Let go of old message bodies and of exported files

Every message opened kept its full copy for as long as the tab was open.
The store now holds bodies for the 40 messages most recently wanted; older
ones go back to the list properties and are fetched in full again if
opened. The open conversation is never released.

Contact, settings and calendar exports go through downloadFile, which
releases the object URL once the download has started; three of them
never released it.

web/src/views/calendar/CalendarSidebar.tsx

@@ -16,6 +16,7 @@ import type { Calendar, Id } from "@/jmap/types";
 import { CalendarDialog } from "./CalendarDialog";
 import { ShareDialog } from "../settings/ShareDialog";
 import { plural, t } from "@/lib/i18n";
+import { downloadFile } from "@/lib/download";
 
 export function CalendarSidebar() {
   const [location, navigate] = useLocation();
@@ -42,19 +43,14 @@ export function CalendarSidebar() {
   const importInto = useRef<Id | null>(null);
 
   /*
-   * Handing the file over, which the browser only does from a click. The
-   * revoke below is what keeps a calendar's worth of text from sitting in
-   * memory after the download has started.
+   * Handing the file over, which the browser only does from a click.
+   * `downloadFile` releases it once started, so a calendar's worth of text
+   * does not sit in memory afterwards.
    */
   const exportFile = async (c: Calendar) => {
     try {
       const { text, count } = await cal.exportIcs(c.id);
-      const url = URL.createObjectURL(new Blob([text], { type: "text/calendar" }));
-      const a = document.createElement("a");
-      a.href = url;
-      a.download = `${c.name.replace(/[^\w.-]+/g, "_") || "calendar"}.ics`;
-      a.click();
-      URL.revokeObjectURL(url);
+      downloadFile(text, "text/calendar", `${c.name.replace(/[^\w.-]+/g, "_") || "calendar"}.ics`);
       toast.success(plural(count, { one: "Exported {n} event", other: "Exported {n} events" }));
     } catch (err) {
       toast.error(t("Could not export this calendar: {error}", { error: (err as Error).message }));

web/src/views/contacts/ContactsView.tsx

@@ -15,6 +15,7 @@ import { useSettings } from "@/store/settings";
 import { ContactEditor } from "./ContactEditor";
 import { avatarColor } from "@/lib/address";
 import { plural, t as translate } from "@/lib/i18n";
+import { downloadFile } from "@/lib/download";
 
 export function ContactsView({ id }: { id?: string }) {
   const [, navigate] = useLocation();
@@ -149,10 +150,7 @@ export function ContactsView({ id }: { id?: string }) {
       toast.error(translate("There is nothing in it to export"));
       return;
     }
-    const a = document.createElement("a");
-    a.href = URL.createObjectURL(new Blob([cards.map(toVCard).join("")], { type: "text/vcard" }));
-    a.download = "contacts.vcf";
-    a.click();
+    downloadFile(cards.map(toVCard).join(""), "text/vcard", "contacts.vcf");
   };
 
   const importFile = async (f: File, intoBookId?: string) => {
@@ -359,7 +357,7 @@ function ContactDetail({ card: c, onBack, onEdit, narrow, onEmail }: { card: Con
         {narrow && <button className="icon-btn" onClick={onBack} aria-label={translate("Back")}><ArrowLeft size={20} /></button>}
         <span className="spacer" />
         <button className="btn btn-sm" onClick={onEdit}><Pencil size={14} />  {translate("Edit")}</button>
-        <button className="btn btn-sm" onClick={() => { const a = document.createElement("a"); a.href = URL.createObjectURL(new Blob([toVCard(c)], { type: "text/vcard" })); a.download = `${name.replace(/[^\w.-]+/g, "_")}.vcf`; a.click(); }}><Download size={14} />  {translate("vCard")}</button>
+        <button className="btn btn-sm" onClick={() => downloadFile(toVCard(c), "text/vcard", `${name.replace(/[^\w.-]+/g, "_")}.vcf`)}><Download size={14} />  {translate("vCard")}</button>
         <button className="btn btn-sm btn-ghost" style={{ color: "var(--danger)" }} onClick={async () => { if (await confirmDialog({ title: translate("Delete {name}?", { name }), confirmLabel: translate("Delete"), danger: true })) { try { const { destroyed, refused } = await contacts.destroyCards([c.id]); if (!destroyed) { toast.error(refused ? setErrorMessage(refused) : translate("It was not deleted")); return; } toast.success(translate("Contact deleted")); navigate("/contacts"); } catch (err) { toast.error((err as Error).message); } } }}><Trash2 size={14} /></button>
       </div>
       <div className="contact-hero">

web/src/views/settings/GeneralSettings.tsx

@@ -25,6 +25,7 @@ import {
   type DateFormat,
 } from "@/lib/datetime";
 import { isEnforced } from "@/lib/settingsPolicy";
+import { downloadFile } from "@/lib/download";
 
 /** Illustrative instant used for the format previews: 22 Nov 2025, 18:23. */
 const SAMPLE = new Date(2025, 10, 22, 18, 23);
@@ -236,7 +237,7 @@ export function GeneralSettings() {
 
       <h2>{t("Backup")}</h2>
       <div className="row wrap">
-        <button className="btn" onClick={() => { const blob = new Blob([exportJson()], { type: "application/json" }); const a = document.createElement("a"); a.href = URL.createObjectURL(blob); a.download = "ihasmail-settings.json"; a.click(); }}>{t("Export settings")}</button>
+        <button className="btn" onClick={() => downloadFile(exportJson(), "application/json", "ihasmail-settings.json")}>{t("Export settings")}</button>
         <label className="btn">
           {t("Import settings")}
           <input type="file" accept="application/json" hidden onChange={async (e) => { const f = e.target.files?.[0]; if (!f) return; const ok = importJson(await f.text()); toast[ok ? "success" : "error"](ok ? t("Settings imported") : t("Invalid settings file")); e.target.value = ""; }} />