[BUG] Parallel Write/Edit tool calls fail — only one succeeds per batch

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When Claude attempts multiple Write or Edit tool calls in the same response (parallel tool use), only one write typically succeeds. The others fail silently or with an error, and Claude reports: "The others failed due to a tool limitation with parallel writes."

This forces all file writes to be done sequentially (one per response turn), which significantly slows down tasks that involve creating or editing multiple files — especially when used with subagents that produce multi-file output.

What Should Happen?

Multiple Write and Edit tool calls issued in the same response should all execute successfully, just like parallel Read, Grep, Glob, and Bash calls do today.

Actual behavior:

When 2+ Write/Edit calls are dispatched in a single response:

Typically only 1 succeeds
The remaining calls fail or are silently dropped
No detailed error message is surfaced to the model — Claude infers the failure from missing confirmation
The user sees incomplete output and Claude has to retry the failed writes one at a time

Error Messages/Logs

Steps to Reproduce

1. Open Claude Code (CLI or VS Code extension)
2. Ask Claude to create 3+ new files in a single task, e.g.: "Create three files: src/utils/a.ts, src/utils/b.ts, and src/utils/c.ts with simple exports"
3. Observe that Claude attempts parallel Write calls
4. Only one file is created; the others fail
5. Claude retries them sequentially in follow-up turns

Alternatively, ask Claude to edit multiple existing files simultaneously (e.g., a rename-across-codebase task where 5+ files need Edit calls).

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.34

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

This is a quality-of-life issue that affects throughput on multi-file tasks. Common scenarios impacted:

Scaffolding new features (creating multiple files)
Bulk refactors (editing many files for a rename or pattern change)
Content generation (writing multiple data/config files)
Any task where subagents or parallel workflows produce multi-file output
Workaround: writing files sequentially (one per turn), but this adds unnecessary round-trips and latency.