fix(input): restore multiball nudge slot updates

Preserve the Win16 key path's two-stage multiball behavior: consume the active-window random formula, then apply one separately recovered slot impulse to both saved ball velocities. This restores the original RNG advancement and prevents ball one and ball two from receiving invented different nudges.

Test Plan:
- cargo test --all-targets
- cargo clippy --all-targets --all-features -- -D warnings
- rumdl check CHANGELOG.md RECONSTRUCTION.md README.md
- git diff --check

tdkpin-rs/CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to
 
 ### Fixed
 
+- Match the multiball nudge path's saved-slot behavior: consume the active
+  formula's random draws, then add one shared fixed/random impulse to both slot
+  velocity records instead of applying different formulas to each ball.
 - Restore auxiliary response thresholds/kicks for bumpers 51-53 and line
   records 55, 74, and 107, including weak-hit bumper scoring, WAVE 2019 on
   kicked unscored rails, and the original tilt suppression.

tdkpin-rs/RECONSTRUCTION.md

@@ -23,7 +23,7 @@ implementation.
 | Audio | Exact samples and recovered dispatch | All 16 mono PCM WAV resources are embedded unchanged. Playback is emitted at the reconstructed call sites, including multi-sound bank completions and nudge-then-tilt ordering. WAV 2022 is loaded by the original generic resource loop but has no playback call and is therefore never played by Rust. |
 | Help and languages | Exact | Original resource images 1001-1005 are displayed directly. |
 | Playfield collision layout | Recovered | All 109 active type-2 line objects and 40 static active type-1 circles are transcribed from the original 175-object registration table. The registration routine converts its sideways inputs with `screen = (y, x - 20)` and accumulates explicitly relative objects. Every static record retains its `+0x49` layer mask; the scanner selects layer 1 below the old Y value 250,000 and layer 2 at or above it, while mask 3 records remain shared. Type-2 records retain every recovered Real48 normal/tangent response pair and registered one-sided orientation. Type-1 records retain their swept-circle radius, radial rebound, tangent coupling, and bumper kick. Each flipper uses its exact two line records plus moving tip circle in both positions. Moving-flipper contact ports `1000:7ed9` rather than fitting live samples: delta-specific pivots/edges, integer cross gates, radial/penetration calculations, response-record gain, and position/velocity publication are tested against all four C harness directions and the raised release geometry. Object 174 is overwritten with the live first ball and Rust handles its ball-to-ball role directly. |
-| Ball launcher and nudge input | Recovered | The initial 32-bit fixed-point coordinates decode to `(325, 413)` in the right shooter lane. Each Down keydown subtracts `15*50 = 750` millipixels, release subtracts another `15*100 = 1500`, and the result follows the recovered randomized `-3800` lower and `-2280` weak upper clamp branches. The ten decoration frames use the same strict 750-millipixel thresholds. Left Shift and keypad 3 apply their directional `(50-Random(20))*15` impulses; Space uses the recovered Real48 horizontal factor and `(60-Random(20))*15` vertical impulse. Each nudge adds 25 to the wrapping 16-bit tilt counter, compares it with `30+Random(10)`, and the detail timer decrements a nonzero counter once per callback. |
+| Ball launcher and nudge input | Recovered | The initial 32-bit fixed-point coordinates decode to `(325, 413)` in the right shooter lane. Each Down keydown subtracts `15*50 = 750` millipixels, release subtracts another `15*100 = 1500`, and the result follows the recovered randomized `-3800` lower and `-2280` weak upper clamp branches. The ten decoration frames use the same strict 750-millipixel thresholds. Left Shift and keypad 3 apply their directional `(50-Random(20))*15` impulses; Space uses the recovered Real48 horizontal factor and `(60-Random(20))*15` vertical impulse. With two balls, the key path still consumes those active-window draws, then applies its separately recovered fixed/shared random slot impulse to both saved velocities. Each nudge adds 25 to the wrapping 16-bit tilt counter, compares it with `30+Random(10)`, and the detail timer decrements a nonzero counter once per callback. |
