fix(installations): send an identifying User-Agent to Overpass (#570)

Supersedes #420 by @GladiatorrX9, ported onto the current component layout with fixes from review.

Verified before merge: format, package boundaries, unit suite, build, and the browser tracking suite; a browser harness for the change where one applies; adversarial review applied.

Co-authored-by: Cyber Knight <[email protected]>

CHANGELOG.md

@@ -137,6 +137,13 @@ of current runtime behavior, see [`docs/CURRENT-STATE.md`](docs/CURRENT-STATE.md
   proxy as `/api/gbfs?url=`, but the proxy reads its upstream target from the
   path, so every request answered 400 and the layer reported a fetch error for
   every city (#441 — thanks @MiguelGFerreira).
+- Overpass requests now carry a User-Agent that names the application, its
+  version and the project address, which is what the OpenStreetMap API usage
+  policy asks for; the previous string identified neither. A mirror may refuse
+  a client it cannot identify, and a refused mirror is one the fan-out has to
+  skip, so this affects every Overpass-backed layer: Mapped Installations,
+  traffic roads and annotation geometry. Mirror rotation, cooldown and cache
+  admission are unchanged (#420 — thanks @GladiatorrX9).
 
 - Draped annotation geometry — area fills and outlines, routes and arrows —
   classifies onto terrain as well as 3D tiles. On a keyless boot, where Cesium's

docs/CURRENT-STATE.md

@@ -2884,6 +2884,7 @@ silently demoting every later lookup for the session.
 - `/api/overpass` fans out across four public mirrors. `overpassPayloadIsData()` governs cache reads, writes, and stale fallback: only a 2xx that is neither rate-limited nor a body-level runtime error qualifies. Previously stored refusals are ignored on both fresh and stale reads, so upgrading does not require manually clearing the disk cache.
 - HTTP refusals such as 406 now rotate alongside the existing network, rate-limit, and runtime-error cases. A refusal from one mirror no longer prevents reaching healthy alternatives or persists under the seven-day road/month-long boundary cache TTLs. Concurrent identical queries share one mirror sequence; if it fails, both the initiating and joined callers can use the same last-good data.
 - A refusal every mirror agrees on is still reported with the first mirror's status and body, so a genuinely malformed query says what upstream said — but only after every mirror has had the chance to answer it. `fetchOverpassPayload` takes injectable endpoints and fetch so the rotation is tested without a live mirror (`src/overpassProxy.test.mjs`).
+- Every mirror is asked with a User-Agent that names the application, its version and the project address (`OVERPASS_USER_AGENT` in `server/providers/overpass/constants.js`), which is what the OSM API usage policy asks for. Mirrors may refuse a client they cannot identify; such a refusal is never treated as data and costs the fan-out that mirror, so the header is what keeps the list at full strength.
 
 ### Share-link v2 layer state (August 2026)
 

server/providers/overpass/constants.js

@@ -3,6 +3,19 @@ import path from 'node:path';
 // ---------------------------------------------------------------------------
 // Overpass API proxy constants and cache state
 // ---------------------------------------------------------------------------
+/**
+ * User-Agent sent to every Overpass mirror.
+ *
+ * The OSM API usage policy asks for a "Valid User-Agent identifying application
+ * and version"; a generic proxy label is not one. A mirror is free to refuse a
+ * client it cannot identify, and `src/overpassProxy.test.mjs` pins what that
+ * costs: a refusal is never data, so the query falls through to whatever
+ * mirrors are left. Keep this honest and stable — if it is ever refused, the
+ * answer is less query volume, not a new name.
+ */
+const OVERPASS_USER_AGENT =
+  'gods-eye-view/0.1 (+https://github.com/bilawalsidhu/gods-eye-view)';
+
 /** Ordered list of Overpass API mirrors; tried sequentially on failure/rate-limit. */
 const OVERPASS_UPSTREAMS = [
   'https://overpass-api.de/api/interpreter',
@@ -130,5 +143,6 @@ export {
   OVERPASS_SIMPLIFY_TOLERANCE_DEG,
   OVERPASS_MAX_RESPONSE_BYTES,
   OVERPASS_UPSTREAMS,
+  OVERPASS_USER_AGENT,
   OVERPASS_TIMEOUT_MS,
 };

