diff --git a/deeptutor/agents/visualize/utils.py b/deeptutor/agents/visualize/utils.py
index 0089b41f28..3633b5e4ce 100644
--- a/deeptutor/agents/visualize/utils.py
+++ b/deeptutor/agents/visualize/utils.py
@@ -37,6 +37,7 @@ def extract_code_block(text: str, language: str = "") -> str:
 
     If *language* is given the block must start with that tag;
     otherwise any triple-backtick fence is accepted.
+    A language miss returns ``""`` so callers can fall back with ``or``.
     """
     # Closing fence may sit on the same line as the last content line.
     if language:
@@ -46,6 +47,9 @@ def extract_code_block(text: str, language: str = "") -> str:
     match = re.search(pattern, text or "", re.IGNORECASE)
     if match:
         return match.group(1).strip()
+    # Language miss must be falsy so `hint or any-fence` can fall through.
+    if language:
+        return ""
     return (text or "").strip()
 
 
diff --git a/tests/agents/visualize/test_extract_code_block.py b/tests/agents/visualize/test_extract_code_block.py
index 79d13244fb..bdbee712e4 100644
--- a/tests/agents/visualize/test_extract_code_block.py
+++ b/tests/agents/visualize/test_extract_code_block.py
@@ -6,11 +6,22 @@
 
 
 def test_extract_code_block_closing_fence_without_leading_newline() -> None:
+    """Extract a closing fence attached to the final content line."""
     raw = "```mermaid\ngraph TD\n  A-->B```"
     assert extract_code_block(raw, "mermaid") == "graph TD\n  A-->B"
     assert extract_code_block(raw) == "graph TD\n  A-->B"
 
 
 def test_extract_code_block_normal_fenced_block() -> None:
+    """Extract a standard fenced block with its requested language."""
     raw = "```javascript\nconst x = 1;\n```"
     assert extract_code_block(raw, "javascript") == "const x = 1;"
+
+
+def test_extract_code_block_language_miss_is_empty_for_or_fallback() -> None:
+    """Return empty on a language miss so generic extraction can run."""
+    cfg = '{"type": "bar", "data": {"labels": ["A"], "datasets": [{"data": [1]}]}}'
+    raw = f"```json\n{cfg}\n```\nThanks."
+    assert extract_code_block(raw, "javascript") == ""
+    extracted = extract_code_block(raw, "javascript") or extract_code_block(raw)
+    assert extracted == cfg