feat: cache mailbox list for 10 minutes and show progress on initial fetch

- Add 10-minute cache after fetching mailbox list from mail accounts
- Display progress during initial mailbox retrieval
- Prevent timeouts when handling large mailbox lists

crates/core/src/cache/imap/download/download_folders.rs

@@ -23,6 +23,7 @@ use crate::{
     {
         account::migration::{AccountModel, AccountType},
         cache::imap::mailbox::{AttributeEnum, MailBox},
+        cache::imap::mailbox_cache,
         error::{code::ErrorCode, BichonResult},
         imap::{executor::ImapExecutor, session::SessionStream},
         mailbox::list::convert_names_to_mailboxes,
@@ -179,6 +180,7 @@ pub async fn detect_mailbox_changes(
     // Update known folders only if there were changes
     if has_changes {
         AccountModel::update_known_folders(account.id, all_names)?;
+        mailbox_cache::invalidate(account.id).await;
     }
     Ok(())
 }

crates/core/src/cache/imap/mailbox_cache.rs

@@ -0,0 +1,114 @@
+//
+// Copyright (c) 2025-2026 rustmailer.com (https://rustmailer.com)
+//
+// This file is part of the Bichon Email Archiving Project
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+use crate::cache::imap::mailbox::MailBox;
+use crate::utc_now;
+use lru::LruCache;
+use std::collections::HashMap;
+use std::num::NonZeroUsize;
+use std::sync::LazyLock;
+use tokio::sync::Mutex;
+
+struct CacheEntry {
+    mailboxes: Vec<MailBox>,
+    fetched_at: i64,
+}
+
+static CACHE: LazyLock<Mutex<LruCache<u64, CacheEntry>>> = LazyLock::new(|| {
+    Mutex::new(LruCache::new(NonZeroUsize::new(64).unwrap()))
+});
+
+const TTL_MS: i64 = 10 * 60 * 1000; // 10 minutes
+
+pub async fn get(account_id: u64) -> Option<Vec<MailBox>> {
+    let mut guard = CACHE.lock().await;
+    if let Some(entry) = guard.get(&account_id) {
+        if utc_now!() - entry.fetched_at < TTL_MS {
+            return Some(entry.mailboxes.clone());
+        }
+        guard.pop(&account_id);
+    }
+    None
+}
+
+pub async fn set(account_id: u64, mailboxes: Vec<MailBox>) {
+    let mut guard = CACHE.lock().await;
+    guard.put(
+        account_id,
+        CacheEntry {
+            mailboxes,
+            fetched_at: utc_now!(),
+        },
+    );
+}
+
+pub async fn invalidate(account_id: u64) {
+    let mut guard = CACHE.lock().await;
+    guard.pop(&account_id);
+}
+
+// Background fetch state tracking
+#[derive(Clone, Debug)]
+pub enum FetchStatus {
+    Fetching { examined: usize, total: usize },
+    Ready,
+    Error(String),
+}
+
+static FETCH_STATES: LazyLock<Mutex<HashMap<u64, FetchStatus>>> =
+    LazyLock::new(|| Mutex::new(HashMap::new()));
+
+pub async fn fetch_status(account_id: u64) -> Option<FetchStatus> {
+    FETCH_STATES.lock().await.get(&account_id).cloned()
+}
+
+pub async fn set_fetching(account_id: u64) {
+    FETCH_STATES.lock().await.insert(
+        account_id,
+        FetchStatus::Fetching {
+            examined: 0,
+            total: 0,
+        },
+    );
+}
+
+pub async fn update_fetch_progress(account_id: u64, examined: usize, total: usize) {
+    let mut guard = FETCH_STATES.lock().await;
+    guard.insert(
+        account_id,
+        FetchStatus::Fetching { examined, total },
+    );
+}
+
+pub async fn set_fetch_ready(account_id: u64) {
+    FETCH_STATES
+        .lock()
+        .await
+        .insert(account_id, FetchStatus::Ready);
+}
+
+pub async fn set_fetch_error(account_id: u64, error: String) {
+    FETCH_STATES
+        .lock()
+        .await
+        .insert(account_id, FetchStatus::Error(error));
+}
+
+pub async fn clear_fetch_state(account_id: u64) {
+    FETCH_STATES.lock().await.remove(&account_id);
+}

crates/core/src/cache/imap/mod.rs

@@ -22,6 +22,7 @@ use mailbox::MailBox;
 
 pub mod download;
 pub mod mailbox;
+pub mod mailbox_cache;
 pub mod task;
 
 pub fn find_missing_mailboxes(