[Bug] windows: claude runtime turns fail with spawn EINVAL (CLAUDE_CODE_EXECUTABLE set to a .cmd shim) #2397

summary

on windows, every turn from a claude code agent fails with -32603 internal error, and the hidden detail is spawn EINVAL. the desktop sets CLAUDE_CODE_EXECUTABLE to the claude.cmd npm shim, and the adapter spawns it without shell: true. node >= 20.12 / 24 refuses to spawn a .cmd/.bat without a shell (the cve-2024-27980 hardening), so the spawn throws EINVAL. this is a sibling of the .cmd handling in #2247, and separate from the runtime path issue in #2327.

environment

• os: windows 11
• runtime: claude code, claude cli v2.1.217 (npm global, so the shim is %APPDATA%\npm\claude.cmd)
• adapter: @agentclientprotocol/claude-agent-acp v0.60.0
• node v24

what happens

buzz shows the agent's harness reported an internal error, and buzz-acp logs:

WARN buzz_acp: agent_returned (application error) outcome="error" configured_model=haiku error=Agent reported error (code -32603): Internal error

root cause

configure_runtime_cli (desktop/src-tauri/src/managed_agents/runtime.rs) does:

if let Some(cli_path) = runtime.underlying_cli.and_then(resolve_command) {
    command.env("CLAUDE_CODE_EXECUTABLE", cli_path);
}

for the claude runtime, resolve_command("claude") returns the npm shim ...\npm\claude.cmd. the adapter then spawns CLAUDE_CODE_EXECUTABLE, and on node >= 20.12/24 spawning a .cmd without shell: true throws spawn EINVAL.

note also that configure_runtime_cli runs after the user-env writes (runtime.rs ~line 1862, after merged_user_env at ~1859), so users can't override CLAUDE_CODE_EXECUTABLE from edit agent env vars.

reproduction

driving the adapter directly reproduces it:

CLAUDE_CODE_EXECUTABLE=<...>\claude.cmd   -> session/new -> {"code":-32603,"message":"Internal error","data":{"details":"spawn EINVAL"}}
CLAUDE_CODE_EXECUTABLE=""                 -> turn succeeds (adapter falls back to its bundled claude-code)

suggested fixes

• on windows, resolve underlying_cli to a spawnable target (prefer a native claude.exe over the .cmd shim), or
• spawn the executable with shell: true on windows, or
• don't set CLAUDE_CODE_EXECUTABLE to a bare .cmd; leaving it unset makes the adapter use its bundled claude-code, which works fine.

workaround

install claude code's native binary so a real claude.exe is on path (irm https://claude.ai/install.ps1 | iex, lands at %USERPROFILE%\.local\bin\claude.exe). resolve_command prefers .exe over .cmd, so the adapter then spawns a real executable and turns succeed.

happy to open a pr if that would help!