diff --git a/tests/playwright/cesium-queries.spec.js b/tests/playwright/cesium-queries.spec.js
index c326b4b..56a6299 100644
--- a/tests/playwright/cesium-queries.spec.js
+++ b/tests/playwright/cesium-queries.spec.js
@@ -16,7 +16,7 @@
 const { test, expect } = require('@playwright/test');
 
 // Configuration
-const BASE_URL = process.env.TEST_URL || 'http://localhost:5860';
+const { siteUrl } = require('./helpers/url');
 const PAGE_PATH = '/tutorials/parquet_cesium.html';
 
 // Test data - PKAP location with known samples
@@ -27,7 +27,7 @@ test.describe('Cesium Query Results UI', () => {
 
   test.beforeEach(async ({ page }) => {
     // Navigate to page
-    await page.goto(`${BASE_URL}${PAGE_PATH}`, {
+    await page.goto(siteUrl(PAGE_PATH), {
       waitUntil: 'domcontentloaded',
       timeout: 60000
     });
diff --git a/tests/playwright/explorer-helper.spec.js b/tests/playwright/explorer-helper.spec.js
index 136bb60..3ef9c2d 100644
--- a/tests/playwright/explorer-helper.spec.js
+++ b/tests/playwright/explorer-helper.spec.js
@@ -35,9 +35,7 @@
  */
 
 const { test, expect } = require('@playwright/test');
-
-const BASE_URL = process.env.TEST_URL || 'http://localhost:5860';
-const EXPLORER_PATH = '/explorer.html';
+const { explorerUrl } = require('./helpers/url');
 
 // Phrases written by `updatePhaseMsg` we check for in tests.
 const FETCHING_SAMPLE_INDEX = 'Fetching sample index';   // the helper's loadingMsg
@@ -218,7 +216,7 @@ async function flyCameraTo(page, lat, lng, alt) {
 test.describe('explorer: tryEnterPointModeIfNeeded short-circuit invariants', () => {
 
   test('boot to cluster mode reaches a done message with cluster counts', async ({ page }) => {
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=${ALT_WORLD}`, {
+    await page.goto(explorerUrl(`#v=1&lat=20&lng=0&alt=${ALT_WORLD}`), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -235,7 +233,7 @@ test.describe('explorer: tryEnterPointModeIfNeeded short-circuit invariants', ()
     // helper after its own loadRes settles; at world altitude the chase
     // should bail at the altitude check WITHOUT painting "Fetching sample
     // index…".
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=${ALT_WORLD}`, {
+    await page.goto(explorerUrl(`#v=1&lat=20&lng=0&alt=${ALT_WORLD}`), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -277,7 +275,7 @@ test.describe('explorer: tryEnterPointModeIfNeeded short-circuit invariants', ()
     // and paints "Fetching sample index…"; warm-cache: currentRes is
     // already 8 so the helper short-circuits its loadRes and goes
     // straight to enterPointMode → "Loading individual samples…".)
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=${ALT_WORLD}`, {
+    await page.goto(explorerUrl(`#v=1&lat=20&lng=0&alt=${ALT_WORLD}`), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -316,7 +314,7 @@ test.describe('explorer: tryEnterPointModeIfNeeded short-circuit invariants', ()
     // wires a chase in, the short-circuit must keep the helper's
     // loadingMsg ("Fetching sample index…") suppressed because we're
     // already in point mode.
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=${ALT_WORLD}`, {
+    await page.goto(explorerUrl(`#v=1&lat=20&lng=0&alt=${ALT_WORLD}`), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
diff --git a/tests/playwright/explorer-layout-stability.spec.js b/tests/playwright/explorer-layout-stability.spec.js
index 352967a..6359949 100644
--- a/tests/playwright/explorer-layout-stability.spec.js
+++ b/tests/playwright/explorer-layout-stability.spec.js
@@ -1,7 +1,5 @@
 const { test, expect } = require('@playwright/test');
-
-const BASE_URL = process.env.TEST_URL || 'http://localhost:5860';
-const EXPLORER_PATH = '/explorer.html';
+const { explorerUrl } = require('./helpers/url');
 
