diff --git a/agent/tools/retrieval.py b/agent/tools/retrieval.py
index 0ccf056a29..02cb3e2ce6 100644
--- a/agent/tools/retrieval.py
+++ b/agent/tools/retrieval.py
@@ -142,6 +142,11 @@ class Retrieval(ToolBase, ABC):
                 return DocMetadataService.get_flatted_meta_by_kbs(kb_ids)
 
             def _resolve_manual_filter(flt: dict) -> dict:
+                # Return a new dict instead of mutating `flt` in place. The
+                # caller passes filters straight out of self._param.meta_data_filter,
+                # so mutating them would replace the variable reference with its
+                # resolved value and every subsequent invocation (e.g. inside an
+                # Iteration component) would reuse that stale value.
                 pat = re.compile(self.variable_ref_patt)
                 s = flt.get("value", "")
                 out_parts = []
@@ -167,8 +172,9 @@ class Retrieval(ToolBase, ABC):
                     last = m.end()
 
                 out_parts.append(s[last:])
-                flt["value"] = "".join(out_parts)
-                return flt
+                resolved = dict(flt)
+                resolved["value"] = "".join(out_parts)
+                return resolved
 
             chat_mdl = None
             if self._param.meta_data_filter.get("method") in ["auto", "semi_auto"]: