Endless set_filter loop on "show no-take MPAs" (tracks geo-agent#243)

[cboettig]

Symptom

"Filter this layer" requests send the agent into an endless set_filter loop until it hits the per-turn cap and gives up. Cleanly reproduced with "Show only no-take marine protected areas" (and "show turtle corridors") on 2026-06-14 with models minimax-m2 and glm-5.

The model derives the correct predicate in its reasoning (NO_TAKE = 'All') but emits set_filter {"layer_id": "wdpa/wdpa-marine", "filter": []} — an empty filter — 15+ times in a row. The empty filter applies as a no-op (it actually clears the layer's default REALM filter, so featuresInView rises 201→270), returns success:true, and the model retries forever. 29 empty set_filter calls that day, zero non-empty.

Root cause (not in this repo)

Weaker models can't serialize the nested MapLibre expression array into the structured tool-call argument, and geo-agent's set_filter silently accepts an empty [] as success. Tracked upstream in boettiger-lab/geo-agent#243 with two proposed framework fixes (empty-filter guard + a flat {property, op, value} filter path).

Not a data/encoding issue (NO_TAKE is a real PMTiles property; values confirmed via get_stac_details) and not the v3.10.0 security PR (#239) — the app runs v3.9.0, which predates it. This is not fixable in system-prompt.md: the model already has the right semantics, and filter-syntax guidance doesn't belong in the app prompt.

App-level work

• Bump geo-agent pin v3.9.0 → v3.11.1 (+ security hardening) #37 — bump geo-agent pin v3.9.0 → v3.11.1 (also pulls in the v3.10.0 security hardening the app was missing). Does not fix the loop on its own.
• After geo-agent/#243 lands in a release, bump the pin again to pick up the fix, then re-test "Show only no-take marine protected areas" on minimax-m2 / glm-5 (expect a single applied filter, featuresInView dropping to the no-take subset, no repeated set_filter).

Upstream

• set_filter loops forever: 'filter' param lacks items schema → grammar-constrained decoding collapses it to [] (server change 2026-06-14); 3.9 removed the local-loop cap geo-agent#243 — set_filter empty-filter retry loop