diff --git a/components/email/__tests__/composer-plugin-surfaces.test.tsx b/components/email/__tests__/composer-plugin-surfaces.test.tsx
index 05772d4f5..60f6691c9 100644
--- a/components/email/__tests__/composer-plugin-surfaces.test.tsx
+++ b/components/email/__tests__/composer-plugin-surfaces.test.tsx
@@ -466,6 +466,42 @@ describe('composer-sidebar and composer-sidebar-right', () => {
     expect(panel('right').dataset.composerSidebarMode).toBe('folded');
   });
 
+  it('hand the panels the composer id, the draft and the selection', () => {
+    stubWidth(1400);
+    offerSlots('p1', ['composer-sidebar-right']);
+    render(<EmailComposer initialData={DRAFT} onClose={vi.fn()} />);
+
+    const props = slotProps(screen.getByTestId('slot-composer-sidebar-right'));
+    expect(typeof props.composerId).toBe('string');
+    expect((props.draft as { subject: string }).subject).toBe('Lunch');
+    expect(props.selection).toEqual({ text: '', empty: true });
+  });
+
+  it('send the panels the selected text a moment after it changes', () => {
+    useSettingsStore.setState({ plainTextMode: true });
+    try {
+      stubWidth(1400);
+      offerSlots('p1', ['composer-sidebar-right']);
+      const { container } = render(<EmailComposer initialData={{ ...DRAFT, body: 'Hello there' }} onClose={vi.fn()} />);
+      vi.useFakeTimers();
+      const textarea = container.querySelector('textarea') as HTMLTextAreaElement;
+
+      textarea.focus();
+      textarea.setSelectionRange(0, 5);
+      act(() => { document.dispatchEvent(new Event('selectionchange')); });
+      expect(slotProps(screen.getByTestId('slot-composer-sidebar-right')).selection).toEqual({ text: '', empty: true });
+
+      act(() => { vi.advanceTimersByTime(200); });
+      expect(slotProps(screen.getByTestId('slot-composer-sidebar-right')).selection).toEqual({ text: 'Hello', empty: false });
+
+      textarea.setSelectionRange(2, 2);
+      act(() => { document.dispatchEvent(new Event('selectionchange')); vi.advanceTimersByTime(200); });
+      expect(slotProps(screen.getByTestId('slot-composer-sidebar-right')).selection).toEqual({ text: '', empty: true });
+    } finally {
+      useSettingsStore.setState({ plainTextMode: false });
+    }
+  });
+
   it('open a folded panel over the composer when there is no room beside it', () => {
     stubWidth(600);
     offerSlots('p1', ['composer-sidebar-right']);
diff --git a/components/email/composer-plugin-sidebars.tsx b/components/email/composer-plugin-sidebars.tsx
index c2fa7860a..46982930f 100644
--- a/components/email/composer-plugin-sidebars.tsx
+++ b/components/email/composer-plugin-sidebars.tsx
@@ -124,11 +124,14 @@ export function ComposerPluginSidebar({
   mode,
   onOpen,
   onClose,
+  extraProps,
 }: {
   side: ComposerSidebarSide;
   mode: ComposerSidebarMode | null;
   onOpen: () => void;
   onClose: () => void;
+  /** What the panel's plugins get: the composer id, the draft and the selection (see the slot catalogue). */
+  extraProps?: Record<string, unknown>;
 }) {
   const t = useTranslations("email_viewer");
   if (!mode) return null;
@@ -181,8 +184,8 @@ export function ComposerPluginSidebar({
       </div>
       <div className="flex-1 min-h-0 overflow-y-auto">
         {side === "left"
-          ? <PluginSlot name="composer-sidebar" className="flex flex-col" />
-          : <PluginSlot name="composer-sidebar-right" className="flex flex-col" />}
+          ? <PluginSlot name="composer-sidebar" className="flex flex-col" extraProps={extraProps} />
+          : <PluginSlot name="composer-sidebar-right" className="flex flex-col" extraProps={extraProps} />}
       </div>
     </div>
   );
diff --git a/components/email/email-composer.tsx b/components/email/email-composer.tsx
index c0daa416b..ddd33ec0d 100644
--- a/components/email/email-composer.tsx
+++ b/components/email/email-composer.tsx
@@ -390,6 +390,9 @@ const DRAFT_HOOK_TIMEOUT_MS = 5000;
 
