diff --git a/.cursor/rules/appointments.mdc b/.cursor/rules/appointments.mdc
index 1a64402..ee9abdf 100644
--- a/.cursor/rules/appointments.mdc
+++ b/.cursor/rules/appointments.mdc
@@ -9,4 +9,6 @@ alwaysApply: false
 - List includes `hasTreatment` when a `Treatment` row is linked (`appointmentId`).
 - **Patient change** blocked while linked → `APPOINTMENT_PATIENT_LOCKED` (UI: `patientLockedHint`).
 - **Delete** blocked while linked → `APPOINTMENT_HAS_TREATMENT` (hide delete + `deleteBlockedHint`). Empty appointments (no treatment yet) remain deletable.
+- **Past days:** new bookings stay blocked. Existing appointments **without** treatment can be edited/deleted; with treatment → toast `infoEditBlockedHasTreatment` (no modal). Banner clicks are not gated by `canBook` (slots still are).
+- **Disabled feedback:** use `title` + click `toast.showInfo` with `common.readOnlyAccess` (same key as Staff/Patients) or the domain reason (`infoPastViewOnly`, `infoEditBlockedHasTreatment`).
 - Prisma: `Treatment.appointmentId` is `onDelete: SetNull` — deleting an appointment does **not** cascade-delete treatments/cases/tasks; do not rely on cascade for cleanup.
diff --git a/.cursor/skills/i18n-formatting/SKILL.md b/.cursor/skills/i18n-formatting/SKILL.md
index 086c398..59d169a 100644
--- a/.cursor/skills/i18n-formatting/SKILL.md
+++ b/.cursor/skills/i18n-formatting/SKILL.md
@@ -36,7 +36,7 @@ Use when adding or changing user-visible dates/times/numbers, RTL layout, or loc
 - `fa`: Jalali display `YYYY/MM/DD` (Persian digits), parse/mask in `persianCalendar.ts`
 - `en` / `nl`: Gregorian display `YYYY-MM-DD`, parse/mask in `dateInputFormat.ts`
 - Calendar icon at **`end-3`** (matches select chevron inset); text uses **`text-start`** (logical — right in RTL, left in LTR)
-- Popup: **`CalendarDayPartsPanel`** (shared with schedule picker)
+- Popup: **`CalendarDayPartsPanel`** (shared with schedule picker); positioned via `useAnchoredPanelPosition` (fixed + viewport clamp / flip) so RTL/LTR edge fields stay on-screen
 - **Do not** add native `<input type="date">` — one component for all locales
 
 **Select chevron**
diff --git a/AGENTS.md b/AGENTS.md
index 0f24565..0a39188 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -56,7 +56,7 @@ frontend/src/
 - **Unread semantics**: Treatment tab badge = count of unread cases **for the user's own treatment plans** (per-case read cursor) and clears when a case is opened/marked read (not on tab visit).
 - **Lab shipment progress + comments**: shown in **Lab dispatch panel** for the active shipment; expanding activity / opening comments marks that case read.
 
-**Appointments (quick ref):** Do not delete (or change patient) when `hasTreatment`; codes `APPOINTMENT_HAS_TREATMENT` / `APPOINTMENT_PATIENT_LOCKED`. Appointment delete does not cascade-delete treatments. See `.cursor/rules/appointments.mdc`.
+**Appointments (quick ref):** Do not delete (or change patient) when `hasTreatment`; codes `APPOINTMENT_HAS_TREATMENT` / `APPOINTMENT_PATIENT_LOCKED`. Past days: no new bookings; edit/delete OK without treatment; with treatment → toast. Appointment delete does not cascade-delete treatments. See `.cursor/rules/appointments.mdc`.
 
