Let the sidebar be resized by dragging its edge

The sidebar's right edge is now a splitter, like the one between the
message list and the reading pane: drag it between 240 and 480px, move it
with the arrow keys, double-click to put it back. The width is a device
setting, and stays null until someone drags, so a width set in the
reader's own CSS through --sidebar-w is kept until they choose otherwise.
Hidden on a phone, where the sidebar is a drawer, and while collapsed.

Arrow keys on either splitter moved the pane and never saved it: the
keyboard path called onResize without onEnd. It ends each key press now,
and both views keep the in-progress size in a ref as well as state, so
the end reads the value set in the same tick.

The message-list splitter's accessible name was an untranslated literal.
It goes through translate() now, and it and the sidebar's new name are in
all nine catalogues.

Closes #345

web/src/lib/__tests__/settingsSync.test.ts

@@ -25,7 +25,7 @@ describe("which settings follow the account", () => {
     const synced = syncedPart(DEFAULT_SETTINGS);
     // A pane width picked on a monitor is wrong on a laptop, and the
     // notification toggles track a per-browser permission grant.
-    for (const key of ["listPaneWidth", "listPaneHeight", "density", "fontSize", "sidebarCollapsed", "desktopNotifications", "notificationSound"]) {
+    for (const key of ["listPaneWidth", "listPaneHeight", "sidebarWidth", "density", "fontSize", "sidebarCollapsed", "desktopNotifications", "notificationSound"]) {
       expect(synced, key).not.toHaveProperty(key);
     }
   });

web/src/locales/de.ts

@@ -1212,6 +1212,8 @@ export const catalog: Catalog = {
     "Maximize": "Maximieren",
     "Full screen": "Vollbild",
     "Resize panes": "Bereichsgröße ändern",
+    "Resize message list": "Größe der Nachrichtenliste ändern",
+    "Resize sidebar": "Größe der Seitenleiste ändern",
     "QR code": "QR-Code",
     "Draft discarded": "Entwurf verworfen",
     "Draft saved": "Entwurf gespeichert",

web/src/locales/es.ts

@@ -1185,6 +1185,8 @@ export const catalog: Catalog = {
     "Maximize": "Maximizar",
     "Full screen": "Pantalla completa",
     "Resize panes": "Cambiar el tamaño de los paneles",
+    "Resize message list": "Cambiar el tamaño de la lista de mensajes",
+    "Resize sidebar": "Cambiar el tamaño de la barra lateral",
     "QR code": "Código QR",
     "Draft discarded": "Borrador descartado",
     "Draft saved": "Borrador guardado",

web/src/locales/fr.ts

@@ -1190,6 +1190,8 @@ export const catalog: Catalog = {
     "Maximize": "Agrandir",
     "Full screen": "Plein écran",
     "Resize panes": "Redimensionner les volets",
+    "Resize message list": "Redimensionner la liste des messages",
+    "Resize sidebar": "Redimensionner la barre latérale",
     "QR code": "QR code",
     "Draft discarded": "Brouillon abandonné",
     "Draft saved": "Brouillon enregistré",

web/src/locales/ja.ts

@@ -1193,6 +1193,8 @@ export const catalog: Catalog = {
     "Maximize": "最大化",
     "Full screen": "全画面",
     "Resize panes": "ペインの大きさを変更",
+    "Resize message list": "メール一覧の大きさを変更",
+    "Resize sidebar": "サイドバーの大きさを変更",
     "QR code": "QR コード",
     "Draft discarded": "下書きを破棄しました",
     "Draft saved": "下書きを保存しました",

web/src/locales/nl.ts

@@ -1181,6 +1181,8 @@ export const catalog: Catalog = {
     "Maximize": "Maximaliseren",
     "Full screen": "Volledig scherm",
     "Resize panes": "Vensterdelen verslepen",
+    "Resize message list": "Grootte van de berichtenlijst wijzigen",
+    "Resize sidebar": "Grootte van de zijbalk wijzigen",
     "QR code": "QR-code",
     "Draft discarded": "Concept weggegooid",
     "Draft saved": "Concept opgeslagen",

