feat(core): the e-mail server after Java, measured against Java

SMTP on port 25 stores mails for the domain's accounts as Java reads
them anew and tells a local sender of unknown recipients; POP3 on port
110 hands them out. The mailboxes are in the snapshot and go back into
the project. EmailRun plays four stories over the network; MailCases
feeds Java's workers without one (26 cases, de and en). 18 cases name
Java bugs that the core does not take.

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

packages/core/src/runtime/engine.ts

@@ -60,6 +60,7 @@ import { forwardsIPv4ByDefault, isPcClassEndpoint, stableGeneratedMacAddress } f
 import type {
   DeviceConfiguration,
   DhcpServerConfiguration,
+  EmailServerAccount,
   FirewallConfiguration,
   GatewayPortForwardingRow,
   FirewallRule,
@@ -115,6 +116,7 @@ import { RuntimeSpeed } from './speed.js';
 import { ApplicationThreads, waitUntil, type Steps, type Wait } from './threads.js';
 import { EchoServer, SimpleClient } from './apps/echo.js';
 import { WebBrowser, WebServer, type WebServerPage } from './apps/web.js';
+import { EmailServer } from './apps/emailServer.js';
 import { firewallLogPage, forwardingTablePage, ripTablePage, routerIndexPage } from './apps/routerPages.js';
 import { applyFirewallSettings, firewallSettingsPage } from './apps/firewallSettings.js';
 import { VirtualFileSystem } from '../model/virtualFileSystem.js';
@@ -910,6 +912,9 @@ export class NetworkRuntimeEngine {
   private readonly simpleClientsByNodeId = new Map<Id, SimpleClient>();
   private readonly webServersByNodeId = new Map<Id, WebServer>();
   private readonly webBrowsersByNodeId = new Map<Id, WebBrowser>();
+  private readonly emailServersByNodeId = new Map<Id, EmailServer>();
+  /** The time of day a program writes into a mail (Java's new Date()). */
+  private readonly wallClock: () => number;
   /** Each node's firewall log; it outlives a stop and a new start, as Java's log page does. */
   private readonly firewallLogsByNodeId = new Map<Id, FirewallLogEntry[]>();
   /** Accepted connections a program has taken (acceptTcpSteps). */
@@ -929,6 +934,9 @@ export class NetworkRuntimeEngine {
    * web administration answers without a socket), likewise.
    *
    * `captureRetention`: how many frames each card's packet capture keeps.
+   *
+   * `wallClock`: the time of day in milliseconds, which a program writes
+   * into a mail (the e-mail server's notice); the host's clock by default.
    */
   constructor(
     seed: bigint | number = DEFAULT_SEED,
@@ -939,8 +947,10 @@ export class NetworkRuntimeEngine {
       readonly swiftSends?: boolean;
       readonly swiftRouters?: boolean;
       readonly captureRetention?: CaptureRetentionPolicy;
+      readonly wallClock?: () => number;
     } = {},
   ) {
+    this.wallClock = options.wallClock ?? Date.now;
     this.packetCapture = new PacketCapture(options.captureRetention ?? PRODUCTION_CAPTURE_RETENTION);
     this.cablesCarryOneFrameAtATime = options.swiftCables !== true;
     this.swiftArp = options.swiftArp === true;
@@ -1032,6 +1042,7 @@ export class NetworkRuntimeEngine {
         this.simpleClientsByNodeId.clear();
         this.webServersByNodeId.clear();
         this.webBrowsersByNodeId.clear();
+        this.emailServersByNodeId.clear();
         this.arpLookups = [];
         this.protocolThreads.clear();
         this.dnsQueriesBySocketId.clear();
@@ -1117,6 +1128,20 @@ export class NetworkRuntimeEngine {
     return this.webBrowsersByNodeId.get(nodeId);
   }
 
+  /** The node's e-mail server while the simulation runs, if it has one installed. */
+  emailServer(nodeId: Id): EmailServer | undefined {
+    return this.emailServersByNodeId.get(nodeId);
+  }
+
+  /** An e-mail server's accounts as a run changed them, into the snapshot (and so into the project saved from it). */
+  private setEmailServerAccounts(nodeId: Id, accounts: readonly EmailServerAccount[]): void {
+    const servers = new Map(this.stateValue.topologySnapshot.emailServersByNodeId);
+    const server = servers.get(nodeId);
+    if (server === undefined) return;
+    servers.set(nodeId, { ...server, accounts });
+    this.stateValue.topologySnapshot = withSnapshot(this.stateValue.topologySnapshot, { emailServersByNodeId: servers });
+  }
+
   /**
    * Each node's programs start with the simulation (Betriebssystem.starten),
    * from the snapshot; what they show starts empty.
@@ -1127,6 +1152,7 @@ export class NetworkRuntimeEngine {
     this.simpleClientsByNodeId.clear();
     this.webServersByNodeId.clear();
     this.webBrowsersByNodeId.clear();
+    this.emailServersByNodeId.clear();
     for (const node of snapshot.nodes) {
       const echoServer = snapshot.echoServersByNodeId.get(node.id);
       if (echoServer !== undefined) this.echoServersByNodeId.set(node.id, new EchoServer(this, node.id, echoServer));
@@ -1137,6 +1163,21 @@ export class NetworkRuntimeEngine {
         this.webServersByNodeId.set(node.id, new WebServer(this, node.id, webServer, snapshot.fileSystemsByNodeId.get(node.id)));
       }
       if (snapshot.webBrowserNodeIds.has(node.id)) this.webBrowsersByNodeId.set(node.id, new WebBrowser(this, node.id));
+      const emailServer = snapshot.emailServersByNodeId.get(node.id);
+      if (emailServer !== undefined) {
+        const nodeId = node.id;
+        this.emailServersByNodeId.set(
+          nodeId,
+          new EmailServer(
+            this,
+            nodeId,
+            emailServer,
+            (accounts) => this.setEmailServerAccounts(nodeId, accounts),
+            () => this.networkInterfaces(nodeId)[0]?.ipAddress ?? 'null',
+            this.wallClock,
+          ),
+        );
+      }
       if ((node.kind === 'router' || node.kind === 'gateway') && !this.swiftRouters) this.startRouterWebServer(node.id, node.kind);
     }
   }