save the admin bot localpart

This will be used later in the run.

src/database.rs

@@ -1071,6 +1071,13 @@ impl KeyValueDatabase {
                 Ok(())
             })?;
 
+            // Ensure the admin bot localpart has been written once
+            if services().globals.saved_admin_bot_localpart()?.is_none() {
+                services().globals.save_admin_bot_localpart(
+                    services().globals.admin_bot_user_id.localpart(),
+                )?;
+            }
+
             assert_eq!(
                 services().globals.database_version().unwrap(),
                 latest_database_version,

src/database/key_value/globals.rs

@@ -385,4 +385,26 @@ lasttimelinecount_cache: {lasttimelinecount_cache}\n"
 
         Ok(Some(server_name))
     }
+
+    fn set_admin_bot_localpart(&self, localpart: &str) -> Result<()> {
+        self.global.insert(b"admin_bot_localpart", localpart.as_bytes())
+    }
+
+    fn admin_bot_localpart(&self) -> Result<Option<String>> {
+        let opt_bytes = self
+            .global
+            .get(b"admin_bot_localpart")
+            .map_err(|_| Error::bad_database("Failed to read from globals"))?;
+
+        // `admin_bot_localpart` has not been set yet
+        let Some(bytes) = opt_bytes else {
+            return Ok(None);
+        };
+
+        let localpart = String::from_utf8(bytes).map_err(|_| {
+            Error::bad_database("Invalid UTF-8 in admin_bot_localpart")
+        })?;
+
+        Ok(Some(localpart))
+    }
 }

src/error.rs

@@ -91,7 +91,9 @@ pub(crate) enum ServerNameChanged {
     Renamed(OwnedServerName, OwnedServerName),
 
     #[error(
-        "couldn't find {0} in the database, `server_name` must have changed"
+        "couldn't find {0} in the database, either the `server_name` changed \
+         or the admin bot localpart was reconfigured without running the \
+         server at least once with the original localpart"
     )]
     MissingAdminBot(OwnedUserId),
 

src/service/admin.rs

@@ -1283,6 +1283,8 @@ impl Service {
 
     /// Create the admin room.
     ///
+    /// This function should only be run on a fresh database.
+    ///
     /// Users in this room are considered admins by grapevine, and the room can
     /// be used to issue admin commands by talking to the server user inside
     /// it.
@@ -1300,6 +1302,9 @@ impl Service {
             .await;
 
         services().users.create(&services().globals.admin_bot_user_id, None)?;
+        services().globals.save_admin_bot_localpart(
+            services().globals.admin_bot_user_id.localpart(),
+        )?;
 
         let room_version_id = services().globals.default_room_version();
         let room_version = RoomVersion::try_from(&room_version_id)?;

src/service/globals.rs

@@ -656,6 +656,17 @@ impl Service {
     pub(crate) fn saved_server_name(&self) -> Result<Option<OwnedServerName>> {
         self.db.server_name()
     }
+
+    pub(crate) fn save_admin_bot_localpart(
+        &self,
+        localpart: &str,
+    ) -> Result<()> {
+        self.db.set_admin_bot_localpart(localpart)
+    }
+
+    pub(crate) fn saved_admin_bot_localpart(&self) -> Result<Option<String>> {
+        self.db.admin_bot_localpart()
+    }
 }
 
 fn reqwest_client_builder(config: &Config) -> Result<reqwest::ClientBuilder> {

src/service/globals/data.rs

@@ -121,4 +121,6 @@ pub(crate) trait Data: Send + Sync {
     fn bump_database_version(&self, new_version: u64) -> Result<()>;
     fn set_server_name(&self, server_name: &ServerName) -> Result<()>;
     fn server_name(&self) -> Result<Option<OwnedServerName>>;
+    fn set_admin_bot_localpart(&self, localpart: &str) -> Result<()>;
+    fn admin_bot_localpart(&self) -> Result<Option<String>>;
 }