web/src/locales/pt-BR.ts

@@ -1188,6 +1188,8 @@ export const catalog: Catalog = {
     "Maximize": "Maximizar",
     "Full screen": "Tela cheia",
     "Resize panes": "Redimensionar os painéis",
+    "Resize message list": "Redimensionar a lista de mensagens",
+    "Resize sidebar": "Redimensionar a barra lateral",
     "QR code": "Código QR",
     "Draft discarded": "Rascunho descartado",
     "Draft saved": "Rascunho salvo",

web/src/locales/ru.ts

@@ -1187,6 +1187,8 @@ export const catalog: Catalog = {
     "Maximize": "Развернуть",
     "Full screen": "Во весь экран",
     "Resize panes": "Изменить размер панелей",
+    "Resize message list": "Изменить размер списка писем",
+    "Resize sidebar": "Изменить размер боковой панели",
     "QR code": "QR-код",
     "Draft discarded": "Черновик удалён",
     "Draft saved": "Черновик сохранён",

web/src/locales/uk.ts

@@ -1181,6 +1181,8 @@ export const catalog: Catalog = {
     "Maximize": "Розгорнути",
     "Full screen": "На весь екран",
     "Resize panes": "Змінити розмір панелей",
+    "Resize message list": "Змінити розмір списку листів",
+    "Resize sidebar": "Змінити розмір бічної панелі",
     "QR code": "QR-код",
     "Draft discarded": "Чернетку видалено",
     "Draft saved": "Чернетку збережено",

web/src/locales/zh-Hans.ts

@@ -1192,6 +1192,8 @@ export const catalog: Catalog = {
     "Maximize": "最大化",
     "Full screen": "全屏",
     "Resize panes": "调整窗格大小",
+    "Resize message list": "调整邮件列表大小",
+    "Resize sidebar": "调整侧边栏大小",
     "QR code": "二维码",
     "Draft discarded": "草稿已放弃",
     "Draft saved": "草稿已保存",

web/src/store/settings.ts

@@ -256,6 +256,13 @@ export interface Settings {
   listPaneWidth: number;
   /** Height (px) of the message list when the reading pane is below. */
   listPaneHeight: number;
+  /**
+   * Width (px) of the sidebar, dragged by its edge (#345). Null until someone
+   * drags it, and null again after a double-click resets it -- which leaves the
+   * width to the stylesheet's `--sidebar-w`, so a reader who already widens the
+   * sidebar with their own CSS keeps what they had until they choose otherwise.
+   */
+  sidebarWidth: number | null;
   /** Outlook-style colour categories for calendar events. */
   eventCategories: Array<{ name: string; color: string }>;
   /** Default sending identity per account (JMAP has no such flag). */
@@ -370,6 +377,7 @@ export const DEFAULT_SETTINGS: Settings = {
   sendAndArchive: false,
   listPaneWidth: 520,
   listPaneHeight: 340,
+  sidebarWidth: null,
   eventCategories: [
     { name: "Important", color: "#dc2626" },
     { name: "Work", color: "#2563eb" },
@@ -400,6 +408,7 @@ export const DEVICE_KEYS: ReadonlySet<keyof Settings> = new Set<keyof Settings>(
   "notificationSound",
   "listPaneWidth",
   "listPaneHeight",
+  "sidebarWidth",
 ]);
 
 /** The part of the settings that is written to the account's settings file. */

web/src/styles/app.css

@@ -1282,8 +1282,17 @@ a.menu-item:hover { color: var(--fg); }
 @keyframes push-pulse { 50% { opacity: .45; } }
 @media (prefers-reduced-motion: reduce) { .push-dot.connecting { animation: none; } }
 
