refactor: separate Overpass and installation services

server/providers/military-installations/constants.js

@@ -0,0 +1,48 @@
+import path from 'node:path';
+
+// ---------------------------------------------------------------------------
+// Military-installation context proxy
+// ---------------------------------------------------------------------------
+// This narrow endpoint deliberately does not expose arbitrary Overpass QL to
+// the browser. It returns only allow-listed mapped context and rejects global,
+// cross-dateline, or oversized requests before touching public OSM mirrors.
+const MILITARY_INSTALLATION_CACHE_MS = 5 * 60_000;
+
+const MILITARY_INSTALLATION_STALE_MS = 60 * 60_000;
+
+const MILITARY_INSTALLATION_MAX_CACHE = 80;
+
+const MILITARY_INSTALLATION_MAX_RESPONSE_BYTES = 16 * 1024 * 1024;
+
+/**
+ * Upstream element cap. A response that hits it exactly is SATURATED — Overpass
+ * truncated, so off-viewport features from the snapped bbox may have crowded out
+ * in-viewport ones. Callers re-ask for the exact viewport in that case.
+ */
+const MILITARY_INSTALLATION_ELEMENT_CAP = 700;
+
+/**
+ * Disk-cache TTL for mapped installations (ms) — 30 days.
+ *
+ * Owner playtest 2026-08-18: "search nearby sites" was slow because every look
+ * around paid a live Overpass round trip, and the 5-minute in-memory tier died
+ * with the dev server. Mapped military features change on a survey timescale,
+ * not a session one, so a month-old answer is still the right answer — the same
+ * reasoning the Overpass proxy already applies to admin boundaries.
+ */
+const MILITARY_INSTALLATION_DISK_TTL_MS = 30 * 86_400_000;
+
+/** Disk-cache directory for mapped installation payloads. */
+const MILITARY_INSTALLATION_DISK_DIR = path.join(process.cwd(), '.gev-cache', 'military-installations');
+
+/**
+ * Cache-key grid step in degrees (~5.5 km).
+ *
+ * The browser sends the raw view rectangle, so every pixel of pan minted a new
+ * key and a new upstream query. Snapping the bbox OUTWARD onto a coarse grid
+ * makes neighbouring viewports share one entry, and because the snap only ever
+ * grows the box, the cached answer is always a superset of what was asked for.
+ */
+const MILITARY_INSTALLATION_BBOX_STEP_DEG = 0.05;
+
+export { MILITARY_INSTALLATION_ELEMENT_CAP, MILITARY_INSTALLATION_MAX_RESPONSE_BYTES, MILITARY_INSTALLATION_DISK_TTL_MS, MILITARY_INSTALLATION_STALE_MS, MILITARY_INSTALLATION_CACHE_MS, MILITARY_INSTALLATION_DISK_DIR, MILITARY_INSTALLATION_MAX_CACHE, MILITARY_INSTALLATION_BBOX_STEP_DEG };