InputMapper tracks a mouse-down over a placed piece and promotes it to
drag mode once the cursor travels past an 8px threshold. Legal drop
cells (those where the piece's start→end vector still fits a legal
placement) are highlighted in green. Releasing on a legal cell emits a
RelocateRequested signal; Main feeds it to MovePieceCommand, which is
already undoable via the existing history stack.
Escape or releasing on an invalid cell cancels. The harness gains a
relocate() helper so UI tests can script drag-and-drop moves without
synthesizing motion events.
Delete autonomous_plan.md (fully shipped), PLAN_playtest.md (all P1-P7
done), PLAN_missions.md and PLAN_leveldesign.md (partial — engine done,
UI polish + 3 final missions + recurring demands + transformer visuals
remain). The surviving TODO list lives in docs/PLAN.md.
Also add the 6-step dev loop to CLAUDE.md (take next topic → implement →
tests → UI test → docs → commit).
