[Bug] Model silently downgraded from Opus 3.5 to Opus 4.8 mid-session without error notification

Bug Description
Working on defensive security engineering for my employer's own app-hardening (RASP) product — analyzing our SDK's architecture (anti-tamper, rooting/debugger detection, crash collection) to improve its design. This is authorized, defensive work on our own product, not offensive or malicious use. Mid-session the model silently switched from Opus 5 (1M) to Opus 4.8; if this was a content-based route rather than a usage-limit fallback, please note the context is legitimate defensive security.

Environment Info

• Platform: linux
• Terminal: ghostty
• Version: 2.1.258
• Feedback ID: 27d05919-e3d9-4d78-bc9f-7bc13767315c

Errors

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