feat(coding-runtime): add managed Pi extension host

electron/coding-runtime/pi/rpc-client.ts

@@ -127,6 +127,19 @@ export class PiRpcClient {
     throw lastError;
   }
 
+  async send(command: PiRpcCommand): Promise<void> {
+    if (!command.type) throw new Error('Pi RPC command type is required');
+    if (this.invalidated) throw this.invalidated;
+    try {
+      await this.write(`${JSON.stringify(command)}\n`);
+    } catch (error) {
+      throw new PiProcessError('PI_RPC_WRITE_FAILED', `Could not write Pi RPC ${command.type}`, {
+        cause: error,
+        generation: this.generation,
+      });
+    }
+  }
+
   accept(value: unknown): void {
     if (!recordValue(value) || typeof value.type !== 'string') {
       throw new PiProcessError('PI_RPC_PROTOCOL_ERROR', 'Pi RPC record must be an object with a type');