diff --git a/skillopt_sleep/harvest.py b/skillopt_sleep/harvest.py
index 7a9e2721..6b1708ff 100644
--- a/skillopt_sleep/harvest.py
+++ b/skillopt_sleep/harvest.py
@@ -63,6 +63,14 @@ def _iter_jsonl(path: str) -> Iterable[Dict[str, Any]]:
         return
 
 
+def _safe_mtime(path: str) -> float:
+    """Return a sortable mtime without failing on a concurrently removed file."""
+    try:
+        return os.path.getmtime(path)
+    except OSError:
+        return 0.0
+
+
 def _text_from_content(content: Any) -> str:
     """Flatten a message.content (str or list of blocks) into text."""
     if isinstance(content, str):
@@ -354,7 +362,7 @@ def harvest(
             if fn.endswith(".jsonl") and not fn.startswith("agent-"):
                 paths.append(os.path.join(root, fn))
     # newest first by mtime
-    paths.sort(key=lambda p: os.path.getmtime(p), reverse=True)
+    paths.sort(key=_safe_mtime, reverse=True)
 
     for p in paths:
         d = digest_transcript(p)
diff --git a/skillopt_sleep/harvest_codex.py b/skillopt_sleep/harvest_codex.py
index c50a237c..51bc776b 100644
--- a/skillopt_sleep/harvest_codex.py
+++ b/skillopt_sleep/harvest_codex.py
@@ -15,6 +15,7 @@
     _is_meta_prompt,
     _iter_jsonl,
     _project_matches,
+    _safe_mtime,
 )
 from skillopt_sleep.staging import _SECRET_PATTERNS
 from skillopt_sleep.types import SessionDigest
@@ -216,7 +217,7 @@ def harvest_codex(
         for fn in os.listdir(archived_sessions_dir)
         if fn.endswith(".jsonl")
     ]
-    paths.sort(key=lambda p: os.path.getmtime(p), reverse=True)
+    paths.sort(key=_safe_mtime, reverse=True)
 
     project_hint = invoked_project if scope == "invoked" else ""
     for path in paths:
diff --git a/tests/test_harvest_race.py b/tests/test_harvest_race.py
new file mode 100644
index 00000000..1b26064f
--- /dev/null
+++ b/tests/test_harvest_race.py
@@ -0,0 +1,78 @@
+"""Regression tests for transcript files disappearing during discovery."""
+from __future__ import annotations
+
+import json
+import os
+import tempfile
+import unittest
+from unittest import mock
+
+from skillopt_sleep.harvest import harvest
+from skillopt_sleep.harvest_codex import harvest_codex
+
+
+class TestHarvestDiscoveryRace(unittest.TestCase):
+    def test_claude_harvest_skips_mtime_race(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            path = os.path.join(tmp, "session.jsonl")
+            with open(path, "w", encoding="utf-8") as handle:
+                handle.write(json.dumps({
+                    "timestamp": "2026-09-20T00:00:00Z",
+                    "cwd": "/repo",
+                    "message": {"role": "user", "content": "Fix the parser bug"},
+                }) + "\n")
+                handle.write(json.dumps({
+                    "timestamp": "2026-09-20T00:00:10Z",
+                    "cwd": "/repo",
+                    "message": {"role": "assistant", "content": "The parser is fixed."},
+                }) + "\n")
+
+            real_mtime = os.path.getmtime
+
+            def mtime_with_race(candidate):
+                if candidate == path:
+                    raise FileNotFoundError(candidate)
+                return real_mtime(candidate)
+
+            with mock.patch("skillopt_sleep.harvest.os.path.getmtime", side_effect=mtime_with_race):
+                digests = harvest(tmp, scope="all")
+
+        self.assertEqual(len(digests), 1)
+        self.assertEqual(digests[0].session_id, "session")
+
+    def test_codex_harvest_skips_mtime_race(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            path = os.path.join(tmp, "session.jsonl")
+            with open(path, "w", encoding="utf-8") as handle:
+                handle.write(json.dumps({
+                    "timestamp": "2026-09-20T00:00:00Z",
+                    "payload": {
+                        "type": "user_message",
+                        "message": "Fix the parser bug",
+                        "cwd": "/repo",
+                    },
+                }) + "\n")
+                handle.write(json.dumps({
+                    "timestamp": "2026-09-20T00:00:01Z",
+                    "payload": {
+                        "type": "agent_message",
+                        "message": "The parser is fixed.",
+                    },
+                }) + "\n")
+
+            real_mtime = os.path.getmtime
+
+            def mtime_with_race(candidate):
+                if candidate == path:
+                    raise FileNotFoundError(candidate)
+                return real_mtime(candidate)
+
+            with mock.patch("skillopt_sleep.harvest.os.path.getmtime", side_effect=mtime_with_race):
+                digests = harvest_codex(tmp, scope="all")
+
+        self.assertEqual(len(digests), 1)
+        self.assertEqual(digests[0].session_id, "session")
+
+
+if __name__ == "__main__":
+    unittest.main()