R2 accounts are safe: email by password and code, recovery only to it, sessions that end

Completion program R2 (docs/ROADMAP.md, 2026-10-17).

- An email address is set only with the password and a 6-digit code sent to it: /clientapi/user/email, /email/verify,
  /email/remove and GET /clientapi/user/account (EmailVerification: an hour, five tries, the code's hash only;
  EmailVerificationJob through the new IMailer). The request answers one sentence whether or not the address is free,
  and nothing goes to an address another login verified. The old POST /clientapi/user/update, which changed the
  address with neither and said when one was taken, answers 422.
- Recovery writes only to a verified address; migration _019 keeps the addresses given before verification existed.
- A changed password ends every session and every persona token, and answers a new JWT for the device that changed it.
- Sessions: every JWT carries its session's id ("si", kept by sniff/again). GET /clientapi/user/logout, which did
  nothing, ends that session alone (RootUser.EndedSessions, until its tokens would expire); POST
  /clientapi/user/logout/everywhere ends them all.
- AppConfiguration:HashingOptions was never bound, so passwords were hashed at the default 9789 iterations: it is
  bound now, at 210,000, and a hash made at other iterations is made again at the next sign-in (matched on the old
  hash, so two sign-ins never undo each other).
- Recovery and verification codes expire through TTL indexes; EmailVerification is never in a backup.
- AppConfigurationService reads appsettings as they are now, not the copy older builds saved in Mongo on first boot.
- ViewUserSettings and RootUserSettings carry SavedAt, so a client signing in keeps its own theme until one saved.
- Pasture: peers/mailpit.sh (Mailpit 1.31.4 as mailpit.test) receives PrivaPub's mail; recovery links open
  https://decepub.test. scenarios/accounts.sh, in sweep batch A, checks all of the above (28 checks).

Verified: dotnet build PrivaPub.sln -c Release; the pasture with gts and mailpit: accounts 28/28 and gts, 91 passed,
0 failed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WpVCoDeM1qUTRp4fXQdfof

PrivaPub/Services/Mailer.cs

@@ -0,0 +1,41 @@
+using MailKit.Net.Smtp;
+
+using Microsoft.Extensions.Options;
+
+using MimeKit;
+
+using PrivaPub.Models;
+
+namespace PrivaPub.Services
+{
+	public interface IMailer
+	{
+		/// <summary>Sends a plain-text email; throws when SMTP fails, so the job that sends it retries.</summary>
+		Task Send(string to, string subject, string body, CancellationToken token);
+	}
+
+	// The server's one way to send an email: through the SMTP account in appsettings (AppConfiguration:EmailConfiguration),
+	// read as it is now. Only jobs call it, so nobody waits on SMTP.
+	public class Mailer : IMailer
+	{
+		readonly IOptionsMonitor<AppConfiguration> _app;
+
+		public Mailer(IOptionsMonitor<AppConfiguration> app) => _app = app;
+
+		public async Task Send(string to, string subject, string body, CancellationToken token)
+		{
+			var email = _app.CurrentValue.EmailConfiguration;
+			var message = new MimeMessage();
+			message.From.Add(new MailboxAddress("PrivaPub", email.SmtpUsername));
+			message.To.Add(MailboxAddress.Parse(to));
+			message.Subject = subject;
+			message.Body = new TextPart("plain") { Text = body };
+			using var smtp = new SmtpClient();
+			await smtp.ConnectAsync(email.SmtpServer, email.SmtpPort, email.UseSSL, token);
+			if (!string.IsNullOrEmpty(email.SmtpPassword))
+				await smtp.AuthenticateAsync(email.SmtpUsername, email.SmtpPassword, token);
+			await smtp.SendAsync(message, token);
+			await smtp.DisconnectAsync(quit: true, token);
+		}
+	}
+}