 const ALT_WORLD = 10000000;
 const ALT_POINT_CYPRUS = 62054;
@@ -95,7 +93,7 @@ async function resolveMapHeightPx(page) {
 test.describe('explorer layout stability', () => {
   test('desktop globe rect is stable across boot, status, and point-mode flight; table is permanent below', async ({ page }) => {
     await page.setViewportSize({ width: 1280, height: 900 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=${ALT_WORLD}`, {
+    await page.goto(explorerUrl(`#v=1&lat=20&lng=0&alt=${ALT_WORLD}`), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -142,7 +140,7 @@ test.describe('explorer layout stability', () => {
   test('mobile globe height override is stable across boot and wrapped status', async ({ page }) => {
     const viewport = { width: 390, height: 844 };
     await page.setViewportSize(viewport);
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=${ALT_WORLD}`, {
+    await page.goto(explorerUrl(`#v=1&lat=20&lng=0&alt=${ALT_WORLD}`), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -172,7 +170,7 @@ test.describe('explorer layout stability', () => {
     // 50vh = 284px — below the 360px floor — so map height = 360px.
     // Covers the clamp-floor branch which the 390×844 case never exercises.
     await page.setViewportSize({ width: 320, height: 568 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=${ALT_WORLD}`, {
+    await page.goto(explorerUrl(`#v=1&lat=20&lng=0&alt=${ALT_WORLD}`), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
diff --git a/tests/playwright/explorer-map-overlay.spec.js b/tests/playwright/explorer-map-overlay.spec.js
index 0b7dc13..b6039ed 100644
--- a/tests/playwright/explorer-map-overlay.spec.js
+++ b/tests/playwright/explorer-map-overlay.spec.js
@@ -1,7 +1,5 @@
 const { test, expect } = require('@playwright/test');
-
-const BASE_URL = process.env.TEST_URL || 'http://localhost:5860';
-const EXPLORER_PATH = '/explorer.html';
+const { explorerUrl } = require('./helpers/url');
 
 // Cesium + OJS boot can be slow on CI; the in-map-overlay specs all wait
 // for #cesiumContainer + toolbar render before measuring.
@@ -31,7 +29,7 @@ async function waitForBootReady(page) {
 test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)', () => {
   test('desktop: overlay does not cover Cesium toolbar buttons', async ({ page }) => {
     await page.setViewportSize({ width: 1280, height: 800 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=10000000`, {
+    await page.goto(explorerUrl('#v=1&lat=20&lng=0&alt=10000000'), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -56,7 +54,7 @@ test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)',
 
   test('mobile (390px): overlay does not cover Cesium toolbar', async ({ page }) => {
     await page.setViewportSize({ width: 390, height: 844 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=10000000`, {
+    await page.goto(explorerUrl('#v=1&lat=20&lng=0&alt=10000000'), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -71,7 +69,7 @@ test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)',
 
   test('iPhone SE (320px): overlay clears toolbar and search buttons do not overflow', async ({ page }) => {
     await page.setViewportSize({ width: 320, height: 568 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=10000000`, {
+    await page.goto(explorerUrl('#v=1&lat=20&lng=0&alt=10000000'), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -102,7 +100,7 @@ test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)',
 
   test('base-layer picker dropdown is clickable (not occluded) above the overlay', async ({ page }) => {
     await page.setViewportSize({ width: 1280, height: 800 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=10000000`, {
+    await page.goto(explorerUrl('#v=1&lat=20&lng=0&alt=10000000'), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -154,7 +152,7 @@ test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)',
     await page.setViewportSize({ width: 1280, height: 900 });
 
     // Load at world zoom and read total.
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=10000000`, {
+    await page.goto(explorerUrl('#v=1&lat=20&lng=0&alt=10000000'), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -203,7 +201,7 @@ test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)',
 
   test('table v2: pagination is server-side, pager shows Page X of Y, Next loads new rows', async ({ page }) => {
     await page.setViewportSize({ width: 1280, height: 900 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=10000000`, {
+    await page.goto(explorerUrl('#v=1&lat=20&lng=0&alt=10000000'), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -236,7 +234,7 @@ test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)',
 
   test('table v2: filter change clears pager text and re-fetches count', async ({ page }) => {
     await page.setViewportSize({ width: 1280, height: 900 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=10000000`, {
+    await page.goto(explorerUrl('#v=1&lat=20&lng=0&alt=10000000'), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -260,7 +258,7 @@ test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)',
 
   test('clicking a table row selects the sample, updates #pid hash, and marks the row selected', async ({ page }) => {
     await page.setViewportSize({ width: 1280, height: 900 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}#v=1&lat=20&lng=0&alt=10000000`, {
+    await page.goto(explorerUrl('#v=1&lat=20&lng=0&alt=10000000'), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
@@ -295,7 +293,7 @@ test.describe('Map search overlay — Cesium toolbar coexistence (#200 / M-1A)',
 
