/compact fails with 'thinking or redacted_thinking blocks cannot be modified' error when context is too long

Bug Report

Description

When a conversation reaches the context limit and the user runs /compact, compaction fails with the following error:

Error: Error during compaction: API Error: 400 messages.9.content.4: thinking or redacted_thinking blocks in the latest assistant message cannot be modified. These blocks must remain as they were in the original response.

This leaves the user completely stuck — the conversation is too long to continue, but /compact also fails, so there's no way to recover the session.

Steps to Reproduce

1. Have a long conversation that reaches the context limit
2. See the "Conversation is too long" error banner
3. Run /compact
4. Compaction fails with the error above

Expected Behavior

/compact should successfully summarize and compress the conversation history, allowing the session to continue.

Actual Behavior

Compaction fails because the last assistant message contains thinking or redacted_thinking blocks, which the API does not allow to be modified during compaction.

Impact

User is completely unable to recover the session — cannot compact, cannot continue, only option is to start a new chat and lose all context.

Suggested Fix

Before compaction, strip or handle thinking/redacted_thinking blocks from the latest assistant message so the API call doesn't fail.

Environment

• Claude Code CLI
• Reported by user via FleetView session