 /** Longest text a plugin may insert into the message at once. */
 const MAX_PLUGIN_INSERT_LENGTH = 100_000;
+/** How long after the last caret move the selection goes to the plugin frames. */
+const PLUGIN_SELECTION_DELAY_MS = 150;
+const EMPTY_SELECTION = { text: '', empty: true } as const;
 
 export function EmailComposer({
   onSend,
@@ -2279,6 +2282,9 @@ export function EmailComposer({
   const pluginAttachmentSourceOffers = usePluginSlotOffers('composer-attachment-source');
   const hasAboveBodyOffers = usePluginSlotOffers('composer-above-body').length > 0;
   const hasBelowBodyOffers = usePluginSlotOffers('composer-below-body').length > 0;
+  const hasLeftSidebarOffers = usePluginSlotOffers('composer-sidebar').length > 0;
+  const hasRightSidebarOffers = usePluginSlotOffers('composer-sidebar-right').length > 0;
+  const hasSidebarOffers = hasLeftSidebarOffers || hasRightSidebarOffers;
   // Plugin entries make the Send and Attach buttons menus even where the app
   // itself has nothing else to put there.
   const hasSendMenuActions = usePluginActions('composer-send-menu').length > 0;
@@ -2619,7 +2625,7 @@ export function EmailComposer({
   // composer-above-body / composer-below-body get the draft when they appear
   // and then 2 seconds after the last change, like onDraftChange: a new prop
   // object on every keystroke would post the whole body into their iframes.
-  const wantsPluginDraft = hasAboveBodyOffers || hasBelowBodyOffers;
+  const wantsPluginDraft = hasAboveBodyOffers || hasBelowBodyOffers || hasSidebarOffers;
   const [pluginDraft, setPluginDraft] = useState<ReturnType<typeof draftSnapshot> | null>(null);
   const pluginDraftShownRef = useRef(false);
   useEffect(() => {
@@ -2737,9 +2743,58 @@ export function EmailComposer({
     return unregister;
   }, []);
 
+  // The selected text of the message, for the plugin frames around it and
+  // the panels beside it (an assistant works on what the user highlights).
+  // Read from the editor's own selection state, which stays put while the
+  // user clicks into a panel, and sent only when it changed, a moment after
+  // the last change: a prop object per caret move would flood the frames.
+  const wantsPluginSelection = wantsPluginDraft;
+  const [pluginSelection, setPluginSelection] = useState<{ text: string; empty: boolean }>(EMPTY_SELECTION);
+  const [pluginEditor, setPluginEditor] = useState<Editor | null>(null);
+  useEffect(() => {
+    if (!wantsPluginSelection) return;
+    let timer: ReturnType<typeof setTimeout> | null = null;
+    const publish = () => {
+      timer = null;
+      let next: { text: string; empty: boolean } = EMPTY_SELECTION;
+      if (plainTextModeRef.current) {
+        const textarea = bodyRef.current;
+        if (textarea) {
+          const text = textarea.value.slice(textarea.selectionStart ?? 0, textarea.selectionEnd ?? 0);
+          next = text ? { text, empty: false } : EMPTY_SELECTION;
+        }
+      } else if (pluginEditor) {
+        const { text, empty } = readEditorSelection(pluginEditor);
+        next = empty ? EMPTY_SELECTION : { text, empty: false };
+      }
+      setPluginSelection((prev) => (prev.empty === next.empty && prev.text === next.text ? prev : next));
+    };
+    const schedule = () => {
+      if (timer) clearTimeout(timer);
+      timer = setTimeout(publish, PLUGIN_SELECTION_DELAY_MS);
+    };
+    // The textarea has no selection event of its own that covers the
+    // keyboard; the document's selectionchange fires for it.
+    const onDocumentSelection = () => {
+      if (plainTextModeRef.current && document.activeElement === bodyRef.current) schedule();
+    };
+    document.addEventListener('selectionchange', onDocumentSelection);
+    pluginEditor?.on('selectionUpdate', schedule);
+    publish();
+    return () => {
+      if (timer) clearTimeout(timer);
+      document.removeEventListener('selectionchange', onDocumentSelection);
+      pluginEditor?.off('selectionUpdate', schedule);
+    };
+  }, [wantsPluginSelection, pluginEditor, plainTextMode]);
+
   const pluginDraftProps = useMemo(
-    () => ({ draft: pluginDraft, insertText: pluginInsertText, getSelectedText: pluginSelectedText, composerId: pluginComposerId }),
-    [pluginDraft, pluginInsertText, pluginSelectedText, pluginComposerId],
+    () => ({ draft: pluginDraft, selection: pluginSelection, insertText: pluginInsertText, getSelectedText: pluginSelectedText, composerId: pluginComposerId }),
+    [pluginDraft, pluginSelection, pluginInsertText, pluginSelectedText, pluginComposerId],
+  );
+  const pluginSidebarProps = useMemo(
+    () => ({ draft: pluginDraft, selection: pluginSelection, composerId: pluginComposerId }),
+    [pluginDraft, pluginSelection, pluginComposerId],
   );
   const pluginToolbarProps = useMemo(
     () => ({ insertText: pluginInsertText, getSelectedText: pluginSelectedText, composerId: pluginComposerId }),
@@ -3519,7 +3574,7 @@ export function EmailComposer({
       className={cn("flex h-full bg-background relative", className)}
       onKeyDownCapture={handleComposerKeyDown}
     >
-      <ComposerPluginSidebar side="left" mode={pluginSidebars.modes.left} onOpen={() => pluginSidebars.open('left')} onClose={() => pluginSidebars.close('left')} />
+      <ComposerPluginSidebar side="left" mode={pluginSidebars.modes.left} onOpen={() => pluginSidebars.open('left')} onClose={() => pluginSidebars.close('left')} extraProps={pluginSidebarProps} />
       {/* Right-side composer sidebar slot is rendered after the main content div below. */}
     <div
       className="flex flex-col h-full bg-background relative flex-1 min-w-0"
@@ -4064,6 +4119,7 @@ export function EmailComposer({
               toolbarPlacement={mvWindow ? (mvShowFormatting ? 'bottom' : 'hidden') : 'top'}
               onEditorReady={(ed) => {
                 editorRef.current = ed;
+                setPluginEditor(ed);
                 if (!replyFocusedRef.current && (mode === 'reply' || mode === 'replyAll')) {
                   replyFocusedRef.current = true;
                   ed.commands.focus('start');
@@ -4670,7 +4726,7 @@ export function EmailComposer({
         />
       )}
     </div>
-      <ComposerPluginSidebar side="right" mode={pluginSidebars.modes.right} onOpen={() => pluginSidebars.open('right')} onClose={() => pluginSidebars.close('right')} />
+      <ComposerPluginSidebar side="right" mode={pluginSidebars.modes.right} onOpen={() => pluginSidebars.open('right')} onClose={() => pluginSidebars.close('right')} extraProps={pluginSidebarProps} />
     </div>
   );
 }
diff --git a/lib/plugin-slot-catalog.ts b/lib/plugin-slot-catalog.ts
index e0b9354b4..455202c0f 100644
--- a/lib/plugin-slot-catalog.ts
+++ b/lib/plugin-slot-catalog.ts
@@ -77,10 +77,10 @@ export const SLOT_CATALOG = {
 
