feat(rules): resolve one-round casts on the following turn

SRD Casting Time: a spell that takes 1 round is a full-round action
that comes into effect just before the caster's turn in the next round;
the caster then acts normally. _cast_spell now spends the slot and runs
the start-of-casting gates, then records a PendingCast (spell, target,
center, metamagic, slot level, hp at cast); delivery (touch attack, SR,
saves, effects) resolves at the start of the caster's next turn, before
the policy runs. Net hp lost in between forces the injured-while-casting
concentration check (DC 10 + damage + spell level, no Combat Casting) or
the spell fizzles; a caster knocked out of the fight loses it. Exposed
in the observation via pending_cast. Bounded model documented: net-hp
measurement instead of a per-damage-site hook; long (1 minute+) casting
stays out of scope.

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

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

README.md

@@ -461,9 +461,11 @@ Règles modélisées :
   courage et est aussi retiré quand le swift est consommé par une immédiate,
   via `immediate_used`) ; `immediate` et `free` → libre (l'immédiate reste
   hors-tour et consomme le prochain swift) ; `full_round` → round complet ;
-  `one_round` → **round complet par clamp** — approximation documentée : le
+  `one_round` → **round complet** — SRD « Casting Time » : « A spell that
-  moteur ne tient pas d'incantation en cours entre les tours, le sort
+  takes 1 round to cast is a full-round action » ; l'emplacement est dépensé
-  d'1 round se résout au bout du tour courant au lieu du suivant ;
+  et les gardes de début d'incantation (AoO, concentration) résolus sur le
+  tour courant, mais **l'effet est différé au début du tour suivant** du
+  lanceur (voir « Incantation d'1 round » ci-dessous) ;
   `long` (> 1 round : 3 rounds, 10 minutes, 1 heure — cast multi-round non
   planifiable dans un tour) → **jeté avant le filtre de budget**, rapporté comme
   `ActionResult(kind="cast_spell", ok=False, reason="downgraded:cast_time")`
@@ -479,6 +481,33 @@ Règles modélisées :
   `_cast_time_of`) : la métamagie d'incanteur spontané qui allonge le temps
   d'incantation à un round complet sans don Quickened — la signature
   `Callable[[Action], CastTime]` du résolveur l'accommodera sans changement.
+- Incantation d'1 round (`cast_time: one_round`) : SRD « Casting Time » —
+  « It comes into effect just before the beginning of your turn in the round
+  after you began casting the spell. You then act normally after the spell is
+  completed. » Sur le tour d'incantation, l'emplacement est dépensé, les
+  gardes de début d'incantation jouent (AoO d'incantation + jet de
+  concentration sur dégât, incantation défensive, agrippé), puis le sort est
+  consigné comme incantation en cours (`PendingCast` sur l'état du lanceur :
+  nom du sort, cible, point de centre, métamagie, niveau d'emplacement, pv au
+  moment de l'incantation) et **rien n'est appliqué** — les décisions
+  d'incantation (attaque de contact, RM, sauvegardes, effets) se prennent à la
+  résolution (« You make all pertinent decisions about a spell [...] when the
+  spell comes into effect »). Au début du tour suivant du lanceur, avant le
+  portail de début de tour et avant l'appel de politique, l'incantation en
+  cours se résout (journalisé `finishes casting X`), puis le lanceur agit
+  normalement. Interruption : toute perte nette de pv entre l'incantation et
+  la résolution impose le jet de concentration « blessé pendant l'incantation »
+  (DD `10 + dégâts + niveau du sort`, **sans** le bonus Combat Casting — même
+  helper `_check_concentration` que l'AoO d'incantation) ; un échec perd le
+  sort (`spell fizzles`, emplacement brûlé). Un lanceur mis hors de combat
+  avant sa résolution perd le sort (journalisé `lost (cannot act)`).
+  Simplifications documentées : l'interruption est mesurée en **perte nette
+  de pv à la résolution** et non par un crochet à chaque site de dégâts — un
+  soin intermédiaire peut masquer des dégâts subis ; l'incantation en cours
+  est exposée dans l'observation via la clé `pending_cast`
+  (`{spell_name, target_id, slot_level}` ou `None`). L'incantation `long`
+  (> 1 round) reste hors périmètre (jetée du budget, voir « Temps
+  d'incantation »).
 - Retard (`Action(kind="delay")`, action standard) : le combattant renonce à
   agir maintenant et agit plus tard dans le **même round** — en fin d'ordre si
   `target_id` est absent, sinon juste avant le combattant désigné. La nouvelle
@@ -582,7 +611,7 @@ Règles modélisées :
    staggered/nauseated (ou swift consommé par une immédiate) →
    `downgraded:action_economy` / `downgraded:cast_time` /
    `downgraded:staggered` / `downgraded:nauseated` /
-   `downgraded:immediate_swift` ;
+   `downgraded:immediate_swift` / `downgraded:surprise` ;
   retard valide → `ok=True, reason="delayed"`, second retard du même round →
   `ok=False, reason="already_delayed"` ; préparation valide →
   `ok=True, reason="ready"` ; relèvement sans `prone` → `ok=False,
@@ -1376,7 +1405,10 @@ Règles modélisées :
     last_turn_results (tuple de {kind, ok, reason} — résultat d'exécution du
     dernier tour, pour que la policy apprenne les actions rejetées/dégradées),
     readied ({kind, trigger} de l'action préparée ou None — préparation en
-    cours, consommée quand le déclencheur la fait tirer),
+    cours, consommée quand le déclencheur la fait tirer), pending_cast
+    ({spell_name, target_id, slot_level} de l'incantation d'1 round en cours
+    ou None — résolue au début du prochain tour du lanceur, voir « Incantation
+    d'1 round »),
     defensive_ac_bonus (int — bonus d'esquive à la CA de la défense totale
     (+4) ou du combat défensif (+2), réinitialisé au début du tour du
     combattant), fight_defensively (bool — combat défensif actif : −4 aux
@@ -1453,11 +1485,14 @@ la lecture mais non appliquée dans la résolution.
 Limites hors périmètre (arrêtées lors de la conformance L1-L10, documentées
 plutôt que bricolées) :
 
