a half-open time range, and slots() lists them in time order. The spacing stage (to_constrained) populates each region's axis from its resolved spring slots (TimeAxisModel::with_placements), and the populated axis is carried on ConstrainedLayoutRegion, so the axis is a real, consumed artifact rather than an empty placeholder. (The slot times are still the prototype's wall-clock spacing columns; mapping a metric region's measure/beat grid to musical times is the next layer, but the axis machinery now genuinely consumes whatever times the spacing assigns.)

• ConstraintStrength is attached by rule, not by widening the IR. Chapter 9 §"Strength Levels" defines ConstraintStrength { Required, Preferred { weight } }, but the spec's LayoutConstraint enum carries no strength field and the "normalized form" the solver consumes never says how strength attaches to a constraint instance (a genuine gap — see Pass 12 candidates below). Rather than invent an IR shape the spec doesn't have, LayoutConstraint::strength() derives strength from the constraint's own shape: a break's BreakKind is its strength (Hard → Required, Soft → Preferred { weight: 1.0 }), the geometric constraints (no-collision / alignment / containment) are Required, and a Registered extension constraint is conservatively Required — an obligation a solver cannot verify must never be silently demoted (Chapter 9: a solver MUST NOT treat Required as Preferred).

• The spacing pass emits real constraints (Chapter 7 pipeline: "Build collision constraints"). try_to_constrained now populates constraints, per region and in a deterministic order: (1) NoCollision chains over successive notehead columns within each staff — adjacent pairs in (column x, glyph id) order, linear in the noteheads, never the O(n²) closure; chord members share a slot (a second or unison may genuinely overlap by design), so only cross-column neighbours carry the obligation. These hold under both v0 solvers: the source layout separates columns collision-free and the engraver's collision-aware advance keeps successive columns separated after its remap. (2) PositionWithin per glyph against its region's envelope: the vertical extent is the exact envelope of the region's glyph boxes (both v0 solvers preserve glyph y verbatim, so this is a genuine obligation a future vertical pass must renegotiate); the horizontal span is the open v0 canvas (POSITION_WITHIN_X_REACH) because v0 does no casting-off — a region imposes no honest horizontal bound. (3) Soft break constraints projected from the logical stage's break overrides, on the spring slot carrying the break anchor's onset (the barline column at that time when one exists, else the note column); an anchor no realized column represents — an event/measure outside the region, a measure end, a region edge — is skipped silently, since there is no slot for a solver to break at. The four SVG golden snapshots' hard_constraint_count moved off 0 accordingly; the golden SVG bytes are unchanged (emission does not touch geometry).

• The stub stays honest — and renderable — under declared constraints. The old StubSolver flipped to InternalError whenever a constraint was present, which conflated "constraints I did not evaluate" with "a malformed input". Now: geometry still passes through verbatim, satisfied_hard_constraints is false (nothing was checked), a warning names the gap, and the status is SolvedWithWarnings — the closest non-claiming renderable status, since Chapter 9 defines no status for "renderable, constraints unevaluated" (a Pass 12 candidate below). Editors gate on SolveStatus::is_renderable(), so stub-driven pipelines (editor-core sessions, the edit-loop harness, the acceptance goldens) keep working; the round-trip harness asserts the stub claims satisfaction exactly when the problem is constraint-free.

• Break overrides carry their anchor; projected from the graph's break lists. Per the updated Chapter 7 §"Engraving Overrides", OverrideKind::SystemBreak / PageBreak now carry anchor: TimeAnchor — a break addresses a position, while the override's ScoreGraph target names the owning region. to_logical projects each region's authoritative user_system_breaks / user_page_breaks (Chapter 5) into Soft, Internal-origin overrides (authorship lives in the op log until P11-C8), ordered by (region id, kind discriminant, anchor canonical bytes), each with a paired EngravingDecision under DecisionSource::UserOverride(id) (Chapter 7 §"Override Resolution" MUST). The override id reuses the MUSCLOID derivation with a literal engraving-override prefix (mirroring the decision id), keyed on (region, kind discriminant, anchor canonical bytes). The variant-shape change is byte-visible only in memory: overrides appear in no codec today (the layout IR chunks cache no override records), so no stored or interchanged artifact changes — the stale "graph exposes no override registry" comment this replaces predated the graph's break lists.

