diff --git a/nanobot/session/manager.py b/nanobot/session/manager.py
index e787eb6f..c6509474 100644
--- a/nanobot/session/manager.py
+++ b/nanobot/session/manager.py
@@ -409,6 +409,18 @@ class SessionManager:
         """Collision-resistant encoding for internal session storage filenames."""
         return base64.urlsafe_b64encode(key.encode()).decode().rstrip("=")
 
+    @staticmethod
+    def _decode_storage_key(stem: str) -> str | None:
+        """Reverse _storage_key(): decode a base64url (no-padding) stem back to the original key."""
+        try:
+            # Restore padding stripped by rstrip("=")
+            padding = 4 - len(stem) % 4
+            if padding != 4:
+                stem += "=" * padding
+            return base64.urlsafe_b64decode(stem).decode("utf-8")
+        except Exception:
+            return None
+
     def _get_session_path(self, key: str) -> Path:
         """Get the collision-resistant workspace path for a session."""
         return self.sessions_dir / f"{self._storage_key(key)}.jsonl"
@@ -804,7 +816,8 @@ class SessionManager:
         sessions = []
 
         for path in self.sessions_dir.glob("*.jsonl"):
-            fallback_key = path.stem.replace("_", ":", 1)
+            decoded = self._decode_storage_key(path.stem)
+            fallback_key = decoded or path.stem.replace("_", ":", 1)
             try:
                 # Read the metadata line and a small preview for session lists.
                 with open(path, encoding="utf-8") as f:
@@ -812,7 +825,7 @@ class SessionManager:
                     if first_line:
                         data = json.loads(first_line)
                         if data.get("_type") == "metadata":
-                            key = data.get("key") or path.stem.replace("_", ":", 1)
+                            key = data.get("key") or fallback_key
                             metadata = data.get("metadata", {})
                             title = _metadata_title(metadata)
                             preview = ""
diff --git a/nanobot/webui/session_list_index.py b/nanobot/webui/session_list_index.py
index 7788aef8..0bc8ce6c 100644
--- a/nanobot/webui/session_list_index.py
+++ b/nanobot/webui/session_list_index.py
@@ -231,21 +231,8 @@ def _indexed_row_for_session(session: Session, path: Path) -> dict[str, Any]:
     }
 
 
-def _try_decode_storage_stem(stem: str) -> str | None:
-    """Try to decode a base64url (no-padding) session storage stem back to the original key."""
-    import base64
-
-    try:
-        padding = 4 - len(stem) % 4
-        if padding != 4:
-            stem += "=" * padding
-        return base64.urlsafe_b64decode(stem).decode("utf-8")
-    except Exception:
-        return None
-
-
 def _scan_session_row(session_manager: SessionManager, path: Path) -> dict[str, Any] | None:
-    storage_key = _try_decode_storage_stem(path.stem)
+    storage_key = SessionManager._decode_storage_key(path.stem)
     fallback_key = storage_key or path.stem.replace("_", ":", 1)
     try:
         with open(path, encoding="utf-8") as f: