# COMPLETED.md — ReaSampler landed milestones

Completed milestone entries removed from `PLAN.md`. Each entry preserves its
original Goal, Verify, and checklist points with boxes marked done.

This file holds the current (1.x) cycle's landed milestones only. For all
pre-1.0 (version-0) history, see `docs/ARCHIVE.md`.

### Comment-reduction pass (tree-wide, twelve parallel tracks)

Cut source comment volume tree-wide: 209 files changed, net **−6,493** lines.
Comment-only lines went from 15,073 to ~8,671, a **~42% cut** — before the
pass, 37% of all source lines were comment-only. **Zero code drift**, verified
across all 209 files by comparing comment-stripped hashes; the sole
intentional exception (Daniel-approved) is two user-facing error strings in
`src/shell/capture/capture.cpp` that lost internal milestone IDs (`M8`, `M3`,
`M7+`). Build clean, 61/61 ctest pass. Code review surfaced 2 Major + 8 Minor
findings — all content cut that should have survived — and all ten were
remediated and re-gated before merge. Driver: Daniel's instruction — *"Brief
concise engineering comments. A little why, and maybe context, never WHAT."*

### CMake build-system split (ad-hoc, Daniel's request)

Split the 1423-line root `CMakeLists.txt` into a 91-line root plus 18 per-directory
`CMakeLists.txt` files under `src/`, with two shared declaration helpers
(`reasampler_pure_library`, `reasampler_test`) factored into a new
`cmake/reasampler_targets.cmake`. The root now keeps only repo-global concerns:
version/channel single-source-of-truth, `configure_file`, vendor path vars,
`LICE_SRC`, `enable_testing()`, and the `add_subdirectory` calls. Comments throughout
were rewritten to the project's comment conventions — phase/wave/ticket IDs removed,
module semantics already owned by `src/**/CLAUDE.md` deleted, load-bearing build
facts kept.

Also fixed two duplicate-object-code defects surfaced by the split: 18 `core/`
translation units were previously compiled directly into the `reaper_reasampler`
module *while also* being linked in as static libraries — those 18 source entries
were removed from the module's source list and 3 missing link edges
(`view_tree`, `guid_diff`, `lane_keys`) added so every `core/` TU now enters through
exactly one static-library link edge. A dead `bridge_marshal` link edge was also
dropped from `reaper_reasampler`, and two inaccurate comments in
`src/app/CMakeLists.txt` were corrected.

No `.cpp`, `.h`, `tests/`, or `vendor/` file was touched. Behaviour is unchanged and
was verified mechanically: same 130 targets, same 65 tests all passing,
`reaper_reasampler.dll` byte-identical at 3,477,504 bytes, both channels
(stable/beta) building to the same artifact names and locations as before.

### Θ-W1-T1 — zone-retirement

ReaSampler 9000's zone-mapping system is retired: one loaded capture, one parameter
set, playing across the full keyboard repitched from root with key-tracking — no zones,
no per-zone divergence, no keymap of captures. The dedicated zone-editing face and its
authoring affordances (add/delete zone, per-zone parameter panel, Low/High/Root zone
legend) are gone; the root note survives as a first-class parameter. `sampler_core`
split along the note-routing/per-voice-render responsibility seam (no virtual `tick()`
on the per-voice path), and the Sample face split into chrome/waveform/decks bands with
a shared band-stack allocator, discharging the wave's two structural deliverables.
Migration adopts a saved multi-zone instance's first zone; single-zone instances lift
losslessly.

