feat: tell the user when a viewer action fails and when mail is sent

The viewer fired its store actions with `void` and went back to the
list, so a refused delete, archive, move, spam report, star, tag or
read change failed silently, and nothing confirmed a sent message.

- each viewer action now reports a failure as an error toast, and a
  refused star, tag or read change is taken back on screen
- the viewer mounts its own toast host, since the list's sits under it
- an immediate send from the composer or the quick reply box shows
  "Email sent"; a send held for the undo delay keeps its undo bar
  (webmail `ec67ab99`, `b03a0c1d`)

src/components/email/QuickReplyBox.tsx

@@ -7,6 +7,7 @@ import { useColors } from '../../theme/colors';
 import { useSettingsStore } from '../../stores/settings-store';
 import { useLocaleStore } from '../../stores/locale-store';
 import { useEmailStore } from '../../stores/email-store';
+import { toast } from '../../stores/toast-store';
 import { sendEmail, patchKeywordsForEmails } from '../../api/email';
 import { jmapClient } from '../../api/jmap-client';
 import { buildReplyRecipients } from '../../lib/reply-recipients';
@@ -78,7 +79,7 @@ export function QuickReplyBox({ email, jmapAccountId, onMoreOptions, onSent }: P
       const quoted = original.split('\n').map((l) => `> ${l}`).join('\n');
       const header = `${formatFullDateTime(emailDisplayDate(email), timeFormat, locale)}, ${from.name ? `${from.name} <${from.email}>` : from.email}:`;
       const threading = computeReplyThreadingHeaders(email);
-      await sendEmail(
+      const result = await sendEmail(
         {
           from: [{ name: identity.name, email: identity.email }],
           to: recipients.to.filter((r) => !!r.email).map((r) => ({ email: r.email!, name: r.name })),
@@ -98,6 +99,8 @@ export function QuickReplyBox({ email, jmapAccountId, onMoreOptions, onSent }: P
       } catch { /* the reply is out; the flag is cosmetic */ }
       onSent?.({ ...email, keywords: { ...email.keywords, $answered: true } });
       setText('');
+      // A reply held for the undo-send delay has not gone out yet (webmail b03a0c1d).
+      if (!result.scheduled) toast.success(t('notifications.email_sent', 'Email sent successfully'));
     } catch (err) {
       Alert.alert(t('email_composer.send_failed', 'Failed to send'), err instanceof Error ? err.message : String(err));
     } finally {

src/screens/ComposeScreen.tsx

@@ -33,6 +33,7 @@ import { useLocaleStore } from '../stores/locale-store';
 import { useSettingsStore } from '../stores/settings-store';
 import { useAccountStore } from '../stores/account-store';
 import { useSendUndoStore } from '../stores/send-undo-store';
+import { toast } from '../stores/toast-store';
 import { type EmailTemplate } from '../stores/templates-store';
 import { getIdentities } from '../api/identity';
 import {
@@ -2032,6 +2033,9 @@ export default function ComposeScreen({ route, navigation }: Props) {
           delaySeconds: holdForSeconds,
           createdAt: Date.now(),
         });
+      } else if (!result.scheduled) {
+        // Held sends get the undo bar instead (webmail b03a0c1d).
+        toast.success(t('notifications.email_sent', 'Email sent successfully'));
       }
       allowLeaveRef.current = true;
       navigation.goBack();

src/screens/EmailThreadScreen.tsx

@@ -19,7 +19,9 @@ import { MessageContent } from '../components/email/MessageContent';
 import { ThreadMessageCard } from '../components/email/ThreadMessageCard';
 import { QuickReplyBox } from '../components/email/QuickReplyBox';
 import { AddressActionSheet } from '../components/email/AddressActionSheet';
+import { ToastHost } from '../components/ToastHost';
 import { useEmailStore } from '../stores/email-store';
+import { toast } from '../stores/toast-store';
 import {
   useSettingsStore,
   normalizeBottomQuickActions,
@@ -41,6 +43,14 @@ import type { RootStackParamList } from '../navigation/types';
 
 type Props = NativeStackScreenProps<RootStackParamList, 'EmailThread'>;
 
+// Actions finish after the viewer may already have gone back, so a failure is
+// reported as a toast instead of vanishing with the promise (webmail
+// `lib/email-action-toast.ts`).
+function toastFailure(title: string, err: unknown): void {
+  console.warn('[viewer]', title, err);
+  toast.error(title, err instanceof Error ? err.message : undefined);
+}
+
 export default function EmailThreadScreen({ route, navigation }: Props) {
   const c = useColors();
   const styles = React.useMemo(() => makeStyles(c), [c]);
@@ -326,7 +336,10 @@ export default function EmailThreadScreen({ route, navigation }: Props) {
     if (next[token]) delete next[token];
     else next[token] = true;
     updateLocalKeywords(email.id, next);
-    void patchKeywordsForEmails([email.id], { [token]: next[token] ?? null }, ownerAccountId);
+    patchKeywordsForEmails([email.id], { [token]: next[token] ?? null }, ownerAccountId).catch((err) => {
+      updateLocalKeywords(email.id, email.keywords);
+      toastFailure(t('notifications.tag_failed', 'Tagging failed'), err);
+    });
   };
 
