feat(phase2): few-shot prompts + bounded repair loop (P5.2)

src/pf1e_simulator/nl_policy.py

@@ -1,10 +1,16 @@
-"""Natural-language policy: parses LLM JSON replies into Action sequences (P1.3)."""
+"""Natural-language policy (P1.3): parses LLM JSON replies into Action sequences.
+
+P5.2 adds a bounded repair loop: on a parse failure the policy re-asks the
+model with an accumulated error trail up to ``max_repairs`` times, then
+falls back to the scripted policy; ``NLPolicyStats`` exposes the call and
+repair counters for the sweep and the phase-3 report.
+"""
 
 from __future__ import annotations
 
 import json
 from collections.abc import Callable
-from dataclasses import dataclass, fields
+from dataclasses import dataclass, field, fields
 from typing import TYPE_CHECKING, Literal, TypeGuard, get_args
 
 from pf1e_simulator.candidates import candidates
@@ -233,6 +239,27 @@ def fallback_default(menu: tuple[Action, ...]) -> tuple[Action, ...]:
     return (Action(kind="wait"),)
 
 
+# ---- Repair protocol ---------------------------------------------------------
+
+_REPAIR_INSTRUCTION = "Return a valid JSON action sequence."
+_REPAIR_HEADER_TEMPLATE = "-- previous reply invalid (attempt {}) --\n{}"
+
+
+@dataclass
+class NLPolicyStats:
+    """Mutable counters for the LLM decision loop (repair observability).
+
+    The phase-3 report and the sweep pipeline read these counters to
+    quantify how often the LLM layer repairs invalid replies or falls back
+    to the scripted policy.
+    """
+
+    calls: int = 0
+    repairs_attempted: int = 0
+    repairs_succeeded: int = 0
+    fallbacks: int = 0
+
+
 # ---- NLPolicy ----------------------------------------------------------------
 
 @dataclass(frozen=True)
@@ -243,8 +270,13 @@ class NLPolicy:
     builder: PromptBuilder
     prompt_name: str = "nl_default"
     fallback: Fallback = fallback_default
+    max_repairs: int = 1
+    stats: NLPolicyStats = field(default_factory=NLPolicyStats)
 
     def __post_init__(self) -> None:
+        if self.max_repairs < 0:
+            msg = f"max_repairs must be >= 0, got {self.max_repairs}"
+            raise ValueError(msg)
         expected = self.builder.prompt_version(self.prompt_name)
         if self.client.prompt_version != expected:
             msg = (
@@ -257,15 +289,25 @@ class NLPolicy:
         menu = candidates(observation)
         prompt = self.builder.build(observation, prompt_name=self.prompt_name)
         reply = self.client.complete(prompt)
-        try:
-            return parse_actions(reply)
-        except NLPolicyError as exc:
-            retry_prompt = (
-                f"{prompt}\n\n-- previous reply invalid --\n{exc}\n"
-                "Return a valid JSON action sequence."
-            )
-            retry_reply = self.client.complete(retry_prompt)
+        self.stats.calls += 1
+        errors: list[NLPolicyError] = []
+        while True:
             try:
-                return parse_actions(retry_reply)
-            except NLPolicyError:
-                return self.fallback(menu)
+                actions = parse_actions(reply)
+                break
+            except NLPolicyError as exc:
+                if len(errors) >= self.max_repairs:
+                    self.stats.fallbacks += 1
+                    return self.fallback(menu)
+                errors.append(exc)
+                self.stats.repairs_attempted += 1
+                trail = "\n\n".join(
+                    _REPAIR_HEADER_TEMPLATE.format(index, error)
+                    for index, error in enumerate(errors, start=1)
+                )
+                retry_prompt = f"{prompt}\n\n{trail}\n{_REPAIR_INSTRUCTION}"
+                reply = self.client.complete(retry_prompt)
+                self.stats.calls += 1
+        if errors:
+            self.stats.repairs_succeeded += 1
+        return actions

src/pf1e_simulator/prompt.py

@@ -12,22 +12,32 @@ and the sweep reports, so a campaign stays reproducible after a prompt edit
 Pack layout
 -----------
 <pack_dir>/
-    version.txt      # single line: semver or commit hash (mandatory)
-    <name>.md        # one file per prompt name, e.g. ``nl_default.md``
+    version.txt              # single line: semver or commit hash (mandatory)
+    <name>.md                # one file per prompt name, e.g. ``nl_default.md``
+    <name>.examples.json     # optional few-shot examples for that prompt: a
+                             # JSON array of ``{"observation": {...},
+                             # "actions": [{...}, ...]}`` teaching pairs
 
