explorer: facet counts use padded viewport, matching the table (#234)

[rdhyee]

What

Facet-legend counts were computed over the exact viewport (pad 0) in updateCrossFilteredCounts, while every other "in view" surface — the samples-table COUNT (loadCount), the point-mode sample loader, the "samples in view" stat, and the heatmap — pads the viewport by VIEWPORT_PAD_FACTOR (0.3). A sample sitting in that 30% margin was counted by the table but not the facet legend, so the legend read one (or more) low.

Reproduction: /explorer.html?material=…/mineral#v=1&lat=35.0900&lng=32.8900&alt=50000&mode=point → the table says "14 samples match the current filters" but the mineral facet shows 13.

Verified against live data (DuckDB queries at that exact view): the facet query returns 13 at pad 0 and 14 at pad 0.3 (== the table). Exactly one mineral sample lives in the pad margin.

Fix

One line in updateCrossFilteredCounts — align the facet-count bbox to the shared contract:

- const bboxSQL = isGlobal ? null : viewerBboxSQL('l.latitude', 'l.longitude', 0);
+ const bboxSQL = isGlobal ? null : viewerBboxSQL('l.latitude', 'l.longitude', VIEWPORT_PAD_FACTOR);

The heatmap hit the identical mismatch earlier and was moved to the padded contract in the #241 follow-up; this aligns the last stray surface.

The durable fix — one shared "in view" bbox source so these surfaces can't drift apart again — is noted as architectural follow-up on #234.

Tests (tests/playwright/facet-viewport.spec.js)

• New coherence regression: active-material legend count == table "N match" count at the repro view (backreference assertion — 14/14 passes, 13/14 fails).
• Hardened flyToAndSettle: the padded (slower) facet query reliably exposed a pre-existing race — the helper waited only for .recomputing to clear, which can be a transient before the new counts apply. It now keys on the full recompute cycle (.recomputing appear → clear) plus a two-consecutive-equal-reads stability gate, so it's correct even for moves that leave counts unchanged. This also confirms there is no real product stale-overwrite race — the restore settles correctly on global.
• Full B1 suite green 2× each (10/10).

Provenance

Claude; empirically verified (DuckDB 13/14 + Playwright); Codex 2-round review (resolved an unchanged-counts hang in the test helper). Deployed to the rdhyee fork staging and verified live (mineral legend now reads 14, matching the table).

🤖 Generated with Claude Code