[Bug] Model silently downgraded from claude-fable-5 to claude-opus without user action or notification

Bug Description
As prepared by Claude: I run Claude Code with my model set to Fable 5 (claude-fable-5). Mid-session, the model was silently reassigned to Opus without any action on my side — it appears a thread-level flag or tag triggered the switch. I only noticed because the assistant's behavior changed; I had to interrupt, /model back to Fable, and effectively hand the thread off to continue. This is the second time this has happened. The earlier instance looked like a false-positive content flag on legitimate, authorized defensive-security work (hardening my own Django application). The current session is ordinary software engineering — a chemical-process-diagram (P&ID/DXF) analysis app — with nothing that should warrant flagging. Impact: it breaks session continuity and forces a restart. My questions: what causes a thread to be flagged and its model reassigned, can it be prevented for this account, and can the switch at least be surfaced to me rather than happening silently? Account: a.moreira@lyfx.ai

Environment Info

• Platform: linux
• Terminal: vscode
• Version: 2.1.200
• Feedback ID: cc16ce80-3270-4840-97af-380083d2d097

Errors

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