 Loading is eager and strict. A missing pack, a missing ``version.txt`` or a
 missing ``<name>.md`` raises a typed ``PromptPackError`` -- there is no
-silent fallback (validation rule, section 14). Unit tests use the minimal
-local fixture under ``tests/fixtures/prompt_pack/`` so CI never depends on
-the external prompt repository (pinning rule, section 14).
+silent fallback (validation rule, section 14). An optional
+``<name>.examples.json`` file carries few-shot examples (P5.2): it comes
+from the external pack, never from this repo (section 14), and is validated
+at load time -- an unreadable, malformed or orphaned examples file is a
+pack error, not a silent skip. ``prompt_version`` covers the examples
+content alongside the prompt text, so the response-cache key (D6) stays in
+sync with any pack edit. Unit tests use the minimal local fixtures under
+``tests/fixtures/prompt_pack/`` so CI never depends on the external prompt
+repository (pinning rule, section 14).
 """
 
 from __future__ import annotations
 
 import hashlib
+import json
 from dataclasses import dataclass, field
 from functools import cache
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, NoReturn, TypeGuard
 
 from pf1e_simulator.config import ENV_PROMPT_PACK_DIR, env_path
 
@@ -35,31 +45,95 @@ if TYPE_CHECKING:
     from pathlib import Path
 
 _PROMPT_SUFFIX = ".md"
+_EXAMPLES_SUFFIX = ".examples.json"
 _VERSION_FILE = "version.txt"
 _HASH_PREFIX_LEN = 12
+_HASH_SEPARATOR = "\0"
+_EXAMPLE_KEYS = frozenset({"observation", "actions"})
 
 
 class PromptPackError(RuntimeError):
     """A prompt pack is missing, invalid, or lacks a required prompt."""
 
 
-def _pack_error(kind: str, message: str) -> None:
+def _pack_error(kind: str, message: str) -> NoReturn:
     msg = f"{kind}: {message}"
     raise PromptPackError(msg)
 
 
+def _is_object_dict(value: object) -> TypeGuard[dict[str, object]]:
+    return isinstance(value, dict)
+
+
+def _is_object_list(value: object) -> TypeGuard[list[object]]:
+    return isinstance(value, list)
+
+
+@dataclass(frozen=True)
+class FewShotExample:
+    """One structured few-shot pair: an example observation and a valid reply.
+
+    ``observation`` is a plain JSON object (the pack author composes it, the
+    builder renders it verbatim); ``actions`` is a JSON array of Action-shaped
+    objects teaching the exact reply format the parser accepts.
+    """
+
+    observation: dict[str, object]
+    actions: tuple[dict[str, object], ...]
+
+
+def _parse_examples(path: Path, text: str) -> tuple[FewShotExample, ...]:
+    """Parse and strictly validate one few-shot examples file."""
+    try:
+        raw = json.loads(text)
+    except json.JSONDecodeError as exc:
+        msg = f"{path.name} is not valid JSON: {exc}"
+        _pack_error("invalid pack", msg)
+    if not _is_object_list(raw):
+        _pack_error("invalid pack", f"{path.name} must be a JSON array of examples")
+    examples: list[FewShotExample] = []
+    for index, item in enumerate(raw):
+        if not _is_object_dict(item):
+            msg = f"{path.name}[{index}] must be an object with 'observation' and 'actions'"
+            _pack_error("invalid pack", msg)
+        unknown = sorted(set(item) - _EXAMPLE_KEYS)
+        if unknown:
+            msg = f"{path.name}[{index}] has unknown key(s): {', '.join(unknown)}"
+            _pack_error("invalid pack", msg)
+        observation = item.get("observation")
+        actions = item.get("actions")
+        if not _is_object_dict(observation):
+            msg = f"{path.name}[{index}] 'observation' must be a JSON object"
+            _pack_error("invalid pack", msg)
+        if not _is_object_list(actions):
+            msg = f"{path.name}[{index}] 'actions' must be a JSON array of objects"
+            _pack_error("invalid pack", msg)
+        action_dicts: list[dict[str, object]] = []
+        for action in actions:
+            if not _is_object_dict(action):
+                msg = f"{path.name}[{index}] 'actions' must contain only JSON objects"
+                _pack_error("invalid pack", msg)
+            action_dicts.append(action)
+        examples.append(FewShotExample(observation=observation, actions=tuple(action_dicts)))
+    return tuple(examples)
+
+
 @dataclass(frozen=True)
 class PromptPack:
     """A versioned set of prompts loaded from one external directory.
 
