diff --git a/tests/tools/relay-bench/README.md b/tests/tools/relay-bench/README.md
index 8661c214469..0db742b5c18 100644
--- a/tests/tools/relay-bench/README.md
+++ b/tests/tools/relay-bench/README.md
@@ -104,7 +104,7 @@ pbpaste | node $BENCH pair ~/.orca/relay-bench/state.json
 
 # Or from a file you protect yourself, which `pair` requires to be mode 0600:
 umask 077 && printf '%s' '<orca://pair?code=...>' > ~/.orca/relay-bench/pair.txt
-node $BENCH pair ~/.orca/relay-bench/state.json --pairing-url-file=~/.orca/relay-bench/pair.txt
+node $BENCH pair ~/.orca/relay-bench/state.json --pairing-url-file="$HOME/.orca/relay-bench/pair.txt"
 rm ~/.orca/relay-bench/pair.txt
 
 # Steady-state foreground reconnect, 10 times, 2 s apart, re-resolving the cell each time.
diff --git a/tests/tools/relay-bench/relay-bench-state-file.mjs b/tests/tools/relay-bench/relay-bench-state-file.mjs
index 32b1d9c22d4..e5ded5c43c5 100644
--- a/tests/tools/relay-bench/relay-bench-state-file.mjs
+++ b/tests/tools/relay-bench/relay-bench-state-file.mjs
@@ -8,6 +8,7 @@ import {
   fchmodSync,
   constants,
   fstatSync,
+  ftruncateSync,
   lstatSync,
   mkdirSync,
   openSync,
@@ -43,7 +44,9 @@ export function writeSecretFile(path, contents) {
   try {
     fd = openSync(
       path,
-      constants.O_WRONLY | constants.O_CREAT | constants.O_TRUNC | NOFOLLOW,
+      // No O_TRUNC: truncating happens only after the descriptor passes the checks below, so a
+      // refused file keeps its previous contents.
+      constants.O_WRONLY | constants.O_CREAT | NOFOLLOW,
       SECRET_FILE_MODE
     )
   } catch (err) {
@@ -57,14 +60,15 @@ export function writeSecretFile(path, contents) {
     if (!stats.isFile()) {
       throw new Error(`refusing to write ${path}: not a regular file`)
     }
-    // Before the write, not after: a pre-existing file owned by someone else would take the
-    // token on O_TRUNC and only then fail the chmod, leaving it readable by its owner.
+    // Before the truncate and write, not after: a pre-existing file owned by someone else would
+    // otherwise lose its contents and then fail the chmod, leaving the token readable by its owner.
     if (process.platform !== 'win32' && stats.uid !== process.getuid()) {
       throw new Error(`refusing to write ${path}: owned by another user`)
     }
     if (process.platform !== 'win32' && (stats.mode & GROUP_AND_OTHER_BITS) !== 0) {
       fchmodSync(fd, SECRET_FILE_MODE)
     }
+    ftruncateSync(fd, 0)
     writeFileSync(fd, contents)
   } finally {
     closeSync(fd)
diff --git a/tests/tools/relay-bench/relay-bench-state-file.test.mjs b/tests/tools/relay-bench/relay-bench-state-file.test.mjs
index 052703e006d..c8ffcb23b1c 100644
--- a/tests/tools/relay-bench/relay-bench-state-file.test.mjs
+++ b/tests/tools/relay-bench/relay-bench-state-file.test.mjs
@@ -67,6 +67,20 @@ describe('writeSecretFile', () => {
     expect(modeOf(join(dir, 'nested'))).toBe(0o700)
   })
 
