fix(mcp): serialize raw plugin tool results

src/mcp/plugin-tools-handlers.ts

@@ -52,10 +52,14 @@ export function createPluginToolsMcpHandlers(tools: AnyAgentTool[]) {
       }
       try {
         const result = await tool.execute(`mcp-${Date.now()}`, params.arguments ?? {});
+        const rawContent =
+          result && typeof result === "object" && "content" in result
+            ? (result as { content?: unknown }).content
+            : result;
         return {
-          content: Array.isArray(result.content)
-            ? result.content
-            : [{ type: "text", text: coerceChatContentText(result.content) }],
+          content: Array.isArray(rawContent)
+            ? rawContent
+            : [{ type: "text", text: coerceChatContentText(rawContent) }],
         };
       } catch (err) {
         return {

src/mcp/plugin-tools-serve.test.ts

@@ -65,6 +65,39 @@ describe("plugin tools MCP server", () => {
     expect(result.content).toEqual([{ type: "text", text: "Stored." }]);
   });
 
+  it("serializes plugin tool results that do not use the MCP content envelope", async () => {
+    const execute = vi.fn().mockResolvedValue({
+      provider: "kitchen-sink-search",
+      results: [{ title: "Kitchen Sink image fixture" }],
+    });
+    const tool = {
+      name: "kitchen_sink_search",
+      description: "Search Kitchen Sink fixture content",
+      parameters: {
+        type: "object",
+        properties: {
+          query: { type: "string" },
+        },
+      },
+      execute,
+    } as unknown as AnyAgentTool;
+
+    const handlers = createPluginToolsMcpHandlers([tool]);
+    const result = await handlers.callTool({
+      name: "kitchen_sink_search",
+      arguments: { query: "kitchen sink" },
+    });
+    expect(result.content).toEqual([
+      {
+        type: "text",
+        text: JSON.stringify({
+          provider: "kitchen-sink-search",
+          results: [{ title: "Kitchen Sink image fixture" }],
+        }),
+      },
+    ]);
+  });
+
   it("returns MCP errors for unknown tools and thrown tool errors", async () => {
     const failingTool = {
       name: "memory_forget",