**Deviations from spec:**
- The key-range open question (**[propose]**) is answered outright rather than left
  open: no key-range concept survives at all — `KeyZone`/`lowNote`/`highNote` are gone
  from the engine, the write format, and the strip. A low/high pair remains re-addable
  later as two ordinary parameters. Θ-W2-T3 consumes this decision.
- **"Which zone is first" (**[verify]**) confirmed:** `PerformanceMap::zones` was an
  ordered vector and `Keymap::resolve` was first-match-in-order, so index 0 was the
  audible zone. Migration adopts index 0, and that zone's `sampleId` supersedes the
  envelope's stored `selectionId`.
- The control row (root strip, preview, velocity knob, curve button, Mono|Stereo) moved
  into the chrome band, directly under the title rather than above the deck —
  user-visible and deliberate; it's what makes Θ-W2's band-disjointness real.
- Loading a capture now clears the three capture-anchored overrides (root, loop span,
  start frame) while keeping the shaping parameters — strictly less destructive than the
  previous whole-zone drop.
- The embed strip became a read-only readout; it lost its click handler since with no
  zones there is nothing to select.
- **Migration side-effect:** a previously-zoned instance with implicit channel mode and
  a stereo capture persisted as Mono will reopen as **Stereo**. It converges on the
  documented rule and is reachable only for old blobs, but "sounds identical" was an
  acceptance bar, so it's a real deviation.
- `sampler_core.{h,cpp}`'s 956-line documented hot-path exception is retired, not
  relocated — the tree now carries no over-ceiling exception at all.
- `note_entry` was deleted as dead code (its only consumer was the removed zone editor).
- **Still unverified:** a real pre-change project reopening through REAPER's `setState`
  has not been exercised in the DAW; migration is proven only in the pure domain against
  hand-laid legacy bytes.

### Θ-W1-T2 — capture-handoff-bugs

Fixed both extension-side capture-handoff defects: drag-out now delivers the capture's
audio at the drop target every time (previously intermittent, retry-fixable); dropping a
capture onto an FX container now loads the instrument with the capture, matching the
FX-button drop path.

**Deviations from spec:**
- Item 5's root cause was three defects, not one: non-atomic COM refcounts racing a drop
  target's background copy; an unverified assumption that REAPER had already called
  `OleInitialize` on the calling thread; and a teardown-before-payload-check ordering bug
  that let an unresolvable payload consume the gesture.
- Item 6's fix rests on an unconfirmed hypothesis — that a bare `instantiate = -1` left
  placement to REAPER's ambient FX-chain insert point, which a container-focused chain
  window moves. It is now pinned to an explicit top-level position; nobody could confirm
  the mechanism without the DAW.
- The opportunistic rider was partly taken: `src/ingest.{h,cpp}` re-homed to
  `src/shell/actions/`. `ext_keys.h` was declined (most consumers sit in another track's
  exclusive surface); `resource.h` was declined (it's a build input paired with
  `src/resource.rc` and the SWELL resgen step).
- **Neither acceptance criterion has actually been met yet.** Item 5's gate is
  explicitly a soak ("a single pass is not a gate") and item 6 needs a live container
  drop; both require REAPER and are outstanding. The code is merged; the acceptance
  gates are not closed.

### Θ-W1-T3 — filter-dsp-port

Lands the per-voice resonant filter as a standalone pure module
(`core/instrument/engine/filter/`, five files: `filter_params`, `filter_coeffs`,
`filter_morph`, `filter_saturate`, `voice_filter`) — concrete `VoiceFilter` type, no
vtable, no allocation in `process()`. **No call site**; Θ-W2-T1 wires it into the voice
path.

**Deviations from spec — the spec itself changed mid-flight, headline first:**
- **The Cortex-M4 biquad port was superseded entirely by a TPT/SVF topology, Daniel's
  call.** Measurement found the firmware's high-pass resonance feedback tap vestigial:
  its stated rationale was inverted (the HP numerator approaches 1 as cutoff falls, not
  zero — it's the LP numerator that collapses), it *reduced* HP resonance everywhere it
  ran, and it carried unwanted sample-rate and input-level dependence. It was a Q15
  fixed-point workaround for a ~17-bit cancellation float32 doesn't suffer. Daniel's
  ruling on the resulting level-dependent resonance bloom: *"was a feature on the
  hardware (one knob colorful HP for master FX), wrong choice for this approach."*
- **Two discrete modes (HP/LP) became a continuous morph, with two selectable morph
  laws** — HP→BP→LP (default) and HP→notch→LP (Oberheim SEM) — chosen at `prepare()`
  via a `MorphLaw` enum on `FilterSettings`. Zero per-sample cost, verified by diffing
  emitted assembly (byte-identical between laws).
- **A configurable drive stage was added:** an in-loop soft limiter on the band-pass
  integrator state, normalized 0..1, with a radial dial planned for Θ-W2. Drive at 0 is
  bit-exact linear.
- **`Biquad1PoleLP` was struck (Daniel's call) and never ported.**
- **Q spans the full 0.1–10 with √2 at the control centre**, replacing the firmware's
  0.707-floored mapping — as originally specified.
- **No reference sample rate exists anywhere in the module** — rate reaches the DSP
  only via `g = tan(π·fc/sr)`. An interim fix that anchored a feedback tap to a
  `1/48000` constant was superseded by the rewrite.
- **The rewrite fixed a float32 conditioning defect the biquad carried:** Direct Form I
  measured −27% peak error at 20 Hz / 192 kHz; TPT measures +0.034%.
- **Still open, deliberately:** drive's maximum depth (4.0, set by measurement — at 64
  the resonant peak inverted below passband) and the absence of makeup gain both await
  an ear pass against the real dial.
- **The module has no call site** — integration is Θ-W2-T1, which also carries three
  recorded decisions of its own: the envelope-order choice (drive is level-dependent, so
  pre- vs post-envelope placement is sound-defining), the drive dial's calibration, and
  the fact that drive authority varies ~11 dB across the morph sweep.

