fix(postprocess): drop tiny carry-over text

Collapse one-word and very short caption carry-over fragments so reprocessed YouTube transcripts do not retain residual prefix chains.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/lib/server/postprocess.ts

@@ -78,6 +78,10 @@ function isMeaningfulPhrase(words: string[]): boolean {
 	return words.length >= MIN_MEANINGFUL_WORDS && words.join(' ').length >= MIN_MEANINGFUL_CHARS;
 }
 
+function isShortCarryover(seg: Segment, words: string[]): boolean {
+	return seg.end - seg.start <= 0.2 || words.length <= 2 || words.join(' ').length <= 16;
+}
+
 function trimLeadingWords(text: string, count: number): string {
 	return splitWords(text).slice(count).join(' ').trim();
 }
@@ -115,7 +119,7 @@ function collapseIncrementalSegments(segments: Segment[]): Segment[] {
 		if (
 			currentWords.length > lastWords.length &&
 			startsWithWords(currentWords, lastWords) &&
-			isMeaningfulPhrase(lastWords)
+			(isMeaningfulPhrase(lastWords) || isShortCarryover(last, lastWords))
 		) {
 			last.text = current.text;
 			last.end = current.end;
@@ -123,7 +127,10 @@ function collapseIncrementalSegments(segments: Segment[]): Segment[] {
 			continue;
 		}
 
-		if (endsWithWords(lastWords, currentWords) && isMeaningfulPhrase(currentWords)) {
+		if (
+			endsWithWords(lastWords, currentWords) &&
+			(isMeaningfulPhrase(currentWords) || isShortCarryover(current, currentWords))
+		) {
 			last.end = Math.max(last.end, current.end);
 			continue;
 		}