• Edit-barrier decode mirrors + the manifest blob codec (PROVISIONAL byte form, Push 3). The barrier tree was encode-only; barrier.rs now carries the exact inverse and the codec for the two opaque manifest fields the bundle preserves verbatim (ExtensionDeclaration.edit_barriers / .affected_object_kinds — the bundle stays semantics-free; no bundle change). The spec defines no normative byte form for EditBarrier/BarrierScope/ BarrierCondition, so this is a provisional canonical encoding on the established pattern (define concretely, golden-lock, submit to the Binary Format companion): both blobs are canonical sets in the crate's existing push_set framing — u64 LE count, then per element a u64 LE length prefix and the element's canonical bytes, elements strictly ascending byte-lexicographic, duplicates removed — an edit_barriers element being an EditBarrier's canonical bytes (scope, affected-kind set, prohibited-tag set, condition, in that order), an affected_object_kinds element being the kind's 2 LE bytes. Golden literal-byte tests (edit_barriers_blob_bytes_are_golden, affected_object_kinds_blob_bytes_are_golden) lock the layout; the testkit adds a generator-driven round-trip gate. Decode discipline is reject-never-normalize (BarrierDecodeError): unknown scope/condition/ operation-kind discriminants, unsorted or duplicated set elements, non-NFC pitch-space text (PitchSpaceId::new would re-spell it, so the bytes are non-canonical), truncation, and trailing bytes are all typed errors, and a decoded barrier must re-encode byte-identically. Two deliberate choices: (1) ObjectKind decodes any u16 — the payload is an open discriminant space (a future core kind or an extension-registered kind is a value, not a decode branch), so there is nothing to reject without breaking append-only forward compatibility; (2) MAX_CONDITION_DEPTH = 64 bounds the recursive BarrierCondition decode — the spec places no bound on the tree, a decoder needs one against adversarial bytes, and 64 is far past any real barrier (spec examples are depth 1–2). Both are named Binary Format companion candidates. Evaluation wiring (the §"Behavior Under Unknown Extensions" MUST) lives in epiphany-editor-core, which decodes injected declarations and gates apply/apply_transaction through EditBarrier::prohibits_edit.

  Ratified (2026-07-02): spec/binary_format.tex v0.1.0 Chapter 8 ratifies the blob byte form (P12-E1, req:binfmt:ext-blobs), pins MAX_CONDITION_DEPTH = 64 as the normative recursion bound (P12-E2, req:binfmt:condition-depth), and adopts the open-value ObjectKind decode stance (P12-E3, req:binfmt:object-kind-open).

• Casting-off support surface (2026-07, the engrave casting-off slice). Three small, non-canonical additions made for epiphany-engrave's casting-off pass, kept here because they are IR-shape/contract concerns:

  1. ConstrainedLayoutIR.break_origins (BreakOrigin) — the spec's LayoutConstraint enum is normative and carries no origin field, but a casting-off solver that honours a user break must record the decision with DecisionSource::UserOverride(id) (Chapter 7 §"Note Layout" / §"Engraving Overrides"), and the override id would otherwise be lost at the logical→constrained boundary. The projection therefore records the attribution alongside the constraint list (slot, break class, override id) rather than widening the normative enum. Non-canonical, like every constrained-stage value.
  2. continuation_instance_key — the stable SynthesisInstanceKey derivation for engraver-synthesized continuations of an existing object (the per-system segments a casting-off break cuts a region-spanning staff line into): keyed on the original object's stable id plus the 1-based continuation ordinal, hashed under MUSCLOID domain separation so segments of different lines cannot collide for one (source, kind) pair.
  3. Round-trip contract: solver-synthesized additions. round_trip_with previously asserted the constrained→resolved provenance maps equal; a casting-off solver legitimately synthesizes new objects (staff-line continuation segments), which Chapter 7 §"Provenance" explicitly allows for engraver-synthesized objects. The contract is now: every constrained object survives with its exact provenance (containment, not equality); every solver addition must declare a SynthesisKind and derive from an already-laid-out source (so the recovered source set is unchanged); the Stub tier must add nothing.