-.app-body { display: grid; grid-template-columns: var(--sidebar-w) minmax(0, 1fr); min-height: 0; transition: grid-template-columns .2s var(--ease); }
+.app-body { position: relative; display: grid; grid-template-columns: var(--sidebar-w) minmax(0, 1fr); min-height: 0; transition: grid-template-columns .2s var(--ease); }
 .app-body.collapsed { grid-template-columns: var(--sidebar-w-collapsed) minmax(0, 1fr); }
+/* A drag follows the pointer; the ease is for the collapse toggle, and applied
+   to every frame of a drag it leaves the edge trailing behind the hand. */
+.app-body.resizing, .app-body.resizing > .sidebar-splitter { transition: none; }
+/* The sidebar edge (#345). Laid over the seam rather than given a grid column:
+   the sidebar and the content meet at the content's own border, and a 6px
+   bar of border colour between them would draw a line the design never had.
+   Out of the flow, it shows only on hover and focus, like the list splitter. */
+.app-body > .sidebar-splitter { position: absolute; top: 0; bottom: 0; left: calc(var(--sidebar-w) - 3px); background: transparent; transition: left .2s var(--ease); }
+.app-body > .sidebar-splitter:hover, .app-body > .sidebar-splitter:focus-visible { background: var(--accent); }
 .sidebar { display: flex; flex-direction: column; min-height: 0; padding: 4px 8px 8px 8px; gap: 2px; overflow: hidden; }
 .sidebar-scroll { overflow-y: auto; overflow-x: hidden; flex: 1; min-height: 0; padding-bottom: 8px; }
 .compose-btn { display: flex; align-items: center; gap: 12px; height: 52px; padding: 0 22px 0 18px; margin: 6px 4px 12px; border-radius: 16px; background: var(--bg-elev); box-shadow: var(--shadow-1); font-weight: 600; font-size: 1em; color: var(--fg); transition: box-shadow .15s, transform .05s, background .12s; white-space: nowrap; }

web/src/ui/Splitter.tsx

@@ -7,15 +7,16 @@ interface Props {
   onEnd?: () => void;
   onReset?: () => void;
   ariaLabel?: string;
+  className?: string;
 }
 
 /** Drag handle between two panes. Calls onResize with the pointer delta since the last event. */
-export function Splitter({ direction, onResize, onEnd, onReset, ariaLabel }: Props) {
+export function Splitter({ direction, onResize, onEnd, onReset, ariaLabel, className }: Props) {
   const last = useRef(0);
   const active = useRef(false);
   return (
     <div
-      className={`splitter ${direction}`}
+      className={`splitter ${direction}${className ? ` ${className}` : ""}`}
       role="separator"
       aria-orientation={direction === "vertical" ? "vertical" : "horizontal"}
       aria-label={ariaLabel ?? t("Resize panes")}
@@ -47,8 +48,13 @@ export function Splitter({ direction, onResize, onEnd, onReset, ariaLabel }: Pro
         onEnd?.();
       }}
       onKeyDown={(e) => {
-        if (e.key === "ArrowLeft" || e.key === "ArrowUp") onResize(-24);
-        if (e.key === "ArrowRight" || e.key === "ArrowDown") onResize(24);
+        const step = e.key === "ArrowLeft" || e.key === "ArrowUp" ? -24 : e.key === "ArrowRight" || e.key === "ArrowDown" ? 24 : 0;
+        if (!step) return;
+        e.preventDefault();
+        // A key press is a whole drag in one: without the end, the size moved on
+        // screen and was never saved.
+        onResize(step);
+        onEnd?.();
       }}
     >
       <span className="splitter-grip" />

