fix(executor): improve antigravity reverse proxy emulation

- force http/1.1 instead of http/2

- explicit connection close

- strip proxy headers X-Forwarded-For and X-Real-IP

- add project id to fetch models payload

internal/runtime/executor/antigravity_executor.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"context"
 	"crypto/sha256"
+	"crypto/tls"
 	"encoding/binary"
 	"encoding/json"
 	"errors"
@@ -45,10 +46,10 @@ const (
 	antigravityModelsPath          = "/v1internal:fetchAvailableModels"
 	antigravityClientID            = "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com"
 	antigravityClientSecret        = "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"
-	defaultAntigravityAgent        = "antigravity/1.104.0 darwin/arm64"
+	defaultAntigravityAgent        = "antigravity/1.18.4 windows/amd64"
 	antigravityAuthType            = "antigravity"
 	refreshSkew                    = 3000 * time.Second
-	systemInstruction              = "You are Antigravity, a powerful agentic AI coding assistant designed by the Google Deepmind team working on Advanced Agentic Coding.You are pair programming with a USER to solve their coding task. The task may require creating a new codebase, modifying or debugging an existing codebase, or simply answering a question.**Absolute paths only****Proactiveness**"
+	systemInstruction              = "<identity> You are Antigravity, a powerful agentic AI coding assistant designed by the Google Deepmind team working on Advanced Agentic Coding. You are pair programming with a USER to solve their coding task. The task may require creating a new codebase, modifying or debugging an existing codebase, or simply answering a question. The USER will send you requests, which you must always prioritize addressing. Along with each USER request, we will attach additional metadata about their current state, such as what files they have open and where their cursor is. This information may or may not be relevant to the coding task, it is up for you to decide. </identity>"
 )
 
 var (
@@ -72,6 +73,22 @@ func NewAntigravityExecutor(cfg *config.Config) *AntigravityExecutor {
 	return &AntigravityExecutor{cfg: cfg}
 }
 
+// newAntigravityHTTPClient creates an HTTP client specifically for Antigravity,
+// enforcing HTTP/1.1 by disabling HTTP/2 to perfectly mimic Node.js https defaults.
+func newAntigravityHTTPClient(ctx context.Context, cfg *config.Config, auth *cliproxyauth.Auth, timeout time.Duration) *http.Client {
+	client := newProxyAwareHTTPClient(ctx, cfg, auth, timeout)
+	if client.Transport == nil {
+		client.Transport = http.DefaultTransport
+	}
+	if tr, ok := client.Transport.(*http.Transport); ok {
+		trClone := tr.Clone()
+		trClone.ForceAttemptHTTP2 = false
+		trClone.TLSNextProto = make(map[string]func(authority string, c *tls.Conn) http.RoundTripper)
+		client.Transport = trClone
+	}
+	return client
+}
+
 // Identifier returns the executor identifier.
 func (e *AntigravityExecutor) Identifier() string { return antigravityAuthType }
 
@@ -103,7 +120,11 @@ func (e *AntigravityExecutor) HttpRequest(ctx context.Context, auth *cliproxyaut
 	if err := e.PrepareRequest(httpReq, auth); err != nil {
 		return nil, err
 	}
-	httpClient := newProxyAwareHTTPClient(ctx, e.cfg, auth, 0)
+	httpReq.Close = true
+	httpReq.Header.Del("Accept")
+	httpReq.Header.Del("X-Forwarded-For")
+	httpReq.Header.Del("X-Real-IP")
+	httpClient := newAntigravityHTTPClient(ctx, e.cfg, auth, 0)
 	return httpClient.Do(httpReq)
 }
 
@@ -150,7 +171,7 @@ func (e *AntigravityExecutor) Execute(ctx context.Context, auth *cliproxyauth.Au
 	translated = applyPayloadConfigWithRoot(e.cfg, baseModel, "antigravity", "request", translated, originalTranslated, requestedModel)
 
 	baseURLs := antigravityBaseURLFallbackOrder(auth)
-	httpClient := newProxyAwareHTTPClient(ctx, e.cfg, auth, 0)
+	httpClient := newAntigravityHTTPClient(ctx, e.cfg, auth, 0)
 
 	attempts := antigravityRetryAttempts(auth, e.cfg)
 
@@ -292,7 +313,7 @@ func (e *AntigravityExecutor) executeClaudeNonStream(ctx context.Context, auth *
 	translated = applyPayloadConfigWithRoot(e.cfg, baseModel, "antigravity", "request", translated, originalTranslated, requestedModel)
 
 	baseURLs := antigravityBaseURLFallbackOrder(auth)
-	httpClient := newProxyAwareHTTPClient(ctx, e.cfg, auth, 0)
+	httpClient := newAntigravityHTTPClient(ctx, e.cfg, auth, 0)
 
 	attempts := antigravityRetryAttempts(auth, e.cfg)
 
@@ -684,7 +705,7 @@ func (e *AntigravityExecutor) ExecuteStream(ctx context.Context, auth *cliproxya
 	translated = applyPayloadConfigWithRoot(e.cfg, baseModel, "antigravity", "request", translated, originalTranslated, requestedModel)
 
 	baseURLs := antigravityBaseURLFallbackOrder(auth)
-	httpClient := newProxyAwareHTTPClient(ctx, e.cfg, auth, 0)
+	httpClient := newAntigravityHTTPClient(ctx, e.cfg, auth, 0)
 
 	attempts := antigravityRetryAttempts(auth, e.cfg)
 
