fix(tui): stabilize streaming viewport reflows

commit: cf8265ca63bf1d65266c338724aeb9a667c9dcef
author: brice · 2mo ago · 2026-08-09 09:12 UTC
committer: brice · 2mo ago · 2026-08-09 09:32 UTC
parent: 1adbe2f
signature: GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email

2 files · +156 -33

M packages/tui/render.go +98 -25


@@ -243,6 +243,35 @@ func imageFootprintBlank(s string) bool {
243	243		return strings.TrimSpace(s) == ""
244	244		}
245	245
	246	+	// visibleTailHasImage reports whether an inline image or its blank terminal
	247	+	// footprint intersects the visible tail. Images earlier in retained scrollback
	248	+	// do not prevent ordinary text reflows from using the stable in-place path.
	249	+	func visibleTailHasImage(lines []string, viewportTop int) bool {
	250	+	if viewportTop < 0 {
	251	+	viewportTop = 0
	252	+	}
	253	+	if viewportTop >= len(lines) {
	254	+	return false
	255	+	}
	256	+	for _, line := range lines[viewportTop:] {
	257	+	if containsImageEscape(line) {
	258	+	return true
	259	+	}
	260	+	}
	261	+	if viewportTop == 0 \|\| !imageFootprintBlank(lines[viewportTop]) {
	262	+	return false
	263	+	}
	264	+	for idx := viewportTop - 1; idx >= 0; idx-- {
	265	+	if containsImageEscape(lines[idx]) {
	266	+	return true
	267	+	}
	268	+	if !imageFootprintBlank(lines[idx]) {
	269	+	return false
	270	+	}
	271	+	}
	272	+	return false
	273	+	}
	274	+
246	275		// paintBackgroundRow applies the optional theme background to a single
247	276		// already-truncated terminal row. It pads with spaces to cols so the
248	277		// background reaches the right edge, and re-applies the background

