Desktop app: assistant text blocks duplicated in transcript and UI when advisorModel is set

Summary

With "advisorModel" set in ~/.claude/settings.json, every assistant text block is written twice to the session transcript (.jsonl) and shown twice in the Claude desktop app (Code tab). Removing advisorModel stops it.

Evidence

• The two copies have the same message.id and requestId, same timestamp, but different uuid and different parentUuid.
• Measured across the 8 most recent local sessions:
• sessions with advisorModel entries: 34/41, 73/73, 280/298, 49/50 text blocks duplicated
• sessions without advisor: 0 duplicated
• The duplicated text also comes back to the model in later turns (it sees each of its own replies twice), which wastes context.

Environment

• Claude desktop app (Code tab), Windows 11
• Claude Code 2.1.289 (CLI 2.1.286 installed)
• Model: claude-opus-5-5, advisorModel: "fable"

Steps to reproduce

1. Set "advisorModel": "fable" in ~/.claude/settings.json.
2. Start a session in the desktop app and ask anything that produces text plus a tool call.
3. Open the session .jsonl: each assistant text block appears in two assistant entries with the same message.id.

Expected

One transcript entry per assistant text block; text displayed once.

Workaround

Remove advisorModel from settings.