feat(provider): enable Kimi thinking via extra_body for k2.5 and k2.6

- Inject `thinking={"type": "enabled|disabled"}` via extra_body for
  Kimi thinking-capable models (kimi-k2.5, k2.6-code-preview).
- Add _is_kimi_thinking_model helper to handle both bare slugs and
  OpenRouter-style prefixed names (e.g. moonshotai/kimi-k2.5).
- reasoning_effort="minimal" maps to disabled; any other value enables it.
- Add tests for enabled/disabled states and OpenRouter prefix handling.

tests/providers/test_litellm_kwargs.py

@@ -730,3 +730,50 @@ def test_openai_no_thinking_extra_body() -> None:
     """Non-thinking providers should never get extra_body for thinking."""
     kw = _build_kwargs_for("openai", "gpt-4o", reasoning_effort="medium")
     assert "extra_body" not in kw
+
+
+def test_kimi_k25_thinking_enabled() -> None:
+    """kimi-k2.5 with reasoning_effort set should opt in to thinking."""
+    kw = _build_kwargs_for("moonshot", "kimi-k2.5", reasoning_effort="medium")
+    assert kw.get("extra_body") == {"thinking": {"type": "enabled"}}
+
+
+def test_kimi_k25_thinking_disabled_for_minimal() -> None:
+    """reasoning_effort='minimal' maps to thinking disabled for kimi-k2.5."""
+    kw = _build_kwargs_for("moonshot", "kimi-k2.5", reasoning_effort="minimal")
+    assert kw.get("extra_body") == {"thinking": {"type": "disabled"}}
+
+
+def test_kimi_k25_no_extra_body_when_reasoning_effort_none() -> None:
+    """Without reasoning_effort the thinking param must not be injected."""
+    kw = _build_kwargs_for("moonshot", "kimi-k2.5", reasoning_effort=None)
+    assert "extra_body" not in kw
+
+
+def test_kimi_k25_thinking_enabled_with_openrouter_prefix() -> None:
+    """OpenRouter-style model names like moonshotai/kimi-k2.5 must trigger thinking."""
+    kw = _build_kwargs_for("openrouter", "moonshotai/kimi-k2.5", reasoning_effort="medium")
+    assert kw.get("extra_body") == {"thinking": {"type": "enabled"}}
+
+def test_kimi_k25_thinking_disabled_with_openrouter_prefix() -> None:
+    """OpenRouter names must NOT trigger thinking without reasoning_effort."""
+    kw = _build_kwargs_for("openrouter", "moonshotai/kimi-k2.5", reasoning_effort=None)
+    assert "extra_body" not in kw
+
+
+def test_kimi_k26_code_preview_thinking_enabled() -> None:
+    """k2.6-code-preview also supports thinking; should behave like k2.5."""
+    kw = _build_kwargs_for("moonshot", "k2.6-code-preview", reasoning_effort="high")
+    assert kw.get("extra_body") == {"thinking": {"type": "enabled"}}
+
+
+def test_kimi_k2_series_no_thinking_injection() -> None:
+    """kimi-k2 (non-thinking) models must NOT receive extra_body.thinking."""
+    kw = _build_kwargs_for("moonshot", "kimi-k2", reasoning_effort="high")
+    assert "extra_body" not in kw
+
+
+def test_kimi_k2_thinking_series_no_thinking_injection() -> None:
+    """kimi-k2-thinking series models must NOT receive extra_body.thinking."""
+    kw = _build_kwargs_for("moonshot", "kimi-k2-thinking", reasoning_effort="high")
+    assert "extra_body" not in kw