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>

docs/project/backlog/WP-37-dev-switcher-reset.md

@@ -0,0 +1,31 @@
+# WP-37 — Dev-switcher reset fix (scenario/role)
+
+Status: done
+Phase: 8 — platform/DX/showcase
+
+## Why
+
+The WP-33 dev switcher can't reset scenario/role back to `default`/`drafter` — it gets "stuck"
+(e.g. on `slow`). Cause: `currentScenario()`/`currentRole()` read the URL `?scenario=`/`?role=`
+param **before** sessionStorage, so once a param is in the address bar, `location.reload()` (same
+URL) re-reads the stale value and overrides what the switcher just stored.
+
+## Decisions
+
+- Once the switcher is used, **sessionStorage is authoritative**; a leftover URL param must not
+  win. Strip both dev params from the URL (`history.replaceState`) before reloading.
+- Extract the URL rewrite as a **pure** `stripDevParams(href)` so it's unit-testable without
+  touching `location.reload()`.
+
+## Files
+
+- `src/app/shared/infrastructure/dev-params.ts` (+ `dev-params.spec.ts`) — pure `stripDevParams`.
+- `src/app/shared/ui/debug-state/debug-state.component.ts` — `switchRole`/`switchScenario` call
+  `applyAndReload()` (replaceState with stripped URL, then reload).
+
+## Acceptance criteria
+
+- [x] Switching scenario/role to any value (incl. default/drafter) sticks after reload, even when
+      a `?scenario=`/`?role=` param was in the URL.
+- [x] `stripDevParams` removes both params, keeps other params + path/hash (spec).
+- [x] `npm run ci` green.

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();
+}

src/app/shared/ui/debug-state/debug-state.component.ts

@@ -7,6 +7,7 @@ import { map } from '@shared/application/remote-data';
 import { Role } from '@shared/domain/role';
 import { ROLES, currentRole, setRole } from '@shared/infrastructure/role';
 import { Scenario, SCENARIOS, currentScenario, setScenario } from '@shared/infrastructure/scenario';
+import { stripDevParams } from '@shared/infrastructure/dev-params';
 import { maskBsn, redactProfile } from './mask';
 
 // CIBG-GAP EXTENSION: n/a — devtool, no corresponding CIBG concept; deliberately
@@ -143,10 +144,18 @@ export class DebugStateComponent {
 
   switchRole(r: Role): void {
     setRole(r);
-    location.reload();
+    this.applyAndReload();
   }
   switchScenario(s: Scenario): void {
     setScenario(s);
+    this.applyAndReload();
+  }
+
+  // Strip the dev params from the URL before reloading (WP-37) so a stale ?scenario=/?role=
+  // in the address bar can't override the value the switcher just stored (currentScenario/
+  // currentRole read the URL first) — otherwise a switch to "default"/"drafter" gets stuck.
+  private applyAndReload(): void {
+    history.replaceState({}, '', stripDevParams(window.location.href));
     location.reload();
   }