nickserv: AJOIN auto-join list

Adds the account auto-join list (AJOIN ADD/DEL/LIST): NickServ SVSJOINs you
into your listed channels each time you identify. The list is a typed
Vec<AjoinEntry> on the account, folded through the event log like the cert and
akick lists (persists and replays; no separate store), reached by modules
through the Store trait. New ForceJoin action serialises to InspIRCd SVSJOIN.
Shown in INFO. Operates on the caller's own account; the oper form for other
users waits on a privilege system.

nickserv/src/ajoin.rs

@@ -0,0 +1,63 @@
+use fedserv_api::Store;
+use fedserv_api::{Sender, ServiceCtx};
+
+// A sane cap so a runaway list can't bloat an account or flood a user on identify.
+const MAX_AJOIN: usize = 25;
+
+// AJOIN [ADD <#channel> [key] | DEL <#channel> | LIST]: manage your auto-join
+// list — the channels NickServ joins you to each time you identify.
+pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db: &mut dyn Store) {
+    let Some(account) = from.account else {
+        ctx.notice(me, from.uid, "You must identify to NickServ to use \x02AJOIN\x02.");
+        return;
+    };
+    match args.get(1).map(|s| s.to_ascii_uppercase()).as_deref() {
+        Some("ADD") => {
+            let Some(&channel) = args.get(2) else {
+                ctx.notice(me, from.uid, "Syntax: AJOIN ADD <#channel> [key]");
+                return;
+            };
+            if !channel.starts_with('#') {
+                ctx.notice(me, from.uid, "That doesn't look like a channel name.");
+                return;
+            }
+            let key = args.get(3).copied().unwrap_or("");
+            if db.ajoin_list(account).len() >= MAX_AJOIN {
+                ctx.notice(me, from.uid, format!("Your auto-join list is full (max {MAX_AJOIN})."));
+                return;
+            }
+            match db.ajoin_add(account, channel, key) {
+                Ok(true) => ctx.notice(me, from.uid, format!("Added \x02{channel}\x02 to your auto-join list.")),
+                Ok(false) => ctx.notice(me, from.uid, format!("Updated the key for \x02{channel}\x02 on your auto-join list.")),
+                Err(_) => ctx.notice(me, from.uid, "Sorry, that didn't work. Please try again in a moment."),
+            }
+        }
+        Some("DEL") => {
+            let Some(&channel) = args.get(2) else {
+                ctx.notice(me, from.uid, "Syntax: AJOIN DEL <#channel>");
+                return;
+            };
+            match db.ajoin_del(account, channel) {
+                Ok(true) => ctx.notice(me, from.uid, format!("Removed \x02{channel}\x02 from your auto-join list.")),
+                Ok(false) => ctx.notice(me, from.uid, format!("\x02{channel}\x02 isn't on your auto-join list.")),
+                Err(_) => ctx.notice(me, from.uid, "Sorry, that didn't work. Please try again in a moment."),
+            }
+        }
+        None | Some("LIST") => {
+            let list = db.ajoin_list(account);
+            if list.is_empty() {
+                ctx.notice(me, from.uid, "Your auto-join list is empty. Add channels with \x02AJOIN ADD <#channel>\x02.");
+                return;
+            }
+            ctx.notice(me, from.uid, format!("Your auto-join list ({}):", list.len()));
+            for e in &list {
+                if e.key.is_empty() {
+                    ctx.notice(me, from.uid, format!("  \x02{}\x02", e.channel));
+                } else {
+                    ctx.notice(me, from.uid, format!("  \x02{}\x02 (key: {})", e.channel, e.key));
+                }
+            }
+        }
+        Some(other) => ctx.notice(me, from.uid, format!("Unknown AJOIN command \x02{other}\x02. Use \x02ADD\x02, \x02DEL\x02 or \x02LIST\x02.")),
+    }
+}