Compaction duplicates advisor server_tool_use blocks; session fails with 400 'server_tool_use ids must be unique per assistant turn'

Summary

With the advisor tool enabled, compaction can leave a session permanently broken. Every request fails with:

400 messages.5.content.95: `server_tool_use` ids must be unique per assistant turn

The session can't recover on its own. Retrying, resuming and further turns all send the same history.

Environment

• Claude Code 2.1.293 and 2.1.296, macOS (desktop app Code tab and CLI)
• Advisor enabled (advisorModel set)
• Seen with built-in compaction and with a plugin session.compact hook

What the transcripts show

Across 30 local sessions with advisor calls in the last 5 days:

• 16 sessions have the same advisor server_tool_use id written more than once to the session JSONL.
• 158 duplicate pairs in total, and every one of them has a compact_boundary between the two copies.
• Each copy carries the same message.id as the original assistant message.
• In most sessions the old copy sits before the boundary and is never sent, so nothing breaks. In at least 2 sessions both copies ended up in the post-compaction chain under one message.id. They merged into one assistant turn, which the API rejects with the error above.

Expected

When building a request, server tool blocks (and their results) should be deduplicated by id within an assistant turn. Alternatively, compaction shouldn't re-write an advisor block that's already in the chain it keeps.

Workaround

Fork the session from a message before the error. Or edit the JSONL so the duplicate entries get a different message.id, which stops them merging.