+  it.runIf(posix)('leaves a refused file untouched instead of truncating it first', () => {
+    // A writable file owned by someone else must be refused before its contents are destroyed.
+    const path = join(dir, 'state.json')
+    writeFileSync(path, 'previous contents')
+    const realGetuid = process.getuid
+    process.getuid = () => realGetuid() + 1
+    try {
+      expect(() => writeSecretFile(path, 'secret')).toThrow(/owned by another user/)
+    } finally {
+      process.getuid = realGetuid
+    }
+    expect(readFileSync(path, 'utf8')).toBe('previous contents')
+  })
+
   it('truncates rather than appending to a longer previous file', () => {
     const path = join(dir, 'state.json')
     writeSecretFile(path, '{"a":"aaaaaaaaaaaaaaaaaaaa"}')
diff --git a/tests/tools/relay-bench/relay-phone-connect-bench.mjs b/tests/tools/relay-bench/relay-phone-connect-bench.mjs
index 9ab88fd3e3f..d9f388b1227 100644
--- a/tests/tools/relay-bench/relay-phone-connect-bench.mjs
+++ b/tests/tools/relay-bench/relay-phone-connect-bench.mjs
@@ -375,6 +375,15 @@ async function loadState(statePath) {
 }
 
 // ---------- commands ----------
+// The peer picks the code, so only a plain identifier is echoed; anything else is named by kind.
+const REMOTE_ERROR_CODE = /^[A-Za-z0-9_.-]{1,64}$/
+export function describeRemoteErrorCode(code) {
+  if (typeof code !== 'string') {
+    return code === undefined ? 'unknown' : `non-string code (${typeof code})`
+  }
+  return REMOTE_ERROR_CODE.test(code) ? code : `unprintable code (${code.length} chars)`
+}
+
 async function pair(pairingUrl, statePath) {
   const offer = decodeOffer(pairingUrl)
   if (!offer.relay) {
@@ -413,7 +422,7 @@ async function pair(pairingUrl, statePath) {
   if (!endpoints.ok || !endpoints.result.relay) {
     // Shape only: the reply is peer-supplied and this line lands in the operator's terminal.
     throw new Error(
-      `getEndpoints failed: ${endpoints.ok ? 'no relay block in result' : `error ${endpoints.error?.code ?? 'unknown'}`}`
+      `getEndpoints failed: ${endpoints.ok ? 'no relay block in result' : `error ${describeRemoteErrorCode(endpoints.error?.code)}`}`
     )
   }
   console.log(`provisionRelay ${provisionMs} ms, getEndpoints ${endpointsMs} ms`)
diff --git a/tests/tools/relay-bench/relay-phone-connect-bench.test.mjs b/tests/tools/relay-bench/relay-phone-connect-bench.test.mjs
index 05613634592..833a60d6b36 100644
--- a/tests/tools/relay-bench/relay-phone-connect-bench.test.mjs
+++ b/tests/tools/relay-bench/relay-phone-connect-bench.test.mjs
@@ -2,7 +2,12 @@
 // missing or malformed pairing link surfaced as a stack trace rather than usage. The link is a
 // live credential, so the failure text has to name the problem without echoing the code.
 import { describe, expect, it, vi } from 'vitest'
-import { decodeOffer, vetCellUrl, vetRelayEndpoint } from './relay-phone-connect-bench.mjs'
+import {
+  decodeOffer,
+  describeRemoteErrorCode,
+  vetCellUrl,
+  vetRelayEndpoint
+} from './relay-phone-connect-bench.mjs'
 
 const encode = (offer) => Buffer.from(JSON.stringify(offer), 'utf8').toString('base64url')
 
@@ -86,3 +91,22 @@ describe('vetRelayEndpoint', () => {
     ).resolves.toEqual({ ok: true })
   })
 })
+
+describe('describeRemoteErrorCode', () => {
+  it('echoes a plain protocol identifier', () => {
+    expect(describeRemoteErrorCode('invalid_install_req')).toBe('invalid_install_req')
+  })
+
+  it('never echoes terminal control bytes the peer put in the code', () => {
+    const out = describeRemoteErrorCode('\u001b[2J\u001b]0;pwned\u0007')
+    expect(out).not.toContain('\u001b')
+    expect(out).toMatch(/unprintable code/)
+  })
+
+  it('names the type instead of stringifying a non-string code', () => {
+    expect(describeRemoteErrorCode({ toString: () => '\u001b[31m' })).toBe(
+      'non-string code (object)'
+    )
+    expect(describeRemoteErrorCode(undefined)).toBe('unknown')
+  })
+})