   test('sidebar search input mirrors in-map search input', async ({ page }) => {
     await page.setViewportSize({ width: 1280, height: 800 });
-    await page.goto(`${BASE_URL}${EXPLORER_PATH}`, {
+    await page.goto(explorerUrl(), {
       waitUntil: 'domcontentloaded',
       timeout: 60000,
     });
diff --git a/tests/playwright/facet-viewport.spec.js b/tests/playwright/facet-viewport.spec.js
index 419e6f6..c74ed8f 100644
--- a/tests/playwright/facet-viewport.spec.js
+++ b/tests/playwright/facet-viewport.spec.js
@@ -40,8 +40,7 @@
  *     the implementation plan logs query latency for visibility.
  */
 const { test, expect } = require('@playwright/test');
-
-const EXPLORER_PATH = '/explorer.html';
+const { explorerUrl } = require('./helpers/url');
 
 // Global view position. alt=15000000 (15,000 km) is above the
 // `GLOBAL_VIEW_ALT_M = 1e7` shortcut in `isGlobalView()`, so the
@@ -133,7 +132,7 @@ test.describe('B1 viewport-aware facet counts (#234 step 3)', () => {
     test.setTimeout(180000);
 
     test('zoom in → counts shrink to viewport; zoom out → counts restore', async ({ page }) => {
-        await page.goto(`${EXPLORER_PATH}${GLOBAL_HASH}`);
+        await page.goto(explorerUrl(GLOBAL_HASH));
         await waitForFacetUI(page);
         await waitForFacetCountsStable(page);
 
@@ -181,7 +180,7 @@ test.describe('B1 viewport-aware facet counts (#234 step 3)', () => {
         // DuckDB since `lite_url` also carries a `source` column) and
         // against the JOIN inadvertently double-counting via duplicate pids.
         // Codex round-1 review of PR #237 called out the coverage gap.
-        await page.goto(`${EXPLORER_PATH}${GLOBAL_HASH}`);
+        await page.goto(explorerUrl(GLOBAL_HASH));
         await waitForFacetUI(page);
         await waitForFacetCountsStable(page);
 
@@ -243,7 +242,7 @@ test.describe('B1 viewport-aware facet counts (#234 step 3)', () => {
     });
 
     test('moveStart marks .recomputing before the debounce can run', async ({ page }) => {
-        await page.goto(`${EXPLORER_PATH}${GLOBAL_HASH}`);
+        await page.goto(explorerUrl(GLOBAL_HASH));
         await waitForFacetUI(page);
         await waitForFacetCountsStable(page);
 
@@ -289,7 +288,7 @@ test.describe('B1 viewport-aware facet counts (#234 step 3)', () => {
         // must NOT leave any `.recomputing` class behind. Guards against a
         // future refactor that moves `markFacetCountsRecomputing()` above
         // the early-return.
-        await page.goto(`${EXPLORER_PATH}${GLOBAL_HASH}`);
+        await page.goto(explorerUrl(GLOBAL_HASH));
         await waitForFacetUI(page);
         await waitForFacetCountsStable(page);
         const stuck = await page.evaluate(
diff --git a/tests/playwright/facetnote-url-load.spec.js b/tests/playwright/facetnote-url-load.spec.js
index d3663fd..f321b5d 100644
--- a/tests/playwright/facetnote-url-load.spec.js
+++ b/tests/playwright/facetnote-url-load.spec.js
@@ -20,8 +20,7 @@
  */
 
 const { test, expect } = require('@playwright/test');
-
-const EXPLORER_PATH = '/explorer.html';
+const { explorerUrl } = require('./helpers/url');
 
 // Cluster-altitude default (well above ENTER_POINT_ALT = 120000).
 const ALT_CLUSTER = 5000000;
@@ -60,7 +59,7 @@ test.describe('#facetNote URL deep-link visibility (issue #234 step 1)', () => {
     // Boot the page once to discover a real material URI from the rendered
     // checkboxes. Hardcoding a URI would couple the test to a specific
     // vocabulary version; reading the live data keeps it self-healing.
-    await page.goto(`${EXPLORER_PATH}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_CLUSTER}`);
+    await page.goto(explorerUrl(`#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_CLUSTER}`));
     await waitForMode(page, 'cluster');
     await waitForFacetCheckboxes(page);
 