### Θ-W2-T1 — filter-voice-path

Wires the pure filter module into ReaSampler 9000's per-voice signal path as a new fixed
processing point between the pitch envelope and the amp stage, gives it its own
knob-deck group, and relays the deck row in signal-flow order (pitch → filter → amp).
Each `Voice` owns its own `VoiceFilter` and a second `AdsrEnvelope` instance — per-voice,
never shared — and neither adds allocation or virtual dispatch to the per-sample path.
Parameters — morph position, cutoff, Q, drive, mod amount (bipolar ±100%, targeting
cutoff), velocity and key-tracking modulation, then AHDSR — live in the one parameter
set; `FilterParams` stores the filter module's own `FilterSettings` by value rather than
a parallel copy of the normalized positions. The filter is off by default and bit-exact
off — a project saved before the change reopens sounding identical, pinned by a
bit-equality test. `ComponentState`'s params payload moves v8 → v9, appending the filter
tail; a v8 blob is a strict prefix and lifts to the off/neutral filter default, with
non-finite filter fields falling back to neutral, pinned by a golden byte-literal
fixture. Deck composition was extracted into a new pure module
`core/instrument/ui/deck_groups`, with the pitch → filter → amp row order pinned by
test; the filter's AHDSR ships as its own `FILTER ENV` group sibling to `FILTER`,
mirroring the existing `PITCH` / `PITCH ENV` split, and a morph-law toggle (`Band` |
`Notch`) ships as the FILTER group's row toggle.

**Deviations from spec:**
- **An initial mod-quantizer was added, then rejected and removed.** A
  `kFilterModSteps = 2048` step gate on the coefficient re-solve stair-stepped the
  corner (~5.8 cents per step); Daniel rejected it. Replaced by a cutoff-only re-solve
  (`VoiceFilter::setCutoffNorm`) that re-derives only `g = tan(π·fc/sr)` — Q's parabola,
  the morph's cos/sin, and the folded mix are all cutoff-independent and stay cached
  from `prepare()`; `filter_params` hoists its constant logs. Measured at 48 kHz,
  Release, net of the sweep generator: kernel alone 2.8 ns/frame, full `prepare()` 56.9
  ns, cutoff-only re-solve 15.5 ns — about 1.2% of a core for 16 continuously-swept
  voices. The corner now sweeps continuously rather than stair-stepping.
- **The editor floor was raised to 840×620**, which is also its new default size, up
  from a 560×460 floor at which the grown deck wrapped to four rows and pushed
  `FILTER ENV` / `AMP ENVELOPE` / `VOICE` / `MASTER` off-screen with no scroll.
  `kEditorMinWidth`/`kEditorMinHeight` now live in `sample_bands`, read by both the
  shell's `checkSizeConstraint` and the opening `ViewRect`. Consequence worth
  recording: a host with a saved editor rect below 840×620 is clamped up on reopen.

### Θ-W2-T2 — stereo-waveform-lanes

Delivered as specified: two stacked lanes, L above R, in stereo mode; one lane in mono;
overlays draw once at full stacked height.

