Windows: Claude Code CLI hits spawn ENAMETOOLONG on long composed prompts (#15 didn't cover Claude)

[lefarcen]

Symptom

On Windows, sending a non-trivial prompt with Claude Code as the active agent fails with:

spawn failed: spawn ENAMETOOLONG

Reproduced at #51 (user @valkryhx, Node v22.17.0, Windows, claude.CMD v2.1.81 npm-installed at d:\\nodejs\\node_global\\claude.CMD).

Why

Windows CreateProcess caps the combined command line + environment block at ~32 KB. OD composes the system prompt from three layers (base output contract + design-system body + skill body) plus the user message — for non-trivial skills (e.g. magazine-web-ppt / guizang-ppt) the composed prompt easily exceeds the cap.

#15 fixed this class of bug for the other non-Claude CLIs by introducing promptViaStdin: true and piping the composed prompt through child.stdin instead of argv. Codex, Gemini CLI, OpenCode, Cursor Agent, Qwen Code are all stdin-delivery now.

Claude was explicitly excluded (per #15's PR description: "Claude Code is unaffected — it uses the -p argv path plus its own stream-json parser"). The argv path still composes the prompt into argv, so on Windows it hits ENAMETOOLONG once the composed prompt grows past ~32 KB.

The current Claude buildArgs in daemon/agents.js:

buildArgs: (prompt, _imagePaths, extraAllowedDirs = [], options = {}) => {
  const args = [
    '-p',
    prompt,                                    // ← argv prompt; ENAMETOOLONG on Windows for long prompts
    '--output-format', 'stream-json',
    '--verbose',
  ];
  ...
}

Likely fix shape

Either:

A. Add stdin support to the Claude buildArgs. Verify Claude Code CLI accepts the prompt via stdin (e.g. claude -p - or omitting -p and piping). If it does, set promptViaStdin: true on the Claude agent def and drop prompt from argv. The stream-json parsing in daemon/claude-stream.js is independent of how the prompt arrives, so this should be a small change.

B. Temp-file fallback. Write the composed prompt to os.tmpdir() and pass the file path via -p @<path> or a documented Claude flag for file-based prompt.

(A) is preferred — symmetrical with the other agents and the lifetime of the file in (B) is awkward.

Workarounds in the meantime

• Switch to Codex / Gemini / OpenCode in the picker — fix: deliver prompt via stdin for non-Claude agents to avoid spawn EN… #15's stdin fix already covers those.
• Use "Anthropic API · BYOK" mode (HTTP request, no command-line cap involved).
• Pick a shorter skill (e.g. simple-deck instead of magazine-web-ppt).

Repro

1. Windows + Node ≥ 20 + claude CLI installed via npm-global.
2. pnpm dev:all, pick Claude as the agent.
3. Pick magazine-web-ppt (guizang-ppt) skill or any skill with a multi-KB SKILL.md.
4. Send a normal-length user prompt. Daemon logs spawn ENAMETOOLONG.

Related

• Closes-with: stdin extension to Claude in a follow-up PR.
• Related: fix: deliver prompt via stdin for non-Claude agents to avoid spawn EN… #15 (the prior wave), fix: spawn agents via resolved absolute path on Windows (closes #10) #13 (Windows resolved-path), spawn claude ENOENT 是什么原因？ #51 (user-reported).

[lefarcen]

Acknowledged — this is the Windows+Claude gap from #15. The proposed fix (stdin delivery for Claude's buildArgs) looks correct. Will track for implementation.

[ONEGAYI]

I ran into the same issue on Windows with claude.EXE (installed via npm install -g @anthropic-ai/claude-code, resolved to C:\Users\...\claude.EXE). The composed prompt was 61,682 chars — well past the ~32 KB CreateProcess limit.

I implemented a temp-file fallback that works alongside the existing promptViaStdin mechanism (which already covers Codex, Gemini, OpenCode, Cursor Agent, and Qwen). The approach:

1. Detect when !def.promptViaStdin && platform === 'win32' && composed.length > threshold
2. Write the full composed prompt to .od-prompt.md in the project's .od/projects/<id>/ directory
3. Replace the prompt with a short bootstrap message telling the agent to Read the file
4. Clean up the temp file on spawn error or child process exit

Thresholds: 4,000 chars when shell:true is needed (.cmd/.bat shims, ~8 KB cmd.exe limit with escaping overhead) and 30,000 chars for direct .exe invocation (~32 KB CreateProcess limit).

Diagnostic logging was added: the daemon prints a [od] prompt-delivery: line on each request showing agent, promptLen, shell, limit, file, and bin values.

The diff is in daemon/server.js around the /api/chat endpoint (before buildArgs is called and in the child.on('close') / spawn catch blocks). Happy to submit a PR if this direction is acceptable.

[lefarcen]

Hi @ONEGAYI! 🎉 This is fantastic — you've implemented exactly the fallback path outlined in the issue body (Option B). The threshold logic (4KB for shell:true / 30KB for direct .exe) is solid, and the diagnostic logging will make debugging Windows edge cases much easier.

Please go ahead and submit a PR! A few things to include:

• The diff in daemon/server.js you described
• A quick test case (manual repro steps are fine — e.g. "pick magazine-web-ppt skill on Windows, verify prompt delivery succeeds")
• Update the issue description or PR body with before/after behavior

We'll review within 24h. Thanks for digging into this!

— open-design team

[lefarcen]

Recap for anyone landing here from search — this got resolved in two waves:

1. fix(daemon): PROMPT_TEMP_FILE function call + Claude Code stdin delivery on Windows #97 (@ONEGAYI) — Windows-only .od-prompt.md temp-file fallback (Option B in the original write-up). Unblocked Windows users immediately.
2. fix(daemon): deliver Claude Code prompt via stdin to avoid spawn E2BIG/ENAMETOOLONG #143 — Replaced both the argv path and the temp-file fallback with promptViaStdin: true for Claude (Option A), matching the pattern other agents already use. Also covered Linux spawn E2BIG, which was tracked separately as After few prompts : "spawn failed: spawn E2BIG" with Claude Code on Windows > WSL #82.

PR #67 (a parallel stdin attempt) is being closed as superseded by #143. Thanks @valkryhx for the original repro and @ONEGAYI for the fallback PR.