The cherry-picked PR #15251 from @tw2818 correctly identified the
DeepSeek 400 root cause but placed the fix in the legacy fallback path
of `build_kwargs`, which DeepSeek never reaches — DeepSeek has a
registered ProviderProfile and goes through `_build_kwargs_from_profile`
instead. The legacy-path block was therefore dead code.
This commit pivots the fix to where it actually fires:
- New `DeepSeekProfile` in `plugins/model-providers/deepseek/__init__.py`
overrides `build_api_kwargs_extras` to emit DeepSeek's expected wire
format (mirrors `KimiProfile`):
{"reasoning_effort": "<low|medium|high|max>",
"extra_body": {"thinking": {"type": "enabled" | "disabled"}}}
- Model gating: only `deepseek-v4-*` and `deepseek-reasoner` emit
thinking control. `deepseek-chat` (V3) is untouched — current behavior.
- Effort mapping: low/medium/high passthrough, xhigh/max → max, unset →
omitted (DeepSeek server applies its own default).
- Revert the legacy-path additions from PR #15251 — they were dead code,
and the `_copy_reasoning_content_for_api` strip block specifically
would have nullified the existing reasoning_content padding machinery
(`_needs_deepseek_tool_reasoning` → space-pad on replay) that the
active provider already relies on for replay correctness.
- Unit tests pin the wire-shape contract and the model gating rules
(26 tests, all passing). Existing transport + provider profile suites
(321 tests) continue to pass.
- AUTHOR_MAP: map twebefy@gmail.com → tw2818 for release notes credit.
Closes#15700, #17212, #17825.
Co-authored-by: tw2818 <twebefy@gmail.com>