web/src/views/AppShell.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useState, type ReactNode } from "react";
+import { useEffect, useRef, useState, type ReactNode } from "react";
 import { Link, useLocation } from "wouter";
 import { BookOpen, Calendar, ChevronsUpDown, FolderOpen, Globe, HelpCircle, LogOut, Mail, Menu as MenuIcon, Moon, PenSquare, Plus, RefreshCw, Settings, ShieldCheck, Sun, Upload, Users, X } from "lucide-react";
 import { useSession } from "@/store/session";
@@ -10,6 +10,7 @@ import { useMail } from "@/store/mail";
 import { draftFromMailto, useCompose } from "@/store/compose";
 import { Avatar, useIsMobile } from "@/ui/misc";
 import { MenuItem, MenuSep, Popover, useMenu } from "@/ui/popover";
+import { Splitter } from "@/ui/Splitter";
 import { SearchBar } from "./SearchBar";
 import { MailboxTree } from "./mail/MailboxTree";
 import { FilesTree } from "./files/FilesTree";
@@ -25,6 +26,16 @@ import { hasAdministration } from "@/lib/adminAccess";
 import { usePermissions } from "./admin/usePermissions";
 import { AdminNav } from "./admin/AdminNav";
 
+/*
+ * How far the sidebar edge can be dragged. Below about 228px the module bar
+ * cuts "Calendar" and "Contacts" short in English; the floor sits a little
+ * above that. Long folder names are allowed to ellipsise -- narrowing the pane
+ * is asking for that. The ceiling keeps a list and a reading pane beside it on
+ * an ordinary laptop screen.
+ */
+const SIDEBAR_MIN = 240;
+const SIDEBAR_MAX = 480;
+
 const PUSH_LABEL = {
   connected: "Live updates connected",
   connecting: "Live updates reconnecting…",
@@ -35,7 +46,19 @@ export function AppShell({ children }: { children: ReactNode }) {
   const [location, navigate] = useLocation();
   const isMobile = useIsMobile();
   const collapsed = useSettings((s) => s.settings.sidebarCollapsed);
+  const sidebarWidth = useSettings((s) => s.settings.sidebarWidth);
   const update = useSettings((s) => s.update);
+  /*
+   * The width while a drag is in progress, kept here and written to settings
+   * once on release -- the same arrangement as the message-list splitter, so a
+   * drag is a re-render per frame and not a localStorage write per frame.
+   */
+  const [liveSidebarWidth, setLiveSidebarWidth] = useState<number | null>(null);
+  // The same value, readable in the same tick it was set: a key press resizes
+  // and ends in one go, before any render could hand the state back.
+  const liveSidebarRef = useRef<number | null>(null);
+  const sidebarRef = useRef<HTMLElement>(null);
+  const shownSidebarWidth = liveSidebarWidth ?? sidebarWidth;
   const [drawer, setDrawer] = useState(false);
   const [helpOpen, setHelpOpen] = useState(false);
   const openCompose = useCompose((s) => s.open);
@@ -185,9 +208,12 @@ export function AppShell({ children }: { children: ReactNode }) {
         </div>
       </header>
 
-      <div className={`app-body ${collapsed && !isMobile ? "collapsed" : ""}`}>
+      <div
+        className={`app-body ${collapsed && !isMobile ? "collapsed" : ""} ${liveSidebarWidth != null ? "resizing" : ""}`}
+        style={shownSidebarWidth != null && !isMobile ? ({ "--sidebar-w": `${shownSidebarWidth}px` } as React.CSSProperties) : undefined}
+      >
         <div className={`drawer-backdrop ${drawer ? "open" : ""}`} onClick={() => setDrawer(false)} />
-        <aside className={`sidebar ${drawer ? "open" : ""}`}>
+        <aside ref={sidebarRef} className={`sidebar ${drawer ? "open" : ""}`}>
           {/*
             The way back out.
 