@@ -75,7 +74,7 @@ test.describe('#facetNote URL deep-link visibility (issue #234 step 1)', () => {
     // syncFacetNote() must run to flip #facetNote visible.
     const encoded = encodeURIComponent(materialUri);
     await page.goto(
-      `${EXPLORER_PATH}?material=${encoded}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_CLUSTER}`
+      explorerUrl(`?material=${encoded}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_CLUSTER}`)
     );
     await waitForMode(page, 'cluster');
     await waitForFacetCheckboxes(page);
@@ -112,7 +111,7 @@ test.describe('#facetNote URL deep-link visibility (issue #234 step 1)', () => {
     // Negative control: arriving with no facet params must keep the note
     // hidden. Guards against an over-eager `syncFacetNote()` that flips
     // visibility independent of `hasFacetFilters()`.
-    await page.goto(`${EXPLORER_PATH}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_CLUSTER}`);
+    await page.goto(explorerUrl(`#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_CLUSTER}`));
     await waitForMode(page, 'cluster');
     await waitForFacetCheckboxes(page);
 
diff --git a/tests/playwright/helpers/url.js b/tests/playwright/helpers/url.js
new file mode 100644
index 0000000..8cfdc9a
--- /dev/null
+++ b/tests/playwright/helpers/url.js
@@ -0,0 +1,57 @@
+// URL helpers for the Playwright suite.
+//
+// Why this exists: all specs in tests/playwright/ navigate to rendered
+// pages on the site (explorer.html, tutorials/*.html, etc.) and accept
+// a TEST_URL env var so they can run against:
+//
+//   - the dev / CI smoke gate's static server (`http://localhost:5860`)
+//   - production (`https://isamples.org`)
+//   - the fork-staging GitHub Pages URL
+//     (`https://rdhyee.github.io/isamplesorg.github.io/`, with sub-path)
+//
+// The historical hand-rolled patterns had two latent gotchas:
+//
+//   1. Some specs called `page.goto('/explorer.html')` and relied on
+//      Playwright's `baseURL` config. Playwright resolves an absolute
+//      path against the ORIGIN of baseURL, so a sub-path TEST_URL like
+//      `https://rdhyee.github.io/isamplesorg.github.io/` silently
+//      resolves to `https://rdhyee.github.io/explorer.html` (404).
+//
+//   2. Specs that string-concat `${BASE_URL}${EXPLORER_PATH}` work on
+//      sub-path TEST_URLs only when TEST_URL has no trailing slash.
+//      A trailing slash produces `//explorer.html` — tolerated by some
+//      servers, but not the intended URL shape.
+//
+// `siteUrl()` / `explorerUrl()` below collapse both gotchas: strip the
+// trailing slash from BASE_URL once, then string-concat a leading-slash
+// path. Same result whether TEST_URL is given with or without a trailing
+// slash, and the sub-path is preserved on fork-staging.
+//
+// History: extracted 2026-05-27 from PR #238 (Codex round-1 review of
+// the facet-viewport.spec.js URL fix recommended a shared helper rather
+// than duplicating the fix into every spec).
+
+const BASE_URL = (process.env.TEST_URL || 'http://localhost:5860').replace(/\/$/, '');
+
+/** Build a URL on the rendered site.
+ *
+ * @param {string} path  Path on the site, should start with `/`
+ *                       (e.g. `/explorer.html`, `/tutorials/parquet_cesium.html`).
+ * @param {string} [suffix]  Optional hash or query suffix appended as-is
+ *                           (e.g. `#v=1&lat=0&lng=0&alt=15000000`).
+ * @returns {string}     Full URL ready for `page.goto()`.
+ */
+function siteUrl(path, suffix = '') {
+    return `${BASE_URL}${path}${suffix}`;
+}
+
+/** Convenience for the most common case: a URL on the explorer page.
+ *
+ * @param {string} [suffix]  Optional hash or query suffix.
+ * @returns {string}         Full URL ready for `page.goto()`.
+ */
+function explorerUrl(suffix = '') {
+    return siteUrl('/explorer.html', suffix);
+}
+
+module.exports = { BASE_URL, siteUrl, explorerUrl };
diff --git a/tests/playwright/search-real-count.spec.js b/tests/playwright/search-real-count.spec.js
index 19e070e..6f8ce6a 100644
--- a/tests/playwright/search-real-count.spec.js
+++ b/tests/playwright/search-real-count.spec.js
@@ -26,8 +26,7 @@
  *     unchanged from pre-#232 ("N results for term" with no "of M").
  */
 const { test, expect } = require('@playwright/test');
-
-const EXPLORER_PATH = '/explorer.html';
+const { explorerUrl } = require('./helpers/url');
 
