From 75bd912f5f339625753268c52eab7c37fb59ebb9 Mon Sep 17 00:00:00 2001
From: Igor Starovierov <inwaar@users.noreply.github.com>
Date: Sat, 20 Jun 2026 12:21:48 +0000
Subject: [PATCH] fix(cli): apply headless default on implicit daemon
 auto-start

The `chrome-devtools start` command handler defaults headless to true
when not explicitly provided, but the implicit auto-start path (triggered
transparently when running a tool command like `new_page` with no
running daemon) bypassed this logic entirely, inheriting the MCP server's
built-in default of headless=false. This caused failures in environments
without an X server (e.g., devcontainers, CI).

Extract a shared getDefaultedStartArgs() helper that applies the same
defaults (`headless: true`, `isolated: true`) for both the explicit
`start` command and the implicit auto-start path.
---
 src/bin/chrome-devtools.ts | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/src/bin/chrome-devtools.ts b/src/bin/chrome-devtools.ts
index cab71cb3a..fefc9d3d9 100644
--- a/src/bin/chrome-devtools.ts
+++ b/src/bin/chrome-devtools.ts
@@ -39,6 +39,18 @@ async function start(args: string[], sessionId: string) {
 
 const defaultArgs = ['--viaCli', '--experimentalStructuredContent'];
 
+function getDefaultedStartArgs(
+  argv: Record<string, unknown>,
+): string[] {
+  if (argv.isolated === undefined && argv.userDataDir === undefined) {
+    argv.isolated = true;
+  }
+  if (argv.headless === undefined) {
+    argv.headless = true;
+  }
+  return serializeArgs(cliOptions, argv);
+}
+
 const startCliOptions = {
   ...cliOptions,
 } as Partial<typeof cliOptions>;
@@ -96,13 +108,7 @@ y.command(
       await stopDaemon(argv.sessionId);
     }
     // Defaults but we do not want to affect the yargs conflict resolution.
-    if (argv.isolated === undefined && argv.userDataDir === undefined) {
-      argv.isolated = true;
-    }
-    if (argv.headless === undefined) {
-      argv.headless = true;
-    }
-    const args = serializeArgs(cliOptions, argv);
+    const args = getDefaultedStartArgs(argv);
     await start(args, argv.sessionId);
     process.exit(0);
   },
@@ -226,7 +232,8 @@ for (const [commandName, commandDef] of Object.entries(commands)) {
       const sessionId = argv.sessionId as string;
       try {
         if (!isDaemonRunning(sessionId)) {
-          await start([], sessionId);
+          const args = getDefaultedStartArgs({});
+          await start(args, sessionId);
         }
 
         const commandArgs: Record<string, unknown> = {};