feat: thread-detection service (T55)

tests/test_thread_detection.py

@@ -0,0 +1,128 @@
+"""Tests for the thread-detection service (T55).
+
+On scene close, the transcript is classified to detect open threads
+(unresolved arcs, dangling questions, promises made). The service can
+also signal **update** to an existing thread when the scene developed
+it, or **close** when the scene resolved it.
+
+These tests cover:
+
+* A new thread the scene introduced — action="open" with a fresh title.
+* An update to an existing thread — action="update" with
+  ``existing_thread_id`` referencing the prior thread.
+* Classifier failure — three bad responses degrade to an empty
+  candidates list (graceful degradation, §3.3).
+* Empty transcript short-circuits before any classifier call.
+"""
+
+from __future__ import annotations
+
+import json
+
+import pytest
+
+from chat.llm.mock import MockLLMClient
+from chat.services.thread_detection import (
+    ThreadCandidate,
+    ThreadDetectionResult,
+    detect_threads,
+)
+
+
+@pytest.mark.asyncio
+async def test_detects_new_thread_open():
+    canned = json.dumps(
+        {
+            "candidates": [
+                {
+                    "action": "open",
+                    "title": "Maya's job hunt",
+                    "summary": "Maya is looking for a new job",
+                    "existing_thread_id": None,
+                }
+            ]
+        }
+    )
+    mock = MockLLMClient(canned=[canned])
+    result = await detect_threads(
+        mock,
+        classifier_model="x",
+        scene_transcript=[
+            {"speaker": "Maya", "text": "I need to find a new job soon."},
+            {"speaker": "Sam", "text": "What kind of role are you looking for?"},
+        ],
+        open_threads=[],
+    )
+    assert isinstance(result, ThreadDetectionResult)
+    assert len(result.candidates) == 1
+    cand = result.candidates[0]
+    assert isinstance(cand, ThreadCandidate)
+    assert cand.action == "open"
+    assert cand.title == "Maya's job hunt"
+    assert cand.summary == "Maya is looking for a new job"
+    assert cand.existing_thread_id is None
+
+
+@pytest.mark.asyncio
+async def test_detects_update_to_existing_thread():
+    canned = json.dumps(
+        {
+            "candidates": [
+                {
+                    "action": "update",
+                    "title": "",
+                    "summary": "Maya interviewed at Acme today",
+                    "existing_thread_id": "thr_jobhunt",
+                }
+            ]
+        }
+    )
+    mock = MockLLMClient(canned=[canned])
+    result = await detect_threads(
+        mock,
+        classifier_model="x",
+        scene_transcript=[
+            {"speaker": "Maya", "text": "I had the Acme interview today."},
+            {"speaker": "Sam", "text": "How did it go?"},
+        ],
+        open_threads=[
+            {
+                "thread_id": "thr_jobhunt",
+                "title": "Maya's job hunt",
+                "summary": "Maya is looking for a new job",
+            }
+        ],
+    )
+    assert len(result.candidates) == 1
+    cand = result.candidates[0]
+    assert cand.action == "update"
+    assert cand.existing_thread_id == "thr_jobhunt"
+    assert cand.summary == "Maya interviewed at Acme today"
+
+
+@pytest.mark.asyncio
+async def test_classifier_failure_returns_empty():
+    """Three malformed classifier responses → empty candidates list."""
+    mock = MockLLMClient(canned=["not json", "still not json", "{bad"])
+    result = await detect_threads(
+        mock,
+        classifier_model="x",
+        scene_transcript=[
+            {"speaker": "Maya", "text": "Anything could happen here."},
+        ],
+        open_threads=[],
+    )
+    assert result.candidates == []
+
+
+@pytest.mark.asyncio
+async def test_empty_transcript_short_circuits():
+    """Empty transcript short-circuits — classifier must not be called."""
+    mock = MockLLMClient(canned=[])
+    result = await detect_threads(
+        mock,
+        classifier_model="x",
+        scene_transcript=[],
+        open_threads=[],
+    )
+    assert result.candidates == []