Drastically reduced quality from Sonnet 4.5 and Claude Code ~Dec 26

Question

**Bug Description**
I've seen drastically reduced quality from Sonnet 4.5 and Claude Code over the last day or two, suspiciously coincident with the Dec 2x usage bonus. It's repeatedly wrestling with me to make changes I've just told it not to, forgetting to run build/typecheck and arguing with me that tests pass so everything is good even though the TS project won't actually build, and has reverted to failing almost every attempted file edit confused about tab characters (#13152) where I'd been