@@ -746,42 +775,86 @@ func (r *Renderer) drawLog(chat, bottom []string, cursorBottomRow, cursorCol, co
746	775		reflowAbove := false
747	776		if delta != 0 {
748	777		overlapEnd := min(len(chatFrame), len(r.logChat))
749		-	for idx := r.logViewportTop; idx < overlapEnd; idx++ {
	778	+	// When the viewport starts in the bottom band there are no chat
	779	+	// rows to compare at the old logical coordinates, but changing
	780	+	// chat height still shifts the entire visible band.
	781	+	reflowAbove = r.logViewportTop >= overlapEnd
	782	+	for idx := r.logViewportTop; !reflowAbove && idx < overlapEnd; idx++ {
750	783		if r.logChat[idx] != chatFrame[idx] {
751	784		reflowAbove = true
752		-	break
753	785		}
754	786		}
755	787		}
756	788		if reflowAbove {
757		-	// Reflow has made the cached logical coordinates unreliable.
758		-	// Repaint only the visible tail: replaying the full transcript
759		-	// duplicates scrollback, while rebasing by the total height delta
760		-	// can drift when some new rows landed inside the viewport.
761		-	w.WriteString(SeqDeleteKittyImages + SeqCursorHome + SeqClearToEnd)
762		-	viewportTop := max(0, len(lines)-r.rows)
763		-	start := viewportTop
764		-	if start > 0 && imageFootprintBlank(lines[start]) {
765		-	for idx := start - 1; idx >= 0; idx-- {
766		-	if containsImageEscape(lines[idx]) {
767		-	start = idx
768		-	break
	789	+	// A text-only logical buffer can be rebased without resetting the
	790	+	// terminal viewport. Advance physical rows when it grows, then
	791	+	// repaint the visible tail in place for both growth and shrinkage.
	792	+	// Cursor-home plus erase-to-end makes several terminals visibly
	793	+	// jump on streaming-markdown reflows.
	794	+	growth := len(lines) - len(r.logLines)
	795	+	newViewportTop := max(0, len(lines)-r.rows)
	796	+	hasVisibleImages := visibleTailHasImage(r.logLines, r.logViewportTop) \|\|
	797	+	visibleTailHasImage(lines, newViewportTop)
	798	+	if !hasVisibleImages && len(lines) >= r.rows {
	799	+	currentScreenRow := r.logHardwareRow - r.logViewportTop
	800	+	if currentScreenRow < 0 {
	801	+	currentScreenRow = 0
	802	+	}
	803	+	if currentScreenRow >= r.rows {
	804	+	currentScreenRow = r.rows - 1
	805	+	}
	806	+	if growth > 0 {
	807	+	if down := r.rows - 1 - currentScreenRow; down > 0 {
	808	+	w.WriteString("\x1b[" + itoa(down) + "B")
769	809		}
770		-	if !imageFootprintBlank(lines[idx]) {
771		-	break
	810	+	for range growth {
	811	+	w.WriteString("\r\n")
772	812		}
	813	+	currentScreenRow = r.rows - 1
773	814		}
774		-	}
775		-	for idx := start; idx < len(lines); idx++ {
776		-	if idx > start {
777		-	w.WriteString("\r\n")
	815	+	if currentScreenRow > 0 {
	816	+	w.WriteString("\x1b[" + itoa(currentScreenRow) + "A")
	817	+	}
	818	+	w.WriteString("\r")
	819	+	for idx := newViewportTop; idx < len(lines); idx++ {
	820	+	if idx > newViewportTop {
	821	+	w.WriteString("\r\n")
	822	+	}
	823	+	w.WriteString("\x1b[0m")
	824	+	w.WriteString(SeqClearLine)
	825	+	w.WriteString(lines[idx])
	826	+	}
	827	+	r.logViewportTop = newViewportTop
	828	+	r.logHardwareRow = len(lines) - 1
	829	+	} else {
	830	+	// Inline-image reflows and buffers shorter than the viewport need
	831	+	// the conservative repaint path. Replaying the full transcript
	832	+	// would duplicate retained scrollback.
	833	+	w.WriteString(SeqDeleteKittyImages + SeqCursorHome + SeqClearToEnd)
	834	+	viewportTop := max(0, len(lines)-r.rows)
	835	+	start := viewportTop
	836	+	if start > 0 && imageFootprintBlank(lines[start]) {
	837	+	for idx := start - 1; idx >= 0; idx-- {
	838	+	if containsImageEscape(lines[idx]) {
	839	+	start = idx
	840	+	break
	841	+	}
	842	+	if !imageFootprintBlank(lines[idx]) {
	843	+	break
	844	+	}
	845	+	}
	846	+	}
	847	+	for idx := start; idx < len(lines); idx++ {
	848	+	if idx > start {
	849	+	w.WriteString("\r\n")
	850	+	}
	851	+	w.WriteString("\x1b[0m")
	852	+	w.WriteString(SeqClearLine)
	853	+	w.WriteString(lines[idx])
778	854		}
779		-	w.WriteString("\x1b[0m")
780		-	w.WriteString(SeqClearLine)
781		-	w.WriteString(lines[idx])
	855	+	r.logViewportTop = viewportTop
	856	+	r.logHardwareRow = len(lines) - 1
782	857		}
783		-	r.logViewportTop = viewportTop
784		-	r.logHardwareRow = len(lines) - 1
785	858		firstChanged = -1
786	859		lastChanged = -1
787	860		} else {