Pass 12 candidates (ambiguities for the spec, not resolved in code)

1. Strength attachment to constraint instances. Chapter 9 §"Strength Levels" defines ConstraintStrength, and §"Constraint Families" says the solver consumes constraints "in normalized form" — but the normalized form is never specified, and Chapter 7's LayoutConstraint enum has no strength field, so there is no normative channel by which a constraint instance carries its strength. v0 attaches strength by rule (LayoutConstraint::strength(), above); the spec should either bless that rule (breaks strength = BreakKind, all other core families Required, extensions conservative) or add an explicit strength/weight field to the normalized constraint record.

2. No renderable status for "constraints not evaluated". A Stub-tier (below-conformance) solver that preserves geometry but evaluates nothing has no honest SolveStatus: every renderable status is documented as "all hard constraints satisfied", and the failure statuses mark the layout diagnostic-only, which a verbatim passthrough is not. v0 uses SolvedWithWarnings with satisfied_hard_constraints == false and a warning; the spec should either define the report shape for a non-evaluating tier or state that SolvedWithWarnings + satisfied_hard_constraints == false is the sanctioned encoding.

Pass 11 candidates (ambiguities for the spec, not resolved in code)

1. Agent E's stated dependency set vs. the edit-barrier types. The QUICKSTART says Agent E "depends on A and B," but assigns it the edit-barrier types, which reference Agent C's OperationKindTag, and the spec's EditBarrier additionally references ObjectKind and ExtensionId (Chapter 8, the bundle's chapter). The dependency note, the type assignment, and the type's chapter home are in tension; the spec should either bless a layout→ops dependency for the discriminator type or relocate the edit-barrier types.

2. Provenance / layout-object id derivation. — RESOLVED (ratified Pass 11; wired P12-I2). Chapter 7 originally declared LayoutObjectId(pub u128) and required stability across relayouts without specifying the derivation, its domain separation, or how multiply-manifested / synthesized objects are keyed. Pass 11 ratified the MUSCLOID-tagged derivation (req:layoutir:object-id-derivation) — single objects keyed on source.canonical_bytes(), multiply-manifested on (source, region), synthesized on (source, synthesis_kind, stable_semantic_instance_key) — and P12-I2 wired it: epiphany-determinism reserves the built-in DomainTag::LAYOUT_OBJECT_ID and provenance.rs (and the engraving-decision id) route through it. See the ratified-block note at the top of this file.

Quality Metric Catalog constants (src/quality.rs, 2026-07)

Decision: the catalog's normative constants live in this crate, as a pure transcription. The Quality Metric Catalog companion (v0.2.0) pins the nine axes' normalization anchors (R_worst), the clamped-linear normalization form n = min(1, raw / R_worst), the Minimal/Standard threshold table, the QualityFloorApproached warning fraction (0.8), and the tier/profile → threshold-column mappings (Minimal has its own column; Standard and Advanced use the Standard column; profiles Draft → Minimal column, Standard and Publication → Standard column, Standard the default). Both consumers — the epiphany-engrave solver (computing vectors and floor diagnostics) and the epiphany-testkit reference-suite harness (asserting per-tier thresholds) — need the same numbers, and this crate is the only one both already depend on, so the constants live here (quality.rs) with doc comments citing the companion by chapter/section. Every value is transcribed, none invented; a change to any of them is a catalog revision first, mirrored here. The module is additive: no canonical encoding is touched (metric values remain diagnostic-only, structurally outside ResolvedLayoutIR — the catalog's own requirement), and the StubSolver still computes nothing and keeps its all-worst unmeasured() vector, which a transcription test pins as excluded by the Minimal column ("measuring is part of the Minimal claim"). The catalog also blesses the existing TieBreakingWeights::default() (all 1.0) as the normative defaults — pinned by test rather than re-declared.

