[BUG] MCP tools running sequentially instead of in parallel in v2.0.71

Description

Multiple MCP tool calls in the same message are running sequentially instead of in parallel after upgrading to Claude Code v2.0.71 (released Dec 17, 2025).

Steps to Reproduce

1. Make three MCP tool calls in a single message block (format, test, inspect)
2. Observe execution time

Expected Behavior

All three tools should run in parallel:

• Total time: ~1m20s (longest individual tool)

Actual Behavior

Tools run sequentially:

• format: 1m20s
• test: 11s
• inspect: 1m20s
• Total: ~3 minutes

Environment

• Claude Code version: 2.0.71
• Date: December 17, 2025
• MCP Server: developer-cli (custom project MCP server)

Additional Context

This worked correctly in previous versions where multiple tool calls in the same message block would execute in parallel. The regression appears to have been introduced in v2.0.71 or a recent version.