@@ -243,6 +243,35 @@ func imageFootprintBlank(s string) bool {
243		return strings.TrimSpace(s) == ""	243		return strings.TrimSpace(s) == ""
244		}	244		}
245			245
			246	+	// visibleTailHasImage reports whether an inline image or its blank terminal
			247	+	// footprint intersects the visible tail. Images earlier in retained scrollback
			248	+	// do not prevent ordinary text reflows from using the stable in-place path.
			249	+	func visibleTailHasImage(lines []string, viewportTop int) bool {
			250	+	if viewportTop < 0 {
			251	+	viewportTop = 0
			252	+	}
			253	+	if viewportTop >= len(lines) {
			254	+	return false
			255	+	}
			256	+	for _, line := range lines[viewportTop:] {
			257	+	if containsImageEscape(line) {
			258	+	return true
			259	+	}
			260	+	}
			261	+	if viewportTop == 0 \|\| !imageFootprintBlank(lines[viewportTop]) {
			262	+	return false
			263	+	}
			264	+	for idx := viewportTop - 1; idx >= 0; idx-- {
			265	+	if containsImageEscape(lines[idx]) {
			266	+	return true
			267	+	}
			268	+	if !imageFootprintBlank(lines[idx]) {
			269	+	return false
			270	+	}
			271	+	}
			272	+	return false
			273	+	}
			274	+
246		// paintBackgroundRow applies the optional theme background to a single	275		// paintBackgroundRow applies the optional theme background to a single
247		// already-truncated terminal row. It pads with spaces to cols so the	276		// already-truncated terminal row. It pads with spaces to cols so the
248		// background reaches the right edge, and re-applies the background	277		// background reaches the right edge, and re-applies the background

@@ -746,42 +775,86 @@ func (r *Renderer) drawLog(chat, bottom []string, cursorBottomRow, cursorCol, co
746		reflowAbove := false	775		reflowAbove := false
747		if delta != 0 {	776		if delta != 0 {
748		overlapEnd := min(len(chatFrame), len(r.logChat))	777		overlapEnd := min(len(chatFrame), len(r.logChat))
749	-	for idx := r.logViewportTop; idx < overlapEnd; idx++ {	778	+	// When the viewport starts in the bottom band there are no chat
			779	+	// rows to compare at the old logical coordinates, but changing
			780	+	// chat height still shifts the entire visible band.
			781	+	reflowAbove = r.logViewportTop >= overlapEnd
			782	+	for idx := r.logViewportTop; !reflowAbove && idx < overlapEnd; idx++ {
750		if r.logChat[idx] != chatFrame[idx] {	783		if r.logChat[idx] != chatFrame[idx] {
751		reflowAbove = true	784		reflowAbove = true
752	-	break
753		}	785		}
754		}	786		}
755		}	787		}
756		if reflowAbove {	788		if reflowAbove {
757	-	// Reflow has made the cached logical coordinates unreliable.	789	+	// A text-only logical buffer can be rebased without resetting the
758	-	// Repaint only the visible tail: replaying the full transcript	790	+	// terminal viewport. Advance physical rows when it grows, then
759	-	// duplicates scrollback, while rebasing by the total height delta	791	+	// repaint the visible tail in place for both growth and shrinkage.
760	-	// can drift when some new rows landed inside the viewport.	792	+	// Cursor-home plus erase-to-end makes several terminals visibly
