feat: event-lifecycle detection service (T52)

tests/test_event_lifecycle.py

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+"""Tests for the event-lifecycle detection service (T52).
+
+Per Phase 3, after each narrated turn we ask a classifier whether any
+active events transitioned (started, completed, cancelled). The bias is
+strongly toward an empty result — most turns do NOT resolve or start a
+known event, and the turn-flow caller (T61) only appends an
+event_started/completed/cancelled record when this service yields one.
+
+These tests cover:
+
+* The classifier returning a single transition is honored end-to-end.
+* An empty ``active_events`` list short-circuits before any LLM call,
+  so callers that hold no live events pay zero classifier cost.
+* Three rounds of malformed JSON exhaust ``classify``'s retries and we
+  fall back to the empty default — graceful degradation per §3.3.
+"""
+
+from __future__ import annotations
+
+import json
+
+import pytest
+
+from chat.llm.mock import MockLLMClient
+from chat.services.event_lifecycle import (
+    EventLifecycleDecision,
+    detect_event_transitions,
+)
+
+
+@pytest.mark.asyncio
+async def test_detects_one_transition_happy_path():
+    canned = json.dumps(
+        {
+            "transitions": [
+                {
+                    "event_id": "evt_1",
+                    "new_status": "completed",
+                    "reason": "they arrived at the park",
+                }
+            ]
+        }
+    )
+    mock = MockLLMClient(canned=[canned])
+    result = await detect_event_transitions(
+        mock,
+        classifier_model="x",
+        narrative_text="They walked through the park gate, finally there.",
+        active_events=[
+            {
+                "event_id": "evt_1",
+                "kind": "date_at_park",
+                "status": "active",
+                "props": {},
+            }
+        ],
+    )
+    assert isinstance(result, EventLifecycleDecision)
+    assert len(result.transitions) == 1
+    assert result.transitions[0].event_id == "evt_1"
+    assert result.transitions[0].new_status == "completed"
+    assert result.transitions[0].reason == "they arrived at the park"
+
+
+@pytest.mark.asyncio
+async def test_empty_active_events_short_circuits_without_classifier_call():
+    """No active events -> no classifier call.
+
+    The mock has an empty canned list; any ``generate`` call would raise
+    ``IndexError`` from ``list.pop(0)``. The test passing proves the
+    short-circuit holds.
+    """
+    mock = MockLLMClient(canned=[])
+    result = await detect_event_transitions(
+        mock,
+        classifier_model="x",
+        narrative_text="Just a quiet moment between them.",
+        active_events=[],
+    )
+    assert isinstance(result, EventLifecycleDecision)
+    assert result.transitions == []
+
+
+@pytest.mark.asyncio
+async def test_classifier_failure_returns_empty_default():
+    """``classify`` retries 3 times; after all fail it returns the empty
+    default so the turn flow keeps moving (§3.3 graceful degradation)."""
+    mock = MockLLMClient(canned=["bad", "bad", "bad"])
+    result = await detect_event_transitions(
+        mock,
+        classifier_model="x",
+        narrative_text="Some text the classifier will choke on.",
+        active_events=[
+            {
+                "event_id": "evt_1",
+                "kind": "date_at_park",
+                "status": "active",
+                "props": {},
+            }
+        ],
+    )
+    assert isinstance(result, EventLifecycleDecision)
+    assert result.transitions == []