[fix]: Anthropic - include_server_side_tool_invocations now reaches the Gemini declaration-drop gate

core/providers/anthropic/responses.go

@@ -3486,6 +3486,25 @@ func (req *AnthropicMessageRequest) ToBifrostResponsesRequest(ctx *schemas.Bifro
 	if include, ok := schemas.SafeExtractStringSlice(req.ExtraParams["include"]); ok {
 		params.Include = include
 	}
+	// Lift the mixed server/client tool opt-in onto the typed parameter: the
+	// Gemini declaration-drop gate reads Params.IncludeServerSideToolInvocations,
+	// so leaving it in ExtraParams silently drops function tools when a request
+	// combines them with a server-side tool (issue #5679). Unregistered fields
+	// are captured as json.RawMessage holding the bare true/false token, so a
+	// string comparison is enough.
+	if raw, exists := req.ExtraParams["include_server_side_tool_invocations"]; exists {
+		switch v := raw.(type) {
+		case bool:
+			params.IncludeServerSideToolInvocations = schemas.Ptr(v)
+		case json.RawMessage:
+			switch strings.TrimSpace(string(v)) {
+			case "true":
+				params.IncludeServerSideToolInvocations = schemas.Ptr(true)
+			case "false":
+				params.IncludeServerSideToolInvocations = schemas.Ptr(false)
+			}
+		}
+	}
 	if req.ServiceTier != nil {
 		mapped := MapAnthropicRequestServiceTierToBifrost(*req.ServiceTier)
 		params.ServiceTier = &mapped

core/providers/anthropic/responses_test.go

@@ -392,3 +392,34 @@ func TestToAnthropicResponsesRequest_ContextManagement_UnsupportedProviderExtraP
 		t.Errorf("expected context_management to be removed from the outgoing request's ExtraParams even though the feature gate is closed")
 	}
 }
+
+// TestAnthropicIngressLiftsServerSideToolOptIn covers issue #5679: the
+// include_server_side_tool_invocations opt-in arrives as an unregistered
+// Anthropic field (captured into ExtraParams) but the Gemini declaration-drop
+// gate reads the typed Params.IncludeServerSideToolInvocations, so the ingress
+// conversion must lift it. Without the lift, combining a server-side tool with
+// a function tool on /anthropic/v1/messages routed to Gemini silently drops
+// the function declarations.
+func TestAnthropicIngressLiftsServerSideToolOptIn(t *testing.T) {
+	body := []byte(`{
+		"model": "gemini-3-pro",
+		"max_tokens": 512,
+		"messages": [{"role": "user", "content": "search and compute"}],
+		"include_server_side_tool_invocations": true
+	}`)
+
+	var req AnthropicMessageRequest
+	if err := req.UnmarshalJSON(body); err != nil {
+		t.Fatalf("unmarshal request: %v", err)
+	}
+
+	bifrostReq := req.ToBifrostResponsesRequest(nil)
+	if bifrostReq == nil || bifrostReq.Params == nil {
+		t.Fatal("converted request or params is nil")
+	}
+	if bifrostReq.Params.IncludeServerSideToolInvocations == nil ||
+		!*bifrostReq.Params.IncludeServerSideToolInvocations {
+		t.Fatalf("include_server_side_tool_invocations not lifted to typed param: %v",
+			bifrostReq.Params.IncludeServerSideToolInvocations)
+	}
+}