fix(rules): block immediate actions while flat-footed

SRD 'Immediate Actions': 'You also cannot use an immediate action if you are flat-footed.' _check_reactions now skips states carrying the flat_footed condition before consulting the reaction policy. The engine never applies flat_footed itself (latent gate), so the unit test injects the condition via active_conditions, with a control test proving the same setup fires when not flat-footed.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

README.md

@@ -670,7 +670,13 @@ Règles modélisées :
   immédiate ne part ce round ; le swift du tour **suivant** reste disponible
    (contrairement à l'immédiate hors-tour). Simplification documentée :
    l'interdiction RAW d'une seconde immédiate s'étend jusqu'au début du tour
-  suivant, le moteur la borne au round en cours.
+   suivant, le moteur la borne au round en cours. Conformance L5 (SRD
+   « Immediate Actions ») : « You also cannot use an immediate action if you
+   are flat-footed » — un combattant portant la condition `flat_footed` est
+   **sauté** par la porte de réaction (`_check_reactions`) : aucune immédiate
+   ne part tant qu'il est à plat (la condition est injectable via
+   `active_conditions` ; le moteur ne la pose jamais lui-même — voie
+   d'entrée future).
    Les actions préparées (`ready`) sont traitées sur ces mêmes
    événements **avant** et indépendamment de la politique de réaction (voir
    « Préparation » plus haut).

src/pf1e_simulator/combat.py

@@ -3914,6 +3914,8 @@ class CombatEngine:
         at most one trigger resolves per event (a fired readied action
         suppresses the policy loop). One immediate per event: the first active
         combatant (in state order) whose policy returns an action gets to act.
+        PF1e (SRD "Immediate Actions"): "You also cannot use an immediate
+        action if you are flat-footed" — flat-footed states are skipped.
         Reactions never cascade — while a reaction is executing, further
         events are ignored.
         """
@@ -3924,7 +3926,12 @@ class CombatEngine:
         if self._reaction_policy is None:
             return
         for state in self._states:
-            if not state.active or state.immediate_used or state.swift_used_this_turn:
+            if (
+                not state.active
+                or state.immediate_used
+                or state.swift_used_this_turn
+                or self._has_condition_named(state, "flat_footed")
+            ):
                 continue
             action = self._reaction_policy(self, state, event)
             if action is None:

tests/test_immediate_actions.py

@@ -19,7 +19,9 @@ from pf1e_simulator.combat import (
     ReactionPolicy,
     default_policy,
 )
+from pf1e_simulator.conditions import CONDITIONS_BY_NAME
 from pf1e_simulator.dice import parse_dice
+from pf1e_simulator.effects import ActiveCondition
 from pf1e_simulator.grid import Grid
 from pf1e_simulator.map import MapSpec, TerrainType
 from pf1e_simulator.models import (
@@ -189,6 +191,91 @@ def test_immediate_attack_reaction_executes() -> None:
     assert goblin_state.hp < 30
 
 
+def test_flat_footed_cannot_use_immediate_action() -> None:
+    """PF1e (SRD "Immediate Actions"): "You also cannot use an immediate
+    action if you are flat-footed." Given: a flat-footed ally whose reaction
+    policy would fire an immediate attack When: the goblin attacks the hero
+    Then: no immediate fires and the ally never strikes."""
+    hero = make_combatant("hero", initiative_mod=5)
+    goblin = make_combatant("goblin")
+    ally = make_combatant("ally")
+    ally_state = make_state(ally, "players", (1, 2))
+    ally_state.active_conditions.append(
+        ActiveCondition(
+            condition=CONDITIONS_BY_NAME["flat_footed"],
+            rounds_left=100,
+            source="test",
+        )
+    )
+    states = [
+        ally_state,
+        make_state(hero, "players", (1, 0)),
+        make_state(goblin, "monsters", (1, 3)),
+    ]
+
+    def wait_policy(
+        _engine: CombatEngine, state: CombatantState
+    ) -> tuple[Action, ...]:
+        if state.combatant.id in ("hero", "ally"):
+            return (Action(kind="wait"),)
+        return default_policy(_engine, state)
+
+    def reaction_policy(
+        _engine: CombatEngine, state: CombatantState, event: ReactionEvent
+    ) -> Action | None:
+        if state.combatant.id == "ally" and event.kind == "attack_resolved":
+            return Action(kind="immediate", target_id="goblin")
+        return None
+
+    engine = CombatEngine(
+        SeededRng(4),
+        make_grid(),
+        states,
+        policy=wait_policy,
+        reaction_policy=reaction_policy,
+    )
+    result = engine.run()
+    assert not any("ally: short sword vs goblin" in line for line in result.transcript)
+
+
+def test_not_flat_footed_ally_immediate_fires_control() -> None:
+    """Control: the same ally WITHOUT the flat_footed condition does fire the
+    immediate reaction — the block above is the condition, not the setup."""
+    hero = make_combatant("hero", initiative_mod=5)
+    goblin = make_combatant("goblin")
+    ally = make_combatant("ally")
+    ally_state = make_state(ally, "players", (1, 2))
+    states = [
+        ally_state,
+        make_state(hero, "players", (1, 0)),
+        make_state(goblin, "monsters", (1, 3)),
+    ]
+
+    def wait_policy(
+        _engine: CombatEngine, state: CombatantState
+    ) -> tuple[Action, ...]:
+        if state.combatant.id in ("hero", "ally"):
+            return (Action(kind="wait"),)
+        return default_policy(_engine, state)
+
+    def reaction_policy(
+        _engine: CombatEngine, state: CombatantState, event: ReactionEvent
+    ) -> Action | None:
+        if state.combatant.id == "ally" and event.kind == "attack_resolved":
+            return Action(kind="immediate", target_id="goblin")
+        return None
+
+    engine = CombatEngine(
+        SeededRng(4),
+        make_grid(),
+        states,
+        policy=wait_policy,
+        reaction_policy=reaction_policy,
+    )
+    result = engine.run()
+    assert any("ally: short sword vs goblin" in line for line in result.transcript)
+
+
 def test_immediate_consumes_next_swift() -> None:
     """An OFF-TURN immediate action consumes the swift action of the next turn."""
     hero = make_combatant("hero", initiative_mod=5)