-- **Incantation `one_round` bornée à un round complet** : le moteur ne tient
+- **Incantation multi-round vraie (`long`) hors périmètre** : le round de
-  pas d'incantation en cours entre les tours ; un sort d'1 round se résout à
+  surprise et l'incantation d'1 round sont modélisés (voir « Round de
-  la fin du tour courant au lieu du suivant (approximation documentée dans
+  surprise » et « Incantation d'1 round ») ; restent hors périmètre les temps
-  « Temps d'incantation »). L'incantation multi-round vraie (> 1 round) est
+  d'incantation > 1 round (3 rounds, 10 minutes, 1 heure — SRD « Casting
-  jetée du budget (`long`).
+  Time » : « These actions must be consecutive and uninterrupted, or the
+  spell automatically fails ») : non planifiables dans un tour, ils sont
+  jetés du budget (`downgraded:cast_time`) plutôt qu'approximés, faute de
+  données d'objectif pour ces sorts rituels.
 - **Gabarits Tiny/Diminutive/Fine abstraits à la grille de 5 ft** : leur
   allonge nulle et la co-occupation de leurs cases (plusieurs créatures
   minuscules sur une même case) ne sont pas modélisées ; seule la substitution
@@ -1579,7 +1614,7 @@ Limites de sorts (conformance D6-D9, documentées plutôt que bricolées) :
 La gate de validation complète (tests + lint + types) :
 
 ```bash
-uv run pytest -q          # 1402 tests
+uv run pytest -q          # 1408 tests
 uv run ruff check src tests
 uv run basedpyright src   # mode strict
 ```