**Deviations from spec:**
- **A mono source under stereo mode draws one lane**, not two — lane count keys off
  `stereoMode && sourceChannels >= 2`, not channel mode alone, since a mono capture in
  stereo mode is dual-mono and a second lane would be the redundant duplicate the spec
  forbids. Review confirmed this is the only reading consistent with the decode path.
- The full-height overlay contract Θ-W3 and Θ-W4 consume is **type-enforced, not
  merely documented**: an `OverlayArea` wrapper type that lane rects cannot satisfy.
- A single-slot per-channel PCM cache was added to the editor session, invalidating
  alongside the existing PCM cache.

### Θ-W2-T3 — toolbar-and-piano-strip

Delivered as specified: one toolbar font, no zone-count label, full-width piano strip,
uniform key widths, note-name tooltips, root displayed and settable.

**Deviations from spec:**
- **The non-uniform key widths were integer quantisation, not aliasing** — the old
  `keyEdgeToX` truncated an exact rational, alternating 6px/7px. Θ-W6's general
  antialiasing audit inherits nothing on key *widths* as a result, though key *edges*
  are still drawn unantialiased.
- **Uniform integer key widths and gap-free edge-to-edge tiling are mutually
  exclusive** — 75 white keys do not divide an arbitrary width. The residue now lands
  in symmetric end gutters, 37px each side at the shipped 840px default — the maximum
  of a sawtooth with period 75px of window width. Daniel accepted this provisionally,
  pending how it looks in REAPER.
- The whole control run moved into the toolbar row, not just preview and mono/stereo —
  the full-width strip left the velocity knob and curve button nowhere else to go.
- Root drag became absolute-tracking rather than pixel-delta, since black keys
  overlaying white give no single pixels-per-semitone rate.
- **Width uniformity is guaranteed in client pixels only.** Nothing in the instrument
  consumes a DPI scale factor, so host-side scaling is unverified — Θ-W6 already
  carries a "confirm the fix survives DPI scaling" item and now genuinely inherits it.
- A stale-hover latch was fixed across **all** drag kinds and both drag-termination
  paths, wider than the strip work that surfaced it.

### Θ-W3-T1 — live-parameter-delivery

Continuous playback controls are now delivered live to sounding voices instead of being
latched at note-on. New `src/core/instrument/engine/live_params.{h,cpp}` holds a
seqlock-published `LiveValues` block owned at **processor-instance scope**, above
`LoadedInstrument`, so `live_` and `draining_` observe the same one (a drain-slot voice
tracks the knob, which is the desired behavior). `foldLive(const PlayParams&)` is the
single derivation from the value type; `PlayParams` stays a plain copyable value type.

**Daniel's two decisions, both implemented:**
- **Reload tier = Grouping B.** Continuous knobs live (filter cutoff/Q/morph/drive/mod
  amount/key-track; every stage time and level on all three envelopes). Root note, loop
  span, and start frame still trigger a full reload.
- **Mid-stage rule = candidate (iv), hold normalized stage position.** φ =
  elapsed/duration held fixed across a duration change, then advancing at
  1/newDuration — expressed over normalized position specifically so Θ-W3-T2's
  per-segment curve exponent composes with it.

**Deviations from spec:**
- **Trigger's %-length and fades are NOT live** — they are baked into `SampleData` at
  build, so reload is the only tier that can deliver them. Consequence: a Trigger-mode
  instance gets zero live amp delivery until Θ-W3-T2 folds the fade pair into the AHD.
  The five non-live exclusions (`kKeyTrack`, `kFilterVel`, `kTrigLength`,
  `kTrigFadeIn`, `kTrigFadeOut`) are documented in `src/core/instrument/ui/deck_groups.h`,
  now their single home.
- Open question 3 resolved as **F2 + seqlock**; open question 4 (sub-block resolution)
  was not built but not foreclosed — the writer interface assumes no UI thread; open
  question 5 verified — a live edit still persists, `commitLive` keeps the
  `setInstrumentParams` write.
- A filter envelope only advances while its depth is non-zero (the exact-skip at
  `modAmount == 0`), which is what keeps the at-rest path byte-identical.

