fix(session): fall back to legacy paths in metadata reads

Fixes #4940

tests/session/test_session_list_repair_legacy.py

@@ -1,4 +1,4 @@
-"""Reproduction test: list_sessions drops corrupt legacy-stem sessions during repair."""
+"""Regression tests for legacy-stem session handling."""
 import json
 from datetime import datetime
 from pathlib import Path
@@ -38,3 +38,39 @@ def test_list_sessions_repairs_corrupt_legacy_stem(tmp_path: Path, monkeypatch)
     # actual legacy filename. The session is silently dropped.
     assert len(sessions) == 1, f"Expected 1 session, got {len(sessions)}"
     assert sessions[0]["key"] == "telegram:12345"
+
+
+def test_read_session_methods_fall_back_to_legacy_lossy_stem(
+    tmp_path: Path,
+    monkeypatch,
+) -> None:
+    monkeypatch.setattr(
+        "nanobot.session.manager.get_legacy_sessions_dir",
+        lambda: tmp_path / "legacy_sessions",
+    )
+    manager = SessionManager(tmp_path / "workspace")
+    session_id = "123e4567-e89b-12d3-a456-426614174000"
+    key = f"websocket:{session_id}"
+    legacy_path = manager._get_legacy_lossy_path(key)
+    assert legacy_path.name == f"websocket_{session_id}.jsonl"
+
+    metadata = {
+        "_type": "metadata",
+        "key": key,
+        "created_at": datetime(2025, 1, 1).isoformat(),
+        "updated_at": datetime(2025, 1, 1).isoformat(),
+        "metadata": {
+            "workspace_scope": "project",
+            "project_path": "/tmp/example-project",
+        },
+    }
+    legacy_path.write_text(json.dumps(metadata) + "\n", encoding="utf-8")
+
+    metadata_result = manager.read_session_metadata(key)
+    file_result = manager.read_session_file(key)
+
+    assert metadata_result is not None
+    assert metadata_result["metadata"] == metadata["metadata"]
+    assert file_result is not None
+    assert file_result["metadata"] == metadata["metadata"]
+    assert file_result["messages"] == []