From 0d455a98291cc7cc56e5d561da83eb679feb7515 Mon Sep 17 00:00:00 2001
From: "Anthony Fu (via agent)" <reg-github-bot@antfu.me>
Date: Thu, 16 Jul 2026 08:30:42 +0000
Subject: [PATCH] fix(terminals): normalize bare LF to CRLF in piped readonly
 output

A piped child process has no controlling TTY, so its stdout/stderr carry
bare \n line endings that xterm renders as a staircase (no cursor return
to column 0). Translate lone \n to \r\n in spawnPipe, mirroring the
kernel's ONLCR translation, while leaving existing \r\n untouched.
---
 plugins/terminals/src/node/backend.ts    | 16 +++++++++++++++-
 plugins/terminals/test/terminals.test.ts | 20 ++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/plugins/terminals/src/node/backend.ts b/plugins/terminals/src/node/backend.ts
index c580ac97..33ff1239 100644
--- a/plugins/terminals/src/node/backend.ts
+++ b/plugins/terminals/src/node/backend.ts
@@ -148,8 +148,22 @@ export function spawnPipe(options: SpawnBackendOptions): TerminalProcess {
   const exitCbs: ((code: number) => void)[] = []
   let exited = false
 
+  // A piped child has no controlling TTY, so its stdout/stderr carry bare `\n`
+  // line endings — a real PTY would apply the kernel's ONLCR translation. xterm
+  // only returns the cursor to column 0 on `\r`, so forwarding bare `\n` renders
+  // a staircase. Translate lone `\n` to `\r\n`, tracking a `\r` left dangling at
+  // a chunk boundary so an existing `\r\n` split across chunks isn't doubled.
+  let pendingCr = false
+  const normalizeNewlines = (data: string): string => {
+    const out = data.replace(/\r?\n/g, (match, offset: number) =>
+      match === '\n' && !(offset === 0 && pendingCr) ? '\r\n' : match)
+    pendingCr = out.endsWith('\r')
+    return out
+  }
+
   const emitData = (data: string): void => {
-    for (const cb of dataCbs) cb(data)
+    const normalized = normalizeNewlines(data)
+    for (const cb of dataCbs) cb(normalized)
   }
   const emitExit = (code: number): void => {
     if (exited)
diff --git a/plugins/terminals/test/terminals.test.ts b/plugins/terminals/test/terminals.test.ts
index e9487d54..4cccfe3c 100644
--- a/plugins/terminals/test/terminals.test.ts
+++ b/plugins/terminals/test/terminals.test.ts
@@ -62,6 +62,26 @@ describe('@devframes/plugin-terminals', () => {
     })
   })
 
+  it('normalizes bare LF from a piped readonly session to CRLF', async () => {
+    const client = bootClient(server.port)
+    await new Promise(r => setTimeout(r, 50))
+
+    // A piped child has no TTY to apply ONLCR, so it emits bare `\n`. Without
+    // normalization xterm renders a staircase; the backend must translate lone
+    // `\n` to `\r\n` while leaving an existing `\r\n` untouched.
+    const info = await call<TerminalSessionInfo>(client, 'devframes-plugin-terminals:spawn', {
+      command: NODE,
+      args: ['-e', 'process.stdout.write("a\\nb\\r\\nc")'],
+      mode: 'readonly',
+    })
+
+    const reader = subscribe(client, info.id)
+    const output = await collectUntil(reader, acc => acc.includes('a') && acc.includes('b') && acc.includes('c'))
+    expect(output).toContain('a\r\nb\r\nc')
+    expect(output).not.toContain('a\nb')
+    expect(output).not.toContain('\r\r\n')
+  })
+
   it('rejects writes to a readonly session', async () => {
     const client = bootClient(server.port)
     await new Promise(r => setTimeout(r, 50))