Physics: solve the board/skater with retail's 50 constraint iterations

The stock RWMaxIterations (25) is only the Simulation's setup value; TU3
solves with 50 on every gameplay frame. With 25 the constraints converged
less: wheels sank ~10x faster at rest, the ollie deck sat ~1 cm low and
the jump velocity the pop sound reads was too small (rolling ollie
0.21-0.29 vs retail 0.50), so pops picked the quiet row.

Maps validate identically; water traces stay within expectations. See
docs/hails-additions/12-solver-iterations.md.

crates/skate-game/src/physics/settings.rs

@@ -18,6 +18,16 @@ use skate_core::{
 };
 use skate_data::collections::Collections;
 
+/// Constraint iterations of the skater's `rw::physics::Simulation` (+176), read by the solver
+/// stages `82AE30F0` / `82AE27D0` as their loop count. Measured in TU3 (recomp, Aletown,
+/// board + skater pipeline with 28 joints / 53 drives): 50 on every solve. Setup `82DC2840`
+/// first copies 25 from the hard-coded config built by `8275DCC8` (`li r27,25`); the value is
+/// 50 before the first gameplay solve (the later writer is not identified yet). The stock
+/// `physics/default.RWMaxIterations` is 25, equal to the setup value but not the live one;
+/// solving with 25 left wheels sinking ~10x faster than retail (-0.012 vs -0.001 m/s at rest)
+/// and the ollie pop's deck ~1 cm low by its 4th frame (retail-matching with 50).
+pub(crate) const SIMULATION_ITERATIONS: u32 = 50;
+
 pub(crate) struct PhysicsSettings {
     pub step: BoardStepSettings,
     pub masses: [RetailBodyMassProperties; 7],
@@ -88,7 +98,7 @@ impl PhysicsSettings {
         );
         let step = BoardStepSettings {
             simulation,
-            iterations: data.integer("physics", "default", "RWMaxIterations")?,
+            iterations: SIMULATION_ITERATIONS,
             base_truck_transforms: calculate_truck_transforms(RetailTruckTransformInputs {
                 deck_mid_length: geometry.deck_mid_length,
                 truck_z_position_front: geometry.truck_z_position_front,
@@ -105,8 +115,8 @@ impl PhysicsSettings {
             }),
             force_point_y_offset: f("physicsdeck", "DeckForceYOffset")?,
         };
-        if wheel_radius <= 0.0 || mass_factor <= 0.0 || step.iterations == 0 {
-            return Err("Invalid stock board radius, mass factor or solver iterations".into());
+        if wheel_radius <= 0.0 || mass_factor <= 0.0 {
+            return Err("Invalid stock board radius or mass factor".into());
         }
         Ok(Self {
             step,

docs/hails-additions/12-solver-iterations.md

@@ -0,0 +1,69 @@
+# Board solver: 50 constraint iterations (retail live value)
+
+## Problem
+
+Ollie pops were too soft. Retail's player audio chooses the pop's loudness row from the
+skater's jump velocity (audio state +468 = |Air+112| / 2.65, thresholds 0.25 / 0.42). A rolling
+ollie in retail measures 0.50 at about 4 m/s. Ours measured 0.21–0.29, so every rolling pop used
+the quiet row. A standing ollie (0.507) was already right.
+
+## Root cause
+
+The board/skater solve ran with `physics/default.RWMaxIterations` from the stock collections,
+which is **25**. Retail's live `rw::physics::Simulation` solves with **50** iterations.
+
+- The solver stages `82AE30F0` / `82AE27D0` read the Simulation's iteration count (+176) as their
+  loop count.
+- Setup (`82DC2840`) first copies 25 from a hard-coded config built by `8275DCC8` (`li r27,25`).
+  The value is 50 before the first gameplay solve. The later writer is not identified yet.
+- `RWMaxIterations` = 25 equals the setup value, not the live one.
+
+With 25 iterations the constraints don't converge as far each tick, and the effects were
+measurable:
+- At rest, wheels sank about 10× faster than retail (−0.012 vs −0.001 m/s).
+- By the pop's 4th frame the ollie deck was about 1 cm low.
+- The jump velocity that the audio state reads was lower.
+
+## Evidence
+
+- TU3 traces in the static recompilation (reference only, not shipped): hooks on the Simulation
+  setup and the solver entry logged the iteration count on every solve, recorded in Aletown with
+  the board + skater pipeline (28 joints / 53 drives).
+- Jump velocity after the change: a rolling ollie at 0.35–0.55 (retail 0.50 at ~4 m/s), standing
+  0.56.
+
+## Change
+
+`crates/skate-game/src/physics/settings.rs`: `SIMULATION_ITERATIONS = 50` replaces the
+`RWMaxIterations` read. The "zero iterations" validation goes away with it, since the value is
+now a constant.
+
+## Verification
+
+- `--validate-maps` on every map, 25 vs 50: identical (collision triangles, support drop, grounded
+  ticks, floor gap).
+- Water drop traces (`water_drop`, ignored test), positions as expected with both counts:
+  - University shallow channel (340.3, 69.94, −294.3): lowest body part 67.996–68.014 on 67.94,
+    board 68.03. Settled mean part speed 0.059 → 0.120 m/s; peak 0.46 → 1.56. The user saw
+    nothing wrong in play.
+  - DownTown Aletown canal (−182.3, 10.93, 465.9): parts 8.3–9.0 vs 8.93, board 8.91, camera
+    11.934. Settled 0.357 → 0.247 m/s.
+  - The differences come only from the iteration count: a build with every other change but 25
+    iterations reproduced the old numbers exactly.
+- In play (user, 2026-10-02): pops, landings and grinds much closer to retail; nothing wrong seen
+  in a shallow-water wipeout.
+
+## Open questions
+
+- `customiser_equipment_reaches_ground_force_and_torque` (ignored test, needs private assets)
+  fails at 50 iterations: "Profile hardness was lost before live straighten torque".
+  - Samples of (side force, deck torque y) for hardness 0 / 0.7 / 1.0:
+    - 25 iterations: (−23.31, −1.114), (−15.15, −1.114), (−11.66, +1.170)
+    - 50 iterations: (−23.31, −1.114), (−15.15, −1.114), (−11.66, −1.114)
+  - Side friction still scales with hardness exactly.
+  - Even at 25, only hardness 1.0 changes the torque. The assertion appears to depend on a branch
+    threshold (82C07000 limits the straighten request by the deck's existing angular velocity) in
+    the test's synthetic one-frame state. This is not proven; the test is unchanged.
+- The code that raises the count from 25 to 50 is not identified yet.
+- Pops at 5–8 m/s still use the soft row. Our pushes reach 6–8 m/s where retail reaches about
+  4 m/s. That is a separate physics issue.