security improvements

backend/execution.py

@@ -25,7 +25,7 @@ import hashlib
 import json
 import uuid
 from copy import deepcopy
-from collections import defaultdict, deque
+from collections import OrderedDict, defaultdict, deque
 from math import isfinite
 from threading import RLock
 from time import perf_counter
@@ -55,9 +55,12 @@ class NodeExecutionError(Exception):
 class ExecutionEngine:
     """Synchronous (blocking) graph executor. Run inside a thread pool from async code."""
 
+    NODE_CACHE_LIMIT = 256
+
     def __init__(self) -> None:
-        self._node_cache: dict[str, dict[str, Any]] = {}
+        self._node_cache: OrderedDict[str, dict[str, Any]] = OrderedDict()
         self._cache_lock = RLock()
+        self._cache_warning_emitted = False
 
     def execute(
         self,
@@ -154,6 +157,7 @@ class ExecutionEngine:
                         input_signature=input_signature,
                         output_signatures=output_signatures,
                         outputs=self._clone_cached_outputs(result),
+                        on_warning=on_warning,
                     )
 
                 # Auto-preview: broadcast a thumbnail for any DATA_FIELD,
@@ -275,6 +279,8 @@ class ExecutionEngine:
                 return None
             if entry.get("input_signature") != input_signature:
                 return None
+            # Move to end for LRU ordering
+            self._node_cache.move_to_end(node_id)
             return entry
 
     def _store_cache_entry(
@@ -285,14 +291,27 @@ class ExecutionEngine:
         input_signature: str,
         output_signatures: tuple[str, ...],
         outputs: tuple,
+        on_warning: Callable[[str, str], None] | None = None,
     ) -> None:
         with self._cache_lock:
+            if node_id in self._node_cache:
+                self._node_cache.move_to_end(node_id)
             self._node_cache[node_id] = {
                 "class_name": class_name,
                 "input_signature": input_signature,
                 "output_signatures": output_signatures,
                 "outputs": outputs,
             }
+            if len(self._node_cache) > self.NODE_CACHE_LIMIT:
+                self._node_cache.popitem(last=False)
+                if not self._cache_warning_emitted and on_warning is not None:
+                    self._cache_warning_emitted = True
+                    on_warning(
+                        node_id,
+                        f"Node cache exceeded {self.NODE_CACHE_LIMIT} entries — "
+                        "oldest cached results are being evicted. "
+                        "Very large workflows may re-compute nodes that would otherwise be cached.",
+                    )
 
     def _build_input_signature(
         self,