fix(runner): aggregation creates per-id accumulators on demand so summoned creature ids in result.stats no longer KeyError run_encounter (totals were seeded from the deployed roster only); duplicate summons of one creature id share a stats slot - noted as a limitation, pinned by a summon-encounter report test

src/pf1e_simulator/runner.py

@@ -190,11 +190,16 @@ def run_encounter(
     states = build_states(spec)
     if spell_registry is None:
         spell_registry = load_spell_registry(SPELLS_DIR)
-    ids = [s.combatant.id for s in states]
     wins = {side.name: 0 for side in spec.sides}
     draws = 0
     total_rounds = 0
-    totals = {cid: CombatantStats() for cid in ids}
+    # Accumulate whatever ids the engine reports: summoned creatures act in the
+    # battle and appear in result.stats, so seeding from the initial states
+    # only would KeyError on them. Ids seen for the first time get a fresh
+    # accumulator. Known limitation: two summons of the same creature id share
+    # one engine stats slot (the engine keys _LiveStats by id), so their
+    # attrition is merged, not split.
+    totals: dict[str, CombatantStats] = {}
     transcript: tuple[str, ...] | None = None
     for index in range(runs):
         if index > 0:
@@ -217,7 +222,10 @@ def run_encounter(
             wins[result.winner] = wins.get(result.winner, 0) + 1
         total_rounds += result.rounds
         for cid, stats in result.stats.items():
-            current = totals[cid]
+            current = totals.get(cid)
+            if current is None:
+                totals[cid] = stats
+                continue
             totals[cid] = CombatantStats(
                 hits=current.hits + stats.hits,
                 crits=current.crits + stats.crits,