src/pf1e_simulator/combat.py

@@ -578,6 +578,31 @@ class RecurringDamage:
     source: str
 
 
+@dataclass(frozen=True)
+class PendingCast:
+    """A one-round cast begun this turn, to be resolved next turn.
+
+    PF1e (SRD "Casting Time"): "A spell that takes 1 round to cast is a
+    full-round action. It comes into effect just before the beginning of
+    your turn in the round after you began casting the spell. You then act
+    normally after the spell is completed." Everything the delivery still
+    needs is frozen at the start of the casting (the slot is already
+    spent): ``slot_level`` carries the metamagic-inflated level (B7) the
+    save DC uses, ``hp_at_cast`` is the caster's hp when the casting began
+    — the net hp lost before resolution is the interruption damage that
+    forces the concentration check (CRB "Concentration": injured while
+    casting, DC 10 + damage + spell level).
+    """
+
+    spell_name: str
+    target_id: str | None
+    center_pos: tuple[int, int] | None
+    metamagic: tuple[str, ...]
+    slot_level: int
+    cast_defensively: bool
+    hp_at_cast: int
+
+
 @dataclass
 class CombatantState:
     """Mutable runtime state of one combatant on the grid."""
@@ -656,6 +681,10 @@ class CombatantState:
     # deals its dice at the start of this combatant's turn for `rounds_left`
     # rounds, reduced by energy resistance/immunity (never DR).
     recurring_damage: list[RecurringDamage] = field(default_factory=list)
+    # PF1e one-round casting (SRD "Casting Time", not in the frozen data
+    # model): the spell begun on this combatant's turn, resolved just before
+    # its NEXT turn begins; None when no casting is in progress.
+    pending_cast: PendingCast | None = None
 
     def usable_attacks(self) -> list[AttackSpec]:
         return [
@@ -1470,6 +1499,15 @@ class CombatEngine:
                 if state.readied is not None
                 else None
             ),
+            "pending_cast": (
+                None
+                if state.pending_cast is None
+                else {
+                    "spell_name": state.pending_cast.spell_name,
+                    "target_id": state.pending_cast.target_id,
+                    "slot_level": state.pending_cast.slot_level,
+                }
+            ),
         }
 
     def _pair_snapshot(
@@ -1557,6 +1595,69 @@ class CombatEngine:
             return _REASON_NO_LINE_OF_EFFECT
         return _REASON_OUT_OF_RANGE
 