 | Physics arithmetic | Recovered Real48 core | Production movement uses the original 10 ms millipixel substep, `+15` vertical acceleration, Real48 `3800/speed` clamp, type-2 distance/cross gates, type-1 midpoint normal, surface-distance candidate ordering, persistent Real48 spin, and the common impulse response. Negative auxiliary thresholds and kick coefficients are retained for bumpers 51-53 and lines 55/74/107, including weak-hit score behavior, unscored-rail WAVE 2019, and tilt suppression. Detail callbacks freeze their starting ball count, run all 5/4/3/2/1 substeps for slot 1 before slot 2, stop a slot after its first collision/reset/removal, and apply effect-seven spawn requests after the current batch. Dynamic records 174/175 transfer normal impulse to the other ball before applying `normal_velocity-1000` to the moving ball; effect seven spawns record/slot 2 from record 148 coordinates `(17000,23000)` with exact `(0,3040)` velocity. Both slots traverse the same type-3/type-4 dispatcher. Capture age is saved per slot, contact words retain ball ownership, a completed multiball capture removes exactly that slot and promotes the survivor when needed, and effect seven's argument-2 guard prevents a third ball. The original Borland seed update, high-word `Random(n)`, and normalized Real48 random register result drive launcher variation, effects, claw terminals, magnetic fields, and trigger response. Type-4 triggers retain a shared transient entry flag; type-3 captures retain per-player 16-bit contact words, deep-inside pull/hold progression to age 300, first-contact sound, and `99`/`2` completion sentinels. Zero-spin C harnesses and retained-spin Wine probes are tested separately rather than conflated. |
 | Rules | Recovered gameplay paths | Player count, controls, the five three-line bumper-value groups, four three-line TDK-diamond groups, five doubling-value lock holes, wheel-reset target, seven-way effect selector/consumer including multiball, permanent double scoring, and four exact media/extra-ball thresholds follow original help/code paths, globals, and object flags. The ninth diamond pays the original 24,464 completion value; the following completed bank enables double scoring, and later completions add 100,000 to the per-player secondary score. Bumpers 51-53 and targets 140-147/150-152 use the original 5/20/10 active-callback countdowns and exact overlay-A render rectangles. Record 121 runs the six-callback DAT600 target rotation with exact 91x90 frames/target points and rotates the five contact/item values at state 6. Completing all five lock holes suspends physics for the full 281-callback panel animation, clears contact/item state at the recovered boundaries, and uses the exact WAVE 2013/2012/stop sequence. Turn changes mirror the original save/load of all 175 collision record states: wheel/top targets, active/contact slots, selected effect, and multiball readiness remain attached to their player. Claw contact and all initially active type-4 targets use recovered records. The top three targets score 500 each and independently enable the left, center, or right magnetic field record; each field pulls the ball upward until it exits and then deactivates. The claw state machine and release table have live differential coverage for all four random terminals. |
 | Numeric scoring | Recovered gameplay values | Static scores come from the initialized 175-object ledger. Dynamic bumper progression, target-bank completion, diamond awards, 10k-160k lock bonuses, 310k transfer, six effect values, multiball mode, and all four media thresholds are transcribed from `1000:b476`, `1000:c4e1`, `1000:bc36`, and live state probes. Lock and effect awards share the original per-player secondary score and display multiplier; the fifth hole transfers and clears it, increments the multiplier, and grants the recovered ball award. Score mutation uses the original 32-bit wrapping behavior, and each add operation can advance at most one media threshold. |

