Independent native shell review
===============================
Reviewed: port1/ui/native.asm after conversion to direct calls for fixed code
and preservation of BX across GCTurn. Review supplements real-runtime tests;
it does not replace them.

Mouse input
- START_SELECT0x00c3 uses CX/DX document coordinates.
- Unsigned comparisons after LEFT/TOP subtraction reject negative and outside
  coordinates; files and vertically reversed ranks produce a1=0..h8=63.
- BX target survives GCTurn's caller-clobbered registers.
- Promotion target rank remains in CL until the queen-default decision.
- MRF_PROCESSED is returned as0x8000, matching the supplied native PERF app.

Keyboard input
- Old CF_RELEASE mask1 is ignored correctly.
- Backspace/Enter/Escape and maximum5 coordinate bytes stay within the typed
  buffer. The terminating NUL is written after each appended character.
- Underpromotion letters b/n/r/q can be entered; mouse promotion defaultsq.
- Optional robustness: CH special-character-set filtering could reject
  extended/function-key low-byte codes before coordinate input handling.

C/native boundary
- Watcom bridge GCGetSquares prologue at resource30:0x422 pushes SI and DI,
  preserving the live graphics handle DI. It may clobber AX/BX/CX/DX/ES.
- Methods preserve DS/ES and general registers; draw preserves ES; the bitmap
  and code-string helpers balance DS. GCTurn's BX clobber is accounted for.
- Calls do not retain live caller-clobbered values across engine operations.
- Native engine arguments follow the existing far-Pascal bridge interface.

Rendering and memory
- Board, typed move, last move, status text and scratch variables do not
  overlap. Highest scratch word isGS0x2346, below initialized DGROUP0x2400.
- View dimensions300x340 include footer text at322 with10-point font.
- Native window and four buttons fit640x480 or larger. A200-line display is
  below the UI's supported geometry; no CGA-fit claim should be made.
- The engine's bounded recursion and48KB stack remain the supplied port's
  engineering constraint. Host perft/search tests and native move/depth tests
  are required; no universal stack high-water proof is claimed.

No additional release blocker found by this static review. The original
GNUChess bridge implements single-turn undo, automatic engine response,
mate/draw status, depth1..4 and coordinate underpromotion. Mouse promotion
is queen-only. No new file-save or position-editor feature was introduced.