server/providers/overpass/transport.js

@@ -1,6 +1,7 @@
 import {
   OVERPASS_MAX_RESPONSE_BYTES,
   OVERPASS_UPSTREAMS,
+  OVERPASS_USER_AGENT,
   OVERPASS_TIMEOUT_MS,
 } from './constants.js';
 import { readResponseTextCapped } from '../common/http.js';
@@ -91,7 +92,7 @@ async function fetchOverpassPayload(
         method: 'POST',
         headers: {
           'Content-Type': 'application/x-www-form-urlencoded',
-          'User-Agent': 'gods-eye-view-overpass-proxy/1.0',
+          'User-Agent': OVERPASS_USER_AGENT,
         },
         body,
         signal: controller.signal,
@@ -125,12 +126,11 @@ async function fetchOverpassPayload(
       }
       // Anything but 2xx is this mirror declining, not an answer. Only 5xx used
       // to rotate, so a 4xx ended the fan-out and was returned — and cached —
-      // as data: overpass-api.de and its lz4 alias answer 406 to this proxy's
-      // User-Agent while kumi.systems and private.coffee answer 200 to the very
-      // same request, so every Overpass-backed layer failed on an Apache error
-      // page with two healthy mirrors untried. The first refusal is kept so a
-      // genuinely bad query still reports what upstream said, but only after
-      // every mirror has had the chance to answer it.
+      // as data: a mirror refusing this client answers 406 while the others
+      // answer 200 to the very same request, so every Overpass-backed layer
+      // failed on an error page with healthy mirrors untried. The first
+      // refusal is kept so a genuinely bad query still reports what upstream
+      // said, but only after every mirror has had the chance to answer it.
       if (status < 200 || status >= 300) {
         if (!lastRefusalPayload) lastRefusalPayload = payload;
         lastError = new Error(

src/overpassProxy.test.mjs

@@ -97,6 +97,89 @@ test('a refusal moves to the next mirror instead of ending the fan-out', async (
   assert.deepEqual(tried, ENDPOINTS.slice(0, 2), 'the healthy mirror must be reached, and no further');
 });
 
+test('every mirror is asked with a User-Agent that identifies the application', async () => {
+  // The OSM API usage policy asks for a "Valid User-Agent identifying
+  // application and version". Every outbound request must carry it, not just
+  // the first: a mirror further down the list refusing an unidentified client
+  // is exactly the case the fan-out exists to survive.
+  const seen = [];
+  const fetchImpl = async (url, options) => {
+    seen.push({ url, agent: options?.headers?.['User-Agent'] });
+    // Refuse everywhere, so the loop is forced through the whole list.
+    return { status: 503, headers: { get: () => 'text/html' } };
+  };
+  await fetchOverpassPayload('data=x', 1e6, {
+    endpoints: ENDPOINTS,
+    fetchImpl,
+    readBody: async () => 'upstream down',
+    simplify: (body) => body,
+  });
+
+  assert.deepEqual(
+    seen.map((request) => request.url),
+    ENDPOINTS,
+    'the fan-out must reach every mirror',
+  );
+  for (const request of seen) {
+    const agent = String(request.agent || '');
+    assert.match(
+      agent,
+      /^gods-eye-view\/\d/,
+      `${request.url} must name the application and its version`,
+    );
+    assert.ok(
+      !/proxy\/1\.0$/.test(agent),
+      `${request.url} must not fall back to the unidentified label`,
+    );
+    assert.match(
+      agent,
+      /github\.com\/bilawalsidhu\/gods-eye-view/,
+      `${request.url} must carry a route back to the project`,
+    );
+  }
+});
+
+test('a mirror that refuses the old label serves the same query under the identifying one', async () => {
+  // Recorded from the canonical instance on 2026-09-14: the unidentified label
+  // is answered with a 406 Not Acceptable HTML page before the query is read,
+  // and the identifying one is served. This stub replays that shape so the
+  // behaviour the header change buys is pinned without a live mirror.
+  const REFUSED = 'gods-eye-view-overpass-proxy/1.0';
+  const answer = (agent) =>
+    String(agent || '').startsWith(REFUSED)
+      ? {
+          status: 406,
+          body: '<!DOCTYPE HTML><title>406 Not Acceptable</title>',
+          contentType: 'text/html',
+        }
+      : { status: 200, body: DATA.body, contentType: 'application/json' };
+
+  let last = null;
+  const run = (agentOverride) =>
+    fetchOverpassPayload('data=x', 1e6, {
+      endpoints: [ENDPOINTS[0]],
+      fetchImpl: async (url, options) => {
+        last = answer(agentOverride ?? options?.headers?.['User-Agent']);
+        return { status: last.status, headers: { get: () => last.contentType } };
+      },
+      readBody: async () => last.body,
+      simplify: (body) => body,
+    });
+
+  const refused = await run(REFUSED);
+  assert.equal(refused.status, 406, 'the old label is refused by the mirror');
+  assert.equal(
+    overpassPayloadIsData(refused),
+    false,
+    'a refusal is never treated as data',
+  );
+
+  const served = await run(undefined);
+  assert.equal(served.status, 200, 'the header the proxy now sends is served');
+  assert.equal(overpassPayloadIsData(served), true);
+  assert.equal(served.body, DATA.body);
+});
+
 test('the first mirror to answer wins, and the rest are left alone', async () => {
   const { payload, tried } = await run({
     [ENDPOINTS[0]]: DATA, [ENDPOINTS[1]]: DATA, [ENDPOINTS[2]]: DATA,