+    def _resolve_pending_cast(self, caster: CombatantState) -> None:
+        """PF1e (SRD "Casting Time"): a one-round cast "comes into effect just
+        before the beginning of your turn in the round after you began casting
+        the spell. You then act normally after the spell is completed." The
+        caster is busy casting through the intervening round: net hp lost
+        between the start of the casting and this moment forces the
+        injured-while-casting concentration check (CRB "Concentration":
+        DC 10 + damage + spell level, no Combat Casting bonus) or the spell
+        is lost.
+        Bounded model (documented): interruption is measured as NET hp loss
+        at resolution instead of a hook at every damage site, so healing in
+        between can mask damage taken.
+        """
+        pending = caster.pending_cast
+        if pending is None:
+            return
+        caster.pending_cast = None
+        spell = self._spell_registry.get(pending.spell_name)
+        if spell is None:
+            return
+        damage = max(0, pending.hp_at_cast - caster.hp)
+        if damage > 0 and not self._check_concentration(
+            caster, pending.slot_level, damage
+        ):
+            dc = self._concentration_dc(caster, pending.slot_level, damage)
+            self._log(
+                f"round {self._current_round} {caster.combatant.id}: "
+                f"one-round cast of {pending.spell_name} interrupted: "
+                f"concentration check failed (DC {dc}), spell fizzles"
+            )
+            return
+        self._log(
+            f"round {self._current_round} {caster.combatant.id}: "
+            f"finishes casting {pending.spell_name}"
+        )
+        target = (
+            next(
+                (s for s in self._states if s.combatant.id == pending.target_id),
+                None,
+            )
+            if pending.target_id is not None
+            else None
+        )
+        self._deliver_cast(
+            caster, target, spell, pending.spell_name, pending.center_pos,
+            metamagic=pending.metamagic, slot_level=pending.slot_level,
+        )
+
+    def _forfeit_pending_cast(self, caster: CombatantState) -> None:
+        """PF1e (SRD "Casting Time"): "you must continue the concentration
+        from the current round to just before your turn in the next round
+        [...] If you lose concentration before the casting is complete, you
+        lose the spell." A caster that reaches its initiative slot unable to
+        act (dead or dying) never gets to resolve the casting."""
+        pending = caster.pending_cast
+        if pending is None:
+            return
+        caster.pending_cast = None
+        self._log(
+            f"round {self._current_round} {caster.combatant.id}: "
+            f"one-round cast of {pending.spell_name} lost (cannot act)"
+        )
+
     def _take_turn(self, state: CombatantState) -> bool:
         """Execute one combatant's full turn; return True if the battle is over."""
         # A freshly-delayed combatant is re-inserted into the round order and
@@ -1569,6 +1670,10 @@ class CombatEngine:
         if not state.delayed_this_round:
             self._expire_readied_action(state)
             self._decrement_durations(state)
+            # SRD "Casting Time": the one-round cast "comes into effect just
+            # before the beginning of your turn" — resolved here, before the
+            # start-of-turn gate, then the turn proceeds normally.
+            self._resolve_pending_cast(state)
             gate = self._turn_gate(state)
             if gate is not None:
                 # A start-of-turn effect (bleed, confusion, cant_act) forfeited
@@ -2068,6 +2173,7 @@ class CombatEngine:
         while i < len(order):
             state = order[i]
             if not state.active:
+                self._forfeit_pending_cast(state)
                 self._process_dying(state)
                 i += 1
                 continue
@@ -5174,6 +5280,9 @@ class CombatEngine:
         penalty" — the spell's own melee/ranged touch attack too.
         Simplification: the spell may target any resolved enemy (the RAW
         spellcasting-as-move restriction and arcane pool cost are not modeled).
+        Spell Combat requires a casting time of 1 standard action; the policy
+        only proposes such spells, and a one-round spell would simply resolve
+        on the caster's next turn via ``PendingCast``.
         """
         if target is None or not target.active or spell_name is None:
             return
@@ -5448,20 +5557,66 @@ class CombatEngine:
             caster, used_level, cast_defensively=cast_defensively
         ):
             return None
+        if spell.cast_time == "one_round":
+            # PF1e (SRD "Casting Time"): "A spell that takes 1 round to cast
+            # is a full-round action. It comes into effect just before the
+            # beginning of your turn in the round after you began casting the
+            # spell." The slot is spent and the start-of-casting gates have
+            # run; delivery (touch attack, SR, saves, effects — "You make all
+            # pertinent decisions about a spell [...] when the spell comes
+            # into effect") is deferred to _resolve_pending_cast.
+            caster.pending_cast = PendingCast(
+                spell_name=spell_name,
+                target_id=target.combatant.id if target is not None else None,
+                center_pos=center_pos,
+                metamagic=applied,
+                slot_level=used_level,
+                cast_defensively=cast_defensively,
+                hp_at_cast=caster.hp,
+            )
+            self._log(
+                f"round {self._current_round} {caster.combatant.id}: "
+                f"begins casting {spell_name} (1 round)"
+            )
+            return None
         # PF1e (CRB): hostile touch delivery needs a melee touch attack (B14)
         # and spell resistance can still turn the spell away. A confirmed
         # touch crit doubles the spell's damage (CRB "Range — Touch").
+        self._deliver_cast(
+            caster, target, spell, spell_name, center_pos,
+            metamagic=applied, slot_level=used_level,
+            attack_penalty=attack_penalty,
+        )
+        return None
+
+    def _deliver_cast(
+        self,
+        caster: CombatantState,
+        target: CombatantState | None,
+        spell: SpellSpec,
+        spell_name: str,
+        center_pos: tuple[int, int] | None,
+        *,
+        metamagic: tuple[str, ...],
+        slot_level: int,
+        attack_penalty: int = 0,
+    ) -> None:
+        """Post-gate delivery: touch attack, spell resistance, then effects.
+
+        Shared by the immediate cast path and the resolution of a pending
+        one-round cast (SRD "Casting Time").
+        """
+        has_area = any(isinstance(e, AreaEffect) for e in spell.effects)
         blocked, delivery_crit = self._spell_delivery_blocked(
             caster, target, spell, has_area=has_area, attack_penalty=attack_penalty
         )
         if blocked:
-            return None
+            return
         self._apply_and_log_cast(
             caster, target, spell, spell_name, center_pos,
-            metamagic=applied, slot_level=used_level, spell_crit=delivery_crit,
+            metamagic=metamagic, slot_level=slot_level, spell_crit=delivery_crit,
             attack_penalty=attack_penalty,
         )
-        return None
 
