Simplify and improve locality of the device name request logic

src/utils/observable.ts

@@ -5,7 +5,17 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type Observable, defer, finalize, scan, startWith, tap } from "rxjs";
+import {
+  type Observable,
+  concat,
+  defer,
+  finalize,
+  map,
+  scan,
+  startWith,
+  takeWhile,
+  tap,
+} from "rxjs";
 
 const nothing = Symbol("nothing");
 
@@ -39,6 +49,29 @@ export function accumulate<State, Event>(
     events$.pipe(scan(update, initial), startWith(initial));
 }
 
+const switchSymbol = Symbol("switch");
+
+/**
+ * RxJS operator which behaves like the input Observable (A) until it emits a
+ * value satisfying the given predicate, then behaves like Observable B.
+ *
+ * The switch is immediate; the value that triggers the switch will not be
+ * present in the output.
+ */
+export function switchWhen<A, B>(
+  predicate: (a: A, index: number) => boolean,
+  b$: Observable<B>,
+) {
+  return (a$: Observable<A>): Observable<A | B> =>
+    concat(
+      a$.pipe(
+        map((a, index) => (predicate(a, index) ? switchSymbol : a)),
+        takeWhile((a) => a !== switchSymbol),
+      ) as Observable<A>,
+      b$,
+    );
+}
+
 /**
  * Reads the current value of a state Observable without reacting to future
  * changes.