diff --git a/tests/test_live_snapshot_single_parse.py b/tests/test_live_snapshot_single_parse.py
new file mode 100644
index 00000000..7d88b08c
--- /dev/null
+++ b/tests/test_live_snapshot_single_parse.py
@@ -0,0 +1,114 @@
+"""Regression: live-snapshot rebuild locates the journal with a single parse.
+
+``_run_journal_live_snapshot`` used ``find_run_summary`` (full parse) and
+then ``read_run_events`` (second full parse) - two passes over the whole
+journal per rebuild (~0.6s+ of a 4.4s rebuild on a 22.7k-row live run).
+``find_run_file`` now locates the file without parsing and the durable
+summary is derived from the single events parse; the historical
+``find_run_summary`` lookup remains as the fallback seam when no journal
+file exists on disk.
+"""
+
+import json
+
+import api.routes as routes
+from api import run_journal as RJ
+
+
+def _write_journal(root, session_id, run_id, count=5):
+    session_root = root / RJ.RUN_JOURNAL_DIR_NAME / session_id
+    session_root.mkdir(parents=True, exist_ok=True)
+    path = session_root / f"{run_id}.jsonl"
+    rows = []
+    for seq in range(1, count + 1):
+        rows.append(
+            json.dumps(
+                {
+                    "version": 1,
+                    "event_id": f"{run_id}:{seq}",
+                    "seq": seq,
+                    "run_id": run_id,
+                    "session_id": session_id,
+                    "event": "token",
+                    "type": "token",
+                    "created_at": 1000 + seq,
+                    "payload": {"text": "x"},
+                }
+            )
+        )
+    path.write_text("\n".join(rows) + "\n", encoding="utf-8")
+    return path
+
+
+def test_find_run_file_locates_without_parsing(tmp_path):
+    path = _write_journal(tmp_path, "session_1", "run_1")
+    located = RJ.find_run_file("run_1", session_dir=tmp_path)
+    assert located is not None
+    session_id, located_path = located
+    assert session_id == "session_1"
+    assert located_path == path
+    assert RJ.find_run_file("missing_run", session_dir=tmp_path) is None
+    assert RJ.find_run_file("../evil", session_dir=tmp_path) is None
+
+
+def _forbid_summary_parse(*_a, **_k):
+    raise AssertionError(
+        "find_run_summary must not be parsed when the journal file exists on "
+        "disk - the single-parse locate path regressed"
+    )
+
+
+def test_live_snapshot_rebuilds_from_single_parse(tmp_path, monkeypatch):
+    _write_journal(tmp_path, "session_1", "run_1", count=3)
+    monkeypatch.setattr(RJ, "_default_session_dir", lambda: tmp_path)
+    # The double-parse fix: when a journal file exists, the rebuild must NOT
+    # route through find_run_summary (that would parse the file a second time).
+    monkeypatch.setattr(routes, "find_run_summary", _forbid_summary_parse)
+
+    snapshot = routes._run_journal_live_snapshot("run_1")
+
+    assert snapshot is not None
+    assert snapshot["session_id"] == "session_1"
+    assert snapshot["stream_id"] == "run_1"
+    assert snapshot["last_seq"] == 3
+    assert snapshot["event_count"] == 3
+    assert snapshot["last_assistant_text"] == "xxx"
+
+
+def test_live_snapshot_summary_fallback_seam(tmp_path, monkeypatch):
+    """No journal file on disk -> the historical find_run_summary seam is used."""
+    monkeypatch.setattr(RJ, "_default_session_dir", lambda: tmp_path)
+    monkeypatch.setattr(
+        routes,
+        "find_run_summary",
+        lambda stream_id: {
+            "session_id": "session_1",
+            "run_id": stream_id,
+            "last_seq": 1,
+            "last_event_id": f"{stream_id}:1",
+        },
+    )
+    monkeypatch.setattr(
+        routes,
+        "read_run_events",
+        lambda sid, rid: {
+            "events": [
+                {
+                    "version": 1,
+                    "event_id": f"{rid}:1",
+                    "seq": 1,
+                    "run_id": rid,
+                    "session_id": sid,
+                    "event": "token",
+                    "type": "token",
+                    "created_at": 1000,
+                    "payload": {"text": "hello"},
+                }
+            ],
+        },
+    )
+
+    snapshot = routes._run_journal_live_snapshot("run_1")
+
+    assert snapshot is not None
+    assert snapshot["last_assistant_text"] == "hello"
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