Docs: reflect Phase D4 landing

Archive D4 (actions + integration) to COMPLETED.md; add track_guid and
Design View action family to CLAUDE.md architecture.

CLAUDE.md

@@ -59,7 +59,8 @@ There is no hot-reload. Copy the built binary into REAPER's `UserPlugins/` folde
 - `bank_panel` — docked LICE-drawn grid: thumbnails, audition, multi-select, keyboard navigation.
 - `persist` — project ext state (`SetProjExtState` / `GetProjExtState`, namespace `"reasampler"`) ↔ `bank_model` JSON + `ViewModeModel` JSON (`"view_state"` key); project-relative path resolution.
 - `view` — Design View shell: reads the folder tree via `view_tree`, snapshots flag values before parking, drives hide + CPU-park on inactive-mode leaves (`B_SHOWINTCP`/`B_SHOWINMIXER`/`B_MAINSEND`/`I_FXEN` + per-FX offline) and derived visibility on parents; restores from snapshot. Never touches master or `B_MUTE`/`I_SOLO`.
-- `actions` — registers the capture/placement/slot action family and routes each to the modules above.
+- `track_guid` — shared `MediaTrack*` → canonical GUID-string formatter; single source of truth for membership keys used by both the view shell and the actions layer.
+- `actions` — registers the capture/placement/slot action family and the Design View action family (toggle active mode, activate Arrange/Design, tag/untag selected tracks, show-both); routes each to the modules above via the `command_id`/`gaccel`/`hookcommand` contract.
 
 ## REAPER extension contract (src/main.cpp)
 

COMPLETED.md

@@ -175,3 +175,28 @@ guessed "on").
 - [x] Reapply active mode on project open (rebuild tree, run the planner).
 - [x] Confirm survival across Save / Save As; snapshot durability across
   save-while-parked.
+
+---
+
+## D4 — actions
+**Goal:** Bindable action set for the mode workflow. CONTEXT.md §Design View
+(actions). **Verify (in DAW):** Each action registered (bindable in Actions list);
+toggle + mode-jumps MIDI-bindable; tag/untag acts on the current track selection.
+
+- [x] Toggle active mode (cycle; extensible to cycle-all for >2 modes).
+- [x] Activate mode: Arrange / Activate mode: Design (direct jumps).
+- [x] Tag selected tracks → Design / → Arrange; Untag selected (= → Arrange).
+- [x] Show-both for selected tracks (toggle).
+- [x] Register each (`command_id`/`gaccel`/`hookcommand`); toggle + jumps MIDI-bindable.
+
+**Notes/decisions:**
+- New `src/actions.{h,cpp}` — the Design View action family registered via the
+  `command_id`/`gaccel`/`hookcommand` contract in `main.cpp`; MIDI-bindable.
+- New `src/track_guid.{h,cpp}` — shared `MediaTrack*` → canonical GUID-string
+  formatter; used by both the view shell and the actions layer (single source of
+  truth for membership keys).
+- Wiring: actions drive the D2 view shell and D3-persisted model; saved active mode
+  is reapplied on project load via a load-signal seam in `persist` (`loadFromProject`
+  raises it; `main.cpp`'s timer drains it) — `persist` stays model-only.
+- A pure `nextModeId` free function added to `view_mode_model` (the N-mode cycle
+  decision behind "toggle"), unit-tested in the existing `view_mode_model_tests`.

PLAN.md

@@ -127,17 +127,6 @@ landed milestone.
 > spec: **CONTEXT.md §Design View**. Product framing: `docs/product/design-view.md`.
 > When a point lands, doc-keeper moves it to `COMPLETED.md`.
 
-## D4 — actions
-**Goal:** Bindable action set for the mode workflow. CONTEXT.md §Design View
-(actions). **Verify (in DAW):** Each action registered (bindable in Actions list);
-toggle + mode-jumps MIDI-bindable; tag/untag acts on the current track selection.
-
-- [ ] Toggle active mode (cycle; extensible to cycle-all for >2 modes).
-- [ ] Activate mode: Arrange / Activate mode: Design (direct jumps).
-- [ ] Tag selected tracks → Design / → Arrange; Untag selected (= → Arrange).
-- [ ] Show-both for selected tracks (toggle).
-- [ ] Register each (`command_id`/`gaccel`/`hookcommand`); toggle + jumps MIDI-bindable.
-
 ## D5 — in-window toggle affordance (UI)
 **Goal:** The segmented mode switch in the ReaSampler / bank_panel window header.
 CONTEXT.md §Design View (UI). **Verify (in DAW):** Segmented control shows current