fix(custom-provider): emit reasoning_effort at the live profile path

PR #57601's original branch added a top-level reasoning_effort emit to the
LEGACY build_kwargs path (agent/transports/chat_completions.py), but
provider=custom resolves to CustomProfile (plugins/model-providers/custom/),
so chat_completion_helpers takes the profile path and returns early — the
added branch was unreachable dead code for every custom endpoint.

Move the fix to its real site, CustomProfile.build_api_kwargs_extras(), and
follow the DeepSeek/Zai profile precedent:
  - disabled            -> extra_body.think = False (unchanged)
  - enabled + effort    -> TOP-LEVEL reasoning_effort (the OpenAI-compatible
                           format GLM-5.2/ARK expect), passed through verbatim
                           incl. max/xhigh
  - enabled + no effort -> omit, so the endpoint's server default applies
                           (avoids silently forcing 'medium' as the original
                           branch did)

Deliberately does NOT force think=True on enable — that flag is Ollama-only
and risks a 400 on GLM/vLLM endpoints that don't recognize it; thinking is
already server-default-on for these backends.

Verified end-to-end through the real profile dispatch (temp HERMES_HOME):
custom+high -> reasoning_effort=high; custom+max -> reasoning_effort=max;
custom+none -> think=False; custom+unset -> nothing; num_ctx composes.

Adds tests/plugins/model_providers/test_custom_profile.py (13 cases).
Addresses the custom-provider half of #55276.

Co-authored-by: huanshan5195 <huanshan5195@users.noreply.github.com>

tests/plugins/model_providers/test_custom_profile.py

@@ -0,0 +1,118 @@
+"""Unit tests for the custom provider profile's reasoning wiring.
+
+``provider=custom`` covers any OpenAI-compatible endpoint the user points
+Hermes at — local Ollama, vLLM, llama.cpp, and hosted reasoning APIs like
+GLM-5.2 on Volcengine ARK. Before #57601's salvage, ``CustomProfile`` emitted
+nothing when reasoning was *enabled*, so a configured ``reasoning_effort``
+was silently dropped for every custom endpoint.
+
+These tests pin the wire-shape contract:
+  - disabled            → extra_body.think = False
+  - enabled + effort    → top-level reasoning_effort (native OpenAI-compat
+                          format GLM/ARK expect), passed through verbatim
+                          including ``max``/``xhigh``
+  - enabled + no effort → nothing emitted (endpoint's server default applies)
+  - ollama_num_ctx      → extra_body.options.num_ctx, orthogonal to reasoning
+"""
+
+from __future__ import annotations
+
+import pytest
+
+
+@pytest.fixture
+def custom_profile():
+    """Resolve the registered custom profile via the global registry.
+
+    Importing ``model_tools`` triggers plugin discovery, which registers the
+    ``custom`` profile. Going through ``get_provider_profile`` keeps the test
+    honest — if the registered class is ever downgraded to a plain
+    ``ProviderProfile``, the assertions below collapse.
+    """
+    import model_tools  # noqa: F401
+    import providers
+
+    profile = providers.get_provider_profile("custom")
+    assert profile is not None, "custom provider profile must be registered"
+    return profile
+
+
+class TestCustomReasoningWireShape:
+    """``build_api_kwargs_extras`` produces the correct wire format."""
+
+    def test_no_reasoning_config_emits_nothing(self, custom_profile):
+        """Unset reasoning → omit everything so the endpoint's default applies."""
+        eb, tl = custom_profile.build_api_kwargs_extras(
+            reasoning_config=None, model="glm-5.2"
+        )
+        assert eb == {}
+        assert tl == {}
+
+    def test_disabled_sends_think_false(self, custom_profile):
+        """enabled=False → extra_body.think = False (Ollama thinking-off flag)."""
+        eb, tl = custom_profile.build_api_kwargs_extras(
+            reasoning_config={"enabled": False}, model="glm-5.2"
+        )
+        assert eb == {"think": False}
+        assert tl == {}
+
+    def test_effort_none_sends_think_false(self, custom_profile):
+        """effort='none' is the disable alias → think=False, no effort."""
+        eb, tl = custom_profile.build_api_kwargs_extras(
+            reasoning_config={"enabled": True, "effort": "none"}, model="glm-5.2"
+        )
+        assert eb == {"think": False}
+        assert tl == {}
+
+    @pytest.mark.parametrize(
+        "effort", ["minimal", "low", "medium", "high", "xhigh", "max"]
+    )
+    def test_enabled_effort_goes_top_level(self, custom_profile, effort):
+        """enabled + effort → TOP-LEVEL reasoning_effort, passed through verbatim.
+
+        GLM-5.2/ARK and OpenAI-compatible reasoning APIs read reasoning_effort
+        as a top-level string, not nested in extra_body. ``max`` is GLM's
+        native deep-reasoning level and must survive.
+        """
+        eb, tl = custom_profile.build_api_kwargs_extras(
+            reasoning_config={"enabled": True, "effort": effort}, model="glm-5.2"
+        )
+        assert tl == {"reasoning_effort": effort}
+        assert "reasoning_effort" not in eb
+        assert "think" not in eb
+
+    def test_enabled_without_effort_emits_nothing(self, custom_profile):
+        """enabled but no effort → omit; do NOT force a level the user didn't pick."""
+        eb, tl = custom_profile.build_api_kwargs_extras(
+            reasoning_config={"enabled": True}, model="glm-5.2"
+        )
+        assert eb == {}
+        assert tl == {}
+
+    def test_does_not_force_think_true_on_enable(self, custom_profile):
+        """We must never send think=True on enable — it's Ollama-only and
+        would 400 on GLM/vLLM endpoints that don't recognize it."""
+        eb, _ = custom_profile.build_api_kwargs_extras(
+            reasoning_config={"enabled": True, "effort": "high"}, model="glm-5.2"
+        )
+        assert eb.get("think") is not True
+
+
+class TestCustomReasoningWithNumCtx:
+    """Ollama num_ctx and reasoning are independent and compose."""
+
+    def test_num_ctx_alone(self, custom_profile):
+        eb, tl = custom_profile.build_api_kwargs_extras(
+            reasoning_config=None, ollama_num_ctx=8192, model="qwen3"
+        )
+        assert eb == {"options": {"num_ctx": 8192}}
+        assert tl == {}
+
+    def test_num_ctx_with_effort(self, custom_profile):
+        eb, tl = custom_profile.build_api_kwargs_extras(
+            reasoning_config={"enabled": True, "effort": "high"},
+            ollama_num_ctx=8192,
+            model="qwen3",
+        )
+        assert eb == {"options": {"num_ctx": 8192}}
+        assert tl == {"reasoning_effort": "high"}