diff --git a/frontend/src/canvas/spring.ts b/frontend/src/canvas/spring.ts
new file mode 100644
index 0000000..d64c52e
--- /dev/null
+++ b/frontend/src/canvas/spring.ts
@@ -0,0 +1,149 @@
+/**
+ * Spring Physics Engine — damped harmonic oscillator for GPU-driven animations.
+ *
+ * Used by SceneManager for drop animations, drag lift/release, delete fade-out,
+ * group/ungroup, and inbox zone slide-in.
+ *
+ * Physics: F = -stiffness * displacement - damping * velocity
+ *          a = F / mass
+ */
+
+// ---------------------------------------------------------------------------
+// Config
+// ---------------------------------------------------------------------------
+
+export interface SpringConfig {
+  stiffness: number;
+  damping: number;
+  mass: number;
+  precision: number;
+}
+
+const DEFAULT_CONFIG: SpringConfig = {
+  stiffness: 180,
+  damping: 12,
+  mass: 1,
+  precision: 0.01,
+};
+
+export const PRESETS = {
+  drop:   { stiffness: 180, damping: 12, mass: 1, precision: 0.01 },
+  gentle: { stiffness: 120, damping: 14, mass: 1, precision: 0.01 },
+  snappy: { stiffness: 300, damping: 20, mass: 1, precision: 0.01 },
+  bounce: { stiffness: 200, damping:  8, mass: 1, precision: 0.01 },
+} as const satisfies Record<string, SpringConfig>;
+
+export type PresetName = keyof typeof PRESETS;
+
+// ---------------------------------------------------------------------------
+// Spring
+// ---------------------------------------------------------------------------
+
+export class Spring {
+  private _value: number;
+  private _target: number;
+  private _velocity: number = 0;
+  private _done: boolean = false;
+
+  private readonly _config: SpringConfig;
+
+  /** Called every tick with the current value. */
+  onUpdate: ((value: number) => void) | null = null;
+
+  /** Called once when the spring settles (snaps to target). */
+  onComplete: (() => void) | null = null;
+
+  constructor(initial: number, target: number, config?: Partial<SpringConfig>) {
+    this._value = initial;
+    this._target = target;
+    this._config = { ...DEFAULT_CONFIG, ...config };
+  }
+
+  // -- Public accessors -----------------------------------------------------
+
+  get value(): number {
+    return this._value;
+  }
+
+  get target(): number {
+    return this._target;
+  }
+
+  set target(t: number) {
+    this._target = t;
+    this._done = false;
+  }
+
+  get velocity(): number {
+    return this._velocity;
+  }
+
+  get done(): boolean {
+    return this._done;
+  }
+
+  // -- Simulation -----------------------------------------------------------
+
+  /**
+   * Advance the simulation by `dt` seconds.
+   *
+   * Uses semi-implicit Euler integration which is cheap, stable enough for
+   * UI springs, and deterministic for a given dt.
+   */
+  tick(dt: number): void {
+    if (this._done) return;
+
+    const { stiffness, damping, mass, precision } = this._config;
+
+    const displacement = this._value - this._target;
+
+    // F = -k * x - c * v
+    const force = -stiffness * displacement - damping * this._velocity;
+    const acceleration = force / mass;
+
+    // Semi-implicit Euler: update velocity first, then position.
+    this._velocity += acceleration * dt;
+    this._value += this._velocity * dt;
+
+    // Settle check
+    if (Math.abs(this._velocity) < precision && Math.abs(this._value - this._target) < precision) {
+      this._value = this._target;
+      this._velocity = 0;
+      this._done = true;
+      this.onUpdate?.(this._value);
+      this.onComplete?.();
+      return;
+    }
+
+    this.onUpdate?.(this._value);
+  }
+}
+
+// ---------------------------------------------------------------------------
+// SpringManager
+// ---------------------------------------------------------------------------
+
+export class SpringManager {
+  private _springs: Set<Spring> = new Set();
+
+  /** Register a spring and return it for chaining. */
+  add(spring: Spring): Spring {
+    this._springs.add(spring);
+    return spring;
+  }
+
+  /** Advance all springs by `dt` seconds, removing settled ones. */
+  tick(dt: number): void {
+    for (const spring of this._springs) {
+      spring.tick(dt);
+      if (spring.done) {
+        this._springs.delete(spring);
+      }
+    }
+  }
+
+  /** Number of currently active (unsettled) springs. */
+  get active(): number {
+    return this._springs.size;
+  }
+}