[Bug] API Error 400: tool_use.name exceeds 200 chars during extended sessions with MCP + agents

Bug Description

During extended Claude Code sessions that use MCP servers, skills, and background agents (Task tool), the session becomes completely unrecoverable with repeated API 400 errors:

API Error: 400
{"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.3.tool_use.name: String should have at most 200 characters"},"request_id":"req_011CXqpzg8a2KML9MmyPtmvr"}

Once triggered, every subsequent message (even simple text) fails with the same error. The session is bricked — no recovery possible except /clear or restarting.

Environment

• Version: 2.1.32
• Platform: macOS (darwin, Apple Silicon)
• Terminal: Ghostty

MCP Servers Installed

• nx-mcp
• playwright
• mcp-gsheets
• claude-in-chrome

Steps to Reproduce

1. Start a Claude Code session with MCP servers active
2. Use skills (via Skill tool) that expand to large prompts
3. Spawn background agents with Task tool (3+ agents)
4. Continue working for ~30+ messages with mixed tool usage
5. Error appears on messages.N.content.M.tool_use.name
6. ALL subsequent messages fail — session is bricked

Key Observations

• Error references messages.1.content.X.tool_use.name — this is in the compacted conversation history, not the latest message
• This suggests context compaction may be corrupting or extending tool names beyond 200 chars
• One commenter on #7370 confirmed it happened "right after compacting a conversation"
• The error blocks ALL messages including plain text, because the corrupted tool name is in conversation history

Expected Behavior

• Tool names should be validated/truncated before API calls
• Context compaction should preserve valid tool names
• If a tool name in history is too long, it should be sanitized rather than bricking the session
• At minimum, provide a recovery mechanism (auto-rewind past the corrupted message)

Previous Reports (auto-closed, unfixed)

• #7370 — [BUG] API Error 400: Tool name exceeds 200 character limit causing complete session failure
• #15695 — [Bug] API Error 400: MCP tool_use.name exceeds 200 character limit, blocking all messages
• #2673 — Validation Error: Tool Use Name Exceeds 200 Character Limit

All three were auto-closed without resolution. The bug persists in v2.1.32.

Suggested Fix

The compaction/summarization logic should validate that tool names in the compressed history don't exceed 200 characters. If they do, truncate or replace with a placeholder before sending to the API. Additionally, when a 400 error references a historical message, Claude Code should attempt to auto-heal by rewinding past the corrupted message rather than failing on every subsequent turn.