From 3308eb3d00aaf9219ab88609ee24d4150765a94a Mon Sep 17 00:00:00 2001
From: Neil <4138956+nwparker@users.noreply.github.com>
Date: Tue, 13 Oct 2026 17:16:03 -0700
Subject: [PATCH] fix(process-host): accept string stdin in synchronous runs
 (#28225)

fix(process-host): accept string stdin in synchronous runs

Request raw subprocess output with null encoding so Node can encode string stdin as UTF-8. Preserve explicit text decoding and byte capture, with real-runner coverage for both output modes.

Co-authored-by: Joe Esposito <joeespo@gmail.com>
---
 .../process-host/src/run-process.test.ts      | 23 +++++++++++++++++++
 src/packages/process-host/src/run-process.ts  |  3 ++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/packages/process-host/src/run-process.test.ts b/src/packages/process-host/src/run-process.test.ts
index 2b333cf89fe..b91fb40c433 100644
--- a/src/packages/process-host/src/run-process.test.ts
+++ b/src/packages/process-host/src/run-process.test.ts
@@ -83,6 +83,29 @@ describe('resolveSpawn', () => {
 })
 
 describe('runProcessSync', () => {
+  it.each([false, true])('accepts string stdin with byte capture %s', (captureStdoutAsBytes) => {
+    const input = 'nonsecret-probe-λ'
+    const result = runProcessSync({
+      program: process.execPath,
+      args: [
+        '-e',
+        'process.stdin.pipe(process.stdout, { end: false }); process.stdin.on("end", () => { process.stdout.write(Buffer.from([0,255])); process.stderr.write("diagnostic λ") })'
+      ],
+      input,
+      captureStdoutAsBytes
+    })
+    expect(result).toMatchObject({
+      code: 0,
+      stdout: captureStdoutAsBytes ? '' : `${input}\u0000�`,
+      stderr: 'diagnostic λ',
+      timedOut: false,
+      outputTruncated: false
+    })
+    expect(result.stdoutBytes).toEqual(
+      captureStdoutAsBytes ? Buffer.concat([Buffer.from(input), Buffer.from([0, 255])]) : undefined
+    )
+  })
+
   it('reports a timeout as timedOut', () => {
     const result = runProcessSync({
       program: process.execPath,
diff --git a/src/packages/process-host/src/run-process.ts b/src/packages/process-host/src/run-process.ts
index a5d5c2d2e37..5bc5a733bc9 100644
--- a/src/packages/process-host/src/run-process.ts
+++ b/src/packages/process-host/src/run-process.ts
@@ -357,7 +357,8 @@ function runResolvedProcessSync(spec: ProcessSpec, resolved: ResolvedSpawn): Pro
     input: spec.input,
     timeout: spec.timeoutMs === null ? undefined : (spec.timeoutMs ?? DEFAULT_PROCESS_TIMEOUT_MS),
     maxBuffer: spec.maxOutputBytes ?? DEFAULT_MAX_OUTPUT_BYTES,
-    encoding: 'buffer'
+    // Keep raw output without applying the nonexistent 'buffer' encoding to string stdin.
+    encoding: null
   })
   const timedOut = result.error
     ? 'code' in result.error && result.error.code === 'ETIMEDOUT'