### Θ-W3-T2 — staged-envelope-curves

Grows the envelope-overlay editor from an amp-only fixture into the shared graphical
surface for all three envelopes (amp, pitch, filter): a corner radio switch per deck
selects which envelope is overlay-active (none by default, exclusive); every sloped
stage on every envelope (Attack/Decay/Release — Hold and Sustain stay flat) gets an
editable curve exponent (0.1–10, 1.0 the linear neutral) via a paired inner knob dial
and a round mid-segment overlay knot, both resolving through the one curve law in
`src/core/util/curve_law.h`; the pitch envelope becomes AHD (Attack → Hold → Decay,
Hold a fraction of the time remaining after Attack and Decay, so A+H+D ≤ span holds by
construction, no clamp); AHDSR envelopes get a right-anchored release, dragged from
its top node with the bottom-right corner fixed; and the Trigger amp/filter
fade-in/fade-out pair is retired in favor of a Trigger AHD, consolidating what were
two staged-shape mechanisms into one — item 8's rule (pitch always AHD; amp and filter
AHDSR in Gate, AHD in Trigger) governs all three. The Trigger × Preserve end-of-sample
click is fixed at its root cause: `freezeTail()` stopping the pitch shifter's writer a
full window before the read head arrives.

**Open question resolved — per-mode stage-value state.** Gate and Trigger keep
SEPARATE stored stage values, on both the amp (`PlaySeconds::adsr` +
`PlaySeconds::trigAhd`) and the filter (`FilterSeconds::env` + `FilterSeconds::trigEnv`).
Migration forces it: an old instance carries both an AHDSR and a fade pair, and one
shared set cannot preserve both modes' prior sound. Cost: ~160 bytes of persisted
state per instance, 6 additional `DeckParam` ids.

**Deviations from spec:**
- **The migration exponent is FITTED, not neutral — Daniel's explicit ruling,
  resolving a spec contradiction.** PLAN.md stated both "pre-existing instances load
  at exponent 1.0" and "exponents at whatever reproduces the prior fade shape";
  those conflict, and the fix resolves toward the second, since it carries the
  migration guarantee. Attack lifts at **p = 0.6133**, decay at **q = 1.7437**; max
  deviation from the retired equal-power (sin/cos) fade shape drops from 0.2105 to
  0.0875. Every non-migrated curve still lifts to the 1.0 neutral.
- **Item 4's fix is deliberately WIDER than spec.** The spec scoped the end-of-sample
  click fix to Trigger × Preserve; the landed fix is not mode-scoped, so Gate ×
  Preserve × source-exhaustion also now rings out (~4 ms) where it previously
  hard-cut. A held Gate note whose source runs out with no loop is cut at sustain
  level, landing on the same recycled synthetic tail — scoping the fix to Trigger
  alone would have knowingly left that click.
- **Migration is lossy under a sample-rate mismatch** — a documented bound, not a
  bug. The retired fades were source frames; the lift divides by the project rate
  while the AHD rebuilds at decode rate, so a rate mismatch shifts migrated stage
  lengths by that ratio. Documented in the v10 version ladder
  (`component_state_io.h`) with a test.
- **Payload version is v10.** `component_state_io.cpp` was split on the format seam
  into `component_state_io.cpp` + a new `params_payload.{h,cpp}`.
- **New pure module:** `src/core/util/curve_law.h` — the one per-segment curve law
  (exponent domain, normalized-position→level map, the mid-segment inverse an overlay
  knot drags through, and the knob's norm↔exponent travel with an exact centre
  detent). The neutral exponent is a bit-identity. Measured cost of a non-neutral
  exponent: ~4.7 ns per evaluation, +224 ns/output frame worst case at 16 voices —
  3.1% → 4.1% of one core at 44.1 kHz.
- **`OverlayEnv` and the overlay-selection state machine live in
  `core/instrument/ui/deck_groups`**, not the shell.
- **The knot-creation gesture differs from spec.** Spec said dragging a segment
  *adds* a knot; the landed behavior draws the knot unconditionally on every sloped
  non-zero segment and responds to a drag within the grab radius. Daniel confirmed
  this reading stands.
- **Loop markers moved from `AccentTertiary` to `AccentSecondary`** — they collided
  exactly with the envelope trace (RGB delta 0) in the same overlay rect. Daniel
  ruled. The palette has since settled: `AccentSecondary` is `#38A8A0` (see the
  palette-rework entry below and `src/core/ui/CLAUDE.md`).

