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/MECHANICS_PROGRESS.md

@@ -105,7 +105,8 @@ The executable image remains unchanged; only the current disposable Wine
 process is modified. Run the injector while the ball is waiting in the launcher
 so it can identify the live game object, or supply the previously reported
 `--object-base` to both the injector and tracer during a sequence of active
-probes.
+probes. `--substeps 1` isolates one collision integration step; omitting it
+retains the original configured detail level.
 
 A probe at `(289,94)` captured the original terminal-18 path. The collision
 suspended the ball while frames advanced from 10 through 18 at the configured
@@ -113,3 +114,11 @@ suspended the ball while frames advanced from 10 through 18 at the configured
 then cleared suspension during the same timer callback. The three default
 physics substeps each added 15 millipixels of vertical velocity, confirming the
 observed total gravity increment of 45 per timer tick.
+
+A one-substep probe against the vertical shooter walls recovered the type-2
+response arithmetic. For unit tangent `t` from the registered start to end and
+left normal `n`, an incoming contact with `vn = dot(v,n)` and `vt = dot(v,t)`
+uses `vn' = -0.6 * vn` and `vt' = vt + 0.1 * vn` for the ordinary rail
+coefficients stored in its two Real48 fields. The new position is the previous
+position plus this response velocity; the original does not separate a circle
+from the line with a modern capsule solver.