@@ -886,7 +907,7 @@ func (e *AntigravityExecutor) CountTokens(ctx context.Context, auth *cliproxyaut
 	payload = deleteJSONField(payload, "request.safetySettings")
 
 	baseURLs := antigravityBaseURLFallbackOrder(auth)
-	httpClient := newProxyAwareHTTPClient(ctx, e.cfg, auth, 0)
+	httpClient := newAntigravityHTTPClient(ctx, e.cfg, auth, 0)
 
 	var authID, authLabel, authType, authValue string
 	if auth != nil {
@@ -917,10 +938,12 @@ func (e *AntigravityExecutor) CountTokens(ctx context.Context, auth *cliproxyaut
 		if errReq != nil {
 			return cliproxyexecutor.Response{}, errReq
 		}
+		httpReq.Close = true
 		httpReq.Header.Set("Content-Type", "application/json")
 		httpReq.Header.Set("Authorization", "Bearer "+token)
 		httpReq.Header.Set("User-Agent", resolveUserAgent(auth))
-		httpReq.Header.Set("Accept", "application/json")
+		httpReq.Header.Del("X-Forwarded-For")
+		httpReq.Header.Del("X-Real-IP")
 		if host := resolveHost(base); host != "" {
 			httpReq.Host = host
 		}
@@ -1014,17 +1037,31 @@ func FetchAntigravityModels(ctx context.Context, auth *cliproxyauth.Auth, cfg *c
 	}
 
 	baseURLs := antigravityBaseURLFallbackOrder(auth)
-	httpClient := newProxyAwareHTTPClient(ctx, cfg, auth, 0)
+	httpClient := newAntigravityHTTPClient(ctx, cfg, auth, 0)
 
 	for idx, baseURL := range baseURLs {
 		modelsURL := baseURL + antigravityModelsPath
-		httpReq, errReq := http.NewRequestWithContext(ctx, http.MethodPost, modelsURL, bytes.NewReader([]byte(`{}`)))
+
+		var payload []byte
+		if auth != nil && auth.Metadata != nil {
+			if pid, ok := auth.Metadata["project_id"].(string); ok && strings.TrimSpace(pid) != "" {
+				payload = []byte(fmt.Sprintf(`{"project": "%s"}`, strings.TrimSpace(pid)))
+			}
+		}
+		if len(payload) == 0 {
+			payload = []byte(`{}`)
+		}
+
+		httpReq, errReq := http.NewRequestWithContext(ctx, http.MethodPost, modelsURL, bytes.NewReader(payload))
 		if errReq != nil {
 			return nil
 		}
+		httpReq.Close = true
 		httpReq.Header.Set("Content-Type", "application/json")
 		httpReq.Header.Set("Authorization", "Bearer "+token)
 		httpReq.Header.Set("User-Agent", resolveUserAgent(auth))
+		httpReq.Header.Del("X-Forwarded-For")
+		httpReq.Header.Del("X-Real-IP")
 		if host := resolveHost(baseURL); host != "" {
 			httpReq.Host = host
 		}
@@ -1157,7 +1194,7 @@ func (e *AntigravityExecutor) refreshToken(ctx context.Context, auth *cliproxyau
 	httpReq.Header.Set("User-Agent", defaultAntigravityAgent)
 	httpReq.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 
-	httpClient := newProxyAwareHTTPClient(ctx, e.cfg, auth, 0)
+	httpClient := newAntigravityHTTPClient(ctx, e.cfg, auth, 0)
 	httpResp, errDo := httpClient.Do(httpReq)
 	if errDo != nil {
 		return auth, errDo
@@ -1228,7 +1265,7 @@ func (e *AntigravityExecutor) ensureAntigravityProjectID(ctx context.Context, au
 		return nil
 	}
 
-	httpClient := newProxyAwareHTTPClient(ctx, e.cfg, auth, 0)
+	httpClient := newAntigravityHTTPClient(ctx, e.cfg, auth, 0)
 	projectID, errFetch := sdkAuth.FetchAntigravityProjectID(ctx, token, httpClient)
 	if errFetch != nil {
 		return errFetch
@@ -1319,14 +1356,12 @@ func (e *AntigravityExecutor) buildRequest(ctx context.Context, auth *cliproxyau
 	if errReq != nil {
 		return nil, errReq
 	}
+	httpReq.Close = true
 	httpReq.Header.Set("Content-Type", "application/json")
 	httpReq.Header.Set("Authorization", "Bearer "+token)
 	httpReq.Header.Set("User-Agent", resolveUserAgent(auth))
-	if stream {
-		httpReq.Header.Set("Accept", "text/event-stream")
-	} else {
-		httpReq.Header.Set("Accept", "application/json")
-	}
+	httpReq.Header.Del("X-Forwarded-For")
+	httpReq.Header.Del("X-Real-IP")
 	if host := resolveHost(base); host != "" {
 		httpReq.Host = host
 	}