feat(phase2): llm report writer (P5.3)

- New module src/pf1e_simulator/report.py with ReportContext, build_report_context,
  LLMReportPolicy, ReportBudget, format_llm_report, build_report_prompt
- Prompt pack fixture: tests/fixtures/prompt_pack_fs/report.md (FR narrator)
- CLI integration: --llm-report + --output flags, mutually exclusive with --transcript
- Budget enforcement: ReportBudget integrates with CostBudget, allows max_retries+1 calls
- Tests: test_report_context, test_report_prompt_pack, test_llm_report_policy,
  test_format_llm_report, test_cli_llm_report, test_report_budget (27 new tests)

tests/test_llm_report_policy.py

@@ -0,0 +1,100 @@
+"""Tests for LLMReportPolicy (P5.3 T3)."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from pf1e_simulator.client import FakeLLMClient
+from pf1e_simulator.prompt import PromptPack
+from pf1e_simulator.prompt_builder import PromptBuilder
+from pf1e_simulator.report import LLMReportPolicy, build_report_context
+from pf1e_simulator.runner import CombatantAttrition, EncounterReport
+
+FIXTURE_DIR = Path(__file__).resolve().parent / "fixtures" / "prompt_pack_fs"
+
+
+def _make_encounter() -> EncounterReport:
+    return EncounterReport(
+        runs=100,
+        seed=1,
+        wins={"players": 65, "monsters": 33},
+        draws=2,
+        avg_rounds=7.2,
+        attrition={
+            "goblin": CombatantAttrition(2.45, 0.12, 18.30, 4.20, 0.00),
+            "orc": CombatantAttrition(3.20, 0.25, 28.40, 15.60, 0.00),
+        },
+    )
+
+
+def _make_policy(
+    script: list[str],
+    *,
+    max_retries: int = 1,
+) -> LLMReportPolicy:
+    pack = PromptPack.load(FIXTURE_DIR)
+    builder = PromptBuilder(pack)
+    expected_version = pack.prompt_version("report")
+    client = FakeLLMClient(script=script, prompt_version=expected_version)  # type: ignore[arg-type]
+    return LLMReportPolicy(
+        client=client, builder=builder, prompt_name="report", max_retries=max_retries
+    )
+
+
+def test_llm_report_policy_returns_text() -> None:
+    """Policy returns the scripted text from FakeLLMClient."""
+    policy = _make_policy(script=["Rapport narratif de test."])
+    ctx = build_report_context(encounter=_make_encounter(), spec_name="test")
+
+    result = policy(ctx)
+
+    assert result == "Rapport narratif de test."
+    assert policy.stats.calls == 1
+    assert policy.stats.retries == 0
+    assert policy.stats.fallbacks == 0
+
+
+def test_llm_report_policy_retry_on_exception() -> None:
+    """Policy retries on exception and increments retries counter."""
+    policy = _make_policy(
+        script=[Exception("boom"), "Rapport après retry."],  # type: ignore[list-item]
+        max_retries=1,
+    )
+    ctx = build_report_context(encounter=_make_encounter(), spec_name="test")
+
+    result = policy(ctx)
+
+    assert result == "Rapport après retry."
+    assert policy.stats.calls == 2
+    assert policy.stats.retries == 1
+    assert policy.stats.fallbacks == 0
+
+
+def test_llm_report_policy_fallback_after_max_retries() -> None:
+    """Policy returns empty string and increments fallbacks after max retries."""
+    policy = _make_policy(
+        script=[Exception("boom"), Exception("boom2")],  # type: ignore[list-item]
+        max_retries=1,
+    )
+    ctx = build_report_context(encounter=_make_encounter(), spec_name="test")
+
+    result = policy(ctx)
+
+    assert result == ""
+    assert policy.stats.calls == 2
+    assert policy.stats.retries == 1
+    assert policy.stats.fallbacks == 1
+
+
+def test_llm_report_policy_prompt_version_mismatch_raises() -> None:
+    """Policy rejects client with mismatched prompt_version."""
+    pack = PromptPack.load(FIXTURE_DIR)
+    builder = PromptBuilder(pack)
+    expected_version = pack.prompt_version("report")
+    client = FakeLLMClient(script=["x"], prompt_version=expected_version)
+    client.prompt_version = "wrong-version"
+
+    with pytest.raises(ValueError, match="prompt_version"):
+        LLMReportPolicy(client=client, builder=builder, prompt_name="report")