fix(editor): preserve full-track duration growth

src/components/video-editor/VideoEditor.tsx

@@ -155,6 +155,7 @@ import {
 	DEFAULT_ZOOM_OUT_DURATION_MS,
 	DEFAULT_ZOOM_OUT_EASING,
 	type EditorEffectSection,
+	extendAutoFullTrackClip,
 	type FigureData,
 	getClipSourceEndMs,
 	type PlaybackSpeed,
@@ -1507,6 +1508,8 @@ export default function VideoEditor() {
 			setTrimRegions(normalizedEditor.trimRegions);
 			setClipRegions(normalizedEditor.clipRegions);
 			clipInitializedRef.current = normalizedEditor.clipRegions.length > 0;
+			autoFullTrackClipIdRef.current = null;
+			autoFullTrackClipEndMsRef.current = null;
 			setSpeedRegions(normalizedEditor.speedRegions);
 			setAnnotationRegions(normalizedEditor.annotationRegions);
 			setAudioRegions(normalizedEditor.audioRegions);
@@ -2336,15 +2339,33 @@ export default function VideoEditor() {
 
 	// Initialize a full-track clip when duration is first known
 	const clipInitializedRef = useRef(false);
+	const autoFullTrackClipIdRef = useRef<string | null>(null);
+	const autoFullTrackClipEndMsRef = useRef<number | null>(null);
 	useEffect(() => {
 		const totalMs = Math.round(duration * 1000);
-		if (totalMs <= 0 || clipInitializedRef.current) return;
-		if (clipRegions.length === 0) {
-			const id = `clip-${nextClipIdRef.current++}`;
-			setClipRegions([{ id, startMs: 0, endMs: totalMs, speed: 1 }]);
+		if (totalMs <= 0) return;
+		if (!clipInitializedRef.current) {
+			if (clipRegions.length === 0) {
+				const id = `clip-${nextClipIdRef.current++}`;
+				autoFullTrackClipIdRef.current = id;
+				autoFullTrackClipEndMsRef.current = totalMs;
+				setClipRegions([{ id, startMs: 0, endMs: totalMs, speed: 1 }]);
+			}
+			clipInitializedRef.current = true;
+			return;
 		}
-		clipInitializedRef.current = true;
-	}, [duration, clipRegions.length]);
+
+		const extendedClipRegions = extendAutoFullTrackClip(
+			clipRegions,
+			autoFullTrackClipIdRef.current,
+			autoFullTrackClipEndMsRef.current,
+			totalMs,
+		);
+		if (!extendedClipRegions) return;
+
+		autoFullTrackClipEndMsRef.current = totalMs;
+		setClipRegions(extendedClipRegions);
+	}, [duration, clipRegions]);
 
 	// Derive trimRegions from clipRegions so export/playback pipelines stay unchanged
 	useEffect(() => {

src/components/video-editor/types.test.ts

@@ -0,0 +1,49 @@
+import { describe, expect, it } from "vitest";
+
+import { extendAutoFullTrackClip } from "./types";
+
+describe("extendAutoFullTrackClip", () => {
+	it("extends the default full-track clip when metadata duration grows", () => {
+		expect(
+			extendAutoFullTrackClip(
+				[{ id: "clip-1", startMs: 0, endMs: 5_000, speed: 1 }],
+				"clip-1",
+				5_000,
+				8_000,
+			),
+		).toEqual([{ id: "clip-1", startMs: 0, endMs: 8_000, speed: 1 }]);
+	});
+
+	it("does not change a clip that no longer matches the auto-created shape", () => {
+		expect(
+			extendAutoFullTrackClip(
+				[{ id: "clip-1", startMs: 0, endMs: 4_000, speed: 1.5 }],
+				"clip-1",
+				5_000,
+				8_000,
+			),
+		).toBeNull();
+	});
+
+	it("does not change multi-clip timelines or non-growing durations", () => {
+		expect(
+			extendAutoFullTrackClip(
+				[
+					{ id: "clip-1", startMs: 0, endMs: 3_000, speed: 1 },
+					{ id: "clip-2", startMs: 4_000, endMs: 8_000, speed: 1 },
+				],
+				"clip-1",
+				8_000,
+				10_000,
+			),
+		).toBeNull();
+		expect(
+			extendAutoFullTrackClip(
+				[{ id: "clip-1", startMs: 0, endMs: 8_000, speed: 1 }],
+				"clip-1",
+				8_000,
+				8_000,
+			),
+		).toBeNull();
+	});
+});

src/components/video-editor/types.ts

@@ -155,6 +155,35 @@ export function getClipSourceEndMs(clip: ClipRegion): number {
 	return Math.round(clip.startMs + displayDurationMs * speed);
 }
 
+export function extendAutoFullTrackClip(
+	clips: ClipRegion[],
+	autoClipId: string | null,
+	previousAutoEndMs: number | null,
+	nextTotalDurationMs: number,
+): ClipRegion[] | null {
+	if (
+		!autoClipId ||
+		!Number.isFinite(previousAutoEndMs) ||
+		!Number.isFinite(nextTotalDurationMs) ||
+		nextTotalDurationMs <= (previousAutoEndMs ?? 0) ||
+		clips.length !== 1
+	) {
+		return null;
+	}
+
+	const [clip] = clips;
+	if (
+		clip.id !== autoClipId ||
+		clip.startMs !== 0 ||
+		clip.speed !== 1 ||
+		clip.endMs !== previousAutoEndMs
+	) {
+		return null;
+	}
+
+	return [{ ...clip, endMs: nextTotalDurationMs }];
+}
+
 /** Convert clip regions (kept segments) to trim regions (gaps to remove). */
 export function clipsToTrims(clips: ClipRegion[], totalDurationMs: number): TrimRegion[] {
 	if (clips.length === 0) return [];