get_agent_as_json claimed to accept both graph IDs and library agent IDs
but only tried direct graph lookup. When a library agent ID was passed,
the function would return None (agent_not_found error).
Now the function:
1. First tries direct graph lookup with the provided ID
2. If not found, resolves the ID as a library agent ID to get the graph_id
3. Then fetches the graph using the resolved graph_id
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