feat(reverse): isolate original physics substeps

Expose the original detail-derived integration count, active-ball count,
gravity, maximum speed, and movement flags in live traces. Allow probes to
force one physics substep so a single collision response can be observed
without the default three-step timer batch obscuring intermediate state.

Record the dynamically verified type-2 rail response: resolve velocity in the
registered line's normal/tangent basis, apply the two original Real48
coefficients, then advance from the previous position using that response.

Test Plan:
- `ruff check original/tools/trace_original_state.py original/tools/inject_original_state.py` -- passed
- one-substep probes against both vertical shooter walls -- passed
- ordinary rail responses matched 0.6 normal rebound and 0.1 tangent coupling
- `git diff --cached --check` -- passed

original/tools/inject_original_state.py

@@ -18,6 +18,7 @@ from trace_original_state import (
     NEXT_BALL_Y,
     OBJECT_BALL_X,
     OBJECT_BALL_Y,
+    PHYSICS_SUBSTEPS,
     PREVIOUS_BALL_X,
     PREVIOUS_BALL_Y,
     VELOCITY_X,
@@ -49,6 +50,12 @@ def parse_args() -> argparse.Namespace:
     parser.add_argument("--y", type=float, required=True, help="ball center y in logical pixels")
     parser.add_argument("--vx", type=float, default=0.0, help="x velocity in pixels per timer tick")
     parser.add_argument("--vy", type=float, default=0.0, help="y velocity in pixels per timer tick")
+    parser.add_argument(
+        "--substeps",
+        type=int,
+        choices=range(1, 6),
+        help="temporarily force the original physics substep count",
+    )
     return parser.parse_args()
 
 
@@ -106,6 +113,8 @@ def main() -> None:
                 (NEXT_BALL_Y, next_y),
             ):
                 memory.write(data_base + offset, value)
+            if args.substeps is not None:
+                memory.write(data_base + PHYSICS_SUBSTEPS, struct.pack("<H", args.substeps))
             for offset, value in (
                 (VELOCITY_X, velocity_x),
                 (VELOCITY_Y, velocity_y),

original/tools/trace_original_state.py

@@ -31,8 +31,12 @@ CLAW_FRAME = 0x086D
 CLAW_TARGET_FRAME = 0x086F
 CLAW_SPRITE_BANK = 0x0873
 CLAW_ANIMATION_BLOCKED = 0x0874
+PHYSICS_SUBSTEPS = 0x0871
 
 # Recovered offsets in the live game-window object.
+MAXIMUM_SPEED = 0x0056
+GRAVITY_PER_SUBSTEP = 0x005A
+ACTIVE_BALL_COUNT = 0x0061
 VELOCITY_X = 0x0BAA
 VELOCITY_Y = 0x0BAE
 PREVIOUS_BALL_X = 0x0BBA
@@ -44,6 +48,8 @@ RIGHT_FLIPPER_POSITION = 0x0BD6
 LEFT_FLIPPER_DOWN = 0x0BDA
 RIGHT_FLIPPER_DOWN = 0x0BDB
 BALL_SUSPENDED = 0x0BDF
+BALL_ACTIVE = 0x0BDD
+COLLISION_DISABLED = 0x0BD8
 OBJECT_READ_SIZE = 0x0BE0
 
 
@@ -208,6 +214,10 @@ CSV_FIELDS = [
     "elapsed_us",
     "player_count",
     "current_player",
+    "physics_substeps",
+    "active_ball_count",
+    "maximum_speed_milli_per_tick",
+    "gravity_milli_per_substep",
     "ball_x_milli",
     "ball_y_milli",
     "next_ball_x_milli",
@@ -222,6 +232,8 @@ CSV_FIELDS = [
     "right_flipper_position",
     "left_flipper_down",
     "right_flipper_down",
+    "ball_active",
+    "collision_disabled",
     "ball_suspended",
     "claw_active",
     "claw_frame",
@@ -235,6 +247,10 @@ def sample_state(data: bytes, obj: bytes) -> tuple[int, ...]:
     return (
         data[PLAYER_COUNT],
         data[CURRENT_PLAYER],
+        unpack_u16(data, PHYSICS_SUBSTEPS),
+        obj[ACTIVE_BALL_COUNT],
+        unpack_i32(obj, MAXIMUM_SPEED),
+        unpack_i32(obj, GRAVITY_PER_SUBSTEP),
         unpack_i32(data, BALL_X),
         unpack_i32(data, BALL_Y),
         unpack_i32(data, NEXT_BALL_X),
@@ -249,6 +265,8 @@ def sample_state(data: bytes, obj: bytes) -> tuple[int, ...]:
         unpack_u16(obj, RIGHT_FLIPPER_POSITION),
         obj[LEFT_FLIPPER_DOWN],
         obj[RIGHT_FLIPPER_DOWN],
+        obj[BALL_ACTIVE],
+        obj[COLLISION_DISABLED],
         obj[BALL_SUSPENDED],
         data[CLAW_ACTIVE],
         unpack_u16(data, CLAW_FRAME),