fix: strip markdown code fences from Claude detector response

Claude sometimes wraps JSON in ```json ... ``` fences even when told
to respond with raw JSON. Strip the fences before parsing. Found
during Phase 6 live test (93 tests).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Joseph Ibrahim

otto_v4/src/otto/detector.py

@@ -60,8 +60,14 @@ async def detect_commitment(message: str, chat_name: str) -> Commitment | None:
         print(f"OTTO detector API error: {e}", file=sys.stderr)
         return None
 
-    raw_text = response.content[0].text
-    print(f"OTTO detector raw: {raw_text}", file=sys.stderr)
+    raw_text = response.content[0].text.strip()
+
+    # Claude sometimes wraps JSON in markdown code fences
+    if raw_text.startswith("```"):
+        lines = raw_text.split("\n")
+        # Drop first line (```json) and last line (```)
+        lines = [l for l in lines if not l.strip().startswith("```")]
+        raw_text = "\n".join(lines).strip()
 
     try:
         data = json.loads(raw_text)

otto_v4/tests/test_detector.py

@@ -136,6 +136,28 @@ async def test_null_deadline_stays_none():
     assert result.deadline is None
 
 
+@pytest.mark.asyncio
+async def test_markdown_fenced_json_stripped():
+    """Claude sometimes wraps JSON in ```json ... ``` code fences."""
+    inner = json.dumps({
+        "found": True,
+        "commitment_text": "send the deck",
+        "who_to": "Alice",
+        "deadline": None,
+        "deadline_source": "none",
+        "confidence": 0.92,
+    })
+    fenced = f"```json\n{inner}\n```"
+    with patch("otto.detector.anthropic.AsyncAnthropic") as mock_cls:
+        mock_cls.return_value.messages.create = AsyncMock(
+            return_value=_mock_response(fenced)
+        )
+        result = await detect_commitment("I'll send the deck", "Work")
+
+    assert result is not None
+    assert result.commitment_text == "send the deck"
+
+
 @pytest.mark.asyncio
 async def test_invalid_json_returns_none():
     with patch("otto.detector.anthropic.AsyncAnthropic") as mock_cls: