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## Summary Fixes #433 — Replace the inaccurate Euclidean distance approximation in `analytics.js` hop distances with proper haversine calculation, matching the server-side computation introduced in PR #415. ## Problem PR #415 moved collision analysis server-side and switched from the frontend's Euclidean approximation (`dLat×111, dLon×85`) to proper haversine. However, the **hop distance** calculation in `analytics.js` (subpath detail panel) still used the old Euclidean formula. This caused: - **Inconsistent distances** between hop distances and collision distances - **Significant errors at high latitudes** — e.g., Oslo→Stockholm: Euclidean gives ~627km, haversine gives ~415km (51% error) - The `dLon×85` constant assumes ~40° latitude; at 60° latitude the real scale factor is ~55.5km/degree, not 85 ## Changes | File | Change | |------|--------| | `public/analytics.js` | Replace `dLat*111, dLon*85` Euclidean with `HopResolver.haversineKm()` (with inline fallback) | | `public/hop-resolver.js` | Export `haversineKm` in the public API for reuse | | `test-frontend-helpers.js` | Add 4 tests: export check, zero distance, SF→LA accuracy, Euclidean vs haversine divergence | | `cmd/server/helpers_test.go` | Add `TestHaversineKm`: zero, SF→LA, symmetry, Oslo→Stockholm accuracy | | `public/index.html` | Cache buster bump | ## Performance No performance impact — `haversineKm` replaces an inline arithmetic expression with another inline arithmetic expression of identical O(1) complexity. Only called per hop pair in the subpath detail panel (typically <10 hops). ## Testing - `node test-frontend-helpers.js` — 248 passed, 0 failed - `go test -run TestHaversineKm` — PASS Co-authored-by: you <you@example.com>