   // ─── Composer ──────────────────────────────────────────────
   'composer-toolbar': S('composer', 'frame', ['ui:composer-toolbar'], { insertText: 'compose:open', getSelectedText: 'email:send', composerId: null }, 'the composer\'s plugin row above its bottom bar, for controls that need their own UI (a button belongs in composer-toolbar-actions)', true),
-  'composer-above-body': S('composer', 'frame', ['ui:composer-toolbar', 'ui:composer-sidebar'], { draft: 'email:send', insertText: 'compose:open', getSelectedText: 'email:send', composerId: null }, 'between the subject and the message text'),
-  'composer-below-body': S('composer', 'frame', ['ui:composer-toolbar', 'ui:composer-sidebar'], { draft: 'email:send', insertText: 'compose:open', getSelectedText: 'email:send', composerId: null }, 'below the message text, above the attachments'),
-  'composer-sidebar': S('composer', 'frame', ['ui:composer-sidebar'], {}, 'a panel left of the composer'),
-  'composer-sidebar-right': S('composer', 'frame', ['ui:composer-sidebar'], {}, 'a panel right of the composer'),
+  'composer-above-body': S('composer', 'frame', ['ui:composer-toolbar', 'ui:composer-sidebar'], { draft: 'email:send', selection: 'compose:read', insertText: 'compose:open', getSelectedText: 'email:send', composerId: null }, 'between the subject and the message text'),
+  'composer-below-body': S('composer', 'frame', ['ui:composer-toolbar', 'ui:composer-sidebar'], { draft: 'email:send', selection: 'compose:read', insertText: 'compose:open', getSelectedText: 'email:send', composerId: null }, 'below the message text, above the attachments'),
+  'composer-sidebar': S('composer', 'frame', ['ui:composer-sidebar'], { draft: 'email:send', selection: 'compose:read', composerId: null }, 'a panel left of the composer; `selection` is the selected text of the message as the user changes it ({ text, empty })'),
+  'composer-sidebar-right': S('composer', 'frame', ['ui:composer-sidebar'], { draft: 'email:send', selection: 'compose:read', composerId: null }, 'a panel right of the composer, with the same props as composer-sidebar'),
   'composer-attachment-source': S('composer', 'frame', ['ui:composer-toolbar', 'ui:composer-sidebar'], { onAttach: null, insertText: 'compose:open', composerId: null }, 'the composer\'s plugin row, next to composer-toolbar, as a source of files (older plugins; an entry in the Attach menu, composer-attach-menu, with api.composer.attach looks like the app\'s own)', true),
   'composer-send-menu': S('composer', 'action', ['ui:composer-toolbar'], { draft: 'email:send', composerId: null }, 'entries in the menu next to Send'),
   'composer-attach-menu': S('composer', 'action', ['ui:composer-toolbar'], { composerId: null }, 'entries in the Attach menu (for example "From Nextcloud"); the click\'s composerId lets api.composer.attach add files'),