Break-origin attribution and system-continuation synthesis (Pass 12 P12-I9/I10, ratified)

Two long-standing layout-ir dispositions were ratified into the core spec by the schema-major-1 track's Phase F (2026-07-06; spec/PASS12_RATIFICATION_LOG.md, schema-major-1 tranche):

• P12-I9 — break-override attribution via a sidecar. Honouring a user break carries DecisionSource::UserOverride(id), but a normalized break constraint (SystemBreakAt/PageBreakAt) carries no override identity. Attribution is threaded through a ConstrainedLayoutIR.break_origins sidecar populated by to_constrained; the normalized constraint record is deliberately not widened (attribution is a projection concern, not a solver input). Ratified as core spec req:layoutir:break-origin-attribution.
• P12-I10 — system-continuation synthesis. A stroke spanning a system boundary is split; the post-first segments are synthesized under SynthesisKind::Registered(SYSTEM_CONTINUATION_SYNTHESIS) with a (original, ordinal) stable_semantic_instance_key. Since LayoutObjectIds are non-canonical and re-derived per layout, the key need only be stable within a layout. Ratified as core spec req:layoutir:continuation-synthesis.

Pass 12 G-pass (2026-07-07): I4/I5/I6 are ratified

Dispositions in spec/PASS12_RATIFICATION_LOG.md ("G-pass tranche"), all adopt-as-implemented; these are deliberate Standard-tier design inputs. I4 strength is kind-determined (req:solver:kind-strength): no instance strength field; breaks by BreakKind (Hard→Required, Soft→Preferred{1.0}), other core families Required, Registered conservative Required; future constraint families declare their strength in their normative definitions. I5 the stub's constraints-present-but-unevaluated report (SolvedWithWarnings + satisfied_hard_constraints == false + warning) is sanctioned (req:solver:subconformant-report). I6 the implemented emission set (successive-notehead no-collision chains + per-glyph containment

• user-break constraints) is the normative Minimal-tier floor (req:layoutir:constraint-floor).

Repeat barlines and volta brackets (schema major 2, E1, 2026-07-07)

Ratified (Phase F, 2026-07-08): these decisions are now the normative Minimal-tier floor req:layoutir:repeat-render in core spec Chapter 7 (§ResolvedLayoutIR); the non-glyph primitives the volta brackets use are req:layoutir:resolved-primitives. Layout geometry is non-canonical, so no wire/companion-version change (PASS12_RATIFICATION_LOG.md, schema-major-2 tranche).

The first repeat-structure ink (Chapter 5 RepeatStructure / RepeatKind / Volta, ratified by the major-2 Phase A). Rendering is spec-unconstrained (Ch7's BarLine payload is undefined and voltas have no layout variant), so these are E1 implementation decisions for the Phase-F ratification pass:

