feat(core): add runtime MCP controls (#37308)

Co-authored-by: Aiden Cline <rekram1-node@users.noreply.github.com>
Co-authored-by: Aiden Cline <aidenpcline@gmail.com>

packages/core/test/fixture/mcp.ts

@@ -9,6 +9,10 @@ export const emptyMcpLayer = Layer.succeed(
   MCP.Service,
   MCP.Service.of({
     servers: () => Effect.succeed([]),
+    add: () => Effect.die("unused mcp.add"),
+    connect: () => Effect.die("unused mcp.connect"),
+    disconnect: () => Effect.die("unused mcp.disconnect"),
+    remove: () => Effect.die("unused mcp.remove"),
     tools: () => Effect.succeed([]),
     callTool: () => Effect.die("unused mcp.callTool"),
     instructions: () => Effect.succeed([]),