feat(core): the e-mail server keeps /mailserver/konten.txt up to date at run time, measured against Java

The account file's writer moves from the export (packages/fls) into the
core, so that the export and the running server write the same. The
server writes the file at its start and whenever its accounts change.
EmailRun now records Java's file as it left it and as Java writes the
accounts it ended with; Java leaves the notice to a local sender out until
its next write.

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

packages/core/test/emailJava.test.ts

@@ -14,7 +14,7 @@ import { readFileSync } from 'node:fs';
 import { dirname, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { describe, expect, it } from 'vitest';
-import { formatMail, withSnapshot, type LogLine, type NetworkRuntimeEngine } from '../src/index.js';
+import { EMAIL_SERVER_ACCOUNTS_FILE, formatMail, withSnapshot, type LogLine, type NetworkRuntimeEngine } from '../src/index.js';
 import { expectSameCaptures, GAP_TOLERANCE_MILLISECONDS, watchedEngine, withClientPortText, type JavaFrame, type JavaTables } from './javaRun.js';
 import { MAIL_ACCOUNTS } from './mailAccounts.js';
 import { clientText, emailServerText, isPolled, POLL_MILLISECONDS } from './programLines.js';
@@ -32,6 +32,9 @@ interface JavaRun extends JavaTables {
   events: [number, Program, string][];
   /** Each account's name and its messages: Email.toString, new, marked for deletion. */
   accounts: [string, ...[string, string, string][]][];
+  /** The account file as Java left it, and as Java writes the accounts it ended with (kontenSpeichern). */
+  file: string;
+  savedFile: string;
 }
 
 type Act = (engine: NetworkRuntimeEngine) => void;
@@ -155,6 +158,23 @@ describe('the e-mail server as Java FILIUS runs it', () => {
         ...account.mailbox.map((entry) => [withoutDate(formatMail(entry.mail)), String(entry.isNew), String(entry.isMarkedForDeletion)]),
       ]);
       expect(accounts).toEqual(java.accounts.map(([username, ...mails]) => [username, ...mails.map(([text, isNew, deleted]) => [withoutDate(text), isNew, deleted])]));
+
+      // The account file at the end: as Java writes those accounts (kontenSpeichern), the engine at every change.
+      const file = snapshotFiles(engine).textFile(EMAIL_SERVER_ACCOUNTS_FILE);
+      expect(fileWithoutDate(file), 'account file').toBe(fileWithoutDate(java.savedFile));
+      expect(fileWithoutDate(java.file) === fileWithoutDate(java.savedFile), "Java's file as it left it is up to date").toBe(!STALE_FILE.has(name));
     });
   }
 });
+
+/**
+ * Where Java left its account file behind its accounts: smtpErrors, the
+ * notice to the local sender (SMTPMitarbeiter saves the accounts before it
+ * sends the notice); the engine writes the file at every change.
+ */
+const STALE_FILE = new Set(['smtpErrors']);
+
+/** A notice's date in the account file, where its line breaks are "|". */
+const fileWithoutDate = (text: string) => text.replace(/\|Date: [^|]*\|/g, '|Date: <date>|');
+
+const snapshotFiles = (engine: NetworkRuntimeEngine) => engine.state.topologySnapshot.fileSystemsByNodeId.get(SERVER)!;