Add Nix flake for mcp and mcp-agent

Exposes two packages:
- default (mcp CLI) for operator workstations
- mcp-agent for managed nodes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/google.golang.org/grpc/internal/experimental.go

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package internal
+
+var (
+	// WithBufferPool is implemented by the grpc package and returns a dial
+	// option to configure a shared buffer pool for a grpc.ClientConn.
+	WithBufferPool any // func (grpc.SharedBufferPool) grpc.DialOption
+
+	// BufferPool is implemented by the grpc package and returns a server
+	// option to configure a shared buffer pool for a grpc.Server.
+	BufferPool any // func (grpc.SharedBufferPool) grpc.ServerOption
+
+	// SetDefaultBufferPool updates the default buffer pool.
+	SetDefaultBufferPool any // func(mem.BufferPool)
+
+	// AcceptCompressors is implemented by the grpc package and returns
+	// a call option that restricts the grpc-accept-encoding header for a call.
+	AcceptCompressors any // func(...string) grpc.CallOption
+)