diff --git a/examples/diagrams/analyze_bi.py b/examples/diagrams/analyze_bi.py
index 837b62e5..d6c1b76b 100644
--- a/examples/diagrams/analyze_bi.py
+++ b/examples/diagrams/analyze_bi.py
@@ -8,7 +8,6 @@
 
 import json
 import re
-import nbformat
 from collections import defaultdict
 from pathlib import Path
 from datetime import datetime
@@ -61,8 +60,10 @@ def parse_all():
         with open(lf) as f:
             for line in f:
                 if line.strip():
-                    try: events.append(json.loads(line))
-                    except: pass
+                    try:
+                        events.append(json.loads(line))
+                    except json.JSONDecodeError:
+                        pass
         if not events:
             continue
 
@@ -134,6 +135,8 @@ def parse_all():
 # Build notebook
 # ---------------------------------------------------------------------------
 def build_notebook(records):
+    import nbformat  # optional dependency, only needed for notebook generation
+
     nb = nbformat.v4.new_notebook()
     data_json = json.dumps(records, indent=2)
 
diff --git a/tests/test_diagrams_analyze_bi.py b/tests/test_diagrams_analyze_bi.py
new file mode 100644
index 00000000..0a653d03
--- /dev/null
+++ b/tests/test_diagrams_analyze_bi.py
@@ -0,0 +1,56 @@
+"""Regression tests for the BI analysis diagram script."""
+
+import importlib.util
+import json
+import sys
+from pathlib import Path
+
+import pytest
+
+
+def _load_analyze_bi():
+    spec = importlib.util.spec_from_file_location(
+        "analyze_bi",
+        Path(__file__).parent.parent / "examples" / "diagrams" / "analyze_bi.py",
+    )
+    module = importlib.util.module_from_spec(spec)
+    sys.modules["analyze_bi"] = module
+    spec.loader.exec_module(module)
+    return module
+
+
+def test_parse_all_skips_invalid_jsonl_lines(tmp_path, monkeypatch):
+    """Malformed JSON lines should be ignored instead of crashing the parser."""
+    module = _load_analyze_bi()
+
+    log_file = tmp_path / "cat-issue-iter1.jsonl"
+    log_file.write_text(
+        json.dumps({"event": "start", "ts": 1.0, "model": "test"}) + "\n"
+        + "this is not valid json\n"
+        + json.dumps({"event": "end", "ts": 2.0}) + "\n"
+    )
+    monkeypatch.setattr(module, "LOG_DIR", tmp_path)
+
+    records = module.parse_all()
+
+    assert len(records) == 1
+    assert records[0]["model"] == "test"
+
+
+def test_parse_all_propagates_non_json_exceptions(tmp_path, monkeypatch):
+    """Non-JSON exceptions must propagate, not be swallowed by bare except."""
+    module = _load_analyze_bi()
+
+    log_file = tmp_path / "cat-issue-iter1.jsonl"
+    log_file.write_text(
+        json.dumps({"event": "start", "ts": 1.0, "model": "test"}) + "\n"
+    )
+    monkeypatch.setattr(module, "LOG_DIR", tmp_path)
+
+    def raise_value_error(*args, **kwargs):
+        raise ValueError("simulated non-JSON failure")
+
+    monkeypatch.setattr(module.json, "loads", raise_value_error)
+
+    with pytest.raises(ValueError, match="simulated non-JSON failure"):
+        module.parse_all()