Merge pull request #2034 from modelcontextprotocol/v2/fix/1860-mrtr-results-panel

fix(web): name an empty tool result instead of "No results yet" (#1860)

clients/web/src/components/groups/ToolResultPanel/ToolResultPanel.test.tsx

@@ -35,11 +35,20 @@ describe("ToolResultPanel", () => {
     expect(screen.getByText("boom")).toBeInTheDocument();
   });
 
-  it("renders the empty state when content is empty", () => {
+  // #1860: this panel only mounts once a result exists, so an empty result must
+  // read as "the call completed and returned nothing" — never as the pre-run
+  // "No results yet" placeholder, which denies a call the user watched succeed.
+  it("names the outcome when a completed result has no content", () => {
     renderWithMantine(
       <ToolResultPanel result={emptyResult} onClear={() => {}} />,
     );
-    expect(screen.getByText("No results yet")).toBeInTheDocument();
+    expect(screen.getByText("Empty result")).toBeInTheDocument();
+    expect(
+      screen.getByText(
+        "The tool call completed successfully and returned no content.",
+      ),
+    ).toBeInTheDocument();
+    expect(screen.queryByText("No results yet")).not.toBeInTheDocument();
   });
 
   it("groups resource_link blocks in a scrollable Resource Links box", async () => {
@@ -141,7 +150,7 @@ describe("ToolResultPanel", () => {
           onClear={() => {}}
         />,
       );
-      expect(screen.queryByText("No results yet")).not.toBeInTheDocument();
+      expect(screen.queryByText("Empty result")).not.toBeInTheDocument();
       expect(
         screen.getByRole("heading", { name: "Structured Output" }),
       ).toBeInTheDocument();

clients/web/src/components/groups/ToolResultPanel/ToolResultPanel.tsx

@@ -5,7 +5,6 @@ import {
   Paper,
   ScrollArea,
   Stack,
-  Text,
   Title,
 } from "@mantine/core";
 import type {
@@ -176,6 +175,16 @@ const ErrorAlert = Alert.withProps({
   title: "Tool Error",
 });
 
+// A completed call whose result renders nothing. `content: []` with no
+// `structuredContent` is a legal CallToolResult, and this panel is only mounted
+// once a result exists — so saying "no results yet" here would deny a call the
+// user just watched succeed (#1860). Name the outcome instead.
+const EmptyResultAlert = Alert.withProps({
+  color: "gray",
+  variant: "light",
+  title: "Empty result",
+});
+
 function ResourceLinksGroup({
   links,
   onReadResource,
@@ -277,7 +286,9 @@ export function ToolResultPanel({
         </ResultScroll>
       ) : result.content.length === 0 && !structuredNode ? (
         <ResultScroll>
-          <Text c="dimmed">No results yet</Text>
+          <EmptyResultAlert>
+            The tool call completed successfully and returned no content.
+          </EmptyResultAlert>
         </ResultScroll>
       ) : hasLinks ? (
         <FillStack>

clients/web/src/test/integration/mcp/inspectorClient-modern-era.test.ts

@@ -18,6 +18,8 @@ import {
   createMrtrSamplingTool,
   createMrtrLoopTool,
   createMrtrEdgeCaseTool,
+  loadConfig,
+  resolveConfig,
 } from "@modelcontextprotocol/inspector-test-server";
 import type { ServerConfig } from "@modelcontextprotocol/inspector-test-server";
 import type {
@@ -26,6 +28,13 @@ import type {
 } from "@modelcontextprotocol/client";
 import { LOG_LEVEL_META_KEY } from "@modelcontextprotocol/client";
 import type { MessageEntry } from "@inspector/core/mcp/types.js";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+// clients/web/src/test/integration/mcp → repo root is six levels up. Derived
+// from the module URL rather than `process.cwd()` so the showcase config
+// resolves the same however vitest is invoked.
+const repoRoot = join(dirname(fileURLToPath(import.meta.url)), "../".repeat(6));
 
 /**
  * Live coverage of the modern (2026-07-28) connection path (#1700). The bundled
@@ -389,6 +398,45 @@ describe("modern-era negotiation (2026-07-28)", () => {
     expect(Object.keys(retry2.inputResponses ?? {})).toHaveLength(0);
   });
 
+  // #1860. Drives the reproduction the README documents, through the SAME
+  // artifacts a human would use — the showcase config file, resolved through the
+  // preset registry — so the config entry, the `mrtr_empty` registry branch, and
+  // the handler are all covered rather than just the fixture factory. The
+  // assertion is that a completed MRTR call really does hand back an empty
+  // `CallToolResult`: that is the input the Tools panel has to render as
+  // "completed, returned nothing" instead of its pre-run placeholder.
+  it("completes an MRTR sequence with an empty result (mrtr_empty, via the showcase config)", async () => {
+    const config = loadConfig(
+      join(repoRoot, "test-servers/configs/mrtr-showcase-http.json"),
+    );
+    expect(config.tools).toContainEqual({ preset: "mrtr_empty" });
+
+    const started = createTestServerHttp(resolveConfig(config));
+    await started.start();
+    server = started;
+    const connected = await connectWithEra(started.url, "modern");
+
+    let pausedAtPendingUi = false;
+    connected.addEventListener("newPendingElicitation", (event) => {
+      pausedAtPendingUi = true;
+      void event.detail.respond({
+        action: "accept",
+        content: { ack: true },
+      });
+    });
+
+    const { tools } = await connected.listTools();
+    const tool = tools.find((t) => t.name === "mrtr_empty");
+    expect(tool).toBeDefined();
+
+    const result = await connected.callTool(tool!, {});
+    expect(result.success).toBe(true);
+    expect(pausedAtPendingUi).toBe(true);
+    expect(result.result!.content).toEqual([]);
+    expect(result.result!.structuredContent).toBeUndefined();
+    expect(result.result!.isError).toBeFalsy();
+  });
+
   it("cancels an in-flight MRTR call while its embedded request is pending", async () => {
     const started = await startMrtrServer(createMrtrTool());
     const connected = await connectWithEra(started.url, "modern");