`enable_thinking: false` came back still thinking, verified on a pod running
the v0.4.65 image with --reasoning-parser qwen3 (the other four checks passed:
reasoning_content populated, content clean, and streamed thinking starting
0.4s in against the answer at 2.8s).

generate_chat negotiates optional kwargs by calling the backend and retrying
on TypeError. Every variant that carried `passthrough` ALSO carried
`enable_thinking`, which a proxy backend does not accept -- so those variants
raised TypeError, and the variant that survived had dropped the passthrough
with it. A caller's `chat_template_kwargs` therefore never reached a pod at
all. `enable_thinking` was merely the visible case: OCR's
`continue_final_message` would have been dropped on a pod the same way.

`_lp` and `_pt` are already SIGNATURE-gated -- empty for a backend that cannot
take them, so they never raise TypeError. Only enable_thinking and the
penalties are negotiated that way, so only those are peeled off now, and the
passthrough is dropped last rather than first.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S8LAP3ueNzQJtwzhgVbq66