fix(ink-win): strip synchronized-update escapes instead of exact-matching them

src/ink-win.ts

@@ -1,14 +1,42 @@
-const BSU = '\x1b[?2026h'
-const ESU = '\x1b[?2026l'
+// Begin/End Synchronized Update (DEC private mode 2026); exported so callers
+// can emit them; on Windows the filter below strips them from every write, so
+// even a concatenated BSU+payload write cannot reach ConPTY (#195).
+export const BSU = '\x1b[?2026h'
+export const ESU = '\x1b[?2026l'
 let patched = false
 
+// split/join removes every occurrence and is hot-path cheap because the
+// includes() gate below runs first.
+export function stripSyncUpdateEscapes(chunk: string): string {
+  return chunk.split(BSU).join('').split(ESU).join('')
+}
+
 export function patchStdoutForWindows(): void {
   if (process.platform !== 'win32' || patched) return
   patched = true
 
   const origWrite = process.stdout.write.bind(process.stdout)
   process.stdout.write = function (chunk: unknown, ...args: unknown[]): boolean {
-    if (chunk === BSU || chunk === ESU) return true
-    return (origWrite as Function)(chunk, ...args)
+    // Non-string chunks pass straight through unchanged; Buffers never carry
+    // these escapes in this codebase, so scanning them is not worth the copy.
+    if (typeof chunk !== 'string') {
+      return (origWrite as Function)(chunk, ...args)
+    }
+    // Neither escape present: pass straight through.
+    if (!chunk.includes(BSU) && !chunk.includes(ESU)) {
+      return (origWrite as Function)(chunk, ...args)
+    }
+    const stripped = stripSyncUpdateEscapes(chunk)
+    if (stripped.length > 0) {
+      return (origWrite as Function)(stripped, ...args)
+    }
+    // The chunk was swallowed entirely. The old exact-match filter dropped the
+    // callback too, which could wedge a callback-style writer; invoke it
+    // asynchronously so a caller awaiting the callback never hangs.
+    const last = args[args.length - 1]
+    if (typeof last === 'function') {
+      queueMicrotask(() => (last as () => void)())
+    }
+    return true
   } as typeof process.stdout.write
 }

tests/ink-win.test.ts

@@ -0,0 +1,42 @@
+import { describe, it, expect } from 'vitest'
+import { BSU, ESU, stripSyncUpdateEscapes, patchStdoutForWindows } from '../src/ink-win.js'
+
+describe('stripSyncUpdateEscapes', () => {
+  it('strips an exact BSU chunk to empty', () => {
+    expect(stripSyncUpdateEscapes(BSU)).toBe('')
+  })
+
+  it('strips an exact ESU chunk to empty', () => {
+    expect(stripSyncUpdateEscapes(ESU)).toBe('')
+  })
+
+  it('strips a leading BSU from a concatenated clear write', () => {
+    // #863 regression shape: the clear sequence glued to a BSU used to slip
+    // through raw and hang Windows ConPTY.
+    expect(stripSyncUpdateEscapes(BSU + '\x1b[2J\x1b[H')).toBe('\x1b[2J\x1b[H')
+  })
+
+  it('strips a trailing ESU, and both ends at once', () => {
+    expect(stripSyncUpdateEscapes('x' + ESU)).toBe('x')
+    expect(stripSyncUpdateEscapes(BSU + 'x' + ESU)).toBe('x')
+  })
+
+  it('removes every occurrence when escapes appear multiple times', () => {
+    expect(stripSyncUpdateEscapes(BSU + 'a' + BSU + 'b' + ESU + 'c' + ESU)).toBe('abc')
+  })
+
+  it('leaves a string without escapes untouched (same reference-equal content)', () => {
+    const plain = 'status line \x1b[2J'
+    expect(stripSyncUpdateEscapes(plain)).toBe(plain)
+  })
+})
+
+describe('patchStdoutForWindows', () => {
+  it('is a no-op off win32: process.stdout.write stays reference-identical', () => {
+    // Skip on actual Windows runners, where the patch legitimately applies.
+    if (process.platform === 'win32') return
+    const before = process.stdout.write
+    patchStdoutForWindows()
+    expect(process.stdout.write).toBe(before)
+  })
+})