 **Lab Tasks tab:** Newest case first; steps ordered 1→N; case grouping when sorted by date; `stepCompleted` filter; prosthesis colors from catalog; task assignment in **Cases** (compact row: status + assignee + last update); on **Tasks**, all staff see every task but only assignee (or unassigned pool) can change status — others see “Assigned to {name}” instead of the status dropdown; **case due dates** set/edited in clinic Treatment lab dispatch, shown on lab Cases/Tasks with overdue filter + sort; **mobile:** larger task status controls, sticky case header when grouped; **tab badges:** `LabCaseActivity` + `GET /notifications/tab-counts` (lab Cases/Tasks split, clinic Treatment) — see `.cursor/skills/lab-tasks/SKILL.md` and `.cursor/skills/lab-notifications/SKILL.md`.
 
diff --git a/frontend/messages/en.json b/frontend/messages/en.json
index b57d8fc..b858ad8 100644
--- a/frontend/messages/en.json
+++ b/frontend/messages/en.json
@@ -573,6 +573,7 @@
     "subtitle": "Search a patient, pick a date, then click a time slot under a provider to book.",
     "loadingSchedule": "Loading schedule…",
     "infoPastViewOnly": "Past appointments are view-only.",
+    "infoEditBlockedHasTreatment": "This appointment cannot be edited because a treatment is linked to it.",
     "infoSelectPatient": "Select a patient before booking.",
     "errorOutsideHours": "This appointment falls outside the provider's current working hours and cannot be edited.",
     "successUpdated": "Appointment updated.",
diff --git a/frontend/messages/fa.json b/frontend/messages/fa.json
index ec8ad15..ef983fa 100644
--- a/frontend/messages/fa.json
+++ b/frontend/messages/fa.json
@@ -574,6 +574,7 @@
     "subtitle": "یک بیمار را جستجو کنید، تاریخ را انتخاب کنید، سپس روی یک زمان در زیر ارائه‌دهنده کلیک کنید تا رزرو کنید.",
     "loadingSchedule": "در حال بارگذاری برنامه...",
     "infoPastViewOnly": "نوبت‌های گذشته فقط قابل مشاهده هستند.",
+    "infoEditBlockedHasTreatment": "این نوبت قابل ویرایش نیست چون یک درمان به آن متصل است.",
     "infoSelectPatient": "قبل از رزرو، یک بیمار را انتخاب کنید.",
     "errorOutsideHours": "این نوبت خارج از ساعات کاری فعلی ارائه‌دهنده است و قابل ویرایش نیست.",
     "successUpdated": "نوبت به‌روزرسانی شد.",
diff --git a/frontend/messages/nl.json b/frontend/messages/nl.json
index b7f32f1..6f23238 100644
--- a/frontend/messages/nl.json
+++ b/frontend/messages/nl.json
@@ -573,6 +573,7 @@
     "subtitle": "Zoek een patiënt, kies een datum en klik vervolgens op een tijdslot onder een aanbieder om te boeken.",
     "loadingSchedule": "Rooster laden...",
     "infoPastViewOnly": "Afspraken uit het verleden zijn alleen-lezen.",
+    "infoEditBlockedHasTreatment": "Deze afspraak kan niet worden bewerkt omdat er een behandeling aan gekoppeld is.",
     "infoSelectPatient": "Selecteer een patiënt voor het boeken.",
     "errorOutsideHours": "Deze afspraak valt buiten de huidige werktijden van de aanbieder en kan niet worden bewerkt.",
     "successUpdated": "Afspraak bijgewerkt.",
diff --git a/frontend/src/components/ui/appointments/AppointmentBookingModal.tsx b/frontend/src/components/ui/appointments/AppointmentBookingModal.tsx
index b576174..9e2abb3 100644
--- a/frontend/src/components/ui/appointments/AppointmentBookingModal.tsx
+++ b/frontend/src/components/ui/appointments/AppointmentBookingModal.tsx
@@ -203,13 +203,16 @@ export function AppointmentBookingModal({
     }
 
     const now = new Date();
-    if (isSameLocalCalendarDay(scheduleDate, now) && startAt.getTime() < now.getTime()) {
+    if (
+      !editingAppointment &&
+      isSameLocalCalendarDay(scheduleDate, now) &&
+      startAt.getTime() < now.getTime()
+    ) {
       setError(t('errorPastSchedule'));
       return;
     }
 
