fix(assignments): resolve op.student → res.users + student search

E2E QA surfaced a silent-drop bug in the exam-schedule endpoint: the
frontend's student picker sends `op.student.id` values (that's what
/api/students returns), but `encoach.exam.schedule.student_ids` is a
Many2many → res.users. The controller was writing the op.student id
straight through, so schedules linked to whichever res.users row
happened to share that integer id (OdooBot, other staff, etc.) — the
target student got 0 assignments and never saw the exam.

- exam_schedules.py: add `_resolve_student_user_ids` and use it in the
  create and update endpoints. Falls back to treating unmatched ids as
  direct res.users ids for back-office callers.
- AssignmentsPage.tsx: add a search input + larger list to the
  Individual Students picker; long lists were leaving Sarah unreachable
  inside the inner scroll container during QA.

Made-with: Cursor

src/pages/AssignmentsPage.tsx

@@ -114,6 +114,7 @@ export default function AssignmentsPage() {
   const [stateFilter, setStateFilter] = useState<ScheduleState | "all">("all");
   const [createOpen, setCreateOpen] = useState(false);
   const [form, setForm] = useState<FormState>(emptyForm());
+  const [studentQuery, setStudentQuery] = useState("");
   const { toast } = useToast();
   const qc = useQueryClient();
 
@@ -144,6 +145,14 @@ export default function AssignmentsPage() {
 
   const studentsQ = useStudents({ size: 200 });
   const students = studentsQ.data?.items ?? [];
+  const filteredStudents = useMemo(() => {
+    const q = studentQuery.trim().toLowerCase();
+    if (!q) return students;
+    return students.filter((s) =>
+      (s.name || "").toLowerCase().includes(q) ||
+      (s.email || "").toLowerCase().includes(q),
+    );
+  }, [students, studentQuery]);
 
   const stateCounts = useMemo(() => {
     const all = schedulesQ.data?.items ?? [];
@@ -468,9 +477,23 @@ export default function AssignmentsPage() {
               {/* Individual student selection */}
               {form.assign_mode === "individual" && (
                 <div className="space-y-1">
+                  <div className="flex items-center justify-between gap-2">
                     <Label className="text-xs">Select Students</Label>
-                  <div className="max-h-48 overflow-y-auto border rounded-md p-2 space-y-1">
+                    <span className="text-[11px] text-muted-foreground">
-                    {students.map((s) => (
+                      {form.student_ids.size} selected · {students.length} total
+                    </span>
+                  </div>
+                  {/* Search box — needed because QA reported long student lists
+                      made bottom entries unreachable inside the inner scroll
+                      container. Filtering keeps the list short and predictable. */}
+                  <Input
+                    placeholder="Search students by name or email…"
+                    value={studentQuery}
+                    onChange={(e) => setStudentQuery(e.target.value)}
+                    className="h-8 text-xs"
+                  />
+                  <div className="max-h-64 overflow-y-auto border rounded-md p-2 space-y-1">
+                    {filteredStudents.map((s) => (
                       <label key={s.id} className="flex items-center gap-2 text-sm cursor-pointer hover:bg-muted/50 rounded px-1 py-0.5">
                         <Checkbox
                           checked={form.student_ids.has(s.id)}
@@ -487,6 +510,11 @@ export default function AssignmentsPage() {
                         {s.email && <span className="text-xs text-muted-foreground ml-auto">{s.email}</span>}
                       </label>
                     ))}
+                    {filteredStudents.length === 0 && students.length > 0 && (
+                      <p className="text-xs text-muted-foreground italic text-center py-2">
+                        No students match “{studentQuery}”.
+                      </p>
+                    )}
                     {students.length === 0 && <p className="text-xs text-muted-foreground italic text-center py-2">No students available</p>}
                   </div>
                 </div>