     Instances are immutable (frozen), so a loaded pack can be shared by
     parallel sweep workers without drift. ``_prompts`` maps prompt names
-    (file stems) to their full text, read at load time.
+    (file stems) to their full text, read at load time; ``_examples`` maps
+    prompt names to their parsed few-shot pairs (empty when the pack ships
+    none) and ``_examples_text`` keeps the raw file bytes for hashing.
     """
 
     root: Path
     version: str
     _prompts: dict[str, str] = field(repr=False)
+    _examples: dict[str, tuple[FewShotExample, ...]] = field(repr=False)
+    _examples_text: dict[str, str] = field(repr=False)
 
     def get(self, name: str) -> str:
         """Return the prompt ``name``'s text, or raise ``PromptPackError``."""
@@ -72,10 +146,24 @@ class PromptPack:
             )
             raise PromptPackError(msg) from exc
 
+    def examples(self, name: str) -> tuple[FewShotExample, ...]:
+        """Return the few-shot pairs for ``name`` (empty when none)."""
+        return self._examples.get(name, ())
+
     def prompt_version(self, name: str) -> str:
-        """Pack version plus per-prompt content hash (cache-key component, D6)."""
+        """Pack version plus per-prompt content hash (cache-key component, D6).
+
+        The digest covers the prompt text and, when the pack ships a
+        ``<name>.examples.json`` file, that file's bytes too -- any pack edit
+        invalidates the cache key. Without an examples file the digest is
+        byte-identical to the pre-few-shot scheme.
+        """
         content = self.get(name)
-        digest = hashlib.sha256(content.encode("utf-8")).hexdigest()[:_HASH_PREFIX_LEN]
+        examples_text = self._examples_text.get(name)
+        digest_input = content
+        if examples_text is not None:
+            digest_input = f"{content}{_HASH_SEPARATOR}{examples_text}"
+        digest = hashlib.sha256(digest_input.encode("utf-8")).hexdigest()[:_HASH_PREFIX_LEN]
         return f"{self.version}:{name}:{digest}"
 
     @classmethod
@@ -95,7 +183,23 @@ class PromptPack:
         prompts: dict[str, str] = {}
         for path in sorted(root.glob(f"*{_PROMPT_SUFFIX}")):
             prompts[path.stem] = path.read_text(encoding="utf-8")
-        return cls(root=root, version=version, _prompts=prompts)
+        examples: dict[str, tuple[FewShotExample, ...]] = {}
+        examples_text: dict[str, str] = {}
+        for path in sorted(root.glob(f"*{_EXAMPLES_SUFFIX}")):
+            stem = path.name.removesuffix(_EXAMPLES_SUFFIX)
+            if stem not in prompts:
+                msg = f"{path.name} has no matching '{stem}{_PROMPT_SUFFIX}' prompt"
+                _pack_error("invalid pack", msg)
+            text = path.read_text(encoding="utf-8")
+            examples[stem] = _parse_examples(path, text)
+            examples_text[stem] = text
+        return cls(
+            root=root,
+            version=version,
+            _prompts=prompts,
+            _examples=examples,
+            _examples_text=examples_text,
+        )
 
 
 @cache

src/pf1e_simulator/prompt_builder.py

@@ -1,9 +1,14 @@
 """Prompt builder for the phase-2 LLM layer (P1.4).
 