**Left open by this track, resolved later.** The envelope overlay's contrast against
the waveform (tertiary purple, measured 1.37:1, below the 3:1 indicator floor) awaited
Daniel's eye on a build; pinned as a flagged deviation in `tests/test_theme.cpp` at the
time. Resolved by the ad-hoc palette rework below (`91f71f9`/`a19d645`): the trace moved
off `AccentTertiary` onto a new `Role::OverlayTrace` (`#816AA6`), clearing the floor at
3.07:1 — the mathematical ceiling for the pairing. See the palette-rework entry below and
`src/core/ui/CLAUDE.md`.

### Ξ-W1-T1 — tracking-consolidation

Consolidates the provenance/usage territory into one system: the retired
`owned_manifest` gives way to a new `src/core/tracking/` directory holding
`origin_ledger` (the record family — `OriginRecord`/`OriginKind`, the insertion-ordered
`OriginLedger`, its JSON codec, and the `Fresh`/`Loaded`/`Unreadable`/`FutureVersion`
load classification) and `tracking_authority` (the one decision surface:
`pruneProtection` and `tiedUsageExists`). Both prune's protected set and the resample's
replace-vs-add decision are computed from one borrowed `TrackingState`, so the two
safety-critical consumers cannot drift apart. `isAbsolutePath` was hoisted out to a new
`src/core/util/relative_path.h`, shared with `bank_model`'s `Sample.relativePath`.

**Deviations from spec:**
- The deferred persisted-instance-identity fix was **not** folded in — open question 5
  resolved as "restate the deferral." `docs/TODO.md` already carries the sharpened
  rationale (the session-epoch candidate and its sibling-drop flaw); not duplicated here.
- `sample_usage` deliberately **stays in `core/wire`** — the consolidation is of the
  *decisions*, not the codecs.
- A realtime record interrupted by a project switch strands an untracked WAV in the old
  project's bank folder. Resolved as document-don't-delete (prune is the exclusive
  deletion authority); `docs/TODO.md` carries the entry.
- `PruneReport` fields were renamed; a malformed ledger is now reported as a distinct
  blocker with its own recovery instructions.

### Ξ-W1-T2 — note-program-model

Lands the programmed-capture-signal model as a new pure module directory,
`src/core/instrument/note/` — a fourth peer of `engine/`/`map/`/`ui/` under
`core/instrument/` — holding `musical_division` (the 1/64–64/1 ladder with
dotted/triplet multipliers, the 39-entry picker order), `tempo` (validated BPM plus
every beats↔seconds↔ms conversion), and `note_program` (`Velocity`, the denominated
`OffsetAmount`, the anchored `StartOffset`/`EndOffset`, the `NoteProgram` record, and
`resolveNote`).

**Deviations / resolutions from spec:**
- Open question "negative offsets" resolved: both directions are legal and the sign is
  uniform (positive is later in time); only an *inverted* window is refused, reported
  via `ResolvedNote::windowCollapsed`.
- Open question "denomination seam" confirmed: note length is musical-division-only;
  the ms/beats duality belongs to the offsets alone. An offset stores the denomination
  it was **entered in**, deriving the other view on demand, so a beats offset follows a
  tempo change and a ms offset holds still.
- Module name/location resolved as `src/core/instrument/note/` — three modules, not
  one, with the layering enforced by the CMake link line.
- **Beyond spec:** every value type closes its domain at construction behind a single
  normalizing door (`makeDivision`, `offsetOf`, `Tempo::fromBpm`, `Velocity::of`), with
  private value constructors. Consequence: `resolveNote` needs no failure path and
  `ResolvedNote` no validity flag, because every returned field is finite for every
  constructible program and tempo. Junk detection is relocated to the future codec,
  which sees both the bytes it read and the value construction produced. `NoteProgram`
  deliberately carries no MIDI note number — render pitch is deferred to Ξ-W2 as an
  additive field.

### Palette rework — accent/secondary darkening + overlay/trace role (ad-hoc, Daniel's request)

Two commits (`91f71f9`, `a19d645`) resolve the envelope-overlay contrast wart Θ-W3-T2 left
open (see above). `accent/secondary` darkened `#84D6D0` → `#38A8A0`; the keyboard strip's
spectral mid stop decoupled from `accent/secondary` into its own constant, since the
darkening had inverted the ramp's lo→mid→hi luminance ordering. A new `Role::OverlayTrace`
(`#816AA6`) was added and the envelope trace + handles repointed onto it: the trace now
measures **3.07:1** against the waveform — the mathematical ceiling for any single color
sitting between the primary accent and `bg/base` (9.41:1 apart; `sqrt(9.41) ≈ 3.068`),
`#816AA6` landing at 99.94% of that optimum. Two below-floor pairs remain deliberately
accepted — the trace inside the 20%-alpha loop-span fill (2.25:1) and against the
waveform's `line/hairline` zero-line (1.92:1) — both asserted as pinned ranges in
`tests/test_theme.cpp` so either direction of drift fails the build.

