fix(ical): stabiliser la clé de déduplication des devoirs

tests/unit/test_ical.py

@@ -398,6 +398,36 @@ def test_collect_homeworks_keeps_distinct_subjects() -> None:
     assert {homework.subject for homework in homeworks} == {"Math", "Physique"}
 
 
+def test_collect_homeworks_deduplicates_teacher_order_variants() -> None:
+    """Deux ordres d'enseignants équivalents ne créent pas de doublon.
+
+    :return: None
+    """
+    homework_block = HomeworkBlock(
+        kind="due",
+        date=date(2026, 9, 10),
+        text="Devoir commun",
+        html="<p>Devoir commun</p>",
+    )
+    lesson = Lesson(
+        id="lesson1",
+        start=datetime(2026, 9, 10, 8, 0),
+        end=datetime(2026, 9, 10, 9, 0),
+        subject="Math",
+        teachers=("M. Martin", "M. Dupont"),
+        group=None,
+        content=None,
+        homework_blocks=(homework_block,),
+    )
+    other_lesson = lesson.model_copy(
+        update={"id": "lesson2", "teachers": ("M. Dupont", "M. Martin")}
+    )
+
+    homeworks = collect_homeworks([lesson, other_lesson], target_date=date(2026, 9, 10))
+
+    assert len(homeworks) == 1
+
+
 def test_parse_body_accepts_html_variants_and_sanitizes() -> None:
     """Les attributs HTML, les espaces et le contenu actif sont traités correctement.