     def _spell_cast_interrupted(
         self, caster: CombatantState, spell_level: int, *, cast_defensively: bool
@@ -7151,9 +7306,10 @@ def _cast_time_slot(cast_time: CastTime) -> _ActionEconomySlot:
     PF1e (CRB, Magic — Casting Time): a standard/swift casting time takes
     that kind of action; an immediate action is off-turn and consumes the
     next swift (handled via immediate_used, so it is budget-free here); a
-    free-action cast is free. one_round is CLAMPED to the full-round slot:
+    free-action cast is free. one_round occupies the full-round slot (it IS
-    the engine resolves it within the current turn instead of tracking a
+    a full-round action, SRD "Casting Time") and additionally defers the
-    pending cast across turns (documented approximation). A long casting
+    spell's effect to the start of the caster's next turn via
+    ``PendingCast``. A long casting
     time (more than 1 round: 3 rounds, 10 minutes, 1 hour, ...) cannot be
     scheduled by the turn budget at all — the
     engine drops such casts before the filter runs, so reaching this

tests/test_conformance_cast_time.py

@@ -8,7 +8,10 @@ distinct reason ``downgraded:cast_time``. A one-round cast is CLAMPED to the
 full-round slot (documented approximation: it resolves within the turn
 instead of spanning rounds). Swift casts compete with the swift bonus (and
 are removed by a consumed swift); full-round casts are illegal for a
-staggered creature, and run is illegal for a nauseated one.
+staggered creature, and run is illegal for a nauseated one. A one-round cast
+occupies the full-round slot AND defers its effect to the start of the
+caster's next turn (SRD "Casting Time", PendingCast — see
+tests/test_one_round_cast.py).
 """
 