@@ -240,6 +266,34 @@ export function AppShell({ children }: { children: ReactNode }) {
             <ModuleLink href="/files" icon={<FolderOpen size={20} />} label={t("Files")} active={section === "files"} />
           </nav>
         </aside>
+        {/* Not on a phone, where the sidebar is a drawer over the page, and not
+            while collapsed to icons, where there is no width to choose. */}
+        {!isMobile && !collapsed && (
+          <Splitter
+            direction="vertical"
+            className="sidebar-splitter"
+            ariaLabel={t("Resize sidebar")}
+            onResize={(delta) => {
+              // From the setting once there is one. Before that it is null and says
+              // nothing about a width set in the reader's own CSS, so the first
+              // drag starts from what is on screen. Not always from the screen:
+              // the width eases, and a second key press lands mid-transition,
+              // where the measured width is still the old one.
+              const start = liveSidebarRef.current ?? useSettings.getState().settings.sidebarWidth ?? sidebarRef.current?.getBoundingClientRect().width ?? 256;
+              const max = Math.max(SIDEBAR_MIN, Math.min(SIDEBAR_MAX, window.innerWidth - 600));
+              const next = Math.round(Math.min(max, Math.max(SIDEBAR_MIN, start + delta)));
+              liveSidebarRef.current = next;
+              setLiveSidebarWidth(next);
+            }}
+            onEnd={() => {
+              const width = liveSidebarRef.current;
+              liveSidebarRef.current = null;
+              setLiveSidebarWidth(null);
+              if (width != null) update({ sidebarWidth: width });
+            }}
+            onReset={() => update({ sidebarWidth: null })}
+          />
+        )}
         {/*
           Scoped to the content, not the shell. If Chrome's translator breaks a
           message list, the top bar, the folder tree and any open composer are

web/src/views/mail/MailView.tsx

@@ -385,18 +385,24 @@ export function MailView({ mailboxId, threadId, search }: { mailboxId?: string;
   const layoutRef = useRef<HTMLDivElement>(null);
   const updateSettings = useSettings((s) => s.update);
   const [liveSize, setLiveSize] = useState<number | null>(null);
+  // Mirrors liveSize for the end of a key press, which follows the resize in
+  // the same tick -- before the state could have come back round.
+  const liveSizeRef = useRef<number | null>(null);
   const paneSize = liveSize ?? (settings.readingPane === "bottom" ? settings.listPaneHeight : settings.listPaneWidth);
   const onSplit = (delta: number) => {
     const el = layoutRef.current;
     const total = el ? (settings.readingPane === "bottom" ? el.clientHeight : el.clientWidth) : 1200;
     const min = settings.readingPane === "bottom" ? 160 : 320;
     const max = Math.max(min, total - (settings.readingPane === "bottom" ? 200 : 420));
-    setLiveSize((cur) => Math.min(max, Math.max(min, (cur ?? paneSize) + delta)));
+    const next = Math.min(max, Math.max(min, (liveSizeRef.current ?? paneSize) + delta));
+    liveSizeRef.current = next;
+    setLiveSize(next);
   };
   const onSplitEnd = () => {
-    if (liveSize == null) return;
-    updateSettings(settings.readingPane === "bottom" ? { listPaneHeight: liveSize } : { listPaneWidth: liveSize });
+    const size = liveSizeRef.current;
+    liveSizeRef.current = null;
     setLiveSize(null);
+    if (size != null) updateSettings(settings.readingPane === "bottom" ? { listPaneHeight: size } : { listPaneWidth: size });
   };
 
   return (
@@ -416,7 +422,7 @@ export function MailView({ mailboxId, threadId, search }: { mailboxId?: string;
         />
       )}
       {showList && showReading && settings.readingPane !== "off" && !narrow && (
-        <Splitter direction={settings.readingPane === "bottom" ? "horizontal" : "vertical"} onResize={onSplit} onEnd={onSplitEnd} onReset={() => updateSettings(settings.readingPane === "bottom" ? { listPaneHeight: 340 } : { listPaneWidth: 520 })} ariaLabel="Resize message list" />
+        <Splitter direction={settings.readingPane === "bottom" ? "horizontal" : "vertical"} onResize={onSplit} onEnd={onSplitEnd} onReset={() => updateSettings(settings.readingPane === "bottom" ? { listPaneHeight: 340 } : { listPaneWidth: 520 })} ariaLabel={translate("Resize message list")} />
       )}
       {showReading && (
         <div className="mail-reading-pane">