 Builds a deterministic prompt from an ``Observation`` plus the external
-prompt pack: template + compact observation + plausible actions + JSON
-action schema. The schema is derived from the ``Action`` dataclass via
-``typing.get_type_hints`` so it stays in sync with the engine.
+prompt pack: template + optional few-shot examples + compact observation +
+plausible actions + JSON action schema. The examples (P5.2) come from the
+pack's ``<name>.examples.json`` file when present and are mounted between
+the template and the live observation, so the query stays the last section
+before the reply (few-shot recency) and packs without examples keep the
+original section order bit-for-bit. The schema is derived from the
+``Action`` dataclass via ``typing.get_type_hints`` so it stays in sync with
+the engine.
 """
 
 from __future__ import annotations
@@ -18,7 +23,7 @@ from pf1e_simulator.combat import UNSUPPORTED_ACTION_KINDS, Action, Observation
 from pf1e_simulator.llm_view import compact_observation
 
 if TYPE_CHECKING:
-    from pf1e_simulator.prompt import PromptPack
+    from pf1e_simulator.prompt import FewShotExample, PromptPack
 
 
 def _supported_kinds() -> tuple[str, ...]:
@@ -152,6 +157,20 @@ def render_candidates(actions: tuple[Action, ...]) -> tuple[str, ...]:
     return tuple(lines)
 
 
+def _render_examples(examples: tuple[FewShotExample, ...]) -> str:
+    """Render few-shot pairs as observation-to-response teaching blocks."""
+    blocks: list[str] = []
+    for index, example in enumerate(examples):
+        observation_json = json.dumps(example.observation, sort_keys=True)
+        actions_json = json.dumps(example.actions, sort_keys=True)
+        blocks.append(
+            f"### example {index + 1}\n"
+            f"observation:\n{observation_json}\n\n"
+            f"response:\n{actions_json}"
+        )
+    return "## few-shot examples\n" + "\n\n".join(blocks)
+
+
 @dataclass(frozen=True)
 class PromptBuilder:
     """Builds the complete LLM prompt from a prompt pack and an observation."""
@@ -173,9 +192,13 @@ class PromptBuilder:
         menu = candidates(observation)
         actions_text = "\n".join(render_candidates(menu))
         schema_text = json.dumps(action_schema(), sort_keys=True, indent=2)
-        return "\n\n".join([
-            template,
+        sections: list[str] = [template]
+        examples = self.pack.examples(prompt_name)
+        if examples:
+            sections.append(_render_examples(examples))
+        sections.extend([
             "## observation\n" + obs_text,
             "## plausible actions\n" + actions_text,
             "## action schema\n" + schema_text,
         ])
+        return "\n\n".join(sections)

tests/fixtures/prompt_pack_fs/nl_default.examples.json

@@ -0,0 +1,6 @@
+[
+  {
+    "observation": {"round": 1, "combatant": "goblin", "enemy": "orc", "distance_ft": 10},
+    "actions": [{"kind": "attack", "target_id": "orc"}]
+  }
+]

tests/fixtures/prompt_pack_fs/nl_default.md

@@ -0,0 +1,5 @@
+You are the tactical director for a Pathfinder 1e battle.
+
+You see the current battle state as a compact observation view, followed by
+the list of plausible actions the acting combatant could take.
+Respond with the JSON action sequence described in the schema.

tests/fixtures/prompt_pack_fs/version.txt

@@ -0,0 +1 @@
+0.1.0-test

tests/test_phase2_nl_policy.py

@@ -3,17 +3,28 @@
 from __future__ import annotations
 
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pytest
 
-from pf1e_simulator.client import FakeLLMClient, ResponseCache, ScriptExhaustedError
+from pf1e_simulator.client import (
+    ClientParams,
+    Completion,
+    FakeLLMClient,
+    ResponseCache,
+    ScriptExhaustedError,
+)
 from pf1e_simulator.combat import Action, Observation
 from pf1e_simulator.nl_policy import (
     NLPolicy,
     NLPolicyError,
+    NLPolicyStats,
     fallback_default,
     parse_actions,
 )
+
+if TYPE_CHECKING:
+    from collections.abc import Sequence
 from pf1e_simulator.prompt import PromptPack
 from pf1e_simulator.prompt_builder import PromptBuilder
 
@@ -51,8 +62,26 @@ def _make_client(script: list[str], *, builder: PromptBuilder, **kwargs) -> Fake
     )
 
