feat: cache viewport bounds, debounce fetches, dedup polygons

[madhavcodez]

What this does

Stops the dashboard from spamming the backend every time the map moves, and stops damage polygons from flickering in and out on each fetch.

Three mechanisms:

1. Bounds cache (useBoundsCache) — tracks the union of regions already fetched. When the current viewport sits inside that cached region, no API call fires at all. When a fetch is needed, bounds expand by 1.5× so pre-loaded surroundings absorb small pans.
2. Debounce (useDebouncedCallback) — viewport changes are collapsed into a single fetch after 300ms of no movement, so rapid zig-zag panning doesn't produce 50 parallel requests.
3. Polygon dedup — polygons are merged into a Map keyed by id, so new fetches never replace what's already drawn. No more flicker.

Safety fixes

• The bounds cache only advances after a fetch succeeds — an aborted or failed fetch won't silently mark a region as "cached with nothing in it."
• The polygon map is capped at 20,000 entries, trimmed to 15,000 when exceeded, so memory and render cost stay bounded across a long session.

How to verify

DevTools → Network → filter locations:

• Pan inside an already-fetched area → zero new requests
• Fast pan across a new area → one request per ~300ms (debounce)
• Pan far, then back → polygons you already saw are still on the map (dedup)

Closes #56
Closes #43
Closes #54

[vercel]

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Project	Deployment	Actions	Updated (UTC)
frontend	Error		Apr 14, 2026 3:57pm