feat(phase2): replay log and replay policy (P0.5)

Add replay.py: a ReplayLog records every (observation, action) pair a
policy produced, keyed by monotonic call_seq, plus the EncounterSpec,
seed and round_cap, and serializes the whole battle to JSONL. replay()
turns a log back into an observation-only LLMPolicy that returns each
recorded action, raising ReplayMismatchError on a differing observation
and ReplayExhaustedError past the last call.

Observations are matched by their canonical JSON (observation_key), not
raw dataclass equality, because JSON collapses tuples and lists and the
snapshot's inner dict[str, object] holds both. Action and the spec are
dumped through Pydantic TypeAdapters (mode=json) so tuple fields survive
as arrays and are coerced back on load.

Move TrickCondition/ReadyTrigger out of the TYPE_CHECKING block in
combat.py: TypeAdapter(Action) must resolve them at runtime to serialize
the dataclass, so the Literal aliases now live at module level.

src/pf1e_simulator/combat.py

@@ -178,6 +178,13 @@ if TYPE_CHECKING:
     from pf1e_simulator.rng import Rng
     from pf1e_simulator.spells import SpellSpec
 
+from pf1e_simulator.los import (
+    cover_bonus_cells,
+    has_line_of_effect_cells,
+)
+
+# Runtime aliases (not only annotations): Pydantic type adapters over ``Action``
+# must resolve them, so they cannot live inside the TYPE_CHECKING block.
 TrickCondition = Literal[
     "dazzled", "blinded", "deafened", "entangled", "shaken", "sickened"
 ]
@@ -186,11 +193,6 @@ if TYPE_CHECKING:
     "enemy_enters_reach", "enemy_casts", "enemy_attacks", "enemy_hits_ally"
 ]
 
-from pf1e_simulator.los import (
-    cover_bonus_cells,
-    has_line_of_effect_cells,
-)
-
 _SQUARE_FT = 5  # Phase 0 maps use 5-ft squares
 _NATURAL_ONE = 1  # PF1e: natural 1 always misses
 _NATURAL_TWENTY = 20  # PF1e: natural 20 always hits and threatens