-    const today = new Date();
-    if (compareLocalDayStart(scheduleDate, today) < 0) {
+    if (!editingAppointment && compareLocalDayStart(scheduleDate, now) < 0) {
       setError(t('errorPastViewOnly'));
       return;
     }
diff --git a/frontend/src/components/ui/appointments/AppointmentScheduleGrid.tsx b/frontend/src/components/ui/appointments/AppointmentScheduleGrid.tsx
index bbbae55..76a61a7 100644
--- a/frontend/src/components/ui/appointments/AppointmentScheduleGrid.tsx
+++ b/frontend/src/components/ui/appointments/AppointmentScheduleGrid.tsx
@@ -81,6 +81,10 @@ interface AppointmentScheduleGridProps {
   appointments: AppointmentRecord[];
   treatmentCatalog: TreatmentCatalogEntry[];
   canBook: boolean;
+  /** Same message used for title + click toast when booking is blocked. */
+  slotBlockReason?: string | null;
+  /** Same message used for title + click toast when editing an appointment is blocked. */
+  appointmentEditBlockReason?: (appointment: AppointmentRecord) => string | null;
   onSlotClick: (startMinute: number, providerUserId: string, providerName: string) => void;
   onAppointmentClick?: (appointment: AppointmentRecord) => void;
   onAppointmentOutsideHours?: (appointment: AppointmentRecord) => void;
@@ -92,6 +96,8 @@ export function AppointmentScheduleGrid({
   appointments,
   treatmentCatalog,
   canBook,
+  slotBlockReason = null,
+  appointmentEditBlockReason,
   onSlotClick,
   onAppointmentClick,
   onAppointmentOutsideHours,
@@ -161,9 +167,6 @@ export function AppointmentScheduleGrid({
       });
       return;
     }
-    if (!canBook) {
-      return;
-    }
     onAppointmentClick?.(apt);
   }
 
@@ -216,7 +219,7 @@ export function AppointmentScheduleGrid({
                 return (
                   <div
                     key={hour}
-                    className="absolute left-0 right-0 text-[11px] text-text-muted flex items-start justify-end pr-1.5 pt-0.5 border-b border-border/50"
+                    className="absolute inset-x-0 text-[11px] text-text-muted flex items-center justify-center px-0.5 border-b border-border/50"
                     style={{ top, height }}
                   >
                     {formatMinuteLabel(hour * 60, locale)}
@@ -247,13 +250,15 @@ export function AppointmentScheduleGrid({
                           SCHEDULE_SLOT_MINUTES,
                           p.dayBlocks,
                         );
-                      const slotDisabled = !canBook || columnFullyDisabled || !slotActive;
+                      const structuralDisabled = columnFullyDisabled || !slotActive;
+                      const bookingBlocked = Boolean(slotBlockReason) || !canBook;
+                      const slotLooksDisabled = structuralDisabled || bookingBlocked;
 