761	-	w.WriteString(SeqDeleteKittyImages + SeqCursorHome + SeqClearToEnd)	793	+	// jump on streaming-markdown reflows.
762	-	viewportTop := max(0, len(lines)-r.rows)	794	+	growth := len(lines) - len(r.logLines)
763	-	start := viewportTop	795	+	newViewportTop := max(0, len(lines)-r.rows)
764	-	if start > 0 && imageFootprintBlank(lines[start]) {	796	+	hasVisibleImages := visibleTailHasImage(r.logLines, r.logViewportTop) \|\|
765	-	for idx := start - 1; idx >= 0; idx-- {	797	+	visibleTailHasImage(lines, newViewportTop)
766	-	if containsImageEscape(lines[idx]) {	798	+	if !hasVisibleImages && len(lines) >= r.rows {
767	-	start = idx	799	+	currentScreenRow := r.logHardwareRow - r.logViewportTop
768	-	break	800	+	if currentScreenRow < 0 {
			801	+	currentScreenRow = 0
			802	+	}
			803	+	if currentScreenRow >= r.rows {
			804	+	currentScreenRow = r.rows - 1
			805	+	}
			806	+	if growth > 0 {
			807	+	if down := r.rows - 1 - currentScreenRow; down > 0 {
			808	+	w.WriteString("\x1b[" + itoa(down) + "B")
769		}	809		}
770	-	if !imageFootprintBlank(lines[idx]) {	810	+	for range growth {
771	-	break	811	+	w.WriteString("\r\n")
772		}	812		}
			813	+	currentScreenRow = r.rows - 1
773		}	814		}
774	-	}	815	+	if currentScreenRow > 0 {
775	-	for idx := start; idx < len(lines); idx++ {	816	+	w.WriteString("\x1b[" + itoa(currentScreenRow) + "A")
776	-	if idx > start {	817	+	}
777	-	w.WriteString("\r\n")	818	+	w.WriteString("\r")
			819	+	for idx := newViewportTop; idx < len(lines); idx++ {
			820	+	if idx > newViewportTop {
			821	+	w.WriteString("\r\n")
			822	+	}
			823	+	w.WriteString("\x1b[0m")
			824	+	w.WriteString(SeqClearLine)
			825	+	w.WriteString(lines[idx])
			826	+	}
			827	+	r.logViewportTop = newViewportTop
			828	+	r.logHardwareRow = len(lines) - 1
			829	+	} else {
			830	+	// Inline-image reflows and buffers shorter than the viewport need
			831	+	// the conservative repaint path. Replaying the full transcript
			832	+	// would duplicate retained scrollback.
			833	+	w.WriteString(SeqDeleteKittyImages + SeqCursorHome + SeqClearToEnd)
			834	+	viewportTop := max(0, len(lines)-r.rows)
			835	+	start := viewportTop
			836	+	if start > 0 && imageFootprintBlank(lines[start]) {
			837	+	for idx := start - 1; idx >= 0; idx-- {
			838	+	if containsImageEscape(lines[idx]) {
			839	+	start = idx
			840	+	break
			841	+	}
			842	+	if !imageFootprintBlank(lines[idx]) {
			843	+	break
			844	+	}
			845	+	}
			846	+	}
			847	+	for idx := start; idx < len(lines); idx++ {
			848	+	if idx > start {
			849	+	w.WriteString("\r\n")
			850	+	}
			851	+	w.WriteString("\x1b[0m")
			852	+	w.WriteString(SeqClearLine)
			853	+	w.WriteString(lines[idx])
778		}	854		}
779	-	w.WriteString("\x1b[0m")	855	+	r.logViewportTop = viewportTop
780	-	w.WriteString(SeqClearLine)	856	+	r.logHardwareRow = len(lines) - 1
781	-	w.WriteString(lines[idx])
782		}	857		}
783	-	r.logViewportTop = viewportTop
784	-	r.logHardwareRow = len(lines) - 1
785		firstChanged = -1	858		firstChanged = -1
786		lastChanged = -1	859		lastChanged = -1
787		} else {	860		} else {

