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

The Tools screen mounts the Results panel only once a call has produced a
result, but the panel's zero-content branch rendered "No results yet" — the
same wording it would use before anything had run. An empty `content` array
with no `structuredContent` is a legal `CallToolResult`, so a call that had
plainly completed reported itself as a call that never happened.

That reads worst after a multi-round-trip (MRTR) sequence, which is how it was
reported: the user answers one or more embedded elicitations, watches the
Protocol tab group the exchange and mark it COMPLETE, and is then told there
are no results yet. Nothing was lost — the result was stored and rendered; the
panel simply had no wording for "completed, returned nothing".

The panel now renders an "Empty result" alert saying the call completed and
returned no content. This is the remaining half of the same gap #1908 closed
for `structuredContent`-only results.

test-servers: new `mrtr_empty` preset (`createMrtrEmptyResultTool`) — one
elicitation round, then a complete result with `content: []` and no
`structuredContent` — added to `mrtr-showcase-http.json` so the shape is
reproducible by hand. README documents it.

Signed-off-by: Cliff Hall <cliff@futurescale.com>
Signed-off-by: cliffhall <cliff@futurescale.com>

test-servers/configs/mrtr-showcase-http.json

@@ -10,6 +10,7 @@
     { "preset": "mrtr_sample" },
     { "preset": "mrtr_roots" },
     { "preset": "mrtr_edge" },
+    { "preset": "mrtr_empty" },
     { "preset": "mrtr_loop" }
   ],
   "transport": {

test-servers/src/preset-registry.ts

@@ -29,6 +29,7 @@ import {
   createMrtrSamplingTool,
   createMrtrLoopTool,
   createMrtrEdgeCaseTool,
+  createMrtrEmptyResultTool,
   createCollectUrlElicitationTool,
   createUrlElicitationFormTool,
   createSendNotificationTool,
@@ -151,6 +152,8 @@ function resolveToolPreset(
       return createMrtrLoopTool();
     case "mrtr_edge":
       return createMrtrEdgeCaseTool();
+    case "mrtr_empty":
+      return createMrtrEmptyResultTool();
     case "collect_url_elicitation":
       return createCollectUrlElicitationTool();
     case "url_elicitation_form":

test-servers/src/test-server-fixtures.ts

@@ -755,6 +755,50 @@ export function createMrtrEdgeCaseTool(): ToolDefinition {
   };
 }
 
+/**
+ * An MRTR tool whose FINAL (complete) result carries an empty `content` array
+ * and no `structuredContent` — a legal `CallToolResult` that renders nothing.
+ *
+ * This is the shape behind #1860: the sequence completes (the Protocol tab shows
+ * the conversation COMPLETE), a real result is stored, and the Results panel had
+ * no way to say so — it fell through to the same "No results yet" placeholder it
+ * shows before anything has run, so a successful call read as a call that never
+ * happened. Kept as an MRTR tool rather than a plain one because the multi-round
+ * case is where the ambiguity actually misleads: the user has answered prompts
+ * and watched rounds complete, so "no results yet" is flatly contradicted by
+ * what they just did.
+ */
+export function createMrtrEmptyResultTool(): ToolDefinition {
+  return {
+    name: "mrtr_empty",
+    description:
+      "MRTR tool that completes with an empty result (no content, no structuredContent).",
+    inputSchema: {},
+    handler: async (
+      _params: Record<string, unknown>,
+      _context?: TestServerContext,
+      extra?: HandlerExtra,
+    ) => {
+      if (extra?.inputResponses?.ack === undefined) {
+        return inputRequired({
+          inputRequests: {
+            ack: inputRequired.elicit({
+              message: "Acknowledge to finish (the result will be empty)",
+              requestedSchema: {
+                type: "object",
+                properties: { ack: { type: "boolean", title: "Acknowledge" } },
+                required: ["ack"],
+              },
+            }),
+          },
+          requestState: `mrtr-empty:${++mrtrMintCount}`,
+        });
+      }
+      return { content: [] } satisfies CallToolResult;
+    },
+  };
+}
+
 /**
  * Create a "url_elicitation_form" tool that spins up a simple HTTP server on a dynamic
  * port with a form page, sends that URL via URL elicitation, and on form submit collects