feat: interjection classifier service

tests/test_interjection.py

@@ -0,0 +1,89 @@
+"""Tests for the interjection classifier service (T39).
+
+Per Requirements §6.2, when a guest is present and the addressee bot has
+just spoken, the *non-addressee* bot may interject with a brief follow-on
+beat. The classifier wrapped here decides whether that interjection
+should fire. The default bias is strongly toward False — the addressee
+has the floor — so an interjection only fires when the silent witness's
+character would plausibly speak up.
+
+These tests cover:
+
+* The classifier returning ``should_interject=True`` is honored.
+* The classifier returning ``should_interject=False`` is honored.
+* Repeated invalid JSON exhausts the classifier retries and falls back
+  to ``should_interject=False`` with ``reason="fallback"``.
+"""
+
+from __future__ import annotations
+
+import json
+
+import pytest
+
+from chat.llm.mock import MockLLMClient
+from chat.services.interjection import (
+    InterjectionDecision,
+    detect_interjection,
+)
+
+
+def _kwargs() -> dict:
+    """Reasonable, non-empty kwargs for ``detect_interjection``."""
+    return dict(
+        classifier_model="x",
+        addressee_name="Alice",
+        addressee_just_said="I think we should leave now.",
+        silent_witness_name="Bob",
+        silent_witness_persona="Skeptical engineer, blunt, protective of the user.",
+        silent_witness_edge_to_addressee={
+            "affinity": 40,
+            "trust": 30,
+            "summary": "old rival; mild distrust",
+        },
+        silent_witness_edge_to_you={
+            "affinity": 70,
+            "trust": 80,
+            "summary": "long-time confidant",
+        },
+        you_just_said="Where do you both think we should go?",
+    )
+
+
+@pytest.mark.asyncio
+async def test_interjection_returns_true_when_classifier_decides_yes():
+    canned = json.dumps({"should_interject": True, "reason": "jealousy"})
+    mock = MockLLMClient(canned=[canned])
+    result = await detect_interjection(mock, **_kwargs())
+    assert isinstance(result, InterjectionDecision)
+    assert result.should_interject is True
+    assert result.reason == "jealousy"
+
+
+@pytest.mark.asyncio
+async def test_interjection_returns_false_when_classifier_decides_no():
+    canned = json.dumps(
+        {"should_interject": False, "reason": "addressee has the floor"}
+    )
+    mock = MockLLMClient(canned=[canned])
+    result = await detect_interjection(mock, **_kwargs())
+    assert isinstance(result, InterjectionDecision)
+    assert result.should_interject is False
+    assert result.reason == "addressee has the floor"
+
+
+@pytest.mark.asyncio
+async def test_interjection_falls_back_to_false_on_classifier_failure():
+    """``classify`` retries 3 times; after all fail it returns the default.
+
+    The default carries ``should_interject=False`` and
+    ``reason="fallback"`` so callers can tell a real "no" from a
+    classifier-degraded "no" if they ever care to.
+    """
+    mock = MockLLMClient(
+        canned=["this is not json", "still not json", "still not json"]
+    )
+    result = await detect_interjection(mock, **_kwargs())
+    assert isinstance(result, InterjectionDecision)
+    assert result.should_interject is False
+    assert result.reason == "fallback"