Archive Milestone 6 in docs

Move completed M6 (insert placement onto selected tracks at edit cursor)
from PLAN.md to COMPLETED.md with a decisions note.

COMPLETED.md

@@ -136,6 +136,24 @@ plays selected sample; multi-select + keyboard nav work.
 
 ---
 
+## Milestone 6 — insert (placement)
+**Goal:** "Insert selected sample at edit cursor" via `InsertMedia`. CONTEXT.md
+§insert, Build order 6.
+**Verify (in DAW):** Selected sample inserts at the edit cursor wrapped in
+`Undo_BeginBlock2` / `Undo_EndBlock2`; conform-to-tempo is an explicit flag —
+**no silent time-stretch** when off.
+
+- [x] `InsertMedia(path, mode)` at edit cursor (verify mode bits against SDK).
+- [x] Conform-to-project-tempo vs literal as an explicit flag (never silent).
+- [x] Undo-block wrapping.
+
+**Notes/decisions:**
+- Placement target: inserts the focused bank sample onto the **currently selected track(s) at the edit cursor** (Daniel's directive — not a new track). Uses `InsertMedia` base mode 0; for multiple selected tracks the sample is placed on each at the same cursor position, then the original track selection and edit-cursor position are restored — non-destructive to editing state. The entire operation is one undo block.
+- No silent time-stretch: the `&4` stretch-to-time-selection bit is never set; a pure `insert_plan` test asserts this across all mode combinations. Conform-to-project-tempo is an explicit separate action (`&8`), never on the default path.
+- Non-destructive to the bank: insert only adds arrange items — no bank/file/ext-state writes.
+
+---
+
 ## 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

PLAN.md

@@ -14,17 +14,6 @@ it here and appends it to `COMPLETED.md`.
 
 ---
 
-## Milestone 6 — insert (placement)
-**Goal:** "Insert selected sample at edit cursor" via `InsertMedia`. CONTEXT.md
-§insert, Build order 6.
-**Verify (in DAW):** Selected sample inserts at the edit cursor wrapped in
-`Undo_BeginBlock2` / `Undo_EndBlock2`; conform-to-tempo is an explicit flag —
-**no silent time-stretch** when off.
-
-- [ ] `InsertMedia(path, mode)` at edit cursor (verify mode bits against SDK).
-- [ ] Conform-to-project-tempo vs literal as an explicit flag (never silent).
-- [ ] Undo-block wrapping.
-
 ## Milestone 7 — capture action family
 **Goal:** Bindable capture actions for master / selected tracks / selected items /
 razor area, each with wet-dry + tail options. CONTEXT.md §actions, Build order 7.