feat(nl): add dynamic graph fallback for un-cached topic and peer group members

[clincoln8]

Summary

In Data Commons Platform (DCP), custom datasets and UN topics are loaded dynamically into Spanner without generating static topic_cache.json files.

Previously, _members() in server/lib/nl/common/topic.py only checked TOPIC_CACHE. When a dynamic custom or UN topic (e.g. undata/topic/theme/S73) was queried, get_members() returned empty, causing dynamic topic traversal in Explore to terminate prematurely without charts.

Changes

1. Fallback in _members(): When a topic is missing from TOPIC_CACHE (or returns empty), fall back to calling _prop_val_ordered(node, prop + 'List').
2. Fallback in _members_raw() and _parents_raw(): Batch-fetch missing nodes from the graph via fetch.raw_property_values().
3. Multi-string Parsing in _prop_val_ordered(): Iterate over all list strings in sv_list across provenances with set deduplication.
4. Unit Tests: Added comprehensive test coverage in server/tests/lib/nl/topic_test.py.

Tested with pytest server/tests/lib/nl/topic_test.py (5 passed) and full pytest server/tests/lib/nl/ (342 passed).

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a dynamic fallback mechanism for the Data Commons Platform to handle custom and UN topics that are not present in the static TOPIC_CACHE. By enabling direct graph queries when cache lookups fail, the system ensures that dynamic topic traversal in Explore functions correctly without missing charts. Additionally, the parsing logic for ordered property values has been improved to better handle multi-string inputs.

Highlights

• Dynamic Topic Fallback: Implemented a fallback mechanism in _members, _members_raw, and _parents_raw to fetch data directly from the graph when topics are missing from the TOPIC_CACHE.
• Enhanced Multi-string Parsing: Updated _prop_val_ordered to handle multiple list strings across provenances with set deduplication for more robust data retrieval.
• Comprehensive Testing: Added a new test suite in server/tests/lib/nl/topic_test.py to verify the fallback logic and parsing improvements.

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[gemini-code-assist]

Code Review

This pull request introduces fallback mechanisms in topic.py to dynamically fetch member and parent properties when they are missing from the TOPIC_CACHE. It also updates _prop_val_ordered to properly split and deduplicate ordered property values, and adds comprehensive unit tests to verify these fallback behaviors. The review feedback suggests deduplicating the list of missing nodes before making API calls in _members_raw and _parents_raw to prevent redundant network requests.

[gemini-code-assist]

To avoid redundant API calls and save network bandwidth, we should deduplicate missing_nodes before passing it to fetch.raw_property_values.

Suggested change

	if missing_nodes:
	raw_res = fetch.raw_property_values(nodes=missing_nodes, prop=prop)
	for n in missing_nodes:
	val_map[n] = raw_res.get(n, [])
	if missing_nodes:
	raw_res = fetch.raw_property_values(nodes=list(dict.fromkeys(missing_nodes)), prop=prop)
	for n in missing_nodes:
	val_map[n] = raw_res.get(n, [])

[gemini-code-assist]

Similarly, we should deduplicate missing_nodes here to prevent redundant API requests when fetching parent properties.

Suggested change

	if missing_nodes:
	parents = fetch.raw_property_values(nodes=missing_nodes,
	prop=prop,
	out=False)
	if missing_nodes:
	parents = fetch.raw_property_values(nodes=list(dict.fromkeys(missing_nodes)),
	prop=prop,
	out=False)