feat(combat): expose weapon reference in observation snapshot

tests/test_dice.py

@@ -6,7 +6,7 @@ from collections import Counter
 
 import pytest
 
-from pf1e_simulator.dice import DiceExpr, DiceParseError, parse_dice
+from pf1e_simulator.dice import DiceExpr, DiceParseError, dice_to_str, parse_dice
 from pf1e_simulator.rng import ScriptedRng
 
 # ── Parsing: accepted forms ──────────────────────────────────────────────────
@@ -194,3 +194,69 @@ class TestDiceExprFlat:
         rng = ScriptedRng([])
         expr = DiceExpr.flat(5)
         assert expr.roll(rng) == 5
+
+
+# ── dice_to_str: canonical string representation ────────────────────────────
+
+
+class TestDiceToStr:
+    """Given: a DiceExpr
+    When: dice_to_str is called
+    Then: returns the canonical string inverse of parse_dice."""
+
+    def test_2d6_plus_3(self) -> None:
+        assert dice_to_str(DiceExpr(count=2, sides=6, bonus=3)) == "2d6+3"
+
+    def test_1d4_no_bonus(self) -> None:
+        assert dice_to_str(DiceExpr(count=1, sides=4, bonus=0)) == "1d4"
+
+    def test_flat_positive(self) -> None:
+        assert dice_to_str(DiceExpr(count=0, sides=0, bonus=7)) == "7"
+
+    def test_flat_negative(self) -> None:
+        assert dice_to_str(DiceExpr(count=0, sides=0, bonus=-5)) == "-5"
+
+    def test_flat_zero(self) -> None:
+        assert dice_to_str(DiceExpr(count=0, sides=0, bonus=0)) == "0"
+
+    def test_negative_bonus(self) -> None:
+        assert dice_to_str(DiceExpr(count=2, sides=6, bonus=-1)) == "2d6-1"
+
+    def test_d20_no_bonus(self) -> None:
+        assert dice_to_str(DiceExpr(count=1, sides=20, bonus=0)) == "1d20"
+
+    def test_large_dice(self) -> None:
+        assert dice_to_str(DiceExpr(count=10, sides=100, bonus=50)) == "10d100+50"
+
+
+class TestDiceToStrRoundTrip:
+    """Given: a valid dice string
+    When: parse_dice → dice_to_str → parse_dice
+    Then: the final DiceExpr equals the first."""
+
+    @pytest.mark.parametrize(
+        "text",
+        [
+            "2d6+3",
+            "2d6-1",
+            "1d4",
+            "d20",
+            "7",
+            "-5",
+            "0",
+            "10d100+50",
+            "1d6",
+            "4d8-2",
+        ],
+    )
+    def test_round_trip_equivalence(self, text: str) -> None:
+        first = parse_dice(text)
+        serialized = dice_to_str(first)
+        second = parse_dice(serialized)
+        assert first == second
+
+    def test_round_trip_any_flat(self) -> None:
+        for n in (-100, -1, 0, 1, 42, 999):
+            expr = parse_dice(str(n))
+            assert dice_to_str(expr) == str(n)
+            assert parse_dice(dice_to_str(expr)) == expr