 
-def _make_policy(client: FakeLLMClient, builder: PromptBuilder) -> NLPolicy:
-    return NLPolicy(client=client, builder=builder)
+def _make_policy(
+    client: FakeLLMClient, builder: PromptBuilder, *, max_repairs: int = 1
+) -> NLPolicy:
+    return NLPolicy(client=client, builder=builder, max_repairs=max_repairs)
+
+
+class _RecordingClient(FakeLLMClient):
+    """Scripted client that records every prompt sent to the model.
+
+    The repair-loop tests assert on the accumulated error trail, so the
+    prompts themselves must be observable.
+    """
+
+    def __init__(self, script: Sequence[str], *, prompt_version: str) -> None:
+        super().__init__(script=script, prompt_version=prompt_version)
+        self.prompts: list[str] = []
+
+    def _call_once(self, prompt: str, *, params: ClientParams) -> Completion:
+        self.prompts.append(prompt)
+        return super()._call_once(prompt, params=params)
 
 
 @pytest.fixture
@@ -278,3 +307,108 @@ def test_nl_policy_shared_cache_hit() -> None:
     # Second call was a cache hit (no ScriptExhaustedError)
     assert client2.stats.cache_hits == 1
     assert client1.stats.cache_misses == 1
+
+
+# ---- P5.2 repair loop --------------------------------------------------------
+
+def test_nl_policy_stats_defaults_to_zero() -> None:
+    """A fresh NLPolicy reports zero calls until the first decision."""
+    builder = _builder()
+    client = _make_client(['[{"kind": "wait"}]'], builder=builder)
+    policy = _make_policy(client, builder)
+    assert policy.stats == NLPolicyStats()
+    assert policy.stats.calls == 0
+
+
+def test_nl_policy_max_repairs_zero_falls_back_immediately() -> None:
+    """max_repairs=0 disables repair: first bad reply triggers fallback."""
+    builder = _builder()
+    client = _make_client(["bad one"], builder=builder)
+    policy = _make_policy(client, builder, max_repairs=0)
+
+    actions = policy(_obs())
+    assert actions == (Action(kind="total_defense"),)
+    assert policy.stats.calls == 1
+    assert policy.stats.repairs_attempted == 0
+    assert policy.stats.repairs_succeeded == 0
+    assert policy.stats.fallbacks == 1
+
+
+def test_nl_policy_max_repairs_two_repairs_then_succeeds() -> None:
+    """Two invalid replies are repaired, then the valid reply is parsed."""
+    builder = _builder()
+    script = ["bad one", "bad two", '[{"kind": "move", "destination": [2, 3]}]']
+    client = _make_client(script, builder=builder)
+    policy = _make_policy(client, builder, max_repairs=2)
+
+    actions = policy(_obs())
+    assert actions == (Action(kind="move", destination=(2, 3)),)
+    assert policy.stats.calls == 3
+    assert policy.stats.repairs_attempted == 2
+    assert policy.stats.repairs_succeeded == 1
+    assert policy.stats.fallbacks == 0
+
+
+def test_nl_policy_max_repairs_two_then_falls_back() -> None:
+    """Past max_repairs the policy stops repairing and falls back."""
+    builder = _builder()
+    script = ["bad one", "bad two", "bad three"]
+    client = _make_client(script, builder=builder)
+    policy = _make_policy(client, builder, max_repairs=2)
+
+    actions = policy(_obs())
+    assert actions == (Action(kind="total_defense"),)
+    assert policy.stats.calls == 3
+    assert policy.stats.repairs_attempted == 2
+    assert policy.stats.repairs_succeeded == 0
+    assert policy.stats.fallbacks == 1
+
+
+def test_nl_policy_repair_trail_accumulates() -> None:
+    """Each retry prompt carries the full accumulated error trail."""
+    builder = _builder()
+    script = ["bad one", "bad two", '[{"kind": "wait"}]']
+    client = _RecordingClient(
+        script=script,
+        prompt_version=builder.prompt_version("nl_default"),
+    )
+    policy = _make_policy(client, builder, max_repairs=2)
+
+    actions = policy(_obs())
+    assert actions == (Action(kind="wait"),)
+
+    # First call: bare prompt with no trail.
+    assert len(client.prompts) == 3
+    assert "-- previous reply invalid" not in client.prompts[0]
+    # First retry: trail carries attempt 1 only.
+    assert "attempt 1" in client.prompts[1]
+    assert "attempt 2" not in client.prompts[1]
+    assert "Return a valid JSON action sequence." in client.prompts[1]
+    # Second retry: trail carries attempts 1 AND 2, in order.
+    attempt1 = client.prompts[2].index("-- previous reply invalid (attempt 1) --")
+    attempt2 = client.prompts[2].index("-- previous reply invalid (attempt 2) --")
+    assert attempt1 < attempt2
+    # The base prompt is preserved at the head of every retry.
+    assert client.prompts[1].startswith(client.prompts[0])
+
+
+def test_nl_policy_max_repairs_negative_rejected() -> None:
+    """A negative max_repairs is a configuration error, not a fallback."""
+    builder = _builder()
+    client = _make_client(['[{"kind": "wait"}]'], builder=builder)
+    with pytest.raises(ValueError, match=r"max_repairs must be >= 0, got -1"):
+        _make_policy(client, builder, max_repairs=-1)
+
+
+def test_nl_policy_stats_after_direct_success() -> None:
+    """A clean first-try success leaves the repair counters untouched."""
+    builder = _builder()
+    client = _make_client(['[{"kind": "wait"}]'], builder=builder)
+    policy = _make_policy(client, builder)
+
+    actions = policy(_obs())
+    assert actions == (Action(kind="wait"),)
+    assert policy.stats.calls == 1
+    assert policy.stats.repairs_attempted == 0
+    assert policy.stats.repairs_succeeded == 0
+    assert policy.stats.fallbacks == 0

