Developer Knowledge fallback search response is not iterable #14609

In which file did you encounter the issue?

developer-knowledge/conftest.py and developer-knowledge/search_document_chunks.py

Did you change the file? If so, how?

No.

Describe the issue

The Developer Knowledge samples include a fallback implementation for environments where the preview client is not installed. The fallback SearchDocumentChunksResponse stores its results but is not iterable, while the sample iterates over the response as a pager.

Reproduction command:

python -m pytest developer-knowledge -q

Result:

3 passed, 1 failed
...
developer-knowledge\\search_document_chunks.py:44: in search_document_chunks
    for chunk in response:
TypeError: 'SearchDocumentChunksResponse' object is not iterable

Expected behavior: all four focused tests pass using the intended fallback. Actual behavior: the search test fails before it can exercise the sample.

Environment: Python 3.12, pytest 9.1.1, repository main at commit 430a87ada6f2d33f318b5d16b77464679905a140.