feat(thinking): add xAI provider support with reasoning.effort implementation

- Implemented `xAI` provider for thinking configurations with support for reasoning.effort levels.
- Registered `xAI` in available providers and updated relevant APIs for compatibility.
- Added unit tests for `xAI` provider functionality, including fallback logic for unsupported levels.
- Integrated `xAI` with executor handling and ensured conformance with OpenAI-compatible standards.

internal/thinking/provider/xai/apply.go

@@ -0,0 +1,26 @@
+// Package xai implements thinking configuration for xAI Grok Responses API models.
+//
+// xAI models use the OpenAI Responses API compatible reasoning.effort format
+// with discrete levels.
+package xai
+
+import (
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking/provider/codex"
+)
+
+// Applier implements thinking.ProviderApplier for xAI models.
+type Applier struct {
+	codex.Applier
+}
+
+var _ thinking.ProviderApplier = (*Applier)(nil)
+
+// NewApplier creates a new xAI thinking applier.
+func NewApplier() *Applier {
+	return &Applier{}
+}
+
+func init() {
+	thinking.RegisterProvider("xai", NewApplier())
+}

internal/thinking/provider/xai/apply_test.go

@@ -0,0 +1,51 @@
+package xai
+
+import (
+	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
+	"github.com/tidwall/gjson"
+)
+
+func TestApplySetsReasoningEffort(t *testing.T) {
+	applier := NewApplier()
+	modelInfo := &registry.ModelInfo{
+		ID: "grok-4.3",
+		Thinking: &registry.ThinkingSupport{
+			ZeroAllowed: true,
+			Levels:      []string{"none", "low", "medium", "high"},
+		},
+	}
+
+	out, err := applier.Apply([]byte(`{"input":"hello"}`), thinking.ThinkingConfig{
+		Mode:  thinking.ModeLevel,
+		Level: thinking.LevelHigh,
+	}, modelInfo)
+	if err != nil {
+		t.Fatalf("Apply() error = %v", err)
+	}
+	if got := gjson.GetBytes(out, "reasoning.effort").String(); got != "high" {
+		t.Fatalf("reasoning.effort = %q, want high; body=%s", got, string(out))
+	}
+}
+
+func TestApplyNoneFallsBackToLowestLevelWhenDisableUnsupported(t *testing.T) {
+	applier := NewApplier()
+	modelInfo := &registry.ModelInfo{
+		ID: "grok-3-mini",
+		Thinking: &registry.ThinkingSupport{
+			Levels: []string{"low", "medium", "high"},
+		},
+	}
+
+	out, err := applier.Apply([]byte(`{"input":"hello"}`), thinking.ThinkingConfig{
+		Mode: thinking.ModeNone,
+	}, modelInfo)
+	if err != nil {
+		t.Fatalf("Apply() error = %v", err)
+	}
+	if got := gjson.GetBytes(out, "reasoning.effort").String(); got != "low" {
+		t.Fatalf("reasoning.effort = %q, want low; body=%s", got, string(out))
+	}
+}