feat: F4.6g1 the echo server and the generic client windows

Oracle EchoWindowRun uses Java's echo server and client windows as a
person does; SaveAfterRunRun echo saves what Java keeps after the run.
The room takes setActive with a port, connect/disconnect/send, sends
both views and writes the server's port and the client's target back.
The editor's windows show Java's buttons, fields and lines; a port that
is no port is marked and not handed over (Java's button throws).
Core fix: an empty message (one empty segment with the push, as Java's
erstelleSegmente makes) counted as a repeat and never arrived.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/sim/src/room.ts

@@ -20,8 +20,9 @@
 //
 // A program's window may show more than its lines (plan §7.3): the browser's
 // page, the web server's button and table, the e-mail program's account and
-// folders, the e-mail server's domain and accounts go to the clients as a
-// view, whole, when they change.
+// folders, the e-mail server's domain and accounts, the echo server's button
+// and port, the generic client's connection go to the clients as a view,
+// whole, when they change.
 //
 // While the simulation runs, the document's programs are watched: a program
 // installed or removed on the desktop (Java's software installation) is
@@ -70,6 +71,8 @@ import {
   type Topic,
   type EmailClientView,
   type EmailServerView,
+  type EchoServerView,
+  type SimpleClientView,
   type TraceFrame,
   type WebServerView,
 } from '@mdg-filius/protocol';
@@ -237,7 +240,12 @@ export class SimulationRoom {
         settings.emailServer = emailServerAfterRun(configured as never, mailServerSettings);
       }
       const echo = this.engine.echoServer(id);
-      if (echo !== undefined) active.echoServer = echo.isActive;
+      if (echo !== undefined) {
+        active.echoServer = echo.isActive;
+        settings.echoServer = { port: echo.port };
+      }
+      const client = this.engine.simpleClient(id);
+      if (client !== undefined) settings.simpleClient = { targetAddress: client.targetAddress, targetPort: client.targetPort };
       settings.emailClient = snapshot.emailClientsByNodeId.get(id);
       settings.firewall = snapshot.firewallConfigurationsByNodeId.get(id);
       if (snapshot.dhcpClientConfigurationsByNodeId.get(id)?.isEnabled === true) settings.device = snapshot.deviceConfigurations.get(id);
@@ -442,6 +450,49 @@ export class SimulationRoom {
         return this.actInEmailClient(input);
       case 'emailServer':
         return this.actInEmailServer(input);
+      case 'echoServer':
+        return this.actInEchoServer(input);
+      case 'simpleClient':
+        return this.actInSimpleClient(input);
+      default:
+        return 'unknownAction';
+    }
+  }
+
+  /** The start button with the port typed (Java's window sets the port before and after it starts the server). */
+  private actInEchoServer(input: Extract<ClientMessage, { kind: 'input' }>): ErrorCode | undefined {
+    const server = this.engine.echoServer(input.node);
+    if (server === undefined) return 'unknownApp';
+    const { args } = input;
+    if (input.action !== 'setActive') return 'unknownAction';
+    if (typeof args.active !== 'boolean') return 'badArgs';
+    if (!args.active) {
+      server.setActive(false);
+      return undefined;
+    }
+    if (!isPort(args.port)) return 'badArgs';
+    server.setPort(args.port);
+    server.setActive(true);
+    return undefined;
+  }
+
+  /** "Verbinden" with the address and port typed, "Trennen", "Senden". */
+  private actInSimpleClient(input: Extract<ClientMessage, { kind: 'input' }>): ErrorCode | undefined {
+    const client = this.engine.simpleClient(input.node);
+    if (client === undefined) return 'unknownApp';
+    const { args } = input;
+    switch (input.action) {
+      case 'connect':
+        if (typeof args.address !== 'string' || !isPort(args.port)) return 'badArgs';
+        client.connect(args.address, args.port);
+        return undefined;
+      case 'disconnect':
+        client.disconnect();
+        return undefined;
+      case 'send':
+        if (typeof args.text !== 'string') return 'badArgs';
+        client.send(args.text);
+        return undefined;
       default:
         return 'unknownAction';
     }
@@ -583,6 +634,18 @@ export class SimulationRoom {
         const view: EmailClientView = { account: client.account, inbox: client.inbox.map((entry) => entry.mail), sent: client.sent.map((entry) => entry.mail) };
         return view;
       }
+      case 'echoServer': {
+        const server = this.engine.echoServer(node);
+        if (server === undefined) return null;
+        const view: EchoServerView = { active: server.isActive, port: server.port };
+        return view;
+      }
+      case 'simpleClient': {
+        const client = this.engine.simpleClient(node);
+        if (client === undefined) return null;
+        const view: SimpleClientView = { connected: client.isConnected, address: client.targetAddress, port: client.targetPort };
+        return view;
+      }
       case 'emailServer': {
         const server = this.engine.emailServer(node);
         if (server === undefined) return null;
@@ -732,6 +795,11 @@ export class SimulationRoom {
   }
 }
 
+/** A port a socket can have. */
+function isPort(value: unknown): value is number {
+  return Number.isInteger(value) && (value as number) >= 0 && (value as number) <= 65_535;
+}
+
 /** A card's frames as the capture window shows them, both views. */
 export function traceFramesOf(frames: readonly CapturedFrame[]): TraceFrame[] {
   const byNumber = (rows: readonly CaptureRow[]) => {