Redesign spawn and thread MCP tools (ADA-115)

apps/server/src/mcp/McpHttpServer.ts

@@ -9,7 +9,10 @@ import * as McpInvocationContext from "./McpInvocationContext.ts";
 import * as McpSessionRegistry from "./McpSessionRegistry.ts";
 import { ThreadToolkitHandlersLive } from "./toolkits/thread/handlers.ts";
 import { ThreadToolkit } from "./toolkits/thread/tools.ts";
-import { SubagentToolkitHandlersLive } from "./toolkits/subagent/handlers.ts";
+import {
+  installPeerSubagentCompatibility,
+  SubagentToolkitHandlersLive,
+} from "./toolkits/subagent/handlers.ts";
 import { SubagentToolkit } from "./toolkits/subagent/tools.ts";
 import { NotifyToolkitHandlersLive } from "./toolkits/notify/handlers.ts";
 import { NotifyToolkit } from "./toolkits/notify/tools.ts";
@@ -91,9 +94,12 @@ export const ThreadToolkitRegistrationLive = McpServer.toolkit(ThreadToolkit).pi
   Layer.provide(ThreadToolkitHandlersLive),
 );
 
-export const SubagentToolkitRegistrationLive = McpServer.toolkit(SubagentToolkit).pipe(
-  Layer.provide(SubagentToolkitHandlersLive),
-);
+export const SubagentToolkitRegistrationLive = Layer.effectDiscard(
+  Effect.gen(function* () {
+    yield* McpServer.registerToolkit(SubagentToolkit);
+    yield* installPeerSubagentCompatibility;
+  }),
+).pipe(Layer.provide(SubagentToolkitHandlersLive), Layer.provide(McpServer.McpServer.layer));
 
 export const NotifyToolkitRegistrationLive = McpServer.toolkit(NotifyToolkit).pipe(
   Layer.provide(NotifyToolkitHandlersLive),

apps/server/src/mcp/McpOfficialClientConformance.test.ts

@@ -43,19 +43,23 @@ const environmentId = EnvironmentId.make("environment-mcp-conformance");
 const threadId = ThreadId.make("thread-mcp-conformance");
 const providerInstanceId = ProviderInstanceId.make("codex");
 
-const expectedToolNamesAfterPreviewRemoval = [
-  "t3_check_subagent",
+const expectedToolNamesAfterSpawnTrim = [
   "t3_get_usage",
   "t3_list_backends",
-  "t3_list_subagents",
   "t3_notify",
   "t3_schedule_create",
   "t3_schedule_delete",
   "t3_schedule_list",
   "t3_schedule_update",
   "t3_spawn_subagent",
   "t3_steer_subagent",
+  "t3_subagents",
   "t3_thread_start",
+] as const;
+
+const removedSubagentToolNames = [
+  "t3_check_subagent",
+  "t3_list_subagents",
   "t3_wait_subagent",
 ] as const;
 
@@ -275,12 +279,35 @@ it.effect("conforms to the official streamable HTTP MCP client", () =>
       const toolsResult = yield* Effect.promise(() => client.listTools());
       ListToolsResultSchema.parse(toolsResult);
       const toolNames = new Set(toolsResult.tools.map((tool) => tool.name));
-      expect([...toolNames].toSorted()).toEqual([...expectedToolNamesAfterPreviewRemoval]);
+      expect([...toolNames].toSorted()).toEqual([...expectedToolNamesAfterSpawnTrim]);
       for (const removedName of removedPreviewToolNames) {
         expect(toolNames.has(removedName), `${removedName} must be absent from tools/list`).toBe(
           false,
         );
       }
+      for (const removedName of removedSubagentToolNames) {
+        expect(toolNames.has(removedName), `${removedName} must be absent from tools/list`).toBe(
+          false,
+        );
+      }
+
+      for (const toolName of ["t3_spawn_subagent", "t3_thread_start"] as const) {
+        const tool = toolsResult.tools.find((candidate) => candidate.name === toolName);
+        expect(tool, `${toolName} must be present`).toBeDefined();
+        expect(Object.keys(tool?.inputSchema.properties ?? {}).toSorted()).toEqual([
+          "branch",
+          "directory",
+          "model",
+          "prompt",
+          "reasoningEffort",
+          "title",
+        ]);
+        expect([...(tool?.inputSchema.required ?? [])].toSorted()).toEqual([
+          "model",
+          "prompt",
+          "title",
+        ]);
+      }
 
       for (const tool of toolsResult.tools) {
         expect(tool.inputSchema.type, `${tool.name} input schema must be an object`).toBe("object");

apps/server/src/mcp/toolSchemas.test.ts

@@ -32,6 +32,6 @@ it("every MCP tool advertises a top-level object input schema", () => {
   }
   // Guard the guard: if toolkit wiring changes shape, this test must not
   // silently pass on an empty list.
-  expect(checked).toHaveLength(13);
+  expect(checked).toHaveLength(11);
   expect(checked).toContain("t3_list_backends");
 });