fix(progress): measure taskID width in runes, not bytes

maxBeforeStatusWidth used len(l.taskID) (bytes) while applyPadding
used utf8.RuneCountInString (runes). For ASCII task IDs the two
agree and no symptom surfaces, but a taskID containing multi-byte
UTF-8 chars (CJK, emoji, accented Latin) reported a width larger
than its visual columns. computeOverflow then triggered truncation
where none was needed, and truncateLongestTaskID's byte-indexed
slice could land mid-multibyte sequence, corrupting the displayed
string.

Align the two measurements on rune count.

Signed-off-by: Guillaume Lours <glours@users.noreply.github.com>

cmd/display/tty.go

@@ -449,7 +449,7 @@ func maxBeforeStatusWidth(lines []lineData) int {
 	var maxWidth int
 	for i := range lines {
 		l := &lines[i]
-		width := 3 + lenAnsi(l.prefix) + len(l.taskID) + lenAnsi(l.progress)
+		width := 3 + lenAnsi(l.prefix) + utf8.RuneCountInString(l.taskID) + lenAnsi(l.progress)
 		if width > maxWidth {
 			maxWidth = width
 		}
@@ -478,18 +478,29 @@ func computeOverflow(lines []lineData, maxBeforeStatus, maxStatusLen, timerLen,
 }
 
 // truncateProgressSize drops the trailing "X.XMB / Y.YMB" size info from the
-// first line whose progress still carries it. Returns true if any line was
-// modified. Used to recover from overflow without abbreviating the taskID.
+// line currently driving maxBeforeStatusWidth — only that line's shrink can
+// reduce overflow. Returns true if any line was modified.
 func truncateProgressSize(lines []lineData) bool {
+	maxIdx := -1
+	var maxWidth int
 	for i := range lines {
 		l := &lines[i]
-		if l.progressSizeBytes > 0 {
-			l.progress = l.progress[:len(l.progress)-l.progressSizeBytes]
-			l.progressSizeBytes = 0
-			return true
+		if l.progressSizeBytes == 0 {
+			continue
+		}
+		w := lenAnsi(l.prefix) + utf8.RuneCountInString(l.taskID) + lenAnsi(l.progress)
+		if maxIdx < 0 || w > maxWidth {
+			maxWidth = w
+			maxIdx = i
 		}
 	}
-	return false
+	if maxIdx < 0 {
+		return false
+	}
+	l := &lines[maxIdx]
+	l.progress = l.progress[:len(l.progress)-l.progressSizeBytes]
+	l.progressSizeBytes = 0
+	return true
 }
 
 // truncateDetails tries to truncate the first line's details to reduce overflow.
@@ -510,13 +521,14 @@ func truncateDetails(lines []lineData, overflow int) bool {
 }
 
 // truncateLongestTaskID truncates the longest taskID to reduce overflow.
-// Returns true if truncation was performed.
+// Returns true if truncation was performed. Lengths and slicing are in runes
+// to avoid emitting invalid UTF-8 when taskID contains multi-byte chars.
 func truncateLongestTaskID(lines []lineData, overflow, minIDLen int) bool {
 	longestIdx := -1
 	longestLen := minIDLen
 	for i := range lines {
-		if len(lines[i].taskID) > longestLen {
-			longestLen = len(lines[i].taskID)
+		if utf8.RuneCountInString(lines[i].taskID) > longestLen {
+			longestLen = utf8.RuneCountInString(lines[i].taskID)
 			longestIdx = i
 		}
 	}
@@ -527,10 +539,9 @@ func truncateLongestTaskID(lines []lineData, overflow, minIDLen int) bool {
 
 	l := &lines[longestIdx]
 	reduction := overflow + 3 // account for "..."
-	newLen := max(len(l.taskID)-reduction, minIDLen-3)
-	if newLen > 0 {
-		l.taskID = l.taskID[:newLen] + "..."
-	}
+	newLen := max(longestLen-reduction, minIDLen-3)
+	runes := []rune(l.taskID)
+	l.taskID = string(runes[:newLen]) + "..."
 	return true
 }
 

cmd/display/tty_test.go

@@ -270,6 +270,69 @@ func TestAdjustLineWidth_TaskIDCorrectlyTruncated(t *testing.T) {
 	assert.Assert(t, strings.HasSuffix(lines[0].taskID, "..."), "truncated taskID should end with ...")
 }
 
+// TestAdjustLineWidth_MultiByteTaskIDFits guards against drift between
+// applyPadding (rune-based) and maxBeforeStatusWidth (formerly byte-based):
+// a byte-based measurement falsely flags overflow for multi-byte taskIDs.
+func TestAdjustLineWidth_MultiByteTaskIDFits(t *testing.T) {
+	w := &ttyWriter{}
+	taskID := "Image 测试测试" // 10 runes, 18 bytes
+	lines := []lineData{{
+		taskID: taskID,
+		status: "Pulling",
+	}}
+
+	// terminalWidth=30 fits in runes (3+10+1+7+1+4 = 26) but not in bytes
+	// (3+18+1+7+1+4 = 34), so a byte-based measurement would truncate.
+	w.adjustLineWidth(lines, 4, 30)
+
+	assert.Equal(t, taskID, lines[0].taskID,
+		"taskID should not be modified when it fits terminal width in runes")
+}
+
+// TestTruncateLongestTaskID_PreservesValidUTF8 verifies that when truncation
+// of a multi-byte UTF-8 taskID is genuinely required, the resulting string
+// remains valid UTF-8. Byte-indexed slicing can land mid-rune and emit
+// replacement characters (<28>) into the rendered output.
+func TestTruncateLongestTaskID_PreservesValidUTF8(t *testing.T) {
+	taskID := "Image 测试测试测试测试" // 14 runes, 30 bytes
+	lines := []lineData{{taskID: taskID}}
+
+	truncateLongestTaskID(lines, 8, 10)
+
+	assert.Assert(t, utf8.ValidString(lines[0].taskID),
+		"truncated taskID must remain valid UTF-8, got %q", lines[0].taskID)
+	assert.Assert(t, strings.HasSuffix(lines[0].taskID, "..."),
+		"truncated taskID should end with ..., got %q", lines[0].taskID)
+}
+
+// TestTruncateProgressSize_PicksWidestLine verifies that dropping the size
+// suffix targets the line currently driving maxBeforeStatusWidth (the only
+// line whose shrink can reduce overflow), preserving size info on narrower
+// lines that are not the bottleneck.
+func TestTruncateProgressSize_PicksWidestLine(t *testing.T) {
+	narrowSuffix := " 5MB / 10MB"
+	wideSuffix := " 50MB / 100MB"
+	lines := []lineData{
+		{
+			taskID:            "Image short",
+			progress:          " [⣿⣿]" + narrowSuffix,
+			progressSizeBytes: len(narrowSuffix),
+		},
+		{
+			taskID:            "Image very-long-named-task",
+			progress:          " [⣿⣿⣿⣿⣿⣿⣿⣿]" + wideSuffix,
+			progressSizeBytes: len(wideSuffix),
+		},
+	}
+
+	truncateProgressSize(lines)
+
+	assert.Equal(t, 0, lines[1].progressSizeBytes,
+		"widest line should lose its size suffix first")
+	assert.Equal(t, len(narrowSuffix), lines[0].progressSizeBytes,
+		"narrower line should retain its size suffix")
+}
+
 func TestAdjustLineWidth_NoTruncationNeeded(t *testing.T) {
 	w := &ttyWriter{}
 	originalDetails := "short"