 /** Wait until the explorer has rendered the search input. Boot sequence:
  *  phase1 (viewer + cluster cache) → facetFilters → search input wiring.
@@ -77,7 +76,7 @@ test.describe('Search real-count display (#232 / #234 step 2)', () => {
 
   test('cap-hit search shows "N of M results" + structured log carries total_count', async ({ page }) => {
     const logs = attachSearchLogCollector(page);
-    await page.goto(EXPLORER_PATH);
+    await page.goto(explorerUrl());
     await waitForSearchReady(page);
 
     await runSearch(page, 'pottery');
@@ -148,7 +147,7 @@ test.describe('Search real-count display (#232 / #234 step 2)', () => {
     // `finally`, this test fails. Both round-1 (predicate snapshot)
     // and round-2 (telemetry snapshot) fixes are exercised.
     const logs = attachSearchLogCollector(page);
-    await page.goto(EXPLORER_PATH);
+    await page.goto(explorerUrl());
     await waitForSearchReady(page);
 
     // Sanity: no facet active at search-fire time.
@@ -222,7 +221,7 @@ test.describe('Search real-count display (#232 / #234 step 2)', () => {
 
   test('no-results search short-circuits without COUNT (total_count remains null)', async ({ page }) => {
     const logs = attachSearchLogCollector(page);
-    await page.goto(EXPLORER_PATH);
+    await page.goto(explorerUrl());
     await waitForSearchReady(page);
 
     await runSearch(page, 'xyzzyqqqplugh');
diff --git a/tests/playwright/url-roundtrip.spec.js b/tests/playwright/url-roundtrip.spec.js
index f35cdd3..55bfdb6 100644
--- a/tests/playwright/url-roundtrip.spec.js
+++ b/tests/playwright/url-roundtrip.spec.js
@@ -24,8 +24,7 @@
  */
 
 const { test, expect } = require('@playwright/test');
-
-const EXPLORER_PATH = '/explorer.html';
+const { explorerUrl } = require('./helpers/url');
 
 // Cyprus / Polis — confirmed dense region (~23k samples), used in #206/#210.
 const LAT = 34.9957;
@@ -145,7 +144,7 @@ test.describe('Explorer URL state round-trip (issue #209)', () => {
 
 
   test('deep-link with mode=point enters point mode (Bug B from #203)', async ({ page }) => {
-    const url = `${EXPLORER_PATH}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_POINT_DEEP}&mode=point`;
+    const url = explorerUrl(`#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_POINT_DEEP}&mode=point`);
     await page.goto(url);
     await waitForMode(page, 'point');
     await waitForPointModeSettled(page);
@@ -156,7 +155,7 @@ test.describe('Explorer URL state round-trip (issue #209)', () => {
 
   test('deep-link with low altitude AND no mode=point still enters point mode (#207 item 4)', async ({ page }) => {
     // No `mode=point` in URL. Boot should enter point based on altitude alone.
-    const url = `${EXPLORER_PATH}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_POINT}`;
+    const url = explorerUrl(`#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_POINT}`);
     await page.goto(url);
     // Wait for the settled point-mode done message — more reliable than
     // waitForMode alone, which can match a transient mode flip during boot
@@ -169,7 +168,7 @@ test.describe('Explorer URL state round-trip (issue #209)', () => {
 
   test('sub-threshold pan updates URL hash via moveEnd (#205)', async ({ page }) => {
     // Start at a settled point-mode view.
-    const url = `${EXPLORER_PATH}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_POINT_DEEP}&mode=point`;
+    const url = explorerUrl(`#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_POINT_DEEP}&mode=point`);
     await page.goto(url);
     await waitForMode(page, 'point');
     await waitForPointModeSettled(page);
@@ -205,7 +204,7 @@ test.describe('Explorer URL state round-trip (issue #209)', () => {
     let ctxB;
     try {
       const pageA = await ctxA.newPage();
-      await pageA.goto(`${EXPLORER_PATH}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_POINT_DEEP}&mode=point`);
+      await pageA.goto(explorerUrl(`#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_POINT_DEEP}&mode=point`));
       await waitForMode(pageA, 'point');
       await waitForPointModeSettled(pageA);
 
@@ -266,7 +265,7 @@ test.describe('Explorer URL state round-trip (issue #209)', () => {
     // by then the handler has executed past line 2272 (which writes a new
     // non-null selectedH3) AND reached line 2285 (the null-clear branch).
     const invalidH3 = '0deadbeefffffff';  // 15 chars but not a real h3 cell
-    await page.goto(`${EXPLORER_PATH}#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_CLUSTER}&h3=${invalidH3}`);
+    await page.goto(explorerUrl(`#v=1&lat=${LAT}&lng=${LNG}&alt=${ALT_CLUSTER}&h3=${invalidH3}`));
     await waitForMode(page, 'cluster');
     // `_globeState.mode` is initialized at explorer.qmd:871, well before the
     // hashchange listener is registered at line 2210; wait for boot settle.