src/pf1e_simulator/replay.py

@@ -0,0 +1,250 @@
+"""Replay log for observation-only policies (docs/phase-2 P0.5).
+
+A ``ReplayLog`` records every ``(observation, action)`` pair an
+observation-only policy produced during one battle, keyed by a monotonic
+``call_seq`` assigned in execution order. It also carries the ``EncounterSpec``
+plus the battle ``seed`` and ``round_cap`` so a recorded battle can be re-run
+standalone. ``replay(log)`` turns a log back into an ``LLMPolicy`` that returns
+the recorded action for each observation, raising a typed ``ReplayError`` (a
+``ValueError``) on an out-of-sequence observation or once the log is exhausted.
+
+Why ``call_seq`` and not the observation as the key: the same observation can
+legitimately recur (a stalled battle), and delayed turns / summons can revisit
+an earlier position — the sequence position is the only unambiguous key.
+
+The JSONL serialization is self-contained (a header line with the spec, seed
+and round cap, then one record per line) so ``ReplayLog.from_jsonl(text)``
+round-trips without any out-of-band state. ``Observation`` uses the engine's
+canonical ``to_dict()`` (``schema_version`` included); ``Action`` and the spec
+are dumped through Pydantic type adapters so their tuple fields survive as
+JSON arrays and are coerced back to tuples on load. Observations are matched
+during playback by :func:`observation_key` (their canonical JSON), not raw
+dataclass equality: JSON collapses tuples and lists, and the snapshot's inner
+``dict[str, object]`` holds both.
+"""
+
+from __future__ import annotations
+
+import json
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Self, TypeGuard
+
+from pydantic import TypeAdapter
+
+from pf1e_simulator.combat import Action, Observation
+from pf1e_simulator.map import MapSpec
+from pf1e_simulator.models import Combatant
+from pf1e_simulator.runner import EncounterSpec
+
+if TYPE_CHECKING:
+    from pf1e_simulator.combat import LLMPolicy
+
+_HEADER_KIND = "header"
+_RECORD_KIND = "record"
+
+# ``EncounterSpec`` is a stdlib dataclass whose annotations reference
+# ``MapSpec``/``Combatant``; ``runner`` imports those only under TYPE_CHECKING,
+# so the adapter's default namespace cannot resolve them. Rebuild it with the
+# two runtime classes in scope.
+_SPEC_ADAPTER = TypeAdapter(EncounterSpec)
+_SPEC_ADAPTER.rebuild(_types_namespace={"MapSpec": MapSpec, "Combatant": Combatant})
+_OBSERVATION_ADAPTER = TypeAdapter(Observation)
+_ACTION_ADAPTER = TypeAdapter(Action)
+
+
+class ReplayError(ValueError):
+    """Base error for replay-log construction and playback."""
+
+
+class ReplayMismatchError(ReplayError):
+    """A replay policy received an observation that differs from the recorded one."""
+
+
+class ReplayExhaustedError(ReplayError):
+    """A replay policy was called past the last recorded ``call_seq``."""
+
+
+@dataclass(frozen=True)
+class ReplayRecord:
+    """One recorded policy call: the snapshot shown and the action chosen.
+
+    ``call_seq`` is the position of this call in the execution order of the
+    battle (0-based, contiguous), assigned by the recorder.
+    """
+
+    call_seq: int
+    observation: Observation
+    action: Action
+
+
+class ReplayLog:
+    """A recorded battle: spec + seed + round cap + ordered policy calls."""
+
+    def __init__(self, *, spec: EncounterSpec, seed: int, round_cap: int) -> None:
+        self.spec = spec
+        self.seed = seed
+        self.round_cap = round_cap
+        self._records: list[ReplayRecord] = []
+
+    def add(self, record: ReplayRecord) -> None:
+        """Append one call; require a strictly increasing ``call_seq``.
+
+        The log is a sequence: a duplicate or out-of-order ``call_seq`` would
+        make the recorded execution order ambiguous, so both are rejected.
+        """
+        if self._records:
+            last = self._records[-1].call_seq
+            if record.call_seq == last:
+                msg = f"duplicate call_seq {record.call_seq}"
+                raise ReplayError(msg)
+            if record.call_seq < last:
+                msg = f"call_seq {record.call_seq} is not after {last}"
+                raise ReplayError(msg)
+        self._records.append(record)
+
+    @property
+    def records(self) -> tuple[ReplayRecord, ...]:
+        """The recorded calls ordered by ``call_seq`` (replay order)."""
+        return tuple(sorted(self._records, key=lambda record: record.call_seq))
+
+    def __len__(self) -> int:
+        return len(self._records)
+
+    def to_jsonl(self) -> str:
+        """Serialize to newline-delimited JSON (header line, then one per call)."""
+        lines = [self._header_json()]
+        lines.extend(self._record_json(record) for record in self.records)
+        return "".join(line + "\n" for line in lines)
+
+    @classmethod
+    def from_jsonl(cls, text: str) -> Self:
