Fixed: #421

feat(antigravity): implement project ID retrieval and integration in payload processing

internal/runtime/executor/antigravity_executor.go

@@ -509,7 +509,14 @@ func (e *AntigravityExecutor) buildRequest(ctx context.Context, auth *cliproxyau
 		requestURL.WriteString(url.QueryEscape(alt))
 	}
 
-	payload = geminiToAntigravity(modelName, payload)
+	// Extract project_id from auth metadata if available
+	projectID := ""
+	if auth != nil && auth.Metadata != nil {
+		if pid, ok := auth.Metadata["project_id"].(string); ok {
+			projectID = strings.TrimSpace(pid)
+		}
+	}
+	payload = geminiToAntigravity(modelName, payload, projectID)
 	payload, _ = sjson.SetBytes(payload, "model", alias2ModelName(modelName))
 
 	if strings.Contains(modelName, "claude") {
@@ -676,9 +683,9 @@ func antigravityBaseURLFallbackOrder(auth *cliproxyauth.Auth) []string {
 		return []string{base}
 	}
 	return []string{
+		antigravityBaseURLProd,
 		antigravityBaseURLDaily,
 		antigravityBaseURLAutopush,
-		// antigravityBaseURLProd,
 	}
 }
 
@@ -702,10 +709,16 @@ func resolveCustomAntigravityBaseURL(auth *cliproxyauth.Auth) string {
 	return ""
 }
 
-func geminiToAntigravity(modelName string, payload []byte) []byte {
+func geminiToAntigravity(modelName string, payload []byte, projectID string) []byte {
 	template, _ := sjson.Set(string(payload), "model", modelName)
 	template, _ = sjson.Set(template, "userAgent", "antigravity")
+
+	// Use real project ID from auth if available, otherwise generate random (legacy fallback)
+	if projectID != "" {
+		template, _ = sjson.Set(template, "project", projectID)
+	} else {
 		template, _ = sjson.Set(template, "project", generateProjectID())
+	}
 	template, _ = sjson.Set(template, "requestId", generateRequestID())
 	template, _ = sjson.Set(template, "request.sessionId", generateSessionID())
 

sdk/auth/antigravity.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
 	"net"
 	"net/http"
 	"net/url"
@@ -127,6 +128,18 @@ func (AntigravityAuthenticator) Login(ctx context.Context, cfg *config.Config, o
 		}
 	}
 
+	// Fetch project ID via loadCodeAssist (same approach as Gemini CLI)
+	projectID := ""
+	if tokenResp.AccessToken != "" {
+		fetchedProjectID, errProject := fetchAntigravityProjectID(ctx, tokenResp.AccessToken, httpClient)
+		if errProject != nil {
+			log.Warnf("antigravity: failed to fetch project ID: %v", errProject)
+		} else {
+			projectID = fetchedProjectID
+			log.Infof("antigravity: obtained project ID %s", projectID)
+		}
+	}
+
 	now := time.Now()
 	metadata := map[string]any{
 		"type":          "antigravity",
@@ -139,6 +152,9 @@ func (AntigravityAuthenticator) Login(ctx context.Context, cfg *config.Config, o
 	if email != "" {
 		metadata["email"] = email
 	}
+	if projectID != "" {
+		metadata["project_id"] = projectID
+	}
 
 	fileName := sanitizeAntigravityFileName(email)
 	label := email
@@ -147,6 +163,9 @@ func (AntigravityAuthenticator) Login(ctx context.Context, cfg *config.Config, o
 	}
 
 	fmt.Println("Antigravity authentication successful")
+	if projectID != "" {
+		fmt.Printf("Using GCP project: %s\n", projectID)
+	}
 	return &coreauth.Auth{
 		ID:       fileName,
 		Provider: "antigravity",
@@ -291,3 +310,84 @@ func sanitizeAntigravityFileName(email string) string {
 	replacer := strings.NewReplacer("@", "_", ".", "_")
 	return fmt.Sprintf("antigravity-%s.json", replacer.Replace(email))
 }
+
+// Antigravity API constants for project discovery
+const (
+	antigravityAPIEndpoint    = "https://cloudcode-pa.googleapis.com"
+	antigravityAPIVersion     = "v1internal"
+	antigravityAPIUserAgent   = "google-api-nodejs-client/9.15.1"
+	antigravityAPIClient      = "google-cloud-sdk vscode_cloudshelleditor/0.1"
+	antigravityClientMetadata = `{"ideType":"IDE_UNSPECIFIED","platform":"PLATFORM_UNSPECIFIED","pluginType":"GEMINI"}`
+)
+
+// fetchAntigravityProjectID retrieves the project ID for the authenticated user via loadCodeAssist.
+// This uses the same approach as Gemini CLI to get the cloudaicompanionProject.
+func fetchAntigravityProjectID(ctx context.Context, accessToken string, httpClient *http.Client) (string, error) {
+	// Call loadCodeAssist to get the project
+	loadReqBody := map[string]any{
+		"metadata": map[string]string{
+			"ideType":    "IDE_UNSPECIFIED",
+			"platform":   "PLATFORM_UNSPECIFIED",
+			"pluginType": "GEMINI",
+		},
+	}
+
+	rawBody, errMarshal := json.Marshal(loadReqBody)
+	if errMarshal != nil {
+		return "", fmt.Errorf("marshal request body: %w", errMarshal)
+	}
+
+	endpointURL := fmt.Sprintf("%s/%s:loadCodeAssist", antigravityAPIEndpoint, antigravityAPIVersion)
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpointURL, strings.NewReader(string(rawBody)))
+	if err != nil {
+		return "", fmt.Errorf("create request: %w", err)
+	}
+	req.Header.Set("Authorization", "Bearer "+accessToken)
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("User-Agent", antigravityAPIUserAgent)
+	req.Header.Set("X-Goog-Api-Client", antigravityAPIClient)
+	req.Header.Set("Client-Metadata", antigravityClientMetadata)
+
+	resp, errDo := httpClient.Do(req)
+	if errDo != nil {
+		return "", fmt.Errorf("execute request: %w", errDo)
+	}
+	defer func() {
+		if errClose := resp.Body.Close(); errClose != nil {
+			log.Errorf("antigravity loadCodeAssist: close body error: %v", errClose)
+		}
+	}()
+
+	bodyBytes, errRead := io.ReadAll(resp.Body)
+	if errRead != nil {
+		return "", fmt.Errorf("read response: %w", errRead)
+	}
+
+	if resp.StatusCode < http.StatusOK || resp.StatusCode >= http.StatusMultipleChoices {
+		return "", fmt.Errorf("request failed with status %d: %s", resp.StatusCode, strings.TrimSpace(string(bodyBytes)))
+	}
+
+	var loadResp map[string]any
+	if errDecode := json.Unmarshal(bodyBytes, &loadResp); errDecode != nil {
+		return "", fmt.Errorf("decode response: %w", errDecode)
+	}
+
+	// Extract projectID from response
+	projectID := ""
+	if id, ok := loadResp["cloudaicompanionProject"].(string); ok {
+		projectID = strings.TrimSpace(id)
+	}
+	if projectID == "" {
+		if projectMap, ok := loadResp["cloudaicompanionProject"].(map[string]any); ok {
+			if id, okID := projectMap["id"].(string); okID {
+				projectID = strings.TrimSpace(id)
+			}
+		}
+	}
+
+	if projectID == "" {
+		return "", fmt.Errorf("no cloudaicompanionProject in response")
+	}
+
+	return projectID, nil
+}