[Bug] Windows: managed-agent harness fails to launch — runtime PATH override drops system Node ("node" is not recognized) #2327

Summary

On Windows, launching a managed agent fails immediately: the harness can't find node, every agent errors with '"node"' is not recognized, and buzz-acp exits non-zero. The cause is that the managed-agent runtime launch overrides the child PATH with an augmented value that omits the real Windows process PATH, so system-installed Node (C:\Program Files\nodejs\) disappears.

This is a sibling of the PATH work in #2247 (install-shell) and #2299 (discovery, Linux/macOS), but at a third site: the runtime launch path (managed_agents/runtime.rs + runtime/path.rs), on Windows.

Environment

• OS: Windows 11 (10.0.26200)
• Runtime: Claude Code — claude CLI v2.1.217, adapter @agentclientprotocol/claude-agent-acp v0.60.0 (installed to the system npm prefix %APPDATA%\npm)
• Node: system install at C:\Program Files\nodejs\node.exe, on the persistent (Machine) PATH. Not Buzz-managed, not nvm.
• Git for Windows / Git Bash: installed

Steps to reproduce

1. Windows 11, Node installed via the official installer only (on the system PATH; no nvm, no Buzz-managed Node runtime present).
2. Install the Claude Code ACP adapter to the system npm prefix: npm install -g @agentclientprotocol/claude-agent-acp.
3. Create/launch a managed agent using the Claude Code runtime.

Actual behavior

The harness exits with status code 1; every agent fails to initialize:

INFO buzz_acp: buzz-acp starting: relay=wss://<redacted> pubkey=<redacted> agent_cmd=C:\Users\<user>\AppData\Roaming\npm\claude-agent-acp.cmd ... model=haiku permission_mode=bypassPermissions respond_to=anyone
'"node"' is not recognized as an internal or external command,
operable program or batch file.
ERROR buzz_acp: agent initialize failed: Agent process exited unexpectedly agent=0
... (repeats for every agent)
Error: all 12 agents failed to start — cannot continue

The claude-agent-acp.cmd shim falls back to bare node (relying on PATH) when there is no node.exe beside it, and the child's PATH has no Node dir.

Root cause

desktop/src-tauri/src/managed_agents/runtime.rs builds an augmented PATH and unconditionally overrides the child's PATH with it:

let augmented_path = build_augmented_path(
    dirs::home_dir(),
    std::env::current_exe().ok().and_then(|exe| exe.parent().map(Path::to_path_buf)),
    login_shell_path(),   // None on Windows (by design, see below)
    nvm_bin,              // ~/.nvm — Unix nvm; None on Windows
);
// ...
if let Some(ref path) = augmented_path {
    command.env("PATH", path);   // <-- overrides the child PATH
}

build_augmented_path (runtime/path.rs) assembles: ~/.local/bin, Buzz-managed npm/node bin dirs (if present), nvm_bin, exe parent, and the login-shell PATH. It never includes the process PATH.

On Windows:

• login_shell_path() returns None on purpose — its own comment says "Return None so they inherit the real Windows PATH instead" (Git Bash returns POSIX colon paths that poison native children).
• nvm_bin is None (Unix ~/.nvm layout).
• Buzz-managed npm/node dirs are None when the user relies on system Node.

But ~/.local/bin and the exe parent are still pushed, so build_augmented_path returns Some(...) — a value with no Node dir and no process PATH. runtime.rs then sets that as the child PATH, defeating the exact inheritance that login_shell_path() == None was meant to preserve. System Node vanishes.

Consequently, adding Node to the system PATH does not help — the runtime replaces PATH rather than extending it.

Proposed fix

Mirror the install-shell fix from #2247: on Windows, base the child PATH on the process PATH and prepend the managed dirs, rather than emitting a managed-only PATH. Concretely, have build_augmented_path (or its runtime.rs caller) include std::env::var("PATH") as the trailing base on Windows when login_shell_path() is None, so managed bins are prepended and the real Windows PATH (with system Node) is retained.

This also aligns the runtime launch with the stated intent of the login_shell_path() Windows branch.

Workaround

Drop a copy of node.exe beside the shims so the .cmd resolves Node without PATH (the shim checks IF EXIST "%dp0%\node.exe" first). This fixes every npm shim in that dir:

copy "C:\Program Files\nodejs\node.exe" "%APPDATA%\npm\node.exe"

Happy to open a PR for the proposed fix if it's welcome.