test(antigravity): cover invalid-signature replay cache clear

Add executor httptest for upstream 400 clearing HOME reasoning replay
items, and a whitespace call_id matcher regression test for replay
filtering.

internal/runtime/executor/antigravity_reasoning_replay_clear_test.go

@@ -0,0 +1,66 @@
+package executor
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	internalcache "github.com/router-for-me/CLIProxyAPI/v7/internal/cache"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/config"
+	cliproxyauth "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/auth"
+	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/executor"
+	sdktranslator "github.com/router-for-me/CLIProxyAPI/v7/sdk/translator"
+)
+
+func TestAntigravityReasoningReplayClearsOnInvalidSignature400(t *testing.T) {
+	internalcache.ClearAntigravityReasoningReplayCache()
+	t.Cleanup(internalcache.ClearAntigravityReasoningReplayCache)
+
+	model := "gemini-3-flash-agent"
+	sessionKey := "session:pr3900-invalid-sig"
+	bad := []byte(`{"type":"thought_signature","thoughtSignature":"INVALID_REPLAY_SIGNATURE_PR3900_XXXXXXXXX","contentIndex":1,"partIndex":0}`)
+	if !internalcache.CacheAntigravityReasoningReplayItems(model, sessionKey, [][]byte{bad}) {
+		t.Fatal("failed to seed replay cache")
+	}
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = io.ReadAll(r.Body)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		_, _ = w.Write([]byte(`{"error":{"message":"Invalid thoughtSignature in model content","code":400}}`))
+	}))
+	defer server.Close()
+
+	exec := NewAntigravityExecutor(&config.Config{RequestRetry: 1})
+	auth := &cliproxyauth.Auth{
+		ID: "auth-pr3900-invalid-sig",
+		Attributes: map[string]string{
+			"base_url": server.URL,
+		},
+		Metadata: map[string]any{
+			"access_token": "token",
+			"project_id":   "project-1",
+			"expired":      time.Now().Add(1 * time.Hour).Format(time.RFC3339),
+		},
+	}
+
+	payload := []byte(`{"sessionId":"pr3900-invalid-sig","request":{"contents":[{"role":"user","parts":[{"text":"hi"}]},{"role":"user","parts":[{"functionResponse":{"id":"id1","name":"Bash","response":{"result":"ok"}}}]}]}}`)
+	_, err := exec.Execute(context.Background(), auth, cliproxyexecutor.Request{
+		Model:   model,
+		Payload: payload,
+	}, cliproxyexecutor.Options{
+		SourceFormat: sdktranslator.FormatAntigravity,
+		Stream:       false,
+	})
+	if err == nil {
+		t.Fatal("expected upstream 400 error")
+	}
+	if _, ok, errGet := internalcache.GetAntigravityReasoningReplayItemsRequired(context.Background(), model, sessionKey); errGet != nil {
+		t.Fatalf("get after clear: %v", errGet)
+	} else if ok {
+		t.Fatal("invalid signature 400 should clear cached replay item")
+	}
+}

internal/runtime/executor/antigravity_reasoning_replay_test.go

@@ -137,3 +137,10 @@ func TestAntigravityReplayToolCallKeysUsesNativeFunctionCallID(t *testing.T) {
 		t.Fatalf("parallel tool calls should not share replay key: %v vs %v", keys, keys2)
 	}
 }
+
+func TestAntigravityRequestHasMatchingFunctionResponseWhitespaceCallID(t *testing.T) {
+	item := gjson.Parse(`{"call_id":" "}`)
+	if !antigravityRequestHasMatchingFunctionResponse(nil, item) {
+		t.Fatal("whitespace-only call_id should be treated as empty => true")
+	}
+}