Hah, that's typical Sonnet v2 for you. It's trained for shorter outputs, and it's causing it to be extremely lazy. It's a well known issue, and coding assistants contain mitigations for this. It's very reluctant to produce longer outputs, usually stopping mid-reply with something like "[Insert another 2k tokens of what you've been asking for, I've done enough]". Sonnet 3.7 seems to fix this.
Not really, these assistants are all trained as yes-men, and the training usually works well.
It might be a conflict between shorter outputs and the "soft reasoning" feature that version of Sonnet has, where it stops mid-reply and reflects on what it has written, in an attempt to reduce hallucinations. I don't know what exactly triggers it, but if it triggers in the middle of the long reply, it notices that it's already too long (which is an error according to its training) and stops immediately.