 from __future__ import annotations

tests/test_one_round_cast.py

@@ -0,0 +1,202 @@
+"""S3b conformance: true one-round casting (SRD "Casting Time").
+
+"A spell that takes 1 round to cast is a full-round action. It comes into
+effect just before the beginning of your turn in the round after you began
+casting the spell. You then act normally after the spell is completed."
+"When you begin a spell that takes 1 round or longer to cast, you must
+continue the concentration from the current round to just before your turn
+in the next round (at least). If you lose concentration before the casting
+is complete, you lose the spell." (CRB "Concentration" — Injury: DC 10 +
+damage taken + spell level, no Combat Casting bonus.)
+"""
+
+from __future__ import annotations
+
+from pf1e_simulator.combat import Action, CombatantState, CombatEngine
+from pf1e_simulator.rng import ScriptedRng
+from pf1e_simulator.spells import ConditionEffect, SpellSpec, SummonEffect
+from tests.test_combat import make_combatant, make_grid
+from tests.test_spells import _make_caster, _make_engine, _make_target
+
+_WAIT: tuple[Action, ...] = (Action(kind="wait"),)
+_CAST_FOG = Action(kind="cast_spell", target_id="target", spell_name="Fog")
+_STRIKE: tuple[Action, ...] = (
+    Action(kind="move", target_id="caster"),
+    Action(kind="attack", target_id="caster"),
+)
+
+
+def _fog() -> SpellSpec:
+    return SpellSpec(
+        name="Fog",
+        level=1,
+        school="conjuration",
+        range="close",
+        save="none",
+        cast_time="one_round",
+        effects=(ConditionEffect(condition_name="asleep", duration_rounds=4),),
+    )
+
+
+def _duel(
+    queue: list[int],
+    caster_actions: dict[int, tuple[Action, ...]],
+    enemy_actions: dict[int, tuple[Action, ...]] | None = None,
+    *,
+    caster_hp: int | None = None,
+    with_ally: bool = False,
+) -> tuple[CombatEngine, CombatantState, CombatantState]:
+    """Caster (init 15+2) vs enemy "target" (init 10) 2 cells apart, 2 rounds.
+
+    Scripted rolls run in queue order; the enemy waits unless given actions.
+    With ``with_ally`` a waiting ally keeps the battle alive if the caster
+    falls (so a dying caster's initiative slot is still reached).
+    """
+    caster = _make_caster().model_copy(update={"spells": ["Fog"]})
+    foe = _make_target()
+    c = CombatantState(combatant=caster, side="players", pos=(0, 0), hp=caster.hp_max)
+    t = CombatantState(combatant=foe, side="monsters", pos=(0, 2), hp=foe.hp_max)
+    states = [c, t]
+    if with_ally:
+        ally = make_combatant("ally")
+        states.insert(1, CombatantState(
+            combatant=ally, side="players", pos=(0, 5), hp=ally.hp_max,
+        ))
+    if caster_hp is not None:
+        c.hp = caster_hp
+
+    def policy(e: CombatEngine, s: CombatantState) -> tuple[Action, ...]:
+        if s.combatant.id == "caster":
+            return caster_actions.get(e._current_round, _WAIT)
+        if s.combatant.id == "target":
+            return enemy_actions.get(e._current_round, _WAIT) if enemy_actions else _WAIT
+        return _WAIT
+
+    engine = CombatEngine(
+        ScriptedRng(queue),
+        make_grid(),
+        states,
+        policy=policy,
+        round_cap=2,
+        spell_registry={"Fog": _fog()},
+    )
+    return engine, c, t
+
+
+def _is_asleep(t: CombatantState) -> bool:
+    return any(ac.condition.name == "asleep" for ac in t.active_conditions)
+
+
+def test_one_round_cast_resolves_on_the_next_turn_not_the_same_turn() -> None:
+    # Given: a caster beginning a one-round cast on round 1
+    # When: the battle runs two rounds
+    # Then: the effect lands at the START of round 2 (before the caster acts)
+    # and the caster then acts normally that same turn.
+    # Rolls: initiative x2, round-2 attack d20=5 (5+2+4 helpless vs AC 10
+    # hit), damage d4=2.
+    engine, _c, t = _duel(
+        [15, 10, 5, 2],
+        {1: (_CAST_FOG,), 2: (Action(kind="move", target_id="target"),
+                               Action(kind="attack", target_id="target"))},
+    )
+    transcript = list(engine.run().transcript)
+    begins = next(i for i, ln in enumerate(transcript) if "begins casting Fog" in ln)
+    finishes = next(i for i, ln in enumerate(transcript) if "finishes casting Fog" in ln)
+    delivered = next(i for i, ln in enumerate(transcript) if "cast Fog vs" in ln)
+    attack = next(i for i, ln in enumerate(transcript) if "dagger vs target" in ln)
+    assert transcript[begins].startswith("round 1 ")
+    assert transcript[finishes].startswith("round 2 ")
+    assert begins < finishes < delivered < attack
+    assert _is_asleep(t)
+
+
+def test_damage_before_resolution_forces_a_concentration_check() -> None:
+    # Given: the enemy hits the caster between the cast and its resolution
+    # When: the caster fails the injured-while-casting check (DC 14)
+    # Then: the spell is lost with no effect.
+    # Rolls: initiative x2, attack d20=10 (13 vs AC 12 hit), damage 3,
+    # concentration d20=1 (1+5+4=10 < 14).
+    engine, _c, t = _duel([15, 10, 10, 3, 1], {1: (_CAST_FOG,)}, {1: _STRIKE})
+    transcript = list(engine.run().transcript)
+    assert any("spell fizzles" in ln and "DC 14" in ln for ln in transcript)
+    assert not any("finishes casting Fog" in ln for ln in transcript)
+    assert not _is_asleep(t)
+
+
+def test_passed_concentration_still_delivers_the_spell() -> None:
+    # Given: the same injury
+    # When: the caster passes the check (20+5+4=29 >= 14)
+    # Then: the spell resolves at the start of the next turn.
+    engine, _c, t = _duel([15, 10, 10, 3, 20], {1: (_CAST_FOG,)}, {1: _STRIKE})
+    transcript = list(engine.run().transcript)
+    assert any("finishes casting Fog" in ln for ln in transcript)
+    assert _is_asleep(t)
+
+
+def test_dead_caster_loses_the_pending_cast() -> None:
+    # Given: a caster at 4 hp beginning a one-round cast, with an ally who
+    # keeps the battle alive after the caster falls
+    # When: the enemy's blow (6 damage) drops it below 0 before resolution
+    # Then: the spell is lost at the caster's initiative slot.
+    # Rolls: initiative x3, attack d20=10 (hit), damage 6, then the dying
+    # caster's failed stabilization check d20=1 (1+1-2 < 10).
+    engine, _c, t = _duel(
+        [15, 15, 10, 10, 6, 1], {1: (_CAST_FOG,)}, {1: _STRIKE},
+        caster_hp=4, with_ally=True,
+    )
+    transcript = list(engine.run().transcript)
+    assert any("one-round cast of Fog lost (cannot act)" in ln for ln in transcript)
+    assert not _is_asleep(t)
+
+
+def test_slot_spent_at_cast_time_delivery_deferred() -> None:
+    # Given: a caster with level-1 slots
+    # When: _cast_spell records the one-round cast
+    # Then: the slot is gone, the effect is not applied yet, and the
+    # observation exposes the pending cast until resolution.
+    engine, c, t = _make_engine(
+        _make_caster().model_copy(update={"spells": ["Fog"]}),
+        _make_target(),
+        [],
+        spell_registry={"Fog": _fog()},
+    )
+    slots_before = c.spell_slots_left[1]
+    engine._cast_spell(c, t, "Fog")
+    assert c.spell_slots_left[1] == slots_before - 1
+    assert c.pending_cast is not None
+    assert c.pending_cast.spell_name == "Fog"
+    assert not _is_asleep(t)
+    pending = engine._build_observation(t).combatants[0]["pending_cast"]
+    assert isinstance(pending, dict)
+    assert pending["spell_name"] == "Fog"
+    engine._resolve_pending_cast(c)
+    assert c.pending_cast is None
+    assert _is_asleep(t)
+    assert engine._build_observation(t).combatants[0]["pending_cast"] is None
+
+
+def test_one_round_summon_arrives_on_the_following_turn() -> None:
+    # Given: Summon Monster I (one_round, SRD) — the creature must not appear
+    # on the casting turn.
+    # When: the pending cast resolves at the start of the next turn
+    # Then: the summoned creature joins the battle.
+    summon = SpellSpec(
+        name="Summon Monster I",
+        level=1,
+        school="conjuration",
+        range="close",
+        cast_time="one_round",
+        effects=(
+            SummonEffect(
+                creature="data/monsters/celestial_wolf.json", duration_rounds=2
+            ),
+        ),
+    )
+    engine, c, t = _make_engine(
+        _make_caster(), _make_target(), [],
+        spell_registry={"Summon Monster I": summon},
+    )
+    engine._cast_spell(c, t, "Summon Monster I")
+    assert not any(s.combatant.id.startswith("celestial") for s in engine.states)
+    engine._resolve_pending_cast(c)
+    assert any(s.combatant.id.startswith("celestial") for s in engine.states)

