reasampler/docs/COMPLETED.md

# 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."*

### 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-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.