Archive into a dated folder

Archiving put everything in one folder, so an Archive that has been
collecting for years is a single flat list with no way to narrow it except
search.

Archive by year and Archive by month file into Archive/2026 and
Archive/2026/09, creating the folders as needed and reusing them after
that, including folders made by hand or by another client.

The names are numeric and zero-padded rather than month names, because
these are real server-side mailboxes rather than anything of ihasmail's.
Every other client sees them: a folder created as "September" by someone
reading in English stays "September" for the same account read in
Japanese, since the name is stored and not translated. And 09 sorts
between 08 and 10 where a name does not.

The date is read in the reader's own timezone rather than UTC so it agrees
with the date shown against the message in the list. A message that
arrived at 00:30 UTC on 1 September is dated 31 August in New York, and
filing it under 09 while the list says August would be the app
disagreeing with itself. A message whose date cannot be read goes to
Archive itself rather than to a folder named after a guess.

A selection spanning two months is two destinations, not one. The moves
are made silently and one toast names where everything went -- the folder
where there is a single answer, the count where there is not -- because
each group raising its own toast with its own Undo would mean undoing a
third of a move. One Undo restores the whole selection to wherever each
message came from, captured before anything moved.

The menu labels name the destination where there is one, so it reads
"Archive to 2026/09" rather than describing the rule, and falls back to
"Archive by month" for a selection with no single answer.

web/src/views/mail/MessageList.tsx

@@ -1,11 +1,12 @@
 import { Fragment, memo, useCallback, useEffect, useMemo, useRef, useState, type DragEvent, type MouseEvent, type ReactNode } from "react";
 import { useVirtualizer } from "@tanstack/react-virtual";
-import { Archive, ArrowLeft, CalendarPlus, CheckSquare, FolderInput, PanelRight, PanelBottom, PanelTop, Filter, Inbox, Mail, MailOpen, MailPlus, MoreVertical, Paperclip, RefreshCw, Reply, Search, Star, Tag, Trash2, AlertOctagon, Forward, Eraser, ShieldCheck, X } from "lucide-react";
+import { Archive, ArrowLeft, CalendarDays, CalendarRange, CalendarPlus, CheckSquare, FolderInput, PanelRight, PanelBottom, PanelTop, Filter, Inbox, Mail, MailOpen, MailPlus, MoreVertical, Paperclip, RefreshCw, Reply, Search, Star, Tag, Trash2, AlertOctagon, Forward, Eraser, ShieldCheck, X } from "lucide-react";
 import { useLocation } from "wouter";
 import { useMail, type ListState } from "@/store/mail";
 import { dateTimeKey, useSettings } from "@/store/settings";
 import type { Email, Id } from "@/jmap/types";
 import { formatListDate } from "@/lib/format";
+import { groupByArchivePath, archivePath, type ArchiveGranularity } from "@/lib/archiveDate";
 import { canEmpty, confirmAndEmpty, emptyLabel } from "@/lib/emptyFolder";
 import { displayName, shortName } from "@/lib/address";
 import { Avatar, Empty, useIsMobile, useIsTouch } from "@/ui/misc";
@@ -224,6 +225,22 @@ export function MessageList({ title, list, openThreadId, focusId, setFocusId, on
   );
 
   const ctxTargets = useMemo(() => (ctxRow ? (selected[ctxRow] ? Object.keys(selected) : [ctxRow]) : []), [ctxRow, selected]);
+
+  /*
+   * Name the destination where there is only one, so the menu says where the
+   * mail is actually going rather than describing the rule. A selection that
+   * spans months has no single answer, and claiming one would be worse than
+   * naming the rule -- so that case falls back to it.
+   */
+  const archiveDateLabel = useCallback(
+    (granularity: ArchiveGranularity) => {
+      const groups = groupByArchivePath(ctxTargets.map((id) => ({ id, receivedAt: emails[id]?.receivedAt })), granularity);
+      const only = groups.length === 1 ? groups[0]! : null;
+      if (only?.segments.length) return t("Archive to {folder}", { folder: archivePath(only.segments) });
+      return granularity === "year" ? t("Archive by year") : t("Archive by month");
+    },
+    [ctxTargets, emails],
+  );
   const allSelected = ids.length > 0 && ids.every((id) => selected[id]);
   const someUnread = ctxTargets.some((id) => !emails[id]?.keywords.$seen);
   const someUnstarred = ctxTargets.some((id) => !emails[id]?.keywords.$flagged);
@@ -478,6 +495,8 @@ export function MessageList({ title, list, openThreadId, focusId, setFocusId, on
         <MenuItem icon={<MailPlus size={16} />} label={t("Compose as new")} onClick={() => { const e = ctxRow ? emails[ctxRow] : undefined; if (e) void useCompose.getState().composeAsNew(e); }} />
         <MenuSep />
         <MenuItem icon={<Archive size={16} />} label={t("Archive")} kbd="e" onClick={() => void actions.archive(ctxTargets)} />
+        <MenuItem icon={<CalendarRange size={16} />} label={archiveDateLabel("year")} onClick={() => void useMail.getState().archiveByDate(ctxTargets, "year")} />
+        <MenuItem icon={<CalendarDays size={16} />} label={archiveDateLabel("month")} onClick={() => void useMail.getState().archiveByDate(ctxTargets, "month")} />
         <MenuItem icon={<Trash2 size={16} />} label={t("Delete")} kbd="#" onClick={() => void actions.trash(ctxTargets)} />
         <MenuItem icon={<AlertOctagon size={16} />} label={mailbox?.role === "junk" ? "Not spam" : "Report spam"} kbd="!" onClick={() => void actions.spam(ctxTargets)} />
         <MenuSep />