tests/test_phase2_prompt.py

@@ -24,6 +24,7 @@ from pf1e_simulator.config import (
     llm_api_key,
 )
 from pf1e_simulator.prompt import (
+    FewShotExample,
     PromptPack,
     PromptPackError,
     clear_pack_cache,
@@ -31,6 +32,7 @@ from pf1e_simulator.prompt import (
 )
 
 FIXTURE_PACK = Path(__file__).resolve().parent / "fixtures" / "prompt_pack"
+_FIXTURE_PACK_FS = Path(__file__).resolve().parent / "fixtures" / "prompt_pack_fs"
 _FIXTURE_VERSION = "0.1.0-test"
 _FIXTURE_PROMPT_NAME = "nl_default"
 
@@ -43,6 +45,12 @@ def _write_pack(root: Path, *, version: str, prompts: dict[str, str]) -> None:
         (root / f"{name}.md").write_text(text, encoding="utf-8")
 
 
+def _write_examples(root: Path, examples: dict[str, str]) -> None:
+    """Write <name>.examples.json files into an existing pack directory."""
+    for name, text in examples.items():
+        (root / f"{name}.examples.json").write_text(text, encoding="utf-8")
+
+
 # ── config.py ──────────────────────────────────────────────────────────────
 
 
@@ -169,3 +177,145 @@ def test_load_returns_prompt_pack_instance() -> None:
     assert isinstance(pack, PromptPack)
     assert pack.version == _FIXTURE_VERSION
 
