Filter out volunteers with approved time off from shift edit picker

The edit form now fetches approved time-off requests and excludes
volunteers whose time off overlaps the shift date from the
selectable list. Unavailable volunteers are shown below the picker
in a "On approved time off" note.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/pages/Schedules.test.tsx

@@ -10,6 +10,7 @@ jest.mock('../api', () => ({
     listShifts: jest.fn(),
     listShiftTemplates: jest.fn(),
     listVolunteers: jest.fn(),
+    listTimeOff: jest.fn(),
     generateShifts: jest.fn(),
     publishShifts: jest.fn(),
     unpublishShifts: jest.fn(),
@@ -146,6 +147,7 @@ describe('Schedules (admin shifts view)', () => {
       { id: 5, name: 'Alice', active: true, operational_roles: 'Dog Shelter Volunteer', is_trainee: false },
       { id: 6, name: 'Bob', active: true, operational_roles: 'Behaviour Team', is_trainee: false },
     ]);
+    (api.listTimeOff as jest.Mock).mockResolvedValue([]);
     renderAt('/schedules');
     await waitFor(() => expect(screen.getByText('Edit')).toBeInTheDocument());
     fireEvent.click(screen.getByText('Edit'));
@@ -154,6 +156,25 @@ describe('Schedules (admin shifts view)', () => {
     expect(screen.getByText(/Edit Shift/)).toBeInTheDocument();
   });
 
+  it('hides volunteers with approved time off on the shift date', async () => {
+    (api.listVolunteers as jest.Mock).mockResolvedValue([
+      { id: 5, name: 'Alice', active: true, operational_roles: 'Dog Shelter Volunteer', is_trainee: false },
+      { id: 6, name: 'Bob', active: true, operational_roles: 'Behaviour Team', is_trainee: false },
+    ]);
+    (api.listTimeOff as jest.Mock).mockResolvedValue([
+      { id: 1, volunteer_id: 6, starts_at: '2026-04-06T00:00:00Z', ends_at: '2026-04-07T00:00:00Z', status: 'approved' },
+    ]);
+    renderAt('/schedules');
+    await waitFor(() => expect(screen.getByText('Edit')).toBeInTheDocument());
+    fireEvent.click(screen.getByText('Edit'));
+    await waitFor(() => expect(screen.getByText('Alice')).toBeInTheDocument());
+    // Bob should not appear as a selectable volunteer
+    expect(screen.queryByLabelText('Bob')).not.toBeInTheDocument();
+    // But should be listed as on time off
+    expect(screen.getByText(/On approved time off/)).toBeInTheDocument();
+    expect(screen.getByText(/Bob/)).toBeInTheDocument();
+  });
+
   it('reads year and month from search params', async () => {
     renderAt('/schedules?year=2025&month=12');
     await waitFor(() => expect(api.listShifts).toHaveBeenCalledWith(2025, 12));

web/src/pages/Schedules.tsx

@@ -5,6 +5,7 @@ import {
   ShiftTemplate,
   ShiftInstance,
   Volunteer,
+  TimeOffRequest,
   CreateShiftTemplateInput,
   TemplateRole,
   OPERATIONAL_ROLES,
@@ -157,6 +158,7 @@ interface ShiftEditFormProps {
 function ShiftEditForm({ instance, templateId, onSave, onCancel }: ShiftEditFormProps) {
   const [volunteers, setVolunteers] = useState<Volunteer[]>([]);
   const [templateRoles, setTemplateRoles] = useState<TemplateRole[]>([]);
+  const [unavailableIds, setUnavailableIds] = useState<Set<number>>(new Set());
   const [selectedIds, setSelectedIds] = useState<Set<number>>(
     new Set(instance.volunteers.map(v => v.volunteer_id))
   );
@@ -169,6 +171,20 @@ function ShiftEditForm({ instance, templateId, onSave, onCancel }: ShiftEditForm
   useEffect(() => {
     const loads: Promise<void>[] = [
       api.listVolunteers().then((vols) => setVolunteers(vols as Volunteer[])),
+      api.listTimeOff().then((requests: TimeOffRequest[]) => {
+        const shiftDate = new Date(instance.date + 'T00:00:00');
+        const off = new Set<number>();
+        for (const r of requests) {
+          if (r.status !== 'approved') continue;
+          const start = new Date(r.starts_at);
+          const end = new Date(r.ends_at);
+          // Shift date falls within the approved time-off range
+          if (shiftDate >= new Date(start.toDateString()) && shiftDate <= new Date(end.toDateString())) {
+            off.add(r.volunteer_id);
+          }
+        }
+        setUnavailableIds(off);
+      }),
     ];
     if (templateId) {
       loads.push(
@@ -179,7 +195,7 @@ function ShiftEditForm({ instance, templateId, onSave, onCancel }: ShiftEditForm
       );
     }
     Promise.all(loads).finally(() => setLoading(false));
-  }, [templateId]);
+  }, [templateId, instance.date]);
 
   function toggleVolunteer(id: number) {
     setSelectedIds(prev => {
@@ -208,8 +224,9 @@ function ShiftEditForm({ instance, templateId, onSave, onCancel }: ShiftEditForm
     }
   }
 
-  // Group active volunteers by their operational roles for display
-  const activeVolunteers = volunteers.filter(v => v.active);
+  // Group active, available volunteers by their operational roles for display
+  const activeVolunteers = volunteers.filter(v => v.active && !unavailableIds.has(v.id));
+  const onTimeOff = volunteers.filter(v => v.active && unavailableIds.has(v.id));
 
   // Build a map of role → volunteers who hold that role
   const byRole = new Map<string, Volunteer[]>();
@@ -287,6 +304,13 @@ function ShiftEditForm({ instance, templateId, onSave, onCancel }: ShiftEditForm
         })}
       </fieldset>
 
+      {onTimeOff.length > 0 && (
+        <p style={{ marginTop: '0.5rem', color: '#999', fontSize: '0.9em' }}>
+          <strong>On approved time off:</strong>{' '}
+          {onTimeOff.map(v => v.name).join(', ')}
+        </p>
+      )}
+
       <div style={{ display: 'flex', gap: '1rem', marginTop: '0.5rem' }}>
         <label>
           Min Capacity