diff --git a/packages/client/ui-primitives/src/ansi.ts b/packages/client/ui-primitives/src/ansi.ts
index 9f1adde2f9..a26d1f2dc7 100644
--- a/packages/client/ui-primitives/src/ansi.ts
+++ b/packages/client/ui-primitives/src/ansi.ts
@@ -177,9 +177,10 @@ function replayLine(line: string, entrySgr: string): { text: string; sgr: string
       if (ZERO_WIDTH.test(char)) {
         // No column of its own: it attaches to the cell already written, so a
         // redraw that covers that cell covers the mark with it.
-        const at = Math.max(0, cursor - 1)
-        const base = columns[at]
-        if (base !== undefined) columns[at] = { sgr: base.sgr, char: base.char + char }
+        // With no cell to attach to (line start, or straight after a redraw to
+        // column 0) a terminal shows nothing rather than a lone accent.
+        const base = cursor > 0 ? columns[cursor - 1] : undefined
+        if (base !== undefined) columns[cursor - 1] = { sgr: base.sgr, char: base.char + char }
         continue
       }
       columns[cursor] = { sgr, char }
@@ -207,7 +208,7 @@ function replayLine(line: string, entrySgr: string): { text: string; sgr: string
       // later write can still land past them.
       // Only the FIRST parameter selects the mode; a terminal ignores the rest
       // (`1;2K` erases exactly as `1K` does — verified against a real terminal).
-      const mode = params.split(';')[0] ?? ''
+      const mode = String(params.split(';')[0])
       if (mode === '1') for (let index = 0; index <= cursor; index++) columns[index] = { sgr, char: ' ' }
       else columns.length = mode === '2' ? 0 : cursor
       continue
diff --git a/packages/client/ui-primitives/tests/ansi.spec.ts b/packages/client/ui-primitives/tests/ansi.spec.ts
index 2de9634406..e06e4a0179 100644
--- a/packages/client/ui-primitives/tests/ansi.spec.ts
+++ b/packages/client/ui-primitives/tests/ansi.spec.ts
@@ -9,6 +9,8 @@ import { parseAnsiLines } from '../src/ansi.ts'
 
 const ESC = '\u001b'
 const BS = '\u0008'
+/** A combining acute accent: zero-width, so it takes no terminal column. */
+const ACCENT = '\u0301'
 
 /** Paint `text` with the SGR `codes`, then reset. */
 function sgr(codes: string, text: string): string {
@@ -318,6 +320,27 @@ describe('parseAnsiLines: line-end state and column widths', () => {
     expect(onlySpan('e\u0301x\rYZ')).toEqual({ text: 'YZ', style: undefined })
   })
 
+  it('drops a combining mark left with no cell to attach to by a redraw', () => {
+    // Verified in a real terminal: `ab` then CR then U+0301 then `x` shows `xb`.
+    // The redraw puts the cursor at column 0, so the mark has no preceding cell
+    // and the terminal shows nothing for it rather than a lone accent.
+    expect(onlySpan(`ab\r${ACCENT}x`)).toEqual({ text: 'xb', style: undefined })
+    // A mark with no movement on its line never reaches the replay at all: it
+    // is width business, not a cursor move, so it stays as authored.
+    expect(onlySpan(`${ACCENT}abc`)).toEqual({ text: `${ACCENT}abc`, style: undefined })
+  })
+
+  it('carries a colour opened after the last write onto the next line', () => {
+    // The mirror of the reset case, verified in a real terminal: `ab` CR `X` then
+    // `\x1b[31m` with nothing after it shows `Xb` UNSTYLED and the next line red.
+    // The scan ends styled while the last cell is not, so the convergence has to
+    // open the run at the line end for it to reach the following line.
+    expect(parseAnsiLines(`ab\rX${ESC}[31m\nnext`)).toEqual([
+      [{ text: 'Xb', style: undefined }],
+      [{ text: 'next', style: { color: 'var(--dsw-alias-state-error-primary)' } }],
+    ])
+  })
+
   it('blanks a wide character\'s spacer once its lead cell is overwritten', () => {
     // Verified in a real terminal: `中x` redrawn with `A` shows `A x` — the wide
     // glyph's second cell becomes a blank rather than closing the gap, so the