M packages/tui/render_test.go +58 -8


@@ -126,7 +126,7 @@ func TestDrawLogInaccessibleChangePreservesScrollbackSelection(t *testing.T) {
126	126		}
127	127		}
128	128
129		-	func TestDrawLogStructuralReflowResetsVisibleViewport(t *testing.T) {
	129	+	func TestDrawLogStructuralGrowthScrollsBeforeRepaintingVisibleTail(t *testing.T) {
130	130		t.Setenv("TERM_PROGRAM", "ghostty")
131	131		var buf bytes.Buffer
132	132		r := NewRenderer(&buf)

@@ -135,16 +135,20 @@ func TestDrawLogStructuralReflowResetsVisibleViewport(t *testing.T) {
135	135		buf.Reset()
136	136
137	137		// Chat and the bottom band both grow while an old row is above the
138		-	// viewport. Rebasing by chat growth alone leaves both tracked terminal
139		-	// coordinates one row behind, so future status updates paint off-screen.
	138	+	// viewport. Scroll by the logical growth before repainting the visible
	139	+	// tail. Homing and clearing the viewport here makes terminals visibly
	140	+	// jump during every streaming markdown reflow.
140	141		chat := []string{"new row", "old 0", "old 1"}
141	142		r.DrawLog(chat, []string{"working 0s", "editor"}, 1, 3)
142	143		got := buf.String()
143		-	if !strings.Contains(got, SeqCursorHome+SeqClearToEnd) {
144		-	t.Fatalf("structural reflow did not reset the visible viewport: %q", got)
	144	+	if strings.Contains(got, SeqCursorHome+SeqClearToEnd) {
	145	+	t.Fatalf("structural growth reset the visible viewport: %q", got)
145	146		}
146	147		if strings.Contains(got, SeqClearScreenNoHome) \|\| strings.Contains(got, SeqClearScrollback) {
147		-	t.Fatalf("structural reflow cleared retained scrollback: %q", got)
	148	+	t.Fatalf("structural growth cleared retained scrollback: %q", got)
	149	+	}
	150	+	if !strings.Contains(got, "\r\n\r\n") {
	151	+	t.Fatalf("structural growth did not advance the viewport by two consecutive rows: %q", got)
148	152		}
149	153		if strings.Contains(got, "old 1") {
150	154		t.Fatalf("viewport repaint included a row above the visible tail: %q", got)

@@ -164,13 +168,59 @@ func TestDrawLogStructuralReflowResetsVisibleViewport(t *testing.T) {
164	168		buf.Reset()
165	169		r.DrawLog(chat, []string{"working 1s", "editor"}, 1, 3)
166	170		if got := buf.String(); !strings.Contains(got, "working 1s") {
167		-	t.Fatalf("status update after viewport reset was lost: %q", got)
	171	+	t.Fatalf("status update after viewport repaint was lost: %q", got)
168	172		}
169	173
170	174		buf.Reset()
171	175		r.DrawLog(append(chat, "next tool"), []string{"working 2s", "editor"}, 1, 3)
172	176		if got := buf.String(); !strings.Contains(got, "next tool") {
173		-	t.Fatalf("append after viewport reset was lost: %q", got)
	177	+	t.Fatalf("append after viewport repaint was lost: %q", got)
	178	+	}
	179	+	}
	180	+
	181	+	func TestDrawLogStructuralShrinkRepaintsVisibleTailInPlace(t *testing.T) {
	182	+	t.Setenv("TERM_PROGRAM", "ghostty")
	183	+	var buf bytes.Buffer
	184	+	r := NewRenderer(&buf)
	185	+	r.Resize(80, 4)
	186	+	r.DrawLog([]string{"partial", "old 0", "old 1", "old 2"}, []string{"working", "editor"}, 1, 2)
	187	+	buf.Reset()
	188	+
	189	+	chat := []string{"old 0", "old 1", "old 2"}
	190	+	r.DrawLog(chat, []string{"working", "editor"}, 1, 2)
	191	+	got := buf.String()
	192	+	if strings.Contains(got, SeqCursorHome+SeqClearToEnd) {
	193	+	t.Fatalf("structural shrink reset the visible viewport: %q", got)
	194	+	}
	195	+	for _, visible := range []string{"old 2", "working", "editor"} {
	196	+	if !strings.Contains(got, visible) {
	197	+	t.Fatalf("viewport repaint missing %q after shrink: %q", visible, got)
	198	+	}
	199	+	}
	200	+	if !strings.Contains(got, "\r\x1b[0m"+SeqClearLine+"old 2") {
	201	+	t.Fatalf("structural shrink did not return to column zero before repaint: %q", got)
	202	+	}
	203	+	if want := len(r.logLines) - r.rows; r.logViewportTop != want {
	204	+	t.Fatalf("viewport top = %d, want %d", r.logViewportTop, want)
	205	+	}
	206	+	}
	207	+
	208	+	func TestDrawLogStructuralGrowthIgnoresImagesOutsideVisibleTail(t *testing.T) {
	209	+	t.Setenv("TERM_PROGRAM", "ghostty")
	210	+	var buf bytes.Buffer
	211	+	r := NewRenderer(&buf)
	212	+	r.Resize(80, 3)
	213	+	image := "\x1b_Ga=T;payload\x1b\\"
	214	+	r.DrawLog([]string{image, "line 1", "line 2", "line 3"}, []string{"input"}, -1, 0)
	215	+	buf.Reset()
	216	+
	217	+	r.DrawLog([]string{"new row", image, "line 1", "line 2", "line 3"}, []string{"input"}, -1, 0)
	218	+	got := buf.String()
	219	+	if strings.Contains(got, SeqCursorHome+SeqClearToEnd) {
	220	+	t.Fatalf("image in retained scrollback forced a viewport reset: %q", got)
	221	+	}
	222	+	if !strings.Contains(got, "line 3") \|\| !strings.Contains(got, "input") {
	223	+	t.Fatalf("visible tail was not repainted after growth: %q", got)
174	224		}
175	225		}
176	226


