Merge Ψ-W1-T4: resolve drop targets per move, not once

# Conflicts:
#	src/shell/actions/CLAUDE.md

src/core/ui/CLAUDE.md

@@ -76,14 +76,20 @@ L7 sub-pass, 2026-07-27):
   geometry modules; the kit's *draw* half is shell, its *geometry* half is pure,
   even where a WDL piece is reused. Look-and-feel work never touches capture,
   placement, or bank data ownership.
-- **L7 drag-gesture precedence is a pure decision helper.** The rule — leave
-  client rect → OS drag-out; else drop on a tab/other bank → move/copy; else
-  same-bank grid → reorder-to-slot (empty slot = place, occupied + no modifier =
-  insert-before-and-shift, occupied + Alt = replace) — is "encoded in a pure
-  decision helper (mirror `drag_out::decideGesture`)"; the shell only reads live
-  pointer/focus/client-rect/modifier state and calls it, then maps the resolved
-  gesture to a cursor via `SetCursor`. No cue or precedence logic belongs in the
-  shell.
+- **Drag-gesture precedence is a pure decision helper, on both sides of the client
+  rect.** Inside: drop on a tab/other bank → move/copy; else same-bank grid →
+  reorder-to-slot (empty slot = place, occupied + no modifier =
+  insert-before-and-shift, occupied + Alt = replace). Outside: `decideDropClass`
+  resolves the surface under the cursor. The shell only reads live
+  pointer/focus/client-rect/modifier state and calls these, then maps the resolved
+  cue to a cursor via `SetCursor`. No cue or precedence logic belongs in the shell.
+- **The drag-out law is per-move and stateless.** The class is resolved from the
+  current pointer on every move and again at the release point; nothing is latched
+  between evaluations. That is what makes every transition reversible and what
+  makes drag speed (WM_MOUSEMOVE coalescing) unable to change an outcome. Leaving
+  REAPER entirely is the one irreversible transition, because the OS hand-off goes
+  modal. A first-move class lock and a drag-lifetime "cannot hand off" latch both
+  existed here and were removed — do not reintroduce either.
 
 ## Modules
 
@@ -91,7 +97,7 @@ L7 sub-pass, 2026-07-27):
 - `bank_grid` — REAPER-free grid layout, selection, keyboard-nav, and thumbnail-cache-key logic for the docked bank panel.
 - `tab_strip` — REAPER-free scrollable tab-strip layout + hit-test for the named-banks strip.
 - `prune_button` — pure layout/hit-test for the `bank_panel` footer Prune button.
-- `drag_out` — pure OS drag-out module: gesture-boundary decision and path-list assembly. The `InstrumentDrop` gesture signals that the shell should execute an instrument-drop rather than a file-copy drag.
+- `drag_out` — the pure drag-out gesture law plus path-list assembly. Owns the `ReaperSurface` vocabulary (OffReaper / TrackPanel / FxSurface / FxEmbed / Arrange / Other — `core/wire/instrument_drop` classifies REAPER's info token INTO it), `decideDropClass` (surface × single-vs-multi payload → Internal / InstrumentDrop / ArrangeInsert / Refuse / OsHandoff / None), and `cueForDropClass`. **No `DropClass` means "nothing happens"**: a surface with no defined outcome for the payload resolves to `Refuse`, which the shell shows as a cursor, so "no silent no-op release" is a property of the enumeration rather than of any call site.
 - `theme` — pure palette module: role→color mapping, REAPER-grey neutral ladder + the pastel accent system, the keyboard strip's spectral ramp, WCAG contrast-floor helpers + `compositeOver` (the effective color of a translucent fill, so alpha overlays are testable). Only the ramp's MID stop is its own constant; lo/hi are still aliases of `accent/primary`/`accent/tertiary`, so a categorical accent move CAN still reorder the ramp — `testSpectralRampLuminanceIsMonotonic` is the build-time catch, not the structure.
 - `component_geometry` — pure button/slider/list-row geometry + hover hit-test helpers.
 - `action_bar` — pure task-grouped action-bar layout/hit-test: clusters (Capture / Placement / Maintenance / Tagging / Switching).
@@ -119,9 +125,12 @@ L7 sub-pass, 2026-07-27):
   worked example. A prior revision wrote the threshold ~25% low and let 15px
   semibold clear a floor it was not entitled to.
 - `card_drag`'s precedence order must stay a pure decision helper mirroring
-  `drag_out::decideGesture` — don't let a shell reimplement gesture precedence
+  `drag_out::decideDropClass` — don't let a shell reimplement gesture precedence
   ad hoc; the cursor-cue mapping in the shell must stay a thin lookup over the
   pure result.
+- `drag_out` is deliberately **dependency-free**, and `instrument_drop` links it
+  rather than the reverse. Inverting that edge would drag the instrument's state
+  serializer into `card_drag` and into every `drag_out` consumer.
 - `rect`'s prior role names survive only as `using` aliases at their old call
   sites — changing `rect.h` itself ripples across every directory that aliases
   it (e.g. `editor_geometry::Rect`); check all alias sites, not just this one.