+        """Rebuild a log from ``to_jsonl`` output; raise ``ReplayError`` if invalid."""
+        lines = [line for line in text.splitlines() if line.strip()]
+        if not lines:
+            msg = "empty replay log"
+            raise ReplayError(msg)
+        header = _as_object(_loads(lines[0]), "header")
+        if _as_str(header.get("kind"), "kind") != _HEADER_KIND:
+            msg = "first line is not a replay header"
+            raise ReplayError(msg)
+        log = cls(
+            spec=_SPEC_ADAPTER.validate_python(header["spec"]),
+            seed=_as_int(header.get("seed"), "seed"),
+            round_cap=_as_int(header.get("round_cap"), "round_cap"),
+        )
+        for line in lines[1:]:
+            data = _as_object(_loads(line), "record")
+            if _as_str(data.get("kind"), "kind") != _RECORD_KIND:
+                msg = "record line is not a replay record"
+                raise ReplayError(msg)
+            log.add(
+                ReplayRecord(
+                    call_seq=_as_int(data.get("call_seq"), "call_seq"),
+                    observation=_OBSERVATION_ADAPTER.validate_python(
+                        data["observation"]
+                    ),
+                    action=_ACTION_ADAPTER.validate_python(data["action"]),
+                )
+            )
+        return log
+
+    def _header_json(self) -> str:
+        payload: dict[str, object] = {
+            "kind": _HEADER_KIND,
+            "seed": self.seed,
+            "round_cap": self.round_cap,
+            "spec": _SPEC_ADAPTER.dump_python(self.spec, mode="json"),
+        }
+        return json.dumps(
+            payload, sort_keys=True, separators=(",", ":"), ensure_ascii=True
+        )
+
+    def _record_json(self, record: ReplayRecord) -> str:
+        payload: dict[str, object] = {
+            "kind": _RECORD_KIND,
+            "call_seq": record.call_seq,
+            "observation": record.observation.to_dict(),
+            "action": _ACTION_ADAPTER.dump_python(
+                record.action, mode="json", exclude_defaults=True
+            ),
+        }
+        return json.dumps(
+            payload, sort_keys=True, separators=(",", ":"), ensure_ascii=True
+        )
+
+
+def observation_key(observation: Observation) -> str:
+    """Return the canonical identity of an observation for replay matching.
+
+    ``Observation.to_dict()`` is already JSON-shaped, so dumping it with sorted
+    keys yields a value that is insensitive to dict insertion order and treats
+    tuples and lists alike (JSON has no tuple type).
+    """
+    return json.dumps(
+        observation.to_dict(), sort_keys=True, separators=(",", ":"), ensure_ascii=True
+    )
+
+
+def replay(log: ReplayLog) -> LLMPolicy:
+    """Build an observation-only policy that replays ``log`` in ``call_seq`` order.
+
+    The returned policy walks the log once, comparing the observation it is
+    handed to the recorded one before returning that call's action (wrapped in
+    a one-action tuple). An out-of-sequence observation raises
+    ``ReplayMismatchError``; a call past the end raises ``ReplayExhaustedError``.
+    """
+    ordered = log.records
+    keys = [observation_key(record.observation) for record in ordered]
+    cursor = 0
+
+    def policy(observation: Observation) -> tuple[Action, ...]:
+        nonlocal cursor
+        if cursor >= len(ordered):
+            msg = f"replay log exhausted after {len(ordered)} calls"
+            raise ReplayExhaustedError(msg)
+        record = ordered[cursor]
+        if keys[cursor] != observation_key(observation):
+            msg = (
+                f"replay mismatch at call_seq {record.call_seq}: "
+                "the observation differs from the recorded one"
+            )
+            raise ReplayMismatchError(msg)
+        cursor += 1
+        return (record.action,)
+
+    return policy
+
+
+def _loads(text: str) -> object:
+    """Parse one JSONL line, mapping a JSON error to a ``ReplayError``."""
+    try:
+        return json.loads(text)
+    except json.JSONDecodeError as exc:
+        msg = f"invalid JSON in replay log: {exc}"
+        raise ReplayError(msg) from exc
+
+
+def _as_object(value: object, what: str) -> dict[str, object]:
+    if _is_str_object_dict(value):
+        return value
+    msg = f"expected a JSON object for {what}"
+    raise ReplayError(msg)
+
+
+def _as_str(value: object, what: str) -> str:
+    if isinstance(value, str):
+        return value
+    msg = f"expected a string for {what}"
+    raise ReplayError(msg)
+
+
+def _as_int(value: object, what: str) -> int:
+    # bool is an int subclass but never a valid call_seq/seed/round_cap.
+    if isinstance(value, int) and not isinstance(value, bool):
+        return value
+    msg = f"expected an integer for {what}"
+    raise ReplayError(msg)
+
+
+def _is_str_object_dict(value: object) -> TypeGuard[dict[str, object]]:
+    return isinstance(value, dict)