@@ -126,7 +126,7 @@ func TestDrawLogInaccessibleChangePreservesScrollbackSelection(t *testing.T) {
126		}	126		}
127		}	127		}
128			128
129	-	func TestDrawLogStructuralReflowResetsVisibleViewport(t *testing.T) {	129	+	func TestDrawLogStructuralGrowthScrollsBeforeRepaintingVisibleTail(t *testing.T) {
130		t.Setenv("TERM_PROGRAM", "ghostty")	130		t.Setenv("TERM_PROGRAM", "ghostty")
131		var buf bytes.Buffer	131		var buf bytes.Buffer
132		r := NewRenderer(&buf)	132		r := NewRenderer(&buf)

@@ -135,16 +135,20 @@ func TestDrawLogStructuralReflowResetsVisibleViewport(t *testing.T) {
135		buf.Reset()	135		buf.Reset()
136			136
137		// Chat and the bottom band both grow while an old row is above the	137		// Chat and the bottom band both grow while an old row is above the
138	-	// viewport. Rebasing by chat growth alone leaves both tracked terminal	138	+	// viewport. Scroll by the logical growth before repainting the visible
139	-	// coordinates one row behind, so future status updates paint off-screen.	139	+	// tail. Homing and clearing the viewport here makes terminals visibly
			140	+	// jump during every streaming markdown reflow.
140		chat := []string{"new row", "old 0", "old 1"}	141		chat := []string{"new row", "old 0", "old 1"}
141		r.DrawLog(chat, []string{"working 0s", "editor"}, 1, 3)	142		r.DrawLog(chat, []string{"working 0s", "editor"}, 1, 3)
142		got := buf.String()	143		got := buf.String()
143	-	if !strings.Contains(got, SeqCursorHome+SeqClearToEnd) {	144	+	if strings.Contains(got, SeqCursorHome+SeqClearToEnd) {
144	-	t.Fatalf("structural reflow did not reset the visible viewport: %q", got)	145	+	t.Fatalf("structural growth reset the visible viewport: %q", got)
145		}	146		}
146		if strings.Contains(got, SeqClearScreenNoHome) \|\| strings.Contains(got, SeqClearScrollback) {	147		if strings.Contains(got, SeqClearScreenNoHome) \|\| strings.Contains(got, SeqClearScrollback) {
147	-	t.Fatalf("structural reflow cleared retained scrollback: %q", got)	148	+	t.Fatalf("structural growth cleared retained scrollback: %q", got)
			149	+	}
			150	+	if !strings.Contains(got, "\r\n\r\n") {
			151	+	t.Fatalf("structural growth did not advance the viewport by two consecutive rows: %q", got)
148		}	152		}
149		if strings.Contains(got, "old 1") {	153		if strings.Contains(got, "old 1") {
150		t.Fatalf("viewport repaint included a row above the visible tail: %q", got)	154		t.Fatalf("viewport repaint included a row above the visible tail: %q", got)