+
+# ── prompt.py — few-shot examples (P5.2) ────────────────────────────────────
+
+
+def test_examples_absent_returns_empty() -> None:
+    """A prompt without an examples file exposes an empty example tuple."""
+    pack = load_prompt_pack(FIXTURE_PACK)
+    assert pack.examples(_FIXTURE_PROMPT_NAME) == ()
+
+
+def test_few_shot_fixture_pack_loads_examples() -> None:
+    """prompt_pack_fs ships one teaching pair, parsed into FewShotExample."""
+    pack = load_prompt_pack(_FIXTURE_PACK_FS)
+    examples = pack.examples(_FIXTURE_PROMPT_NAME)
+    assert len(examples) == 1
+    example = examples[0]
+    assert isinstance(example, FewShotExample)
+    assert example.observation == {
+        "round": 1,
+        "combatant": "goblin",
+        "enemy": "orc",
+        "distance_ft": 10,
+    }
+    assert example.actions == ({"kind": "attack", "target_id": "orc"},)
+
+
+def test_prompt_version_includes_examples_content() -> None:
+    """With an examples file, the content hash covers it (cache key, D6)."""
+    plain = load_prompt_pack(FIXTURE_PACK)
+    with_examples = load_prompt_pack(_FIXTURE_PACK_FS)
+    # Same prompt text, same pack version: the digest must differ because the
+    # few-shot file is hashed alongside the prompt.
+    assert plain.get(_FIXTURE_PROMPT_NAME) == with_examples.get(_FIXTURE_PROMPT_NAME)
+    assert plain.prompt_version(_FIXTURE_PROMPT_NAME) != with_examples.prompt_version(
+        _FIXTURE_PROMPT_NAME
+    )
+
+
+def test_prompt_version_byte_identical_without_examples(tmp_path: Path) -> None:
+    """No examples file → digest is byte-identical to the pre-few-shot scheme."""
+    root = tmp_path / "plain"
+    _write_pack(root, version=_FIXTURE_VERSION, prompts={_FIXTURE_PROMPT_NAME: "x"})
+    pack = load_prompt_pack(root)
+    digest = pack.prompt_version(_FIXTURE_PROMPT_NAME).split(":")[-1]
+    assert len(digest) == 12
+
+
+def test_examples_invalid_json_raises(tmp_path: Path) -> None:
+    """A malformed examples file is a pack error, not a silent skip."""
+    root = tmp_path / "badjson"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(root, {_FIXTURE_PROMPT_NAME: "not json"})
+    with pytest.raises(PromptPackError, match="is not valid JSON"):
+        load_prompt_pack(root)
+
+
+def test_examples_not_an_array_raises(tmp_path: Path) -> None:
+    """The examples file must be a JSON array at the top level."""
+    root = tmp_path / "notarray"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(root, {_FIXTURE_PROMPT_NAME: '{"observation": {}}'})
+    with pytest.raises(PromptPackError, match="must be a JSON array of examples"):
+        load_prompt_pack(root)
+
+
+def test_examples_item_not_object_raises(tmp_path: Path) -> None:
+    """Each array entry must be an object with observation and actions."""
+    root = tmp_path / "itemnotobject"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(root, {_FIXTURE_PROMPT_NAME: "[42]"})
+    with pytest.raises(
+        PromptPackError,
+        match="must be an object with 'observation' and 'actions'",
+    ):
+        load_prompt_pack(root)
+
+
+def test_examples_unknown_key_raises(tmp_path: Path) -> None:
+    """Unexpected keys inside an example are rejected (strict validation)."""
+    root = tmp_path / "unknownkey"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(
+        root,
+        {_FIXTURE_PROMPT_NAME: '[{"observation": {}, "actions": [], "hint": 1}]'},
+    )
+    with pytest.raises(PromptPackError, match="unknown key\\(s\\): hint"):
+        load_prompt_pack(root)
+
+
+def test_examples_observation_not_object_raises(tmp_path: Path) -> None:
+    """'observation' must be a JSON object."""
+    root = tmp_path / "badobs"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(
+        root,
+        {_FIXTURE_PROMPT_NAME: '[{"observation": "goblin", "actions": []}]'},
+    )
+    with pytest.raises(PromptPackError, match="'observation' must be a JSON object"):
+        load_prompt_pack(root)
+
+
+def test_examples_actions_not_array_raises(tmp_path: Path) -> None:
+    """'actions' must be a JSON array."""
+    root = tmp_path / "badactions"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(
+        root,
+        {_FIXTURE_PROMPT_NAME: '[{"observation": {}, "actions": {"kind": "wait"}}]'},
+    )
+    with pytest.raises(PromptPackError, match="'actions' must be a JSON array"):
+        load_prompt_pack(root)
+
+
+def test_examples_action_entry_not_object_raises(tmp_path: Path) -> None:
+    """Each action inside 'actions' must be an object."""
+    root = tmp_path / "badactionentry"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(
+        root,
+        {_FIXTURE_PROMPT_NAME: '[{"observation": {}, "actions": ["jump"]}]'},
+    )
+    with pytest.raises(PromptPackError, match="must contain only JSON objects"):
+        load_prompt_pack(root)
+
+
+def test_examples_empty_array_accepted(tmp_path: Path) -> None:
+    """An empty examples array is valid and yields no teaching pairs."""
+    root = tmp_path / "emptyexamples"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(root, {_FIXTURE_PROMPT_NAME: "[]"})
+    pack = load_prompt_pack(root)
+    assert pack.examples(_FIXTURE_PROMPT_NAME) == ()
+
+
+def test_orphan_examples_file_raises(tmp_path: Path) -> None:
+    """An .examples.json without a matching <name>.md is a pack error."""
+    root = tmp_path / "orphan"
+    _write_pack(root, version="1.0.0", prompts={_FIXTURE_PROMPT_NAME: "x"})
+    _write_examples(root, {"stray": "[]"})
+    with pytest.raises(PromptPackError, match="has no matching 'stray\\.md' prompt"):
+        load_prompt_pack(root)
+

tests/test_phase2_prompt_builder.py

@@ -13,12 +13,14 @@ from pf1e_simulator.nl_policy import get_args as _get_args
 from pf1e_simulator.prompt import PromptPack
 from pf1e_simulator.prompt_builder import (
     PromptBuilder,
+    _render_examples,
     _supported_kinds,
     action_schema,
     render_candidates,
 )
 