                       return (
                         <button
                           key={`${p.userId}-${slotStartMinute}`}
                           type="button"
-                          disabled={slotDisabled}
+                          disabled={structuralDisabled}
                           title={
                             columnFullyDisabled
                               ? p.hasWorkingHours
@@ -261,14 +266,16 @@ export function AppointmentScheduleGrid({
                                 : t('slotHoursNotConfigured')
                               : !slotActive
                                 ? t('slotOutsideHours')
-                                : slotDisabled
-                                  ? t('slotCannotCreate')
-                                  : t('slotBookAt', {
-                                      time: formatMinuteLabel(slotStartMinute, locale),
-                                    })
+                                : slotBlockReason
+                                  ? slotBlockReason
+                                  : bookingBlocked
+                                    ? t('slotCannotCreate')
+                                    : t('slotBookAt', {
+                                        time: formatMinuteLabel(slotStartMinute, locale),
+                                      })
                           }
                           className={`absolute left-0 right-0 border-b border-border/50 transition-colors ${
-                            slotDisabled
+                            slotLooksDisabled
                               ? 'cursor-not-allowed bg-background-secondary/35 opacity-60'
                               : 'hover:bg-primary/8 cursor-pointer'
                           }`}
@@ -302,8 +309,10 @@ export function AppointmentScheduleGrid({
                           p.dayBlocks,
                         );
                       const patientName = `${apt.patient.firstName} ${apt.patient.lastName}`;
+                      const editBlockReason = appointmentEditBlockReason?.(apt) ?? null;
                       const bannerTitle = [
                         patientName,
+                        editBlockReason,
                         outsideHours ? t('outsideHoursBlocked') : null,
                         clusterSize > 1
                           ? t('overlappingChoose', { count: clusterSize })
@@ -328,7 +337,11 @@ export function AppointmentScheduleGrid({
                             )
                           }
                           className={`absolute min-h-0 overflow-hidden rounded-[var(--radius-sm)] border pointer-events-auto z-10 flex text-center focus:outline-none focus-visible:ring-2 focus-visible:ring-primary/35 ${
-                            outsideHours ? 'opacity-70 ring-1 ring-amber-500/60' : ''
+                            outsideHours || editBlockReason
+                              ? 'opacity-70'
+                              : ''
+                          } ${
+                            outsideHours ? 'ring-1 ring-amber-500/60' : ''
                           } ${
                             isUnderOneHour
                               ? 'items-center justify-center px-0.5 py-0'
@@ -377,10 +390,6 @@ export function AppointmentScheduleGrid({
           treatmentCatalog={treatmentCatalog}
           anchorRect={overlapPopover.anchorRect}
           onSelect={(apt) => {
-            if (!canBook) {
-              setOverlapPopover(null);
-              return;
-            }
             const provider = providers.find((p) => p.userId === apt.providerUserId);
             if (
               provider &&
diff --git a/frontend/src/components/ui/appointments/AppointmentsPage.tsx b/frontend/src/components/ui/appointments/AppointmentsPage.tsx
index dffcbd9..f5c69cd 100644
--- a/frontend/src/components/ui/appointments/AppointmentsPage.tsx
+++ b/frontend/src/components/ui/appointments/AppointmentsPage.tsx
@@ -25,6 +25,7 @@ import { compareLocalDayStart, getLocalDayIsoRange, startOfLocalDay } from '@/co
 export function AppointmentsPage() {
   const t = useTranslations('appointments');
   const tErrors = useTranslations('errors');
+  const tCommon = useTranslations('common');
   const router = useRouter();
   const { currentOrganization } = useAuth();
   const [scheduleDate, setScheduleDate] = useState(() => startOfLocalDay(new Date()));
@@ -117,8 +118,19 @@ export function AppointmentsPage() {
       .catch(() => {});
   }, []);
 
+  function appointmentEditBlockReason(appointment: AppointmentRecord): string | null {
+    if (!canManageAppointments) {
+      return tCommon('readOnlyAccess');
+    }
+    if (isViewingPastDay && appointment.hasTreatment) {
+      return t('infoEditBlockedHasTreatment');
+    }
+    return null;
+  }
+
   function handleSlotClick(startMinute: number, providerUserId: string, providerName: string) {
     if (!canManageAppointments) {
+      toast.showInfo(tCommon('readOnlyAccess'));
       return;
     }
     if (isViewingPastDay) {
@@ -133,11 +145,9 @@ export function AppointmentsPage() {
   }
 