Separately: the bank panel's region title enlarged into WCAG large class via a new
`Font::RegionTitle` (19px bold); `theme.h`'s large-text thresholds were corrected (a prior
revision had them ~25% low, letting 15px semibold self-classify as Large); `compositeOver`
was added to `theme` (the composited-fill arithmetic the loop-span-fill contrast pair
depends on); and the grabbed envelope handle was repointed off hue onto a size + ring
treatment, since no two values that clear the overlay-trace ceiling differ enough to carry
a state by color alone.

Full detail — the two-neighbour contrast rule, the WCAG threshold correction, and the
accepted below-floor pairs — lives in `src/core/ui/CLAUDE.md` and
`docs/product/visual-design-language.md` §4 Direction B; not duplicated here.

### Θ-W4-T1 — gate-loop-sustain

Establishes loop points as a usable feature and makes a Gate-mode loop function as the
sustain — indefinite playback until note-off, with a crossfaded seam. The regression
half resolved as **present but unreachable, not removed**: nothing in any capture path
ever wrote `Sample::loop`, so every capture opened with `hasLoop == false`; the ghost
default parked `loopStart` at frame 0 directly under the start marker, where
`markerAtPoint`'s first-in-draw-order tie-break made the handle ungrabbable; and no
crossfade existed at all. Fixed by moving the ghost span to `defaultLoopBounds` (last
quarter of the sample, both handles clear), making a collapsed span the explicit OFF
gesture, and adding a parameterized crossfade.

New pure module `src/core/instrument/engine/loop/` (`loop_span`, its own CMake target,
its own `CLAUDE.md`, `loop_span_tests`) holds `resolveLoop`, `defaultLoopBounds`,
`maxCrossfade`, `crossfadeWeight`, `lerpSource`, `crossfadedSource`. Params payload
bumped to **v11** (`kParamsLoopVersion`), appended at the tail; slot 12 is reserved for
Θ-W4-T2.

**Open questions resolved:**
- **Crossfade units and range.** Stored in source FRAMES, not ms — deliberately against
  the plan's ms lean, because `sample_map.h`'s rule keeps source-timeline quantities in
  source frames and the seconds path is documented lossy under a sample-rate mismatch.
  Default 0 frames (a hard seam, which is what makes the migration bar hold by
  construction); range is the derived `[0, min(loopStart, loopEnd − loopStart)]`.
- **Editing surface.** The waveform markers, plus a new `markerHandleRect` top-strip
  grab tab (top 10px, hit-tested before the full-height marker columns) so markers
  sharing a frame stay independently grabbable — a general fix for the tie-break
  defect, not a crossfade special case.
- **Crossfade shape.** Settled during implementation, not specified in the source doc:
  linear, not equal-power (correlated taps one loop length apart; no transcendental on
  the per-sample path), with a decorrelated full-mix/stem exception recorded in the
  module's own `CLAUDE.md`.

**Deviations from spec / code review:**
- Code review found one Major: the crossfade normalizer left an avoidable residual
  seam discontinuity, and the module's own `CLAUDE.md` had enshrined that limitation as
  a mathematical impossibility. Remediated — `crossfadeWeight` now normalizes over
  `crossfade − 1` so the last rendered frame lands exactly on the incoming tap, the
  false invariant was corrected, and the seam test now asserts against the material's
  natural one-frame step rather than a proportionality band. Six review minors were
  also fixed.
- `voice.h` sits at ~650 lines after `lerpSource`/`crossfadedSource` moved out to
  `loop_span.h` — still over the ~600-line ceiling under the standing documented
  hot-path exception.

**Left open by this track, deferred to Daniel (not defects):** whether the seam sounds
smooth on real material, whether the top-strip tab is discoverable, and the LICE
rendering of the tab and crossfade fill. Also open: whether the crossfade default
should stay 0 (a smooth seam becomes opt-in).