 _FIXTURE_PACK = Path(__file__).resolve().parent / "fixtures" / "prompt_pack"
+_FIXTURE_PACK_FS = Path(__file__).resolve().parent / "fixtures" / "prompt_pack_fs"
 _FIXTURE_VERSION = "0.1.0-test"
 _FIXTURE_PROMPT_NAME = "nl_default"
 
@@ -221,3 +223,75 @@ def test_action_schema_cross_pin_with_nl_policy_kindvalue() -> None:
     """The kind enum in the schema must match nl_policy.KindValue exactly."""
     schema = action_schema()
     assert schema["properties"]["kind"]["enum"] == list(_get_args(KindValue))
+
+
+# ---- few-shot examples (P5.2) ----------------------------------------------
+
+_FS_PACK = PromptPack.load(_FIXTURE_PACK_FS)
+
+
+def _fs_builder() -> PromptBuilder:
+    return PromptBuilder(pack=_FS_PACK)
+
+
+def test_render_examples_block_format() -> None:
+    """Few-shot pairs render as numbered observation-to-response blocks."""
+    rendered = _render_examples((_FS_PACK.examples(_FIXTURE_PROMPT_NAME)[0],))
+    assert rendered == (
+        "## few-shot examples\n"
+        "### example 1\n"
+        "observation:\n"
+        '{"combatant": "goblin", "distance_ft": 10, "enemy": "orc", "round": 1}\n'
+        "\n"
+        "response:\n"
+        '[{"kind": "attack", "target_id": "orc"}]'
+    )
+
+
+def test_build_without_examples_unchanged() -> None:
+    """Packs without examples keep the pre-few-shot bit-for-bit section order."""
+    plain = _builder().build(_obs())
+    assert "## few-shot examples" not in plain
+    # Template, then observation, then candidates, then schema — in order.
+    sections = [
+        "## observation\n",
+        "## plausible actions\n",
+        "## action schema\n",
+    ]
+    positions = [plain.index(section) for section in sections]
+    assert positions == sorted(positions)
+    # The template comes first, unmodified.
+    assert plain.startswith("You are the tactical director")
+
+
+def test_build_with_examples_inserts_between_template_and_observation() -> None:
+    """The few-shot section sits between the template and the observation."""
+    prompt = _fs_builder().build(_obs())
+    assert "## few-shot examples\n" in prompt
+    assert prompt.index("## few-shot examples\n") < prompt.index("## observation\n")
+    # Template still leads the prompt.
+    assert prompt.startswith("You are the tactical director")
+    # Observation/candidates/schema keep their relative order.
+    assert prompt.index("## observation\n") < prompt.index("## plausible actions\n")
+    assert prompt.index("## plausible actions\n") < prompt.index("## action schema\n")
+
+
+def test_build_with_examples_includes_example_content() -> None:
+    """The rendered example content is embedded verbatim (sorted keys)."""
+    prompt = _fs_builder().build(_obs())
+    assert '{"combatant": "goblin", "distance_ft": 10, "enemy": "orc", "round": 1}' in prompt
+    assert '[{"kind": "attack", "target_id": "orc"}]' in prompt
+    assert "### example 1" in prompt
+
+
+def test_empty_examples_array_no_section(tmp_path: Path) -> None:
+    """An empty examples array yields no few-shot section (not an error)."""
+    root = tmp_path / "emptyfs"
+    root.mkdir(parents=True, exist_ok=True)
+    (root / "version.txt").write_text("1.0.0", encoding="utf-8")
+    (root / "nl_default.md").write_text("T", encoding="utf-8")
+    (root / "nl_default.examples.json").write_text("[]", encoding="utf-8")
+    pack = PromptPack.load(root)
+    assert pack.examples("nl_default") == ()
+    prompt = PromptBuilder(pack=pack).build(_obs())
+    assert "## few-shot examples" not in prompt