Docs: reflect Phase D1 landing

Rename view_model -> view_mode_model across Design View spec docs;
archive D1 to COMPLETED.md; add view_mode_model_tests to CLAUDE.md
targets table and pure-core list.

COMPLETED.md

@@ -115,3 +115,29 @@ folder still resolves the bank).
 - Project identity: keyed off a **minted GUID** stored in ext state (REAPER exposes no native per-project GUID), not the raw `ReaProject*` — a recycled pointer cannot misread a project switch as a Save-As.
 - Save-As: **copy** semantics (Daniel's decision) — the `reasampler_bank/` folder is copied under the new `.rpp`; the old project's bank stays intact. Every ext-state write calls `MarkProjectDirty` so captures/GUID changes flush on the normal save.
 - Known limitation (narrow, accepted): if a user does Save-As, closes the copy *without saving*, then reopens that copy to a *different* folder while the original is also open, identities can collide. Force-saving after Save-As would close the hole but was rejected as violating non-destructive.
+
+---
+
+## D1 — view_mode_model (pure)
+**Goal:** REAPER-free mode registry + membership index + folder-tree-aware
+visibility derivation + parking/restore planner + JSON round-trip. The heart of the
+phase; mirror of `bank_model`. CONTEXT.md §Design View (Module architecture — pure).
+**Verify:** CTest green. N-mode model (not a boolean); Arrange + Design seeded.
+Restore-planner round-trip (snapshot → park → restore) returns every driven flag to
+its captured value. Parent-derivation correct against a supplied folder tree.
+JSON round-trip lossless across modes + membership + show-both + snapshots + active
+mode.
+
+- [x] Mode registry: ordered (id, display name, ordinal); Arrange + Design seeded;
+  add/query more modes (prove N-mode, not binary).
+- [x] Membership index: `GUID → { mode ids }` + per-track show-both flag;
+  add / remove / retag / query; untagged = Arrange.
+- [x] Folder-tree-aware visibility derivation: given a supplied parent↔child tree +
+  active mode, compute the visible set (active leaves, derived-visible parents,
+  show-both leaves, master always in).
+- [x] Parking/restore planner: emit exact (track, flag, value) op-lists for park and
+  restore from active mode + snapshot record.
+- [x] JSON round-trip: modes + membership + show-both + snapshots + active 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.