Document numeric HUD opcode contracts

docs/engine-re.md

@@ -2467,6 +2467,38 @@ Focused tests cover stability, overflow, and zero count. A real-script regressio
 SYSTEM4-to-SC0000 state into CHMENU and stops after `0x1db8`, proving selected slot 2 survives the first
 release roster sort without a fallback. No startup seed or menu-specific roster injection is involved.
 
+### Numeric glyph styles/draws and half-byte string length — `0x13a` / `0x23b` / `0x1a6` (2026-07-21)
+
+The missing values in the first working `DEBUGMAP` field HUD are not missing globals or a failed texture
+load. They are generated by a dedicated decimal-glyph subsystem whose two opcodes were still skipped by
+the port:
+
+- `op_0x13a_register_numeric_glyph_style@0x421ab0` takes
+  `(style_index, surface_slot, atlas_x, atlas_y, digit_width, digit_height)`. It accepts style indices
+  `0..10` and stores the remaining five operands in the 20-byte record at
+  `EngineCtx+0x55180+style_index*0x14`; an invalid index raises the standard script error. The corpus has
+  74 registrations in 24 scripts, including eight in `DRAWCHP.BIN`.
+- `op_0x23b_draw_decimal_glyphs@0x424190` takes
+  `(base_handle, style_index, value, x, y, digit_capacity, flags)`. It first erases the destination handle
+  range, splits the signed integer through division/remainder by ten, and binds one retained object per
+  displayed digit using horizontally adjacent cells from the selected style record. Flag bit `0x1`
+  includes leading zeroes, bit `0x2` centers the used digits, and bit `0x4` left-aligns them; without an
+  alignment flag the value is right-aligned in the requested capacity. An invalid or unregistered style
+  raises the script error. The corpus has 147 draws in the same 24 scripts; `DRAWCHP.BIN` has 22 and uses
+  them for the field HUD's turn/control/mana/level/HP/SP/FS values.
+
+This path creates ordinary retained graphics objects, so the existing atlas decode and compositor are
+already the correct backend. The missing engine model is the 11 style records plus the two VM dispatches;
+it is not an immediate `GodotAdvHost.DrawTexture` raster operation.
+
+The absent unit and weapon names are a separate layout-compute gap. `DRAWCHP.BIN` does populate both
+strings and calls `draw-string` at `0x9c6`/`0x9f5`, but first centers each one with opcode `0x1a6`.
+`op_0x1a6_half_byte_strlen@0x427020` resolves the NUL-terminated engine byte string and writes
+`strlen(bytes) >> 1`. The script multiplies that result by 21 and subtracts it from x=257 on a 263-pixel
+scratch surface. With the opcode skipped, x remains 257 and Godot correctly clips nearly all of the text.
+An implementation must preserve the original encoded byte count (or reproduce it with CP932 encoding),
+not use the .NET UTF-16 character count.
+
 ---
 
 ## Native walls backlog (targets for this loop)