feat(api): add request body decoding with Content-Encoding support

- Introduced `ReadRequestBody` helper function to support decoding request bodies based on "Content-Encoding" (e.g., `zstd`).
- Replaced `c.GetRawData()` with `ReadRequestBody` across handlers to enable decoding.
- Added test case to validate `zstd` decoding for compact responses.

sdk/api/handlers/openai/openai_responses_compact_test.go

@@ -1,6 +1,7 @@
 package openai
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"net/http"
@@ -9,6 +10,7 @@ import (
 	"testing"
 
 	"github.com/gin-gonic/gin"
+	"github.com/klauspost/compress/zstd"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
 	"github.com/router-for-me/CLIProxyAPI/v7/sdk/api/handlers"
 	coreauth "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/auth"
@@ -118,3 +120,55 @@ func TestOpenAIResponsesCompactExecute(t *testing.T) {
 		t.Fatalf("body = %s", resp.Body.String())
 	}
 }
+
+func TestOpenAIResponsesCompactDecodesZstdRequestBody(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	executor := &compactCaptureExecutor{}
+	manager := coreauth.NewManager(nil, nil, nil)
+	manager.RegisterExecutor(executor)
+
+	auth := &coreauth.Auth{ID: "auth3", Provider: executor.Identifier(), Status: coreauth.StatusActive}
+	if _, err := manager.Register(context.Background(), auth); err != nil {
+		t.Fatalf("Register auth: %v", err)
+	}
+	registry.GetGlobalRegistry().RegisterClient(auth.ID, auth.Provider, []*registry.ModelInfo{{ID: "test-model"}})
+	t.Cleanup(func() {
+		registry.GetGlobalRegistry().UnregisterClient(auth.ID)
+	})
+
+	base := handlers.NewBaseAPIHandlers(&sdkconfig.SDKConfig{}, manager)
+	h := NewOpenAIResponsesAPIHandler(base)
+	router := gin.New()
+	router.POST("/v1/responses/compact", h.Compact)
+
+	var compressed bytes.Buffer
+	encoder, err := zstd.NewWriter(&compressed)
+	if err != nil {
+		t.Fatalf("zstd.NewWriter: %v", err)
+	}
+	if _, errWrite := encoder.Write([]byte(`{"model":"test-model","input":"hello"}`)); errWrite != nil {
+		t.Fatalf("zstd write: %v", errWrite)
+	}
+	if errClose := encoder.Close(); errClose != nil {
+		t.Fatalf("zstd close: %v", errClose)
+	}
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/responses/compact", bytes.NewReader(compressed.Bytes()))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Content-Encoding", "zstd")
+	resp := httptest.NewRecorder()
+	router.ServeHTTP(resp, req)
+
+	if resp.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d; body=%s", resp.Code, http.StatusOK, resp.Body.String())
+	}
+	if executor.calls != 1 {
+		t.Fatalf("executor calls = %d, want 1", executor.calls)
+	}
+	if executor.alt != "responses/compact" {
+		t.Fatalf("alt = %q, want %q", executor.alt, "responses/compact")
+	}
+	if strings.TrimSpace(resp.Body.String()) != `{"ok":true}` {
+		t.Fatalf("body = %s", resp.Body.String())
+	}
+}