   function handleAppointmentClick(appointment: AppointmentRecord) {
-    if (!canManageAppointments) {
-      return;
-    }
-    if (isViewingPastDay) {
-      toast.showInfo(t('infoPastViewOnly'));
+    const blockReason = appointmentEditBlockReason(appointment);
+    if (blockReason) {
+      toast.showInfo(blockReason);
       return;
     }
     const provider = providers.find((p) => p.userId === appointment.providerUserId);
@@ -254,6 +264,14 @@ export function AppointmentsPage() {
             appointments={appointments}
             treatmentCatalog={treatmentCatalog}
             canBook={canManageAppointments && !isViewingPastDay}
+            appointmentEditBlockReason={appointmentEditBlockReason}
+            slotBlockReason={
+              !canManageAppointments
+                ? tCommon('readOnlyAccess')
+                : isViewingPastDay
+                  ? t('infoPastViewOnly')
+                  : null
+            }
             onSlotClick={(startMinute, uid, name) => handleSlotClick(startMinute, uid, name)}
             onAppointmentClick={(apt) => handleAppointmentClick(apt)}
             onAppointmentOutsideHours={(apt) => handleAppointmentOutsideHours(apt)}
@@ -281,7 +299,6 @@ export function AppointmentsPage() {
         loading={savingAppointment}
         canDelete={
           canManageAppointments &&
-          !isViewingPastDay &&
           !!activeEditingAppointment &&
           !activeEditingAppointment.hasTreatment
         }
diff --git a/frontend/src/components/ui/shared/AppDateInput.tsx b/frontend/src/components/ui/shared/AppDateInput.tsx
index 1433f23..617530a 100644
--- a/frontend/src/components/ui/shared/AppDateInput.tsx
+++ b/frontend/src/components/ui/shared/AppDateInput.tsx
@@ -6,6 +6,7 @@ import { CalendarDays } from 'lucide-react';
 import { parseDateInput, startOfLocalDay, toDateInputValue } from '@/components/appointments/appointmentTime';
 import { FORM_DATE_INPUT_CLASS } from '@/components/shared/formSelectStyles';
 import { CalendarDayPartsPanel } from '@/components/ui/shared/CalendarDayPartsPanel';
+import { useAnchoredPanelPosition } from '@/lib/hooks/useAnchoredPanelPosition';
 import {
   formatIsoAsGregorianDateInput,
   maskGregorianDateTyping,
@@ -45,6 +46,11 @@ export function AppDateInput({
   const rootRef = useRef<HTMLDivElement>(null);
   const [text, setText] = useState('');
   const [panelOpen, setPanelOpen] = useState(false);
+  const { panelRef, style: panelStyle } = useAnchoredPanelPosition({
+    open: panelOpen && !disabled,
+    anchorRef: rootRef,
+    align: 'start',
+  });
 
   useEffect(() => {
     setText(
@@ -56,9 +62,11 @@ export function AppDateInput({
     if (!panelOpen) return;
 
     function onPointerDown(event: MouseEvent) {
-      if (!rootRef.current?.contains(event.target as Node)) {
-        setPanelOpen(false);
+      const target = event.target as Node;
+      if (rootRef.current?.contains(target) || panelRef.current?.contains(target)) {
+        return;
       }
+      setPanelOpen(false);
     }
 
     function onKeyDown(event: KeyboardEvent) {
@@ -73,7 +81,7 @@ export function AppDateInput({
       document.removeEventListener('mousedown', onPointerDown);
       document.removeEventListener('keydown', onKeyDown);
     };
-  }, [panelOpen]);
+  }, [panelOpen, panelRef]);
 
   const panelAnchorDate = value ? parseDateInput(value) : startOfLocalDay(new Date());
   const placeholder = persian ? '۱۴۰۴/۰۴/۲۲' : '2026-07-13';
@@ -154,9 +162,19 @@ export function AppDateInput({
 
