email: HTML templates and multipart messages

Emails now render an HTML template from templates/email with a plaintext
fallback, sent as multipart/alternative. A configurable brand name shows
in the template. Reset and confirmation mails share one styled base.

src/engine/db.rs

@@ -456,6 +456,8 @@ pub struct Db {
     pub(crate) scram_iterations: u32,
     // Whether outbound email is configured, so email features can gate themselves.
     email_enabled: bool,
+    // Display name for email templates.
+    email_brand: String,
     // Node-local, non-persisted email codes: account -> (purpose, code, expiry).
     codes: HashMap<String, (CodeKind, String, Instant)>,
 }
@@ -504,7 +506,7 @@ impl Db {
             apply(&mut accounts, &mut channels, &mut grouped, event);
         }
         tracing::info!(accounts = accounts.len(), channels = channels.len(), "account store loaded");
-        Self { accounts, channels, grouped, log, scram_iterations: scram::DEFAULT_ITERATIONS, email_enabled: false, codes: HashMap::new() }
+        Self { accounts, channels, grouped, log, scram_iterations: scram::DEFAULT_ITERATIONS, email_enabled: false, email_brand: "Network Services".to_string(), codes: HashMap::new() }
     }
 
     /// Fold an entry authored by another node into the store — the services-side
@@ -731,6 +733,15 @@ impl Db {
         self.email_enabled = on;
     }
 
+    /// Display name used in email templates.
+    pub fn email_brand(&self) -> &str {
+        &self.email_brand
+    }
+
+    pub fn set_email_brand(&mut self, brand: &str) {
+        self.email_brand = brand.to_string();
+    }
+
     /// Issue a fresh emailed code for `account` and purpose, valid for 15 minutes.
     pub fn issue_code(&mut self, account: &str, kind: CodeKind) -> String {
         let code = gen_code();

src/engine/mod.rs

@@ -548,11 +548,8 @@ impl Engine {
         if ok && !self.db.is_verified(account) {
             if let (Some(addr), RegReply::NickServ { agent, uid, .. }) = (addr, &reply) {
                 let code = self.db.issue_code(account, db::CodeKind::Confirm);
-                out.push(NetAction::SendEmail {
-                    to: addr,
-                    subject: format!("Confirm your {account} registration"),
-                    body: format!("Welcome! Confirm your account {account} with:\n  /msg NickServ CONFIRM {code}\nThe code expires in 15 minutes."),
-                });
+                let mail = crate::email::confirm(self.db.email_brand(), account, &code);
+                out.push(NetAction::SendEmail { to: addr, subject: mail.subject, text: mail.text, html: Some(mail.html) });
                 out.push(NetAction::Notice { from: agent.clone(), to: uid.clone(), text: "A confirmation code has been emailed to you. Confirm with \x02CONFIRM <code>\x02.".to_string() });
             }
         }
@@ -1237,7 +1234,7 @@ mod tests {
         // Request: a code is emailed to the address on file.
         let out = to_ns(&mut e, "RESETPASS alice");
         let (to, body) = out.iter().find_map(|a| match a {
-            NetAction::SendEmail { to, body, .. } => Some((to.clone(), body.clone())),
+            NetAction::SendEmail { to, text, .. } => Some((to.clone(), text.clone())),
             _ => None,
         }).expect("a reset code is emailed");
         assert_eq!(to, "alice@example.org");
@@ -1279,7 +1276,7 @@ mod tests {
         let out = e.complete_register(&account, Db::derive_credentials(&password, 4096), email, reply);
         assert!(!e.db.is_verified("newbie"), "registering with email starts unverified");
         let body = out.iter().find_map(|a| match a {
-            NetAction::SendEmail { body, .. } => Some(body.clone()),
+            NetAction::SendEmail { text, .. } => Some(text.clone()),
             _ => None,
         }).expect("a confirm code is emailed");
         let code = body.split("CONFIRM ").nth(1).unwrap().split_whitespace().next().unwrap().to_string();

src/engine/service.rs

@@ -58,8 +58,8 @@ impl ServiceCtx {
     }
 
     // Send an email (the link layer pipes it to the configured mail command).
-    pub fn send_email(&mut self, to: impl Into<String>, subject: impl Into<String>, body: impl Into<String>) {
-        self.actions.push(NetAction::SendEmail { to: to.into(), subject: subject.into(), body: body.into() });
+    pub fn send_email(&mut self, to: impl Into<String>, subject: impl Into<String>, text: impl Into<String>, html: Option<String>) {
+        self.actions.push(NetAction::SendEmail { to: to.into(), subject: subject.into(), text: text.into(), html });
     }
 
     // Hand a password change to the engine to finish: its derivation runs off the