Add combat facts layer with tests

Pure computation: lethal damage lines, block values, threat model,
deck counts, affordability. Jev never does arithmetic; facts.py
computes the numbers and passes conclusions in.

test_facts.py

@@ -0,0 +1,178 @@
+#!/usr/bin/env python3
+"""
+test_facts.py -- regression tests for the fact layer.
+
+The first case is the exact scenario where jev-1.13.0 failed: it answered
+"is lethal available?" as 0.79 YES when the true answer was NO. facts.py
+must get this right, because Jev is never allowed to do this arithmetic.
+
+Run: python3 test_facts.py
+"""
+
+from __future__ import annotations
+
+import json
+import pathlib
+import sys
+
+import facts
+
+PASS = 0
+FAIL = 0
+
+
+def check(label: str, got, want) -> None:
+    global PASS, FAIL
+    if got == want:
+        PASS += 1
+        print(f"  ok   {label}: {got!r}")
+    else:
+        FAIL += 1
+        print(f"  FAIL {label}: got {got!r}, want {want!r}")
+
+
+def card(name, cost, description, ctype="Attack", target="AnyEnemy", index=0, can_play=True):
+    return {
+        "id": name.upper(),
+        "name": name,
+        "type": ctype,
+        "cost": str(cost),
+        "star_cost": None,
+        "description": description,
+        "rarity": "Basic",
+        "is_upgraded": False,
+        "keywords": [],
+        "index": index,
+        "target_type": target,
+        "can_play": can_play,
+        "unplayable_reason": None,
+    }
+
+
+def enemy(entity_id, hp, max_hp=None, block=0, intent_damage=0, status=None):
+    intents = []
+    if intent_damage:
+        intents = [{
+            "type": "Attack",
+            "label": str(intent_damage),
+            "title": "Aggressive",
+            "description": f"This enemy intends to Attack for {intent_damage} damage.",
+        }]
+    return {
+        "entity_id": entity_id,
+        "combat_id": 1,
+        "name": entity_id.split("_")[0],
+        "hp": hp,
+        "max_hp": max_hp or hp,
+        "block": block,
+        "status": status or [],
+        "intents": intents,
+    }
+
+
+def observation(hand, enemies, energy=3, hp=80, max_hp=80, block=0, status=None):
+    return {
+        "state_type": "monster",
+        "battle": {
+            "round": 1,
+            "turn": "player",
+            "is_play_phase": True,
+            "enemies": enemies,
+        },
+        "run": {"act": 1, "floor": 1, "ascension": 0},
+        "player": {
+            "character": "The Ironclad",
+            "hp": hp,
+            "max_hp": max_hp,
+            "block": block,
+            "energy": energy,
+            "max_energy": energy,
+            "status": status or [],
+            "hand": hand,
+            "draw_pile": [],
+            "draw_pile_count": 0,
+            "discard_pile": [],
+            "discard_pile_count": 0,
+            "exhaust_pile": [],
+            "exhaust_pile_count": 0,
+            "gold": 99,
+            "relics": [],
+            "potions": [],
+            "max_potion_slots": 3,
+        },
+    }
+
+
+print("=== 1. Jev's failing case: energy 3, Strike x3 + Bash, target 19 HP ===")
+jev_hand = [
+    card("Strike", 1, "Deal 6 damage.", index=0),
+    card("Strike", 1, "Deal 6 damage.", index=1),
+    card("Strike", 1, "Deal 6 damage.", index=2),
+    card("Bash", 2, "Deal 8 damage. Apply 2 Vulnerable.", index=3),
+]
+f19 = facts.combat_facts(observation(jev_hand, [enemy("NIBBIT_0", 19)]))
+check("max damage subset", facts._subset_damage(f19.playable, 3, [], f19.enemies[0]), 18)
+check("lethal vs 19 HP (Jev said 0.79 YES -- wrong)", f19.lethal_available, False)
+
+f18 = facts.combat_facts(observation(jev_hand, [enemy("NIBBIT_0", 18)]))
+check("lethal vs 18 HP", f18.lethal_available, True)
+check("killable list", f18.killable, ["NIBBIT_0"])
+
+print()
+print("=== 2. damage parsing ===")
+multi = card("Dagger Spray", 1, "Deal 3 damage 2 times.")
+d = facts.parse_card_damage(multi)
+check("multi-hit base", d.base, 3)
+check("multi-hit hits", d.hits, 2)
+check("multi-hit total", d.raw_total, 6)
+
+aoe = card("Cleave", 1, "Deal 8 damage to ALL enemies.")
+check("aoe flag", facts.parse_card_damage(aoe).is_aoe, True)
+
+plain = card("Defend", 1, "Gain 5 Block.", ctype="Skill", target="Self")
+check("non-damage card", facts.parse_card_damage(plain).raw_total, 0)
+
+print()
+print("=== 3. modifiers ===")
+strike = card("Strike", 1, "Deal 6 damage.")
+check("bare strike", facts.damage_to_target(strike, [], [], 0), 6)
+check("+2 Strength", facts.damage_to_target(strike, [{"name": "Strength", "amount": 2}], [], 0), 8)
+check("target Vulnerable (x1.5)", facts.damage_to_target(strike, [], [{"name": "Vulnerable", "amount": 2}], 0), 9)
+check("attacker Weak (x0.75)", facts.damage_to_target(strike, [{"name": "Weak", "amount": 1}], [], 0), 4)
+check("enemy block absorbed", facts.damage_to_target(strike, [], [], 4), 2)
+check("block exceeds damage", facts.damage_to_target(strike, [], [], 10), 0)
+
+print()
+print("=== 4. threat buckets (incoming vs max HP) ===")
+for incoming, want in [(0, "none"), (10, "chip"), (30, "heavy"), (50, "severe"), (80, "lethal")]:
+    f = facts.combat_facts(observation([], [enemy("X_0", 10, intent_damage=incoming)]))
+    check(f"incoming {incoming}", f.threat, want)
+
+print()
+print("=== 5. unplayable cards are excluded ===")
+locked = card("Ascender's Bane", 1, "Unplayable.", index=0, can_play=False)
+locked["unplayable_reason"] = "Unplayable"
+strikes = [card("Strike", 1, "Deal 6 damage.", index=i) for i in range(1, 4)]
+f = facts.combat_facts(observation([locked] + strikes, [enemy("NIBBIT_0", 18)]))
+check("playable count excludes locked", len(f.playable), 3)
+check("lethal still reachable", f.lethal_available, True)
+
+print()
+print("=== 6. real captured state ===")
+real = pathlib.Path("capture/09_now.json")
+if real.exists():
+    f = facts.combat_facts(json.loads(real.read_text()))
+    check("state is play phase", f.in_play_phase, True)
+    check("energy", f.energy, 3)
+    check("hand size", len(f.hand), 5)
+    check("incoming", f.incoming_damage, 12)
+    check("threat", f.threat, "chip")
+    check("lethal", f.lethal_available, False)
+    check("deck composition counted by name", f.deck_counts.get("Strike"), 5)
+    print(f"  deck: {f.deck_counts}")
+else:
+    print("  (no capture/09_now.json, skipped)")
+
+print()
+print(f"=== {PASS} passed, {FAIL} failed ===")
+sys.exit(1 if FAIL else 0)