fix(ci): bound JSON nesting across Python versions

Author: caohy1988

src/google/adk/plugins/bigquery_agent_analytics_plugin.py

@@ -445,6 +445,12 @@ def _extract_tool_declarations(
 # values beyond it fail closed.
 _MAX_JSON_INSPECT_CHARS = 4_000_000
 
+# Keep deeply nested JSON behavior deterministic across Python versions.
+# CPython <=3.13 rejects extreme nesting from json.loads with RecursionError,
+# while 3.14's iterative decoder accepts it. A fixed ceiling preserves the
+# fail-closed contract and bounds the materialized object graph everywhere.
+_MAX_JSON_NESTING_DEPTH = 1_000
+
 
 def _strip_bom_ws(value: str) -> str:
   """Strips BOMs and ALL Unicode whitespace from the start of a string.
@@ -465,6 +471,36 @@ def _strip_bom_ws(value: str) -> str:
   return value[i:] if i else value
 
 
+def _json_nesting_exceeds_limit(value: str) -> bool:
+  """Returns whether JSON structural nesting exceeds the fixed ceiling.
+
+  Brackets and braces inside strings are payload, not structure. This linear
+  preflight runs only after the existing character-size bound, before
+  ``json.loads`` can materialize a runtime-dependent deep object graph.
+  """
+  depth = 0
+  in_string = False
+  escaped = False
+  for char in value:
+    if in_string:
+      if escaped:
+        escaped = False
+      elif char == "\\":
+        escaped = True
+      elif char == '"':
+        in_string = False
+      continue
+    if char == '"':
+      in_string = True
+    elif char in "[{":
+      depth += 1
+      if depth > _MAX_JSON_NESTING_DEPTH:
+        return True
+    elif char in "]}":
+      depth -= 1
+  return False
+
+
 def _normalize_json_native(
     obj: Any,
     max_len: int,
@@ -719,6 +755,9 @@ def _sanitize_json_blob(
   if len(stripped) > inspect_limit:
     return "[UNPARSEABLE_JSON_BLOB]", True, True
 
+  if _json_nesting_exceeds_limit(stripped):
+    return "[UNPARSEABLE_JSON_BLOB]", True, True
+
   # json.loads silently keeps only the LAST duplicate member, so a blob like
   # {"access_token":"SECRET","access_token":"x"} can compare equal after
   # sanitization while the raw string still carries the secret (#6360 review

tests/unittests/plugins/test_bigquery_agent_analytics_plugin.py

@@ -10201,17 +10201,25 @@ def test_mapping_views_are_redacted(self):
     assert out["userdict"]["refresh_token"] == "[REDACTED]"
 
   def test_deep_json_blob_fails_closed(self):
-    """A blob too deep to parse becomes a sentinel, not a pass-through.
+    """A blob beyond the fixed nesting limit fails closed on every runtime.
 
-    json.loads raises RecursionError before the bounded traversal ever
-    runs; the row keeps flowing with the blob replaced (#6360 review
-    round 2 P2-5).
+    Older Python runtimes raise RecursionError while Python 3.14's iterative
+    JSON decoder accepts this input. The row must keep flowing with the same
+    whole-blob sentinel regardless (#6360 review round 2 P2-5).
     """
     truncate = bigquery_agent_analytics_plugin._recursive_smart_truncate
     deep = "[" * 10000 + "]" * 10000
     out, _ = truncate({"blob": deep}, 500 * 1024)
     assert out["blob"] == "[UNPARSEABLE_JSON_BLOB]"
 
+  def test_json_nesting_limit_ignores_brackets_inside_strings(self):
+    """Payload punctuation does not count as structural JSON nesting."""
+    truncate = bigquery_agent_analytics_plugin._recursive_smart_truncate
+    blob = json.dumps({"note": "prose " + "[" * 1001 + "]" * 1001})
+    out, truncated = truncate({"blob": blob}, 500 * 1024)
+    assert out["blob"] == blob
+    assert truncated is False
+
   @pytest.mark.asyncio
   async def test_shutdown_timeout_counts_lost_rows(self):
     """Rows stranded by a shutdown timeout are counted, not silent.