tests/test_phase2_replay.py

@@ -0,0 +1,234 @@
+"""Phase-2 replay log (docs/phase-2-llm-architecture.md P0.5).
+
+``replay.py`` records every ``(observation, action)`` pair a policy produced,
+keyed by the execution-order ``call_seq``, and serializes the whole battle
+(spec + seed + round cap + calls) to JSONL. ``replay()`` turns the log back
+into an observation-only policy returning the recorded actions.
+
+These tests pin the contract: JSONL round-trips to canonically-equal records
+(``observation_key`` ignores JSON's tuple/list collapse), a replayed battle is
+bit-identical to the recorded one (including from a serialized log), a
+duplicate ``call_seq`` is rejected, and playback fails loudly on a mismatched
+observation and once the log is exhausted.
+"""
+
+from __future__ import annotations
+
+from dataclasses import replace
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+import pytest
+
+from pf1e_simulator.candidates import candidates
+from pf1e_simulator.loaders import load_combatant
+from pf1e_simulator.map import load_map
+from pf1e_simulator.replay import (
+    ReplayError,
+    ReplayExhaustedError,
+    ReplayLog,
+    ReplayMismatchError,
+    ReplayRecord,
+    observation_key,
+    replay,
+)
+from pf1e_simulator.runner import EncounterSpec, Side, run_encounter
+from pf1e_simulator.spells import SPELLS_DIR, load_spell_registry
+
+if TYPE_CHECKING:
+    from pf1e_simulator.combat import Action, CombatantState, Observation
+    from pf1e_simulator.models import Combatant
+    from pf1e_simulator.runner import EncounterReport
+
+ROOT = Path(__file__).resolve().parents[1]
+MAP = ROOT / "data" / "maps" / "sample_arena.yaml"
+SEED = 7
+
+
+def _c(path: str) -> Combatant:
+    return load_combatant(ROOT / "data" / path)
+
+
+def _duel_spec() -> EncounterSpec:
+    """A fast 1v1 (goblin archer vs orc) on the sample arena."""
+    return EncounterSpec(
+        map=load_map(MAP),
+        round_cap=20,
+        sides=(
+            Side(name="players", combatants=(_c("monsters/goblin.json"),), zone="A"),
+            Side(name="monsters", combatants=(_c("monsters/orc.json"),), zone="B"),
+        ),
+    )
+
+
+class _Recorder:
+    """Legacy two-argument policy: log every call, then pick ``candidates[0]``."""
+
+    def __init__(self, spec: EncounterSpec, seed: int, round_cap: int) -> None:
+        self.log = ReplayLog(spec=spec, seed=seed, round_cap=round_cap)
+
+    def policy(
+        self, observation: Observation, _state: CombatantState
+    ) -> tuple[Action, ...]:
+        action = candidates(observation)[0]
+        self.log.add(
+            ReplayRecord(
+                call_seq=len(self.log),
+                observation=observation,
+                action=action,
+            )
+        )
+        return (action,)
+
+
+def _record(spec: EncounterSpec, *, seed: int = SEED) -> tuple[_Recorder, EncounterReport]:
+    """Record one battle and return the recorder plus its captured report."""
+    registry = load_spell_registry(SPELLS_DIR)
+    recorder = _Recorder(spec, seed=seed, round_cap=spec.round_cap)
+    report = run_encounter(
+        spec,
+        runs=1,
+        seed=seed,
+        llm_policy=recorder.policy,
+        spell_registry=registry,
+        capture_first_transcript=True,
+    )
+    return recorder, report
+
+
+def test_jsonl_round_trip_preserves_records() -> None:
+    """A log serializes to JSONL and loads back to structurally-equal records."""
+    spec = _duel_spec()
+    recorder, _report = _record(spec)
+    log = recorder.log
+
+    assert len(log) > 0
+    assert [record.call_seq for record in log.records] == list(range(len(log)))
+
+    text = log.to_jsonl()
+    restored = ReplayLog.from_jsonl(text)
+
+    assert len(restored) == len(log)
+    assert [record.call_seq for record in restored.records] == [
+        record.call_seq for record in log.records
+    ]
+    assert [
+        observation_key(record.observation) for record in restored.records
