fix(trees): replace child/synonym LEFT JOINs with scalar subqueries

[grantfitzsimmons]

Fixes #8242

Note

The scalar query logic was suggested by DeepSeek V4 Pro. There may be more performant ways of accomplishing this. Feedback is welcome.

The tree view endpoint constructed queries with three independent LEFT OUTER JOINs on the same tree table, one for counting children, one for looking up the accepted parent, and one for aggregating synonyms. When expanding a node with many children, the result set would balloon as children * accepted_matches * synonyms, overwhelming the database and causing a 504 gateway timeout.

This happened because each join added rows multiplicatively before GROUP BY collapsed them with DISTINCT aggregates like count(DISTINCT ...) and GROUP_CONCAT(DISTINCT ...). For a storage tree node like "Rack 001" at SAIAB, which has hundreds of direct child storage locations, the query would run for 40+ seconds and continue executing even after the HTTP connection was severed. Page refreshes would spawn additional instances, all consuming database resources.

Testing instructions

Compare against the same database on both v7 and on issue-8242.

1. Use the SAIAB database backup provided in the linked issue
2. Log into any collection (e.g. "Biodiversity Occurrences")
3. Search for "Rack 001" in the Storage tree
4. Expand the node. It should load normally without 504

• Browse tree nodes generally (Taxon, Geography, Storage) to confirm child_count and synonyms still display correctly.

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[lexiclevenger]

I tried to recreate the issue on the test panel using the v7 and v7.12.06 branches but didn't notice a slowdown or see the console error.

Screen.Recording.2026-07-02.at.4.07.51.PM.mov