docs: close out wave Theta-W4, and defer the deck layout rework to TODO

docs/PLAN.md

@@ -197,83 +197,15 @@ is the Gate-mode sustain the AHDSR releases out of, and T2's bipolar pitch/filte
 modulate targets whose envelopes W3 just reshaped. T2 additionally depends on W2-T1 for
 the filter's existence and on W2-T3 for the preview button's toolbar position.
 
-**Two tracks, in priority order.** Disjoint: T1 owns the engine loop path and the
-waveform band's marker layer; T2 owns the deck band, the curve popup, and the preview
-button in the chrome band. Neither touches the other's band.
-
-#### Θ-W4-T1 — `gate-loop-sustain`
-
-**Has landed** — see `docs/COMPLETED.md` for the full narrative. Loop points are now a
-usable feature and a Gate-mode loop functions as the sustain. 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`, and 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. Fixed by moving the ghost
-span to `defaultLoopBounds` (last quarter, both handles clear), making a collapsed span
-the explicit OFF gesture, and adding a parameterized crossfade — stored in source
-frames, not ms (a deliberate divergence from the plan's ms lean, following
-`sample_map.h`'s source-frame rule), linear rather than equal-power, and normalized over
-`crossfade − 1` (a review Major fixed a residual seam discontinuity) so the last
-rendered frame lands exactly on the incoming tap. New pure module
-`src/core/instrument/engine/loop/` (`loop_span`) holds the loop math; the editing
-surface is the waveform markers plus a new top-strip `markerHandleRect` grab tab, a
-general fix for markers sharing a frame. Params payload is v11 (`kParamsLoopVersion`);
-slot 12 is reserved for T2. Left to Daniel: whether the seam sounds smooth on real
-material, the top-strip tab's discoverability, the LICE rendering of the tab and
-crossfade fill, and whether the crossfade default should stay 0.
-
----
-
-#### Θ-W4-T2 — `velocity-deck-and-bipolar-curves`
-
-**Goal.** Give the three velocity-curve popups one home, make the pitch and filter curves
-bipolar and off-by-default, and replace the preview button's text with a glyph.
-
-**Consolidates item 11.**
-
-**Surface boundary — owns:** `core/instrument/engine/velocity_curve` (bipolar y-domain),
-`core/instrument/ui/curve_popup`, the **deck band** (the new VELOCITY group), and **the
-preview button in the chrome band** at the toolbar position W2-T3 gave it. Does not touch
-the waveform band.
-
-**Behavior.**
-- **The VELOCITY deck.** All three velocity-curve popup buttons (amp, pitch, filter) live
-  **together in a new control deck group labelled "VELOCITY", placed to the left of the
-  VOICE group.** This **supersedes the original ask's per-section placement** — Daniel
-  confirmed the MASTER placement was a real contention point: **MASTER is reserved for
-  other, post-voice-mixer concerns** he will add to later, so the velocity curves do not
-  belong there. No velocity-curve button appears in MASTER, PITCH, or Filter.
-- **Bipolar pitch/filter transfer functions.** Pitch and filter velocity transfer
-  functions are **bipolar: y range [−1, 1], default y = 0** — flat at zero, meaning
-  velocity modulation of pitch and filter is **off until the user draws a curve**.
-- **Amp stays unipolar at [0, 1]**, and its existing flat-unity default is unchanged.
-- **Storage:** the curves live in the instrument's one parameter set.
-- **Preview glyph.** The preview button's inner text is replaced with a glyph. Proposed
-  at product level: a right-pointing **play triangle** — the universal audition read.
-  **Daniel's constraint: no new dependencies** — a statically embedded bitmap or
-  equivalent that plays nicely with the existing LICE drawing path.
-
-**Acceptance criteria.**
-- The three velocity-curve buttons sit together in a deck group labelled **VELOCITY**,
-  immediately to the left of the VOICE group; no velocity-curve button appears in MASTER,
-  PITCH, or Filter.
-- Opening the pitch or filter curve shows a **bipolar editor ([−1, 1]) defaulted flat at
-  y = 0**; played velocities produce no pitch/filter modulation until a curve is drawn,
-  then audibly follow it.
-- The amp curve's domain ([0, 1]) and flat-unity default are unchanged.
-- The velocity curves persist in the one parameter set and round-trip save/reload.
-- The preview button shows the glyph (no text) and stays legible in **all** interaction
-  states; **no new build or runtime dependency is introduced.**
-
-**Open questions.**
-- **Does a user-facing pitch velocity transfer curve already exist, or does this item
-  introduce it? [verify]** Unverifiable in the source doc under its no-code-reads
-  constraint. If absent, this track introduces it. Check before scoping.
-- **Bipolar rendering in the shared spline editor [propose].** Item 3 (Θ-W5) enhances the
-  one spline implementation for hard points; this track must render and edit a bipolar
-  y-domain alongside the amp curve's unipolar one. Land the bipolar domain here in the
-  existing editor; Θ-W5 then adds hard points to the same editor without re-deciding the
-  domain.
+**Both tracks have landed** — Θ-W4-T1 (`gate-loop-sustain`) and Θ-W4-T2
+(`velocity-deck-and-bipolar-curves`) — see `docs/COMPLETED.md` for the full narrative of
+each. Between them: loop points are now a usable feature, with a Gate-mode loop acting
+as the sustain and a parameterized crossfade at the seam; and the three velocity-curve
+popups (amp, pitch, filter) now live together in a new VELOCITY deck group, with the
+pitch and filter curves bipolar and flat-by-default so their modulation is off until
+drawn, while the amp curve stays unipolar and unchanged, and the preview button's text
+is replaced by a drawn play-triangle glyph. Params payload reached v11 with T1's loop
+block and v12 with T2's velocity→pitch curve appended after it.
 
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