Docs: reflect Phase D2/D3 landing

Archive D2 (view shell) and D3 (persist slice) to COMPLETED.md;
add view/view_tree to CLAUDE.md architecture + view_tree_tests target.

CLAUDE.md

@@ -22,7 +22,7 @@ Vendors two submodules (see `.gitmodules`):
     cmake --build build
     ctest --test-dir build
 
-Five targets:
+Six targets:
 
 | Target | Kind | Purpose |
 |---|---|---|
@@ -30,6 +30,7 @@ Five targets:
 | `peaks_tests` | executable | Pure unit tests for `peaks` — no REAPER, no DAW. |
 | `capture_paths_tests` | executable | Pure unit tests for `capture_paths` — no REAPER, no DAW. |
 | `view_mode_model_tests` | executable | Pure unit tests for `view_mode_model` — no REAPER, no DAW. |
+| `view_tree_tests` | executable | Pure unit tests for `view_tree` — no REAPER, no DAW. |
 | `reaper_reasampler` | loadable module | The actual extension binary (`.dll` / `.dylib` / `.so`). |
 
 ### macOS / Linux: SWELL dialog resources
@@ -50,12 +51,14 @@ There is no hot-reload. Copy the built binary into REAPER's `UserPlugins/` folde
 - `bank_model` — `Sample` metadata struct + `BankIndex` (add/remove/query/tier/dedup-by-hash + JSON round-trip). Test it hard — it is the heart.
 - `peaks` — waveform min/max bin computation from raw PCM. Fed a known signal, asserts envelope. Does not depend on REAPER's peak API.
 - `view_mode_model` — Design View mode system: mode registry, GUID-keyed membership, folder-tree-aware visibility derivation, snapshot-based park/restore planner, JSON round-trip. Mirror of `bank_model` for the Design View phase.
+- `view_tree` — pure `I_FOLDERDEPTH`→FolderTree helper for the Design View shell; no REAPER types at the boundary.
 
 **REAPER-facing shells:**
 - `capture` — `ICaptureBackend` interface; `OfflineRenderBackend` (deterministic default) and `RealtimeRecordBackend`. Input: `CaptureRequest`. Output: finished file + populated `Sample` handed to `bank_model`.
 - `insert` — placement via `InsertMedia`; conform-to-project-tempo is an explicit opt-in flag, never silent stretching.
 - `bank_panel` — docked LICE-drawn grid: thumbnails, audition, multi-select, keyboard navigation.
-- `persist` — project ext state (`SetProjExtState` / `GetProjExtState`, namespace `"reasampler"`) ↔ `bank_model` JSON; project-relative path resolution.
+- `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.
 
 ## REAPER extension contract (src/main.cpp)

COMPLETED.md

@@ -141,3 +141,37 @@ mode.
 - [x] Tests: N-mode add/query; parent follows tagged leaf (multi-mode parent);
   restore-round-trip returns snapshot values (never hardcoded "on"); show-both leaf
   never parked; unknown/stale GUID tolerated; JSON lossless.
+
+---
+
+## D2 — view shell (apply flags in the DAW)
+**Goal:** Read the folder tree and drive REAPER flags per the planner.
+CONTEXT.md §Design View (view shell, REAPER API surface).
+**Verify (in DAW):** Toggling active mode hides + parks inactive leaves
+(`B_SHOWINTCP`/`B_SHOWINMIXER`/`B_MAINSEND`/`I_FXEN` + per-FX offline) and restores
+active ones from snapshot. **Master untouched. `B_MUTE`/`I_SOLO` untouched.**
+Untagged tracks untouched. Parents follow their tagged descendants.
+
+- [x] Build parent↔child tree from `I_FOLDERDEPTH`; feed to `view_mode_model`.
+- [x] Snapshot prior flag values (`GetMediaTrackInfo_Value`) before parking.
+- [x] Apply park/restore ops (`SetMediaTrackInfo_Value` for the four flags;
+  `TrackFX_GetCount` + per-FX `TrackFX_SetOffline`). Verify flag names/signatures.
+- [x] GUID resolution: `GetTrackGUID` / `guidToString` / `stringToGuid` (never index).
+- [x] Review gate: no path touches master visibility or `B_MUTE`/`I_SOLO`, or any
+  untagged track's owned flags.
+
+---
+
+## D3 — persist slice (view state ↔ project ext state)
+**Goal:** Serialize the view section into the `"reasampler"` namespace alongside the
+bank; reapply the active mode on project open. CONTEXT.md §Design View (persist).
+**Verify (in DAW):** Membership + active mode + snapshots survive Save / Save As /
+close+reopen; on open, the active mode's visibility + processing is reapplied.
+Saved-while-parked project restores parked tracks from persisted snapshots (not to a
+guessed "on").
+
+- [x] Serialize/deserialize the view section under `"reasampler"` (shared blob,
+  distinct section from the bank index).
+- [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.

PLAN.md

@@ -127,36 +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`.
 
-## D2 — view shell (apply flags in the DAW)
-**Goal:** Read the folder tree and drive REAPER flags per the planner.
-CONTEXT.md §Design View (view shell, REAPER API surface).
-**Verify (in DAW):** Toggling active mode hides + parks inactive leaves
-(`B_SHOWINTCP`/`B_SHOWINMIXER`/`B_MAINSEND`/`I_FXEN` + per-FX offline) and restores
-active ones from snapshot. **Master untouched. `B_MUTE`/`I_SOLO` untouched.**
-Untagged tracks untouched. Parents follow their tagged descendants.
-
-- [ ] Build parent↔child tree from `I_FOLDERDEPTH`; feed to `view_mode_model`.
-- [ ] Snapshot prior flag values (`GetMediaTrackInfo_Value`) before parking.
-- [ ] Apply park/restore ops (`SetMediaTrackInfo_Value` for the four flags;
-  `TrackFX_GetCount` + per-FX `TrackFX_SetOffline`). Verify flag names/signatures.
-- [ ] GUID resolution: `GetTrackGUID` / `guidToString` / `stringToGuid` (never index).
-- [ ] Review gate: no path touches master visibility or `B_MUTE`/`I_SOLO`, or any
-  untagged track's owned flags.
-
-## D3 — persist slice (view state ↔ project ext state)
-**Goal:** Serialize the view section into the `"reasampler"` namespace alongside the
-bank; reapply the active mode on project open. CONTEXT.md §Design View (persist).
-**Verify (in DAW):** Membership + active mode + snapshots survive Save / Save As /
-close+reopen; on open, the active mode's visibility + processing is reapplied.
-Saved-while-parked project restores parked tracks from persisted snapshots (not to a
-guessed "on").
-
-- [ ] Serialize/deserialize the view section under `"reasampler"` (shared blob,
-  distinct section from the bank index).
-- [ ] Reapply active mode on project open (rebuild tree, run the planner).
-- [ ] 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);