docs(reverse): decode claw release arithmetic

Correct the coordinate model from guessed 16.16 values to the millipixel arithmetic shown by the 16-bit division routine.

Decode the Borland Real48 direction constants and record the exact position and velocity tables used by every claw terminal.

Test Plan:
- git diff --cached --check
- Compare constants against segment 1 disassembly at 9bca and eab1

original/MECHANICS_PROGRESS.md

@@ -42,17 +42,22 @@ renamed.
   destination is `(238,47)`; closing rows begin at source y=0 and opening rows
   at source y=148.
 - Claw capture/contact uses sound 2015; release uses sound 2016.
+- The release-coordinate projection is `(raw + 500) / 1000` for rendering;
+  decoded physics centers are `(258,78)`, `(270,94)`, `(275,97)`, and
+  `(325,92)` for the four selectable terminal frames.
+- The speed scalar is 3800 millipixels per tick. Its Borland Real48 direction
+  constants are decoded for all release cases in the readable C companion.
 
 ## Explicit pending evidence
 
-- Decode the runtime/FPU conversion used to project the claw's raw 16.16
-  release coordinates and non-frame-18 velocity into playfield pixels.
-- Recover or differentially measure the timer cadence used for each claw frame.
+- Differentially verify the recovered 10/20/30/40/50 ms timer choices against
+  live original captures; the Rust port intentionally uses the default 30 ms
+  claw cadence independently of render rate.
 - Transcribe the full fixed-point flipper impulse calculation, then compare it
   with the Rust floating-point collision response.
 - Validate the reconstructed sequences against deterministic Rust traces and
   captured frames from the original executable.
 
-Those four items are intentionally not counted as semantic parity. The readable
+Those items are intentionally not counted as semantic parity. The readable
 C file preserves their raw constants and labels the unresolved conversion so a
 later implementation cannot silently turn an estimate into claimed evidence.

original/TDKPIN_MECHANICS_RESTORED.c

@@ -51,13 +51,18 @@ typedef struct {
 typedef struct {
     uint16_t low;
     int16_t high;
-} Fixed32Words;
+} MillipixelWords;
 
 typedef struct {
-    Fixed32Words x;
-    Fixed32Words y;
+    MillipixelWords x;
+    MillipixelWords y;
 } RawClawReleasePosition;
 
+typedef struct {
+    float x;
+    float y;
+} Vec2F;
+
 /*
  * FUN_1008_0002 at 1008:0002.
  * The called loader/player resolves argument N as Win16 WAVE resource 2000+N.
@@ -154,9 +159,10 @@ static void render_claw(uint16_t frame, ClawSpriteBank bank)
 static const uint16_t CLAW_TERMINAL_FRAMES[4] = {1, 6, 7, 18};
 
 /*
- * Raw 16.16 positions assigned by export ordinal 10 at 1000:eab1.
- * These words are preserved until the original coordinate projection is
- * fully decoded; do not substitute guessed screen pixels here.
+ * Raw signed 32-bit millipixel positions assigned by export ordinal 10 at
+ * 1000:eab1. FUN_1000_9bca adds 500, divides by 1000, then subtracts the
+ * eight-pixel ball radius only for bitmap placement. The physics position is
+ * therefore the raw value divided by 1000, not a 16.16 fixed-point number.
  */
 static RawClawReleasePosition raw_claw_release_position(uint16_t frame)
 {
@@ -186,6 +192,44 @@ static RawClawReleasePosition raw_claw_release_position(uint16_t frame)
     }
 }
 
+static int32_t join_millipixel_words(MillipixelWords value)
+{
+    return ((int32_t)value.high << 16) | value.low;
+}
+
+static Vec2F claw_release_position_pixels(uint16_t frame)
+{
+    RawClawReleasePosition raw = raw_claw_release_position(frame);
+    return (Vec2F){
+        join_millipixel_words(raw.x) / 1000.0f,
+        join_millipixel_words(raw.y) / 1000.0f,
+    };
+}
+
+/*
+ * Real48 constants loaded in 1000:eab1 after converting speed scalar 3800.
+ * The result is millipixels per timer tick. Only 1, 6, 7, and 18 are selected
+ * as random terminal frames, but all switch cases are retained here.
+ */
+static Vec2F claw_release_velocity_millipixels_per_tick(uint16_t frame)
+{
+    switch (frame) {
+    case 1:  return (Vec2F){3800.0f * -0.60f, 3800.0f * 0.00f};
+    case 2:  return (Vec2F){3800.0f * -0.45f, 3800.0f * 0.05f};
+    case 3:  return (Vec2F){3800.0f * -0.70f, 3800.0f * 0.30f};
+    case 4:  return (Vec2F){3800.0f * -0.30f, 3800.0f * 0.20f};
+    case 5:  return (Vec2F){3800.0f * -0.32f, 3800.0f * 0.22f};
+    case 6:  return (Vec2F){3800.0f * -0.40f, 3800.0f * 0.60f};
+    case 7:  return (Vec2F){3800.0f * -0.31f, 3800.0f * 0.70f};
+    case 8:  return (Vec2F){3800.0f * -0.20f, 3800.0f * 0.80f};
+    case 9:  return (Vec2F){3800.0f * -0.10f, 3800.0f * 0.90f};
+    case 18: return (Vec2F){0.0f, 1000.0f};
+    default:
+        unreachable_original_state();
+        return (Vec2F){0.0f, 0.0f};
+    }
+}
+
 /* Object-id 0x59 branch inside FUN_1000_c79c at 1000:c79c. */
 static void begin_claw_capture(ClawState *claw, uint16_t random_0_to_3)
 {
@@ -231,13 +275,9 @@ static void update_claw(ClawState *claw)
     claw->target_frame = 10;
     claw->bank = CLAW_OPENING_OR_IDLE;
     reset_ball_forces();
-    set_ball_position_raw(raw_claw_release_position(claw->frame));
-
-    if (claw->frame == 18) {
-        set_ball_velocity_raw(0, 1000);
-    } else {
-        set_ball_velocity_from_original_speed_scalar(); /* projection pending */
-    }
+    set_ball_position_pixels(claw_release_position_pixels(claw->frame));
+    set_ball_velocity_millipixels_per_tick(
+        claw_release_velocity_millipixels_per_tick(claw->frame));
 
     commit_ball_position();
     play_sound_number(16);