Door tween leak: tutorial fade spawned an 800ms tween per frame — now pure tutorialAlpha() driven from update()

Ported from claude/epic-faraday-332679 (6c5889c) — merge was permission-blocked,
same diff applied directly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scenes/door/DoorScene.ts

@@ -27,6 +27,7 @@ import { ClipboardPanel, type ClipboardTab } from './ClipboardPanel';
 import { encounterById } from '../../rules/encounters';
 import { SobrietyModal } from './SobrietyModal';
 import { stamp, type StampHandle } from '../../ui/Stamp';
+import { tutorialAlpha } from './tutorialFade';
 import { Button, DOOR_PALETTE, MeterBar, MONO, panel, text } from './ui';
 import { shouldRecordStrike, type NightContext } from './NightScene';
 
@@ -39,7 +40,6 @@ const KAYDEN_RULE_MS = 5000;
 const UP_FOOT_Y = 244;
 const DOOR_X = 566;
 const QUEUE_FOOT_Y = 228;
-const TUTORIAL_MS = 26_000;
 
 /**
  * TODO(contract): CCR-4 — `dazza:text` carries `rule?: DressCodeRule`, so a rule
@@ -894,8 +894,10 @@ export class DoorScene extends Phaser.Scene {
     const locked = this.night.state.clockMin >= LOCKOUT_MIN;
     this.clockText.setText(locked ? `${this.night.clock.label} · LOCKOUT` : this.night.clock.label);
     this.clockText.setColor(locked ? '#ff8080' : '#9fe8a0');
-    if (this.tutorial.alpha > 0 && this.elapsedMs > TUTORIAL_MS) {
-      this.tweens.add({ targets: this.tutorial, alpha: 0, duration: 800 });
+    if (this.tutorial.visible) {
+      const a = tutorialAlpha(this.elapsedMs);
+      this.tutorial.setAlpha(a);
+      if (a <= 0) this.tutorial.setVisible(false);
     }
 
     this.syncQueueSprites();

src/scenes/door/tutorialFade.ts

@@ -0,0 +1,17 @@
+/** How long the door tutorial text stays fully lit before it starts to fade. */
+export const TUTORIAL_MS = 26_000;
+/** Length of the fade once the hold expires. */
+export const TUTORIAL_FADE_MS = 800;
+
+/**
+ * Tutorial text alpha at `elapsedMs` into the night. Pure update()-driven math,
+ * deliberately NOT a tween: the old `if (alpha > 0) tweens.add(...)` guard
+ * spawned a fresh 800ms tween every frame (each new tween re-captured the
+ * current alpha and kept it above zero, so the guard never closed — ~1,100 live
+ * tweens by night's end), and tweens stall under the preview pane's stepped
+ * clock anyway.
+ */
+export function tutorialAlpha(elapsedMs: number): number {
+  if (elapsedMs <= TUTORIAL_MS) return 1;
+  return Math.max(0, 1 - (elapsedMs - TUTORIAL_MS) / TUTORIAL_FADE_MS);
+}

tests/tutorialFade.test.ts

@@ -0,0 +1,40 @@
+import { describe, expect, it } from 'vitest';
+import { TUTORIAL_FADE_MS, TUTORIAL_MS, tutorialAlpha } from '../src/scenes/door/tutorialFade';
+
+// Regression guard for the door-tutorial fade. The original implementation was
+// `if (alpha > 0) tweens.add({ alpha: 0, duration: 800 })` inside update():
+// each frame's new tween re-captured the still-positive alpha, so the guard
+// never closed and DoorScene accumulated one live 800ms tween per frame
+// (~1,100 by the end of a night). The fade is now this pure function; these
+// tests pin the property that killed the tween version — it must actually
+// reach 0 and stay there.
+
+describe('tutorialAlpha', () => {
+  it('holds at full alpha through the tutorial window', () => {
+    expect(tutorialAlpha(0)).toBe(1);
+    expect(tutorialAlpha(TUTORIAL_MS)).toBe(1);
+  });
+
+  it('fades linearly once the hold expires', () => {
+    expect(tutorialAlpha(TUTORIAL_MS + TUTORIAL_FADE_MS / 2)).toBeCloseTo(0.5);
+    expect(tutorialAlpha(TUTORIAL_MS + TUTORIAL_FADE_MS / 4)).toBeCloseTo(0.75);
+  });
+
+  it('reaches exactly 0 at fade end and never goes negative after', () => {
+    expect(tutorialAlpha(TUTORIAL_MS + TUTORIAL_FADE_MS)).toBe(0);
+    expect(tutorialAlpha(TUTORIAL_MS + TUTORIAL_FADE_MS + 1)).toBe(0);
+    // A whole night later it is still pinned at 0 — the condition the old
+    // tween-spawning guard could never satisfy.
+    expect(tutorialAlpha(TUTORIAL_MS + 4 * 60 * 60 * 1000)).toBe(0);
+  });
+
+  it('is monotonically non-increasing frame over frame', () => {
+    let prev = Infinity;
+    for (let ms = 0; ms < TUTORIAL_MS + 2 * TUTORIAL_FADE_MS; ms += 16.67) {
+      const a = tutorialAlpha(ms);
+      expect(a).toBeLessThanOrEqual(prev);
+      expect(a).toBeGreaterThanOrEqual(0);
+      prev = a;
+    }
+  });
+});