Desktop app fails at session init with "tools.122.custom.input_schema: int too big to convert" — CLI works with identical config

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?

Starting a session in the Claude desktop app (1.2278.0, build e5213f, 2026-04-13) fails immediately at session init with a 400 API error about an oversized integer in a tool's input schema. The error fires before any user message is processed — it's in the tool registration payload. The same config works fine in the Claude Code CLI (2.1.107) via the VS Code extension.

What Should Happen?

The desktop app should load the same tool set as the CLI without triggering an oversized-integer serialization error. Session should initialize normally.

Error Messages/Logs

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools.122.custom.input_schema: int too big to convert"},"request_id":"req_011Ca3nwVVH7zMCxMY4srxEy"}

Tool at index 122 has an input_schema containing an integer value that exceeds what the API accepts (likely i64 overflow). The CLI either doesn't load this tool, loads it differently, or serializes the schema differently.

Steps to Reproduce

1. Launch the Claude desktop app (macOS, version 1.2278.0) with the config below
2. Start a new session — fails at init with the 400 error above
3. Open the same repo in VS Code, launch Claude Code via the extension (CLI 2.1.107) with the identical ~/.claude.json and ~/.claude/settings.json → works fine

Troubleshooting attempted (none resolved the desktop app error):

• Removed sequential-thinking MCP server from ~/.claude.json
• Disabled all six plugins in ~/.claude/settings.json
• Verified both config files are valid JSON

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.107 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

Environment:

• Claude desktop app: 1.2278.0 (e5213f), built 2026-04-13
• Claude Code CLI: 2.1.107
• OS: macOS

Enabled plugins (from ~/.claude/settings.json):

• superpowers@claude-plugins-official
• context7@claude-plugins-official
• github@claude-plugins-official
• firecrawl@claude-plugins-official
• vercel@claude-plugins-official
• code-simplifier@claude-plugins-official

MCP servers:

• sequential-thinking (stdio, @modelcontextprotocol/server-sequential-thinking)
• computer-use

The fact that the CLI and desktop app produce different tool registration payloads from identical config suggests the desktop app is either loading an extra tool definition, serializing schemas differently, or hitting an encoding path the CLI doesn't.