M2: set17.toml game constants + validating loader

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/tests/test_constants.py

@@ -0,0 +1,42 @@
+import pytest
+
+from tft.constants.loader import load_constants, validate
+
+
+@pytest.fixture
+def c():
+    return load_constants(17)
+
+
+def test_loads_and_validates(c):
+    assert c["set"] == 17
+
+
+def test_shop_odds_shape(c):
+    assert len(c["shop"]["odds"]) == c["xp"]["max_level"]
+    for row in c["shop"]["odds"]:
+        assert sum(row) == 100
+
+
+def test_xp_reaches_max_level(c):
+    assert len(c["xp"]["to_next"]) == c["xp"]["max_level"] - 1
+    assert all(x > 0 for x in c["xp"]["to_next"])
+
+
+def test_interest_and_streaks(c):
+    g = c["gold"]
+    assert g["interest_cap"] >= 1
+    streaks = g["streak_gold"]
+    assert streaks == sorted(streaks)
+    assert all(gold > 0 for _, gold in streaks)
+
+
+def test_missing_set_raises():
+    with pytest.raises(FileNotFoundError):
+        load_constants(99)
+
+
+def test_validation_catches_bad_odds(c):
+    c["shop"]["odds"][0] = [99, 0, 0, 0, 0]
+    with pytest.raises(ValueError, match="sum to 99"):
+        validate(c)