[Bug] Anthropic API Error: 400 Tool Use Concurrency Issues

Bug Description
I have been using CC for a month now without issue. Today I have been using it for about 8 hours, but in the last hour it stopped working. all prompts end with an API error 400 concurrency. I have rebooted my mac, and restarted a new session, but the same error keeps happening, regardless of prompt, regardless of project. I use CC inside VS Code on my Mac, and everything is up to date. an example error message is this: I'll look into how suit symbol widths are calculated in the text metrics system.

Read text_metrics.rs
Read fonts.rs
API Error: 400 due to tool use concurrency issues.

Environment Info

• Platform: darwin
• Terminal: WezTerm
• Version: 2.1.19
• Feedback ID: afe1ae1d-d279-44b8-9b90-72113faf97a4

Errors

[{"error":"Error: ENOENT: no such file or directory, scandir '/Library/Application Support/ClaudeCode/.claude/skills'\n    at Module.readdirSync (node:fs:1502:26)\n    at file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:9:1766\n    at yO (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:8:35112)\n    at Object.readdirSync (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:9:1736)\n    at _D1 (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:2284:369)\n    at file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:2284:4279\n    at q (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:8:6814)\n    at CB2 (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:4920:4362)\n    at file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:4920:6961\n    at q (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:8:6814)","timestamp":"2026-01-26T21:17:14.268Z"},{"error":"Error: ENOENT: no such file or directory, scandir '/Users/rick/.claude/skills'\n    at Module.readdirSync (node:fs:1502:26)\n    at file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:9:1766\n    at yO (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:8:35112)\n    at Object.readdirSync (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:9:1736)\n    at _D1 (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:2284:369)\n    at file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:2284:4322\n    at q (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:8:6814)\n    at CB2 (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:4920:4362)\n    at file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:4920:6961\n    at q (file:///Users/rick/.npm-packages/lib/node_modules/@anthropic-ai/claude-code/cli.js:8:6814)","timestamp":"2026-01-26T21:17:14.268Z"}]