fix: model editor time as wasm MediaTime ticks end-to-end

3 files changed, 130 insertions, 4 deletions

diff --git a/apps/web/src/wasm/index.ts b/apps/web/src/wasm/index.ts
index 60031a0e..c979b620 100644
--- a/apps/web/src/wasm/index.ts
+++ b/apps/web/src/wasm/index.ts
@@ -1 +1 @@
-export * from "./ticks";
+export * from "./media-time";
diff --git a/apps/web/src/wasm/media-time.ts b/apps/web/src/wasm/media-time.ts
new file mode 100644
index 00000000..7209e81c
--- /dev/null
+++ b/apps/web/src/wasm/media-time.ts
@@ -0,0 +1,129 @@
+import {
+	TICKS_PER_SECOND as _TICKS_PER_SECOND,
+	mediaTimeFromSeconds as _mediaTimeFromSeconds,
+	mediaTimeToSeconds as _mediaTimeToSeconds,
+} from "opencut-wasm";
+
+/**
+ * Integer-tick time. Mirrors `MediaTime(i64)` in `rust/crates/time/src/media_time.rs`.
+ *
+ * `opencut-wasm` exposes `MediaTime` as a bare `number` alias because tsify
+ * collapses tuple structs. The brand here is the TS-side discipline that
+ * recovers the invariant: a `MediaTime` is an integer count of ticks, and the
+ * only legal way to construct one from a fractional `number` is `roundMediaTime`
+ * (or `mediaTimeFromSeconds`, which rounds inside the wasm boundary).
+ *
+ * Reading is free — `MediaTime` is assignable to `number`. Writing is gated —
+ * a bare `number` is not assignable to `MediaTime`.
+ */
+export type MediaTime = number & { readonly __mediaTime: unique symbol };
+
+export const TICKS_PER_SECOND = _TICKS_PER_SECOND();
+
+export const ZERO_MEDIA_TIME = 0 as MediaTime;
+
+/**
+ * Construct a `MediaTime` from a known-integer tick count. Asserts in dev that
+ * the value is actually an integer; cast in release. Use `roundMediaTime` when
+ * the input may be fractional.
+ */
+export function mediaTime({ ticks }: { ticks: number }): MediaTime {
+	if (process.env.NODE_ENV !== "production" && !Number.isInteger(ticks)) {
+		throw new Error(
+			`mediaTime() requires an integer tick count, got ${ticks}. Use roundMediaTime() for fractional values.`,
+		);
+	}
+	return ticks as MediaTime;
+}
+
+/**
+ * Project a fractional value onto the integer-tick lattice.
+ *
+ * Rounds half away from zero (`-1.5 → -2`, `1.5 → 2`) and normalises `-0` to
+ * `0`. The away-from-zero rule matches Rust's `.round()` and avoids the
+ * `Math.round(-0.5) === -0` quirk that propagates `-0` into stored data.
+ */
+export function roundMediaTime({ time }: { time: number }): MediaTime {
+	const roundedMagnitude = Math.round(Math.abs(time));
+	if (roundedMagnitude === 0) {
+		return 0 as MediaTime;
+	}
+	return (time < 0 ? -roundedMagnitude : roundedMagnitude) as MediaTime;
+}
+
+export function mediaTimeFromSeconds({
+	seconds,
+}: {
+	seconds: number;
+}): MediaTime {
+	const result = _mediaTimeFromSeconds({ seconds });
+	if (result === undefined) {
+		throw new Error(
+			`mediaTimeFromSeconds: rust returned undefined for seconds=${seconds}`,
+		);
+	}
+	return result as MediaTime;
+}
+
+export function mediaTimeToSeconds({ time }: { time: MediaTime }): number {
+	return _mediaTimeToSeconds({ time });
+}
+
+/**
+ * Sum `MediaTime` values. Inputs are integer ticks, so the sum is integer too;
+ * the cast is a no-op at runtime, only re-establishes the brand for the type
+ * system.
+ */
+export function addMediaTime({
+	a,
+	b,
+}: {
+	a: MediaTime;
+	b: MediaTime;
+}): MediaTime {
+	return (a + b) as MediaTime;
+}
+
+export function subMediaTime({
+	a,
+	b,
+}: {
+	a: MediaTime;
+	b: MediaTime;
+}): MediaTime {
+	return (a - b) as MediaTime;
+}
+
+export function maxMediaTime({
+	a,
+	b,
+}: {
+	a: MediaTime;
+	b: MediaTime;
+}): MediaTime {
+	return (a > b ? a : b) as MediaTime;
+}
+
+export function minMediaTime({
+	a,
+	b,
+}: {
+	a: MediaTime;
+	b: MediaTime;
+}): MediaTime {
+	return (a < b ? a : b) as MediaTime;
+}
+
+export function clampMediaTime({
+	time,
+	min,
+	max,
+}: {
+	time: MediaTime;
+	min: MediaTime;
+	max: MediaTime;
+}): MediaTime {
+	if (time < min) return min;
+	if (time > max) return max;
+	return time;
+}
diff --git a/apps/web/src/wasm/ticks.ts b/apps/web/src/wasm/ticks.ts
deleted file mode 100644
index ababe6b3..00000000
--- a/apps/web/src/wasm/ticks.ts
+++ /dev/null
@@ -1,3 +0,0 @@
-import { TICKS_PER_SECOND as _TICKS_PER_SECOND } from "opencut-wasm";
-
-export const TICKS_PER_SECOND = _TICKS_PER_SECOND();