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diff --git a/apps/web/src/test-utils/mock-opencut-wasm.ts b/apps/web/src/test-utils/mock-opencut-wasm.ts
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+++ b/apps/web/src/test-utils/mock-opencut-wasm.ts
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+/**
+ * Test mock for the `opencut-wasm` package.
+ *
+ * The published package is wasm-pack bundler-target glue that imports
+ * `opencut_wasm_bg.wasm` as an ESM module with instance exports. Bun (1.3.x)
+ * does not instantiate `.wasm` imports that way, so any test transitively
+ * importing `@/wasm` fails at module evaluation. This file is registered as a
+ * bun test preload (root `bunfig.toml` → `[test] preload`) so a faithful
+ * pure-TS stand-in for the `opencut-wasm` functions used by
+ * `@/wasm/media-time.ts` is in place before any test module evaluates.
+ *
+ * Semantics mirror rust/crates/time/src/media_time.rs (TICKS_PER_SECOND =
+ * 120_000, i64 tick lattice, round-half-away-from-zero).
+ */
+import { mock } from "bun:test";
+
+const TICKS_PER_SECOND = 120_000;
+
+function ticksPerFrame({
+	rate,
+}: {
+	rate: { numerator: number; denominator: number };
+}): number | null {
+	if (rate.numerator <= 0 || rate.denominator <= 0) {
+		return null;
+	}
+	return Math.trunc((TICKS_PER_SECOND * rate.denominator) / rate.numerator);
+}
+
+function toFrameRound({
+	time,
+	rate,
+}: {
+	time: number;
+	rate: { numerator: number; denominator: number };
+}): number | null {
+	const perFrame = ticksPerFrame({ rate });
+	if (perFrame === null || perFrame === 0) {
+		return null;
+	}
+	const remainder = ((time % perFrame) + perFrame) % perFrame;
+	const floor = Math.floor(time / perFrame);
+	return remainder * 2 >= perFrame ? floor + 1 : floor;
+}
+
+function fromFrame({
+	frame,
+	rate,
+}: {
+	frame: number;
+	rate: { numerator: number; denominator: number };
+}): number | null {
+	const perFrame = ticksPerFrame({ rate });
+	if (perFrame === null) {
+		return null;
+	}
+	return frame * perFrame;
+}
+
+function floorToFrame({
+	time,
+	rate,
+}: {
+	time: number;
+	rate: { numerator: number; denominator: number };
+}): number | null {
+	const perFrame = ticksPerFrame({ rate });
+	if (perFrame === null || perFrame === 0) {
+		return null;
+	}
+	return Math.floor(time / perFrame) * perFrame;
+}
+
+mock.module("opencut-wasm", () => ({
+	TICKS_PER_SECOND: () => TICKS_PER_SECOND,
+	mediaTimeFromSeconds: ({ seconds }: { seconds: number }): number | null => {
+		if (!Number.isFinite(seconds)) {
+			return null;
+		}
+		// Rust f64::round is half away from zero; Math.round is half up.
+		const ticks = seconds * TICKS_PER_SECOND;
+		return Math.sign(ticks) * Math.round(Math.abs(ticks));
+	},
+	mediaTimeToSeconds: ({ time }: { time: number }): number =>
+		time / TICKS_PER_SECOND,
+	roundToFrame: (options: {
+		time: number;
+		rate: { numerator: number; denominator: number };
+	}): number | null => {
+		const frame = toFrameRound(options);
+		return frame === null ? null : fromFrame({ frame, rate: options.rate });
+	},
+	lastFrameTime: (options: {
+		duration: number;
+		rate: { numerator: number; denominator: number };
+	}): number | null => {
+		if (options.duration <= 0) {
+			return 0;
+		}
+		return floorToFrame({ time: options.duration - 1, rate: options.rate });
+	},
+	snappedSeekTime: (options: {
+		time: number;
+		duration: number;
+		rate: { numerator: number; denominator: number };
+	}): number | null => {
+		const frame = toFrameRound({ time: options.time, rate: options.rate });
+		if (frame === null) {
+			return null;
+		}
+		const snapped = fromFrame({ frame, rate: options.rate });
+		if (snapped === null) {
+			return null;
+		}
+		return Math.min(Math.max(snapped, 0), options.duration);
+	},
+	// Timecode parsing is not exercised by command tests; fail loudly rather
+	// than silently returning a plausible-but-wrong value.
+	parseTimecode: (): null => {
+		throw new Error("parseTimecode is not implemented in the test mock");
+	},
+	// GPU/compositor functions are statically linked through `@/core` →
+	// renderer-manager but never called by command tests.
+	formatTimecode: (): string => {
+		throw new Error("formatTimecode is not implemented in the test mock");
+	},
+	initializeGpu: (): Promise<void> => {
+		throw new Error("initializeGpu is not implemented in the test mock");
+	},
+	applyEffectPasses: (): never => {
+		throw new Error("applyEffectPasses is not implemented in the test mock");
+	},
+	applyMaskFeather: (): never => {
+		throw new Error("applyMaskFeather is not implemented in the test mock");
+	},
+	initCompositor: (): never => {
+		throw new Error("initCompositor is not implemented in the test mock");
+	},
+	getCompositorCanvas: (): never => {
+		throw new Error(
+			"getCompositorCanvas is not implemented in the test mock",
+		);
+	},
+	getLastFrameProfile: (): never => {
+		throw new Error(
+			"getLastFrameProfile is not implemented in the test mock",
+		);
+	},
+	releaseTexture: (): never => {
+		throw new Error("releaseTexture is not implemented in the test mock");
+	},
+	renderFrame: (): never => {
+		throw new Error("renderFrame is not implemented in the test mock");
+	},
+	resizeCompositor: (): never => {
+		throw new Error("resizeCompositor is not implemented in the test mock");
+	},
+	uploadTexture: (): never => {
+		throw new Error("uploadTexture is not implemented in the test mock");
+	},
+}));