fix(dev): WP-37 — dev-switcher resets scenario/role instead of sticking

currentScenario()/currentRole() read the URL param before sessionStorage, so a
stale ?scenario=/?role= in the address bar overrode the switcher on reload
("stuck on slow"). The switcher now strips both dev params from the URL
(pure stripDevParams + history.replaceState) before reloading, so the stored
value wins.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/shared/infrastructure/dev-params.spec.ts

@@ -0,0 +1,22 @@
+import { describe, it, expect } from 'vitest';
+import { stripDevParams } from './dev-params';
+
+describe('stripDevParams (WP-37)', () => {
+  it('removes ?scenario and ?role so the stored dev value wins on reload', () => {
+    expect(stripDevParams('http://localhost:4200/dashboard?scenario=slow&role=admin')).toBe(
+      'http://localhost:4200/dashboard',
+    );
+  });
+
+  it('keeps unrelated query params and the path/hash', () => {
+    expect(stripDevParams('http://localhost:4200/beheer/zaken?scenario=error&tab=2#top')).toBe(
+      'http://localhost:4200/beheer/zaken?tab=2#top',
+    );
+  });
+
+  it('is a no-op when neither param is present', () => {
+    expect(stripDevParams('http://localhost:4200/dashboard')).toBe(
+      'http://localhost:4200/dashboard',
+    );
+  });
+});

src/app/shared/infrastructure/dev-params.ts

@@ -0,0 +1,14 @@
+/**
+ * Remove the dev-only `?scenario=` and `?role=` params from a URL (WP-37). Once the
+ * dev switcher (debug-state) has been used, sessionStorage is the authoritative source
+ * for both — `currentScenario()`/`currentRole()` read the URL FIRST, so a stale param
+ * left in the address bar would override the switcher on reload (the "stuck on slow"
+ * bug). Stripping the params before reload lets the stored value win. Pure: returns the
+ * rewritten href, mutates nothing.
+ */
+export function stripDevParams(href: string): string {
+  const url = new URL(href);
+  url.searchParams.delete('scenario');
+  url.searchParams.delete('role');
+  return url.toString();
+}