fix(cli): keep punctuation-only speaker turns in tts --multi-speaker

Bounding `lineMarkerStart` at the previous label also made "only whitespace since the previous label" count as the start of a line, so a punctuation-only turn after a label on the same line was read as the next label's list marker and dropped with it (`Alice: ... Bob: Yes?`, `Alice: — Bob: Sorry, go on.`, and `Alice: ?! Bob: What?` each sent only Bob's turn).

Judge the line start on the whole text (`text[:floor+len(rest)]`) for every marker. The scan still stops at the previous label (`floor`), so emoji names (`😀: 🤖:`) do not overlap or panic.

PiperOrigin-RevId: 994686637

Author: Google Team Member

internal/cli/custom/custom_test.go

@@ -516,11 +516,13 @@ func TestSpeakerTurns(t *testing.T) {
 		{"Alice: 42. Bob: That is correct.", []string{"Alice", "Bob"}, []speakerTurn{turn("Alice", "42."), turn("Bob", "That is correct.")}},
 		// A combining mark is part of the word: neither "\u0936\u094d\u0930\u0940\u0930\u093e\u092e:" nor "\u0930\u093e\u092e\u0940:" holds a label for "\u0930\u093e\u092e".
 		{"Alice: \u0936\u094d\u0930\u0940\u0930\u093e\u092e: \u0930\u093e\u092e\u0940: hi. \u0930\u093e\u092e: yo.", []string{"Alice", "\u0930\u093e\u092e"}, []speakerTurn{turn("Alice", "\u0936\u094d\u0930\u0940\u0930\u093e\u092e: \u0930\u093e\u092e\u0940: hi."), turn("\u0930\u093e\u092e", "yo.")}},
-		// Marker scanning stops at the previous label: names made of marker runes
-		// stay labels, and a marker right after an empty label goes with the next.
+		// Marker scanning stops at the previous label, so names made of marker
+		// runes stay labels; a punctuation-only turn after a label is kept.
 		{"\U0001F600: \U0001F916: hi.", []string{"\U0001F600", "\U0001F916"}, []speakerTurn{turn("\U0001F916", "hi.")}},
 		{"\U0001F600: hi.\n\U0001F916: yo.", []string{"\U0001F600", "\U0001F916"}, []speakerTurn{turn("\U0001F600", "hi."), turn("\U0001F916", "yo.")}},
-		{"Alice: - Bob: yo.", []string{"Alice", "Bob"}, []speakerTurn{bob}},
+		{"Alice: - Bob: yo.", []string{"Alice", "Bob"}, []speakerTurn{turn("Alice", "-"), bob}},
+		{"Alice: ... Bob: yo.", []string{"Alice", "Bob"}, []speakerTurn{turn("Alice", "..."), bob}},
+		{"Alice: \u2014 Bob: yo.", []string{"Alice", "Bob"}, []speakerTurn{turn("Alice", "\u2014"), bob}},
 		// "Annual:" is not a label for "Ann"; an undeclared "Carol:" stays in the turn.
 		{"Ann: Annual: report. Carol: yes. Bo: ok.", []string{"Ann", "Bo"}, []speakerTurn{turn("Ann", "Annual: report. Carol: yes."), turn("Bo", "ok.")}},
 		// The longer name wins over a declared prefix of it.

internal/cli/custom/tts.go

@@ -264,23 +264,21 @@ func isMarkerRune(r rune) bool {
 // the label at start begins ("- Alice:", "> Alice:", "“Alice:", "1. Alice:"),
 // so the marker goes with the label instead of the previous turn or the text
 // before the first label. Without one, it returns start: punctuation or a
-// number after words on the same line ("hi. - Bob:", "Alice: 42. Bob:") stays
-// in the previous turn. The scan stops at floor, the end of the previous
-// label, so a name made of marker runes ("😀: 🤖:") is never claimed as the
-// next label's marker.
+// number after words or a label on the same line ("hi. - Bob:",
+// "Alice: 42. Bob:", "Alice: ... Bob:") stays in the previous turn. The scan
+// stops at floor, the end of the previous label, so a name made of marker
+// runes ("😀: 🤖:") is never claimed as the next label's marker; the line
+// start is still judged on the whole text.
 func lineMarkerStart(text string, floor, start int) int {
 	before := strings.TrimRightFunc(text[floor:start], isHorizontalSpace)
 	rest := strings.TrimRightFunc(before, isMarkerRune)
 	if rest == before {
 		return start
 	}
-	check := rest
 	if marker := before[len(rest):]; marker == "." || marker == ")" {
-		if digits := strings.TrimRightFunc(rest, unicode.IsDigit); len(digits) < len(rest) {
-			rest, check = digits, text[:floor+len(digits)]
-		}
+		rest = strings.TrimRightFunc(rest, unicode.IsDigit)
 	}
-	if line := strings.TrimRightFunc(check, isHorizontalSpace); line != "" {
+	if line := strings.TrimRightFunc(text[:floor+len(rest)], isHorizontalSpace); line != "" {
 		if last, _ := utf8.DecodeLastRuneInString(line); !isLineBreak(last) {
 			return start
 		}