fix(voice): browser speech recognition on Android no longer repeats phrases

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/lib/voice.ts

@@ -186,3 +186,27 @@ export class VoiceRecorder {
     this.analyser = null;
   }
 }
+
+/**
+ * Text of one speech recognition session from its results. Desktop browsers deliver consecutive
+ * pieces ("Test 1 2 3", " und weiter"); Chrome on