   // Toggle the star on a specific message — used both by the toolbar (current
@@ -336,21 +349,28 @@ export default function EmailThreadScreen({ route, navigation }: Props) {
     if (next.$flagged) delete next.$flagged;
     else next.$flagged = true;
     updateLocalKeywords(target.id, next);
-    void patchKeywordsForEmails([target.id], { $flagged: next.$flagged ?? null }, ownerAccountId);
-  }, [updateLocalKeywords, ownerAccountId]);
+    patchKeywordsForEmails([target.id], { $flagged: next.$flagged ?? null }, ownerAccountId).catch((err) => {
+      updateLocalKeywords(target.id, target.keywords);
+      toastFailure(t('notifications.error_updating', 'Failed to update email'), err);
+    });
+  }, [updateLocalKeywords, ownerAccountId, t]);
 
   const onToggleStar = () => { if (email) toggleStarFor(email); };
 
   const onToggleUnread = () => {
     if (!email) return;
+    const failed = (err: unknown) => {
+      updateLocalKeywords(email.id, email.keywords);
+      toastFailure(t('notifications.error_updating', 'Failed to update email'), err);
+    };
     if (unread) {
-      void markSeen(email.id);
+      markSeen(email.id).catch(failed);
       updateLocalKeywords(email.id, { ...email.keywords, $seen: true });
     } else {
       const next = { ...email.keywords };
       delete next.$seen;
       updateLocalKeywords(email.id, next);
-      void patchKeywordsForEmails([email.id], { $seen: null }, ownerAccountId);
+      patchKeywordsForEmails([email.id], { $seen: null }, ownerAccountId).catch(failed);
     }
   };
 
@@ -361,7 +381,8 @@ export default function EmailThreadScreen({ route, navigation }: Props) {
 
   const performDelete = () => {
     if (!email || !sourceMailbox || !trashMailbox) return;
-    void deleteEmail(email.id, trashMailbox.id, sourceMailbox.id, { email, accountId: ownerAccountId });
+    deleteEmail(email.id, trashMailbox.id, sourceMailbox.id, { email, accountId: ownerAccountId })
+      .catch((err) => toastFailure(t('notifications.error_deleting', 'Failed to delete email'), err));
     navigation.goBack();
   };
 
@@ -394,7 +415,8 @@ export default function EmailThreadScreen({ route, navigation }: Props) {
 
   const onArchive = () => {
     if (!email || !canArchive) return;
-    void archiveEmailAction(email.id, { email, accountId: ownerAccountId });
+    archiveEmailAction(email.id, { email, accountId: ownerAccountId })
+      .catch((err) => toastFailure(t('notifications.error_archiving', 'Failed to archive email'), err));
     navigation.goBack();
   };
 
@@ -405,8 +427,13 @@ export default function EmailThreadScreen({ route, navigation }: Props) {
     if (!email || !canToggleSpam) return;
     setMoreMenuOpen(false);
     const viewed = { email, accountId: ownerAccountId };
-    if (isInJunk) void unmarkSpam([email.id], viewed);
-    else void markSpam([email.id], viewed);
+    if (isInJunk) {
+      unmarkSpam([email.id], viewed)
+        .catch((err) => toastFailure(t('email_viewer.spam.error_not_spam', 'Failed to restore email'), err));
+    } else {
+      markSpam([email.id], viewed)
+        .catch((err) => toastFailure(t('email_viewer.spam.error', 'Failed to report spam'), err));
+    }
     navigation.goBack();
   };
 
@@ -414,7 +441,8 @@ export default function EmailThreadScreen({ route, navigation }: Props) {
     if (!email || !sourceMailbox || toId === sourceMailbox.id) return;
     setMoveMenuOpen(false);
     setMoreMenuOpen(false);
-    void moveToMailbox(email.id, sourceMailbox.id, toId, { email, accountId: ownerAccountId });
+    moveToMailbox(email.id, sourceMailbox.id, toId, { email, accountId: ownerAccountId })
+      .catch((err) => toastFailure(t('notifications.move_failed', 'Move failed'), err));
     navigation.goBack();
   };
 
@@ -786,6 +814,9 @@ export default function EmailThreadScreen({ route, navigation }: Props) {
       />
 
       <AddressActionSheet address={addressSheet} onClose={() => setAddressSheet(null)} />
+
+      {/* The list's host sits under this screen; failures in here need their own. */}
+      <ToastHost />
     </SafeAreaView>
   );
 }