       {panelOpen && !disabled ? (
         <div
+          ref={panelRef}
           id={`${panelId}-parts`}
           role="dialog"
-          className="absolute start-0 top-full z-50 mt-1 min-w-[17.5rem] w-max max-w-[calc(100vw-1.5rem)] rounded-[var(--radius-md)] border border-border bg-background-secondary p-3 shadow-lg"
+          style={
+            panelStyle ?? {
+              position: 'fixed',
+              top: 0,
+              left: 0,
+              visibility: 'hidden',
+              pointerEvents: 'none',
+            }
+          }
+          className="min-w-[17.5rem] rounded-[var(--radius-md)] border border-border bg-background-secondary p-3 shadow-lg"
         >
           <CalendarDayPartsPanel
             panelId={panelId}
diff --git a/frontend/src/components/ui/shared/CalendarDaySelect.tsx b/frontend/src/components/ui/shared/CalendarDaySelect.tsx
index 5a14db3..d23a74e 100644
--- a/frontend/src/components/ui/shared/CalendarDaySelect.tsx
+++ b/frontend/src/components/ui/shared/CalendarDaySelect.tsx
@@ -8,6 +8,7 @@ import { formatAppPickerDateLabel } from '@/lib/i18n/format';
 import { CalendarDayPartsPanel } from '@/components/ui/shared/CalendarDayPartsPanel';
 import { addCalendarDays, compareLocalDayStart, startOfLocalDay } from '@/components/appointments/appointmentTime';
 import { Checkbox } from '@/components/ui/shared/Checkbox';
+import { useAnchoredPanelPosition } from '@/lib/hooks/useAnchoredPanelPosition';
 
 export type CalendarDaySelectProps = {
   value: Date;
@@ -50,6 +51,11 @@ export function CalendarDaySelect({
   const panelId = useId();
   const rootRef = useRef<HTMLDivElement>(null);
   const [panelOpen, setPanelOpen] = useState(false);
+  const { panelRef, style: panelStyle } = useAnchoredPanelPosition({
+    open: panelOpen && !disabled,
+    anchorRef: rootRef,
+    align: 'stretch',
+  });
 
   const normalizedValue = startOfLocalDay(value);
   const today = startOfLocalDay(new Date());
@@ -63,10 +69,12 @@ export function CalendarDaySelect({
     if (!panelOpen) return;
 
     function onPointerDown(event: MouseEvent) {
-      if (!rootRef.current?.contains(event.target as Node)) {
-        setPanelOpen(false);
-        onBlur?.();
+      const target = event.target as Node;
+      if (rootRef.current?.contains(target) || panelRef.current?.contains(target)) {
+        return;
       }
+      setPanelOpen(false);
+      onBlur?.();
     }
 
     function onKeyDown(event: KeyboardEvent) {
@@ -82,7 +90,7 @@ export function CalendarDaySelect({
       document.removeEventListener('mousedown', onPointerDown);
       document.removeEventListener('keydown', onKeyDown);
     };
-  }, [onBlur, panelOpen]);
+  }, [onBlur, panelOpen, panelRef]);
 
   const triggerButton = (
     <button
@@ -166,17 +174,27 @@ export function CalendarDaySelect({
 
