Windows: Bash/PowerShell tool calls spawn visible conhost console windows (missing windowsHide)

Summary

On Windows, the Claude Code CLI spawns a visible conhost.exe console window for every Bash and PowerShell tool call. During an agent session that runs many shell commands, the user sees constant black-flash popup windows on their desktop (one per tool call, ~100–300ms each). With rapid tool use this reads as "tons of popups."

Root cause

The CLI spawns bash.exe / powershell.exe (console-subsystem executables) via Node's child_process.spawn() without windowsHide: true (equivalently, without the CREATE_NO_WINDOW 0x08000000 process-creation flag). Windows therefore allocates and briefly shows a console window for each spawned shell.

Expected

Shell subprocesses for tool calls should be spawned windowless on Windows — no visible console flash — the same way pythonw.exe runs windowless.

Proposed fix

Add windowsHide: true to the child_process.spawn() options used by the Bash/PowerShell tool execution path on Windows:

spawn(shell, args, { windowsHide: true /* + existing opts */ });

This hides the console window without affecting stdout/stderr capture.

Impact

• Highly disruptive for long autonomous/agentic sessions on Windows (the flashing is constant).
• There is currently no user-side mitigation: no settings.json key, env var, or CLI flag controls this. The only workaround is "use fewer shell tool calls," which is impractical.

Environment

• OS: Windows 11
• Claude Code CLI (native Windows)
• Affects: every Bash tool call and every PowerShell tool call

Verification done

Confirmed empirically with a Win32_ProcessStartTrace capture: console spawns correlate 1:1 with agent shell-tool activity and stop entirely when the agent stops issuing shell commands. Scheduled tasks and third-party apps were ruled out as the cause.