fix: don't return a snapshot path when saving the pipeline snapshot fails (#13174)

haystack/core/pipeline/breakpoint.py

@@ -162,14 +162,15 @@ def _save_pipeline_snapshot(
     the function will return None without saving to a file (custom callbacks are still invoked).
 
     :param pipeline_snapshot: The pipeline snapshot to save.
-    :param raise_on_failure: If True, raises an exception if saving fails. If False, logs the error and returns.
+    :param raise_on_failure: If True, raises an exception if saving fails. If False, logs the error and returns None.
     :param snapshot_callback: Optional callback function that receives the PipelineSnapshot.
         If provided, the callback is invoked instead of the default file-saving behavior.
         The callback should return an optional string (e.g., a file path or identifier) or None.
 
     :returns:
         The full path to the saved JSON file (or the value returned by the callback), or None if
-        `snapshot_file_path` is None, no callback is provided, or snapshot saving is disabled.
+        `snapshot_file_path` is None, no callback is provided, snapshot saving is disabled, or saving fails and
+        `raise_on_failure` is False.
     :raises:
         Exception: If saving the JSON snapshot fails (when raise_on_failure is True).
     """
@@ -217,6 +218,7 @@ def _save_pipeline_snapshot(
         logger.exception("Failed to save pipeline snapshot to '{full_path}'. Error: {e}", full_path=full_path, e=error)
         if raise_on_failure:
             raise
+        return None
 
     return str(full_path)
 

releasenotes/notes/pipeline-snapshot-save-failure-path-205f77be978a264c.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    When a pipeline fails and its snapshot can't be written to disk, ``error.pipeline_snapshot_file_path`` is now
+    ``None``. Before, it held the path of the snapshot file that was never written.

test/core/pipeline/test_breakpoint.py

@@ -537,8 +537,9 @@ def test_save_pipeline_snapshot_raises_on_failure(tmp_path, caplog, monkeypatch)
         _save_pipeline_snapshot(snapshot)
 
     with caplog.at_level(logging.ERROR):
-        _save_pipeline_snapshot(snapshot, raise_on_failure=False)
+        result = _save_pipeline_snapshot(snapshot, raise_on_failure=False)
         assert any("Failed to save pipeline snapshot to" in msg for msg in caplog.messages)
+    assert result is None
 
 
 class TestSnapshotCallback: