feat: add mini-turbo boost mechanic to drifting

- Track drift charge duration while sliding and payout a speed boost
  when the drift is released cleanly (not stalled or reversed)
- Boost strength scales with drift duration, capped at maximum charge
- Added configurable mini-turbo parameters (min/max ms, boost ms,
  boost multiplier range) to superkart-rules.json
- Increase drift visual rotation angle from 6° to 14° for more
  pronounced drift feedback
- Reset charge on respawn, spin, and new drift start

data/superkart-rules.json

@@ -25,6 +25,11 @@
     "driftTurnMult": 1.6,
     "driftSlipRate": 240,
     "driftGripSpread": 170,
+    "miniTurboMinMs": 500,
+    "miniTurboMaxMs": 1800,
+    "miniTurboBoostMs": 650,
+    "miniTurboBoostMultMin": 1.1,
+    "miniTurboBoostMultMax": 1.4,
     "slipDecay": 3.2,
     "hopMs": 260,
     "hopCooldownMs": 160,

src/games/superkart/SuperKartGame.js

@@ -713,8 +713,7 @@ export default class SuperKartGame extends Phaser.Scene {
     if (kart.spinMs > 0) {
       frame = Math.floor((this.raceState.timeMs / 60)) % KART_ROT_FRAMES;
     } else if (kart.drifting) {
-      frame = kart.driftDir > 0 ? 1 : KART_ROT_FRAMES - 1;
-      angle = kart.driftDir * 6;
+      angle = kart.driftDir * 14;
     } else if (inputs.steer !== 0 && hasLean) {
       frame = inputs.steer < 0 ? KART_ROT_FRAMES : KART_ROT_FRAMES + 1;
     } else if (inputs.steer !== 0) {

src/games/superkart/SuperKartLogic.js

@@ -91,6 +91,7 @@ function makeKart(index, racer, isPlayer, slot, physics) {
     airborne: false,
     drifting: false,
     driftDir: 0,
+    driftChargeMs: 0,   // mini-turbo charge accrued while committed to the slide
     prevHop: false,
     prevItem: false,
     surface: SURFACE.ROAD,
@@ -201,6 +202,7 @@ function respawnAtCheckpoint(state, kart) {
   kart.velAngle = kart.heading;
   kart.speed = 0;
   kart.drifting = false;
+  kart.driftChargeMs = 0;
   kart.airborne = false;
   kart.hopMs = 0;
   kart.offroadMs = 0;
@@ -214,6 +216,7 @@ function startSpin(state, kart, cause) {
   kart.spinMs = state.physics.spinMs;
   kart.spinSpin = 0;
   kart.drifting = false;
+  kart.driftChargeMs = 0;
   const dropped = Math.min(kart.coins, state.physics.coinsLostOnHit);
   kart.coins -= dropped;
   emit(state, 'spin', { kart: kart.index, cause });
@@ -359,14 +362,30 @@ function stepKart(state, kart, inputs, dt) {
       if (inputs.hop && steer !== 0 && kart.speed > effTopSpeed(state, kart) * 0.3) {
         kart.drifting = true;
         kart.driftDir = Math.sign(steer);
+        kart.driftChargeMs = 0;
         emit(state, 'drift-start', { kart: kart.index });
       }
     }
   }
   if (kart.drifting) {
+    kart.driftChargeMs += STEP_MS;
     const top = effTopSpeed(state, kart);
-    if (!inputs.hop || kart.speed < top * 0.25 || (steer !== 0 && Math.sign(steer) !== kart.driftDir)) {
+    const speedDropped = kart.speed < top * 0.25;
+    const steerReversed = steer !== 0 && Math.sign(steer) !== kart.driftDir;
+    if (!inputs.hop || speedDropped || steerReversed) {
       kart.drifting = false;
+      // Mini-turbo: only a clean release (hop let go, not a stall/reversal
+      // cutting the slide short) with enough committed charge pays out —
+      // stronger the longer the slide, capped at miniTurboMaxMs.
+      if (!speedDropped && !steerReversed && kart.driftChargeMs >= physics.miniTurboMinMs) {
+        const span = Math.max(1, physics.miniTurboMaxMs - physics.miniTurboMinMs);
+        const t = Math.min(1, (kart.driftChargeMs - physics.miniTurboMinMs) / span);
+        kart.boostMs = physics.miniTurboBoostMs;
+        kart.boostMult = physics.miniTurboBoostMultMin
+          + (physics.miniTurboBoostMultMax - physics.miniTurboBoostMultMin) * t;
+        emit(state, 'boost', { kart: kart.index, pad: false });
+      }
+      kart.driftChargeMs = 0;
       emit(state, 'drift-end', { kart: kart.index });
     }
   }