       {panelOpen && !disabled ? (
         <div
+          ref={panelRef}
           id={panelId}
           role="dialog"
           aria-label={t('chooseDate')}
-          className="absolute left-0 right-0 top-full z-50 mt-2 rounded-[var(--radius-md)] border border-border bg-background-secondary p-3 shadow-lg"
+          style={
+            panelStyle ?? {
+              position: 'fixed',
+              top: 0,
+              left: 0,
+              visibility: 'hidden',
+              pointerEvents: 'none',
+            }
+          }
+          className="rounded-[var(--radius-md)] border border-border bg-background-secondary p-3 shadow-lg"
         >
           <CalendarDayPartsPanel
             panelId={panelId}
             value={normalizedValue}
             onChange={onChange}
             closePanelOnDaySelect={closePanelOnDaySelect}
-            onAfterSelect={(day) => {
+            onAfterSelect={() => {
               setPanelOpen(false);
               onBlur?.();
             }}
diff --git a/frontend/src/lib/hooks/useAnchoredPanelPosition.ts b/frontend/src/lib/hooks/useAnchoredPanelPosition.ts
new file mode 100644
index 0000000..b30f9ed
--- /dev/null
+++ b/frontend/src/lib/hooks/useAnchoredPanelPosition.ts
@@ -0,0 +1,96 @@
+'use client';
+
+import { useLayoutEffect, useRef, useState, type CSSProperties, type RefObject } from 'react';
+
+const VIEWPORT_PADDING = 12;
+const DEFAULT_GAP = 8;
+
+export type AnchoredPanelAlign = 'start' | 'stretch';
+
+type UseAnchoredPanelPositionArgs = {
+  open: boolean;
+  /** Element the panel should attach to (field / trigger shell). */
+  anchorRef: RefObject<HTMLElement | null>;
+  /** Prefer aligning the panel's inline-start with the anchor's inline-start. */
+  align?: AnchoredPanelAlign;
+  gap?: number;
+};
+
+/**
+ * Positions a panel with `position: fixed`, clamped to the viewport.
+ * Flips above the anchor when there is not enough room below.
+ * Handles LTR/RTL via `document.documentElement.dir`.
+ */
+export function useAnchoredPanelPosition({
+  open,
+  anchorRef,
+  align = 'start',
+  gap = DEFAULT_GAP,
+}: UseAnchoredPanelPositionArgs) {
+  const panelRef = useRef<HTMLDivElement>(null);
+  const [style, setStyle] = useState<CSSProperties | undefined>(undefined);
+
+  useLayoutEffect(() => {
+    if (!open) {
+      setStyle(undefined);
+      return;
+    }
+
+    function update() {
+      const anchor = anchorRef.current;
+      const panel = panelRef.current;
+      if (!anchor || !panel) return;
+
+      const anchorRect = anchor.getBoundingClientRect();
+      const panelRect = panel.getBoundingClientRect();
+      const vw = window.innerWidth;
+      const vh = window.innerHeight;
+      const isRtl = document.documentElement.dir === 'rtl';
+
+      let width =
+        align === 'stretch'
+          ? Math.min(anchorRect.width, vw - VIEWPORT_PADDING * 2)
+          : Math.min(panelRect.width || panel.offsetWidth, vw - VIEWPORT_PADDING * 2);
+
+      if (width < 1) width = Math.min(280, vw - VIEWPORT_PADDING * 2);
+
+      let left: number;
+      if (align === 'stretch') {
+        left = anchorRect.left;
+      } else if (isRtl) {
+        left = anchorRect.right - width;
+      } else {
+        left = anchorRect.left;
+      }
+      left = Math.max(VIEWPORT_PADDING, Math.min(left, vw - width - VIEWPORT_PADDING));
+
+      const height = panelRect.height || panel.offsetHeight;
+      let top = anchorRect.bottom + gap;
+      if (top + height > vh - VIEWPORT_PADDING) {
+        const above = anchorRect.top - height - gap;
+        top = above >= VIEWPORT_PADDING ? above : Math.max(VIEWPORT_PADDING, vh - height - VIEWPORT_PADDING);
+      }
+
+      setStyle({
+        position: 'fixed',
+        top,
+        left,
+        width,
+        zIndex: 50,
+      });
+    }
+
+    update();
+    // Second pass after fonts/layout settle panel size.
+    const raf = window.requestAnimationFrame(update);
+    window.addEventListener('resize', update);
+    window.addEventListener('scroll', update, true);
+    return () => {
+      window.cancelAnimationFrame(raf);
+      window.removeEventListener('resize', update);
+      window.removeEventListener('scroll', update, true);
+    };
+  }, [align, anchorRef, gap, open]);
+
+  return { panelRef, style };
+}