• Kind → ink mapping. SimpleRepeat and Volta draw repeat barlines at their boundaries; DaCapo/DalSegno draw no Minimal-tier ink (segno / coda / instruction marks need a text primitive — a later tranche) but keep their traced anchors. Volta brackets draw for the voltas list of any kind.
• Morph, standalone, or dots. A boundary whose column carries a measure's own barline morphs that barline into the precomposed SMuFL sign (repeatLeft / repeatRight / repeatRightLeft when an end meets a start) — a name change only: the measure's exact provenance is preserved verbatim because the round-trip provenance floor compares it exactly; repeat-edit invalidation is carried by the ScoreVersion (v0 relayouts wholesale), and an incremental tranche would add the dependency at the logical stage where dependencies are established. A boundary with no coinciding measure barline stands alone as a repeat-synthesized sign at its own barline-role column (REPEAT_BARLINE_SYNTHESIS; one per (column, staff); coinciding structures merge into one sign whose synthesis owner is the smallest (structure id, boundary site) — a semantic instance key, (site << 32) | staff index, stable under unrelated edits where a positional column rank would re-derive). The region-closing column: an end repeat there adds the repeatDots pair beside a staff's final barline (the final barline never morphs, keeping the casting-off solver's final-barline classification truthful), or draws the full end sign on a staff whose run continues (no final barline there); a start repeat at the region close draws nothing on any staff — a sign after the close would misstate the structure.
• Source-geometry clearance. An end-facing sign's ink reaches ~1.1–1.3 staff spaces left of its column (its heavy line right-aligns to the plain barline's span), so the mark's column reserves that reach through the accidental-overhang mechanism and the source layout stays collision-free. A morphed measure's time-signature digits shift right by the sign's right extension (repeatLeft/repeatRightLeft are wider than the barline they replace); both adjustments are zero for the plain barlines, so repeat-free geometry is untouched.
• Honest placement. Repeat boundaries resolve via RepeatPlacement at projection time (to_constrained has no Score): At(time), RegionEnd (zero-offset anchors to an existing region's end edge or to the end of an instance's last measure — the column is knowable where the time is not; zero-ness is judged by value, so a Musical(0) offset earns the same verdict as the Zero variant), or Unresolved, which draws no ink — unlike resolve_time_anchor's origin fallback, a repeat sign at a false position would misstate the musical structure. A bare wall-clock boundary is Unresolved: it references no graph object, so nothing pins it to the region it would draw in — the sign would land wherever its time happens to sort among that region's columns (repeat ink for wall-clock-synchronized material is a later tranche; wall-clock TimePoints reached through an object anchor place normally). Cross-region repeats keep the traced anchor only (content is dropped on the cross-region path — a documented Minimal boundary until repeat ink learns to split). Repeat dependencies now come from RepeatStructure::anchor_sites() (THE single site-set walk), so volta spans and jump targets are real invalidation and region-membership evidence.
• Volta brackets. Three strokes above the top staff (line at VOLTA_Y = 6.5 staff spaces, two descending hooks) plus the ending numbers as timeSig0..9 digit glyphs (the Minimal tier has no text primitive), all synthesized under VOLTA_SYNTHESIS, endings drawn verbatim in authored order. A reversed / zero-width / unresolvable span draws no bracket (advisory volta well-formedness is the authoring layer's jurisdiction). Bracket strokes are ordinary re-spaceable strokes, so the engraver's system-splitting (StrokeFate::Split) applies unchanged.
• Glyphs. The precomposed Bravura signs over hand-compositing heavy/thin/dot primitives; metrics extracted from the same SHA-pinned bravura-1.392 as the rest of the table. The heavy line is aligned to the plain barline's span by a box approximation (repeat_sign_x: start signs left-aligned, end signs right-aligned, the combined sign centred). is_barline_glyph is exported so the casting-off solver classifies measure-boundary columns from this crate's name vocabulary instead of a string prefix.

Slur curves + the cubic-bézier curve primitive (schema major 2, E2, 2026-07-08)

Ratified (Phase F, 2026-07-08): the slur rendering floor is req:layoutir:slur-curve and the Curve/Stroke primitive vocabulary is req:layoutir:resolved-primitives in core spec Chapter 7 (§ResolvedLayoutIR) — the struct listing now carries strokes/curves and the Stroke/Curve shapes, and the RenderIR provenance requirement was widened to name all three primitive kinds. Non-canonical, so no wire/companion-version change (PASS12_RATIFICATION_LOG.md, schema-major-2 tranche).

Extended (Push 3, 2026-07-08): the three E2 deferrals landed and req:layoutir:slur-curve was extended — dashed/dotted lines render faithfully (the Curve listing gains line), break-spanning slurs split into per-system sub-curves (de Casteljau), and slur_shape_penalty is measured (only the curvature algorithm stays forward-referenced out now). See the Push-3 tranche in PASS12_RATIFICATION_LOG.md and the engrave DECISIONS.

