initial impl

tests/test_codex.py

@@ -0,0 +1,17 @@
+from agentci.adapters.codex import _session_id
+
+
+def test_extracts_thread_id_from_jsonl() -> None:
+    output = '\n'.join(
+        [
+            '{"type":"turn.started"}',
+            '{"type":"thread.started","thread_id":"abc-123"}',
+            "not json",
+        ]
+    )
+    assert _session_id(output) == "abc-123"
+
+
+def test_missing_thread_id_returns_none() -> None:
+    assert _session_id('{"type":"turn.completed"}') is None
+