fix(mcp): narrow call tool results

packages/opencode/src/mcp/catalog.ts

@@ -64,6 +64,7 @@ export function convertTool(mcpTool: MCPToolDef, client: Client, timeout?: numbe
           timeout,
         },
       )
+      if (!isCallToolResult(result)) return result
       if (result.isError) throw new Error(errorText(result))
       if (result.structuredContent === undefined || result.structuredContent === null) return result
       return {
@@ -74,6 +75,10 @@ export function convertTool(mcpTool: MCPToolDef, client: Client, timeout?: numbe
   })
 }
 
+function isCallToolResult(result: Awaited<ReturnType<Client["callTool"]>>): result is CallToolResult {
+  return "content" in result && Array.isArray(result.content)
+}
+
 function errorText(result: CallToolResult) {
   const content = result.content.flatMap((item) => {
     if (item.type === "text") return [item.text]

packages/opencode/test/mcp/catalog.test.ts

@@ -9,7 +9,7 @@ const definition = {
   inputSchema: { type: "object" as const, properties: {} },
 }
 
-function tool(result: CallToolResult) {
+function tool(result: CallToolResult | { toolResult: unknown }) {
   const callTool = mock(async () => result)
   const converted = convertTool(definition, { callTool } as unknown as Client)
   if (!converted.execute) throw new Error("expected executable tool")
@@ -31,6 +31,13 @@ describe("mcp catalog", () => {
     expect(converted.callTool).toHaveBeenCalledTimes(1)
   })
 
+  test("returns task tool results", async () => {
+    const result = { toolResult: { taskId: "task-1" } }
+    const converted = tool(result)
+
+    await expect(converted.execute({}, { toolCallId: "call-1", messages: [] })).resolves.toBe(result)
+  })
+
   test("throws MCP tool errors with text and structured diagnostics", async () => {
     const converted = tool({
       isError: true,