Chat UI answers section-specific questions correctly, but Chat API ignores indexed nodes and falls back to generic assistant

[parthpaliwal-49]

Hi PageIndex team,

I’m integrating PageIndex via the Python SDK and I’m seeing a consistent difference between the Chat UI and the Chat API (chat_completions) behavior.

What works in the UI:

Upload a PDF (e.g., an air-conditioner operating manual)

Ask a section-specific question like “Give me OPERATING TIPS from the document”

The UI correctly retrieves and summarizes the exact section

What fails via the API:

The same document is uploaded and fully processed (status=completed)

get_tree() shows nodes with titles, page indexes, and extracted text (e.g., OPERATING TIPS)

Calling chat_completions(messages, doc_id=...) with the same question

The model calls recent_documents, claims the document is missing, and answers generically

From MCP traces, it appears that when retrieval confidence is low, the Chat API silently falls back to a generic assistant and ignores the document — even though the node content exists and is retrievable via get_tree().

Questions:

Is this difference between the Chat UI and Chat API expected behavior?

Does the UI use additional retrieval orchestration (retries, node/page binding, forced grounding) that is not exposed via the API?

Is there a documented or recommended way to force the Chat API to answer only from indexed document content or specific nodes?

If not, should section-level or procedural Q&A be implemented using the retrieval endpoints instead of chat_completions?

I’m trying to understand the intended usage boundaries here

Thanks in advance for clarification.