+    ] == [observation_key(record.observation) for record in log.records]
+    assert [record.action for record in restored.records] == [
+        record.action for record in log.records
+    ]
+    assert restored.spec == log.spec
+    assert restored.seed == log.seed
+    assert restored.round_cap == log.round_cap
+    assert restored.to_jsonl() == text
+
+
+def test_replay_reproduces_the_recorded_battle() -> None:
+    """Replaying the in-memory log matches the recorded battle exactly."""
+    spec = _duel_spec()
+    registry = load_spell_registry(SPELLS_DIR)
+    recorder, recorded = _record(spec)
+
+    replayed = run_encounter(
+        spec,
+        runs=1,
+        seed=SEED,
+        llm_policy=replay(recorder.log),
+        spell_registry=registry,
+        capture_first_transcript=True,
+    )
+
+    assert replayed.wins == recorded.wins
+    assert replayed.draws == recorded.draws
+    assert replayed.avg_rounds == recorded.avg_rounds
+    assert replayed.transcript == recorded.transcript
+
+
+def test_replay_from_serialized_log_reproduces_the_battle() -> None:
+    """A log thawed from JSONL replays the battle bit-for-bit."""
+    spec = _duel_spec()
+    registry = load_spell_registry(SPELLS_DIR)
+    recorder, recorded = _record(spec)
+
+    restored = ReplayLog.from_jsonl(recorder.log.to_jsonl())
+    replayed = run_encounter(
+        spec,
+        runs=1,
+        seed=SEED,
+        llm_policy=replay(restored),
+        spell_registry=registry,
+        capture_first_transcript=True,
+    )
+
+    assert replayed.wins == recorded.wins
+    assert replayed.draws == recorded.draws
+    assert replayed.avg_rounds == recorded.avg_rounds
+    assert replayed.transcript == recorded.transcript
+
+
+def test_replay_rejects_a_mismatched_observation() -> None:
+    """An observation that differs from the recorded one raises a mismatch error."""
+    spec = _duel_spec()
+    recorder, _report = _record(spec)
+    log = recorder.log
+    policy = replay(log)
+    first = log.records[0].observation
+    tampered = replace(first, round=first.round + 1)
+
+    with pytest.raises(ReplayMismatchError):
+        policy(tampered)
+
+
+def test_replay_returns_each_recorded_action_then_exhausts() -> None:
+    """Playback walks every record in order, then raises once past the end."""
+    spec = _duel_spec()
+    recorder, _report = _record(spec)
+    log = recorder.log
+    policy = replay(log)
+
+    for record in log.records:
+        assert policy(record.observation) == (record.action,)
+
+    with pytest.raises(ReplayExhaustedError):
+        policy(log.records[-1].observation)
+
+
+def test_replay_log_rejects_a_duplicate_call_seq() -> None:
+    """Adding two records with the same ``call_seq`` is an ambiguity error."""
+    spec = _duel_spec()
+    recorder, _report = _record(spec)
+    record = recorder.log.records[-1]
+
+    with pytest.raises(ReplayError, match="duplicate call_seq"):
+        recorder.log.add(
+            ReplayRecord(
+                call_seq=record.call_seq,
+                observation=record.observation,
+                action=record.action,
+            )
+        )
+
+
+def test_replay_log_rejects_an_out_of_order_call_seq() -> None:
+    """A ``call_seq`` below the last one is an ambiguity error (not a duplicate)."""
+    spec = _duel_spec()
+    recorder, _report = _record(spec)
+    record = recorder.log.records[0]
+
+    with pytest.raises(ReplayError, match="is not after"):
+        recorder.log.add(
+            ReplayRecord(
+                call_seq=record.call_seq,
+                observation=record.observation,
+                action=record.action,
+            )
+        )
+
+
+def test_from_jsonl_rejects_garbage() -> None:
+    """An empty or unparseable payload raises ``ReplayError``, not a raw error."""
+    with pytest.raises(ReplayError):
+        ReplayLog.from_jsonl("")
+    with pytest.raises(ReplayError):
+        ReplayLog.from_jsonl("{not json}")