tdkpin-rs/src/game.rs

@@ -622,24 +622,34 @@ impl Game {
             }
             Nudge::None => return,
         }
-        self.ball.velocity = velocity.to_velocity_per_second();
-
         if let Some(secondary) = &mut self.secondary_ball {
-            let mut slot_velocity = MilliVec::from_velocity_per_second(secondary.velocity);
-            match nudge {
+            let slot_impulse = match nudge {
                 Nudge::Left | Nudge::Right => {
-                    let amount = if nudge == Nudge::Left { -600 } else { 600 };
-                    slot_velocity.x = slot_velocity.x.wrapping_add(amount);
+                    MilliVec {
+                        x: if nudge == Nudge::Left { -600 } else { 600 },
+                        y: 0,
+                    }
                 }
                 Nudge::Center => {
                     let horizontal = (i32::from(self.random.below(21)) - 10) * SCALAR;
                     let vertical = -(i32::from(self.random.below(100)) + 50) * SCALAR;
-                    slot_velocity.x = slot_velocity.x.wrapping_add(horizontal);
-                    slot_velocity.y = slot_velocity.y.wrapping_add(vertical);
+                    MilliVec {
+                        x: horizontal,
+                        y: vertical,
+                    }
                 }
-                Nudge::None => {}
-            }
-            secondary.velocity = slot_velocity.to_velocity_per_second();
+                Nudge::None => MilliVec::default(),
+            };
+            let mut primary_slot = MilliVec::from_velocity_per_second(self.ball.velocity);
+            primary_slot.x = primary_slot.x.wrapping_add(slot_impulse.x);
+            primary_slot.y = primary_slot.y.wrapping_add(slot_impulse.y);
+            self.ball.velocity = primary_slot.to_velocity_per_second();
+            let mut secondary_slot = MilliVec::from_velocity_per_second(secondary.velocity);
+            secondary_slot.x = secondary_slot.x.wrapping_add(slot_impulse.x);
+            secondary_slot.y = secondary_slot.y.wrapping_add(slot_impulse.y);
+            secondary.velocity = secondary_slot.to_velocity_per_second();
+        } else {
+            self.ball.velocity = velocity.to_velocity_per_second();
         }
 
         self.nudge_shake = 0.18;
@@ -2690,6 +2700,47 @@ mod tests {
         assert_eq!(game.tilt_counter, 24);
     }
 
+    #[test]
+    fn multiball_nudge_consumes_active_draws_then_updates_both_saved_slots() {
+        let mut game = Game::new_with_seed(1, 7);
+        game.ball.in_launcher = false;
+        game.ball.velocity = MilliVec { x: 100, y: 200 }.to_velocity_per_second();
+        game.secondary_ball = Some(Ball {
+            position: vec2(200.0, 200.0),
+            velocity: MilliVec { x: -300, y: 400 }.to_velocity_per_second(),
+            in_launcher: false,
+            spin: Real48::ZERO,
+            capture_age: 0,
+        });
+        let mut reference = BorlandRandom::new(7);
+        let _discarded_active_x = reference.real48();
+        let _discarded_active_y = reference.below(20);
+        let shared_impulse = MilliVec {
+            x: (i32::from(reference.below(21)) - 10) * 15,
+            y: -(i32::from(reference.below(100)) + 50) * 15,
+        };
+        let _tilt_threshold = reference.below(10);
+
+        game.apply_nudge(Nudge::Center, &mut Vec::new());
+
+        assert_eq!(
+            MilliVec::from_velocity_per_second(game.ball.velocity),
+            MilliVec {
+                x: 100 + shared_impulse.x,
+                y: 200 + shared_impulse.y,
+            }
+        );
+        let secondary = game.secondary_ball.expect("slot two must remain active");
+        assert_eq!(
+            MilliVec::from_velocity_per_second(secondary.velocity),
+            MilliVec {
+                x: -300 + shared_impulse.x,
+                y: 400 + shared_impulse.y,
+            }
+        );
+        assert_eq!(game.random.seed(), reference.seed());
+    }
+
     #[test]
     fn claw_sprite_rects_follow_the_recovered_four_row_sheet() {
         let source = |frame, bank| {