tests/test_spells.py

@@ -355,7 +355,9 @@ class TestAreaSavesPerSpellSaveType:
     save-free, and secondary creatures do not always roll Reflex."""
 
     def test_sleep_secondary_creature_rolls_will_and_negates(self) -> None:
-        # Sleep (Will negates, save_for_half=False): primary target saves on
+        # Sleep (one-round cast, Will negates, save_for_half=False): casting
+        # records the pending cast; resolution (start of the caster's next
+        # turn, no damage taken) delivers it — primary target saves on
         # natural 20 (first roll), the caster — second creature in the area —
         # rolls its own Will and fails on natural 1 (second roll).
         caster = _make_caster()
@@ -365,6 +367,8 @@ class TestAreaSavesPerSpellSaveType:
         )
         engine._cast_spell(c, t, "Sleep")
         assert not any(ac.condition.name == "asleep" for ac in t.active_conditions)
+        engine._resolve_pending_cast(c)
+        assert not any(ac.condition.name == "asleep" for ac in t.active_conditions)
         assert any(ac.condition.name == "asleep" for ac in c.active_conditions)
 
     def test_color_spray_primary_save_is_not_discarded(self) -> None:
@@ -709,8 +713,9 @@ class TestSpellDamageWithDr:
 
 
 class TestSummonMonster:
-    """Given: a caster casting Summon Monster II
+    """Given: a caster casting Summon Monster II (one-round cast)
-    When: _cast_spell is called
+    When: _cast_spell is called and the pending cast resolves on the
+    caster's next turn (SRD "Casting Time")
     Then: a celestial wolf is summoned adjacent to the caster."""
 
     def test_summon_creature(self) -> None:
@@ -719,6 +724,7 @@ class TestSummonMonster:
         engine, c, t = _make_engine(caster, target, [3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3])
         hp_before = len(engine._states)
         engine._cast_spell(c, t, "Summon Monster II")
+        engine._resolve_pending_cast(c)
         # Caster + target + summoned = 3 combatants
         assert len(engine._states) == hp_before + 1
         # Find the summoned creature