@@ -164,13 +168,59 @@ func TestDrawLogStructuralReflowResetsVisibleViewport(t *testing.T) {
164		buf.Reset()	168		buf.Reset()
165		r.DrawLog(chat, []string{"working 1s", "editor"}, 1, 3)	169		r.DrawLog(chat, []string{"working 1s", "editor"}, 1, 3)
166		if got := buf.String(); !strings.Contains(got, "working 1s") {	170		if got := buf.String(); !strings.Contains(got, "working 1s") {
167	-	t.Fatalf("status update after viewport reset was lost: %q", got)	171	+	t.Fatalf("status update after viewport repaint was lost: %q", got)
168		}	172		}
169			173
170		buf.Reset()	174		buf.Reset()
171		r.DrawLog(append(chat, "next tool"), []string{"working 2s", "editor"}, 1, 3)	175		r.DrawLog(append(chat, "next tool"), []string{"working 2s", "editor"}, 1, 3)
172		if got := buf.String(); !strings.Contains(got, "next tool") {	176		if got := buf.String(); !strings.Contains(got, "next tool") {
173	-	t.Fatalf("append after viewport reset was lost: %q", got)	177	+	t.Fatalf("append after viewport repaint was lost: %q", got)
			178	+	}
			179	+	}
			180	+
			181	+	func TestDrawLogStructuralShrinkRepaintsVisibleTailInPlace(t *testing.T) {
			182	+	t.Setenv("TERM_PROGRAM", "ghostty")
			183	+	var buf bytes.Buffer
			184	+	r := NewRenderer(&buf)
			185	+	r.Resize(80, 4)
			186	+	r.DrawLog([]string{"partial", "old 0", "old 1", "old 2"}, []string{"working", "editor"}, 1, 2)
			187	+	buf.Reset()
			188	+
			189	+	chat := []string{"old 0", "old 1", "old 2"}
			190	+	r.DrawLog(chat, []string{"working", "editor"}, 1, 2)
			191	+	got := buf.String()
			192	+	if strings.Contains(got, SeqCursorHome+SeqClearToEnd) {
			193	+	t.Fatalf("structural shrink reset the visible viewport: %q", got)
			194	+	}
			195	+	for _, visible := range []string{"old 2", "working", "editor"} {
			196	+	if !strings.Contains(got, visible) {
			197	+	t.Fatalf("viewport repaint missing %q after shrink: %q", visible, got)
			198	+	}
			199	+	}
			200	+	if !strings.Contains(got, "\r\x1b[0m"+SeqClearLine+"old 2") {
			201	+	t.Fatalf("structural shrink did not return to column zero before repaint: %q", got)
			202	+	}
			203	+	if want := len(r.logLines) - r.rows; r.logViewportTop != want {
			204	+	t.Fatalf("viewport top = %d, want %d", r.logViewportTop, want)
			205	+	}
			206	+	}
			207	+
			208	+	func TestDrawLogStructuralGrowthIgnoresImagesOutsideVisibleTail(t *testing.T) {
			209	+	t.Setenv("TERM_PROGRAM", "ghostty")
			210	+	var buf bytes.Buffer
			211	+	r := NewRenderer(&buf)
			212	+	r.Resize(80, 3)
			213	+	image := "\x1b_Ga=T;payload\x1b\\"
			214	+	r.DrawLog([]string{image, "line 1", "line 2", "line 3"}, []string{"input"}, -1, 0)
			215	+	buf.Reset()
			216	+
			217	+	r.DrawLog([]string{"new row", image, "line 1", "line 2", "line 3"}, []string{"input"}, -1, 0)
			218	+	got := buf.String()
			219	+	if strings.Contains(got, SeqCursorHome+SeqClearToEnd) {
			220	+	t.Fatalf("image in retained scrollback forced a viewport reset: %q", got)
			221	+	}
			222	+	if !strings.Contains(got, "line 3") \|\| !strings.Contains(got, "input") {
			223	+	t.Fatalf("visible tail was not repainted after growth: %q", got)
174		}	224		}
175		}	225		}
176			226