Never repeat an exercise within a mission; remove near-duplicate sentences (0.5.5)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/data/test_exercise_picker.gd

@@ -31,3 +31,25 @@ func test_returns_the_only_candidate_even_if_excluded() -> void:
     var candidates: Array[Dictionary] = [{"id": "a"}]
     var picked: Dictionary = ExercisePicker.pick(candidates, "a", rng)
     assert_eq(picked["id"], "a")
+
+
+func test_pick_unseen_never_repeats_while_others_remain() -> void:
+    var rng := RandomNumberGenerator.new()
+    rng.seed = 3
+    var candidates: Array[Dictionary] = [{"id": "a"}, {"id": "b"}, {"id": "c"}]
+    var seen: Array[String] = []
+    for _i in range(3):
+        var picked: Dictionary = ExercisePicker.pick_unseen(candidates, candidates, seen, rng)
+        assert_false(seen.has(picked["id"]), "un exercice deja vu a ete redonne")
+        seen.append(picked["id"])
+    assert_eq(seen.size(), 3)
+
+
+func test_pick_unseen_falls_back_to_other_difficulty_then_to_repeat() -> void:
+    var rng := RandomNumberGenerator.new()
+    var preferred: Array[Dictionary] = [{"id": "a"}]
+    var all: Array[Dictionary] = [{"id": "a"}, {"id": "b"}]
+    var picked: Dictionary = ExercisePicker.pick_unseen(preferred, all, ["a"], rng)
+    assert_eq(picked["id"], "b")
+    var again: Dictionary = ExercisePicker.pick_unseen(preferred, all, ["a", "b"], rng)
+    assert_true(["a", "b"].has(again["id"]))