The third pipeline primitive kind. Primitives were two parallel flat Vecs (glyphs, strokes) at each of the three IR stages; a Curve (four control points + thickness/layer/style/provenance, mirroring Stroke) adds a third curves Vec at constrained/resolved/render, threaded through canonical encode (a fifth u32 count prefix — the width-lock test moved 4→5), the round-trip provenance chains and count identity, and to_render. Rendering is spec-unconstrained (Ch7's primitive vocabulary delegates drawing to RenderIR, out of scope), so these are E2 decisions for the Phase-F ratification pass:

• Slur geometry (Minimal tier). A slur engraves to ONE cubic bézier arcing between its two endpoint event columns — the slur's exact provenance rides the curve (no synthesis; one primitive per slur), so a drawn slur adds no traced anchor. Endpoints resolve at to_logical to SlurEndpoint::At(onset) / Unresolved (a LayoutContent::Slur payload, exactly the E1 repeat pattern); the constrained stage looks up each onset's Note column. A symmetric arc: endpoints tucked SLUR_INSET in from the columns and SLUR_ENDPOINT_GAP outside the staff on the arc side; control points lifted so the apex (t=0.5) sits height from the endpoint line (lift = 4/3·height, since B(0.5) weights the controls by ¾).
• curvature_override honored structurally. direction (Above/Below; default Auto = above) flips the arc; height (a SpaceUnit) sets the apex, else a span-proportional default clamped to [SLUR_MIN_HEIGHT, SLUR_MAX_HEIGHT].
• Kind and line style: carried, and the deferral is surfaced (review fix). SlurContent carries kind (SlurKind) and line (LineStyle) through the projection — nothing is dropped — but the Minimal tier draws one canonical solid arc for every kind (a phrase mark's longer curve, an editorial slur's distinct line are kind-aware higher-tier work). style.line (dashed/ dotted) is likewise a Push-3 refinement; rather than silently rendering an authored dashed slur solid, a non-Solid line style emits a LayoutDiagnosticKind::SlurLineStyleNotRendered — the curve still draws (solid, ink and provenance preserved), but the ignored intent is surfaced, not papered over (the crate's non-overreach discipline).
• Honest non-drawing. No curve is drawn — the traced anchor keeps provenance, the same discipline as an unresolvable repeat boundary — when: an endpoint is unresolved (dangling event, or a column in another region); the span is not left-to-right after the endpoint inset; or (review fix) the slur resolved to no single staff — endpoints on different staves of one region, where the arc would float at yo = 0 detached from a note on the other staff (cross-staff slurs, like cross-region ones, defer to a later tranche). A cross-region (system-spanning) slur stays the deferred CrossRegionObject anchor-only path.
• Authored dimensions sanitized to defaults (review fix). curvature_override.height and style.thickness are the first user-authored values to reach primitive geometry, and neither the codec nor the invariants bound them positive. A non-positive height (which would flip or collapse the arc) or a non-positive thickness (a zero draws an invisible, unhittable curve; a negative one fails InvalidCurveGeometry and would blank the whole layout) falls back to the engraver's default rather than reaching the Curve. Out-of-range authored dimensions are an authoring-validation concern; the engraver draws something sensible instead of a broken or missing score.
• Hit-testing. A HitShape::Curve { p0..p3, half_width } — Copy-preserving (four points + a scalar) — flattens the cubic into CURVE_FLATTEN_SEGMENTS capsule segments inside its contains/intersects_rect tests, so a curve is ONE hit region (the round-trip and hit-map counts stay + curves.len()), and its AABB is the control-point hull ± half-width (a cubic never bows past its hull). A slur click flows through click()/select() generically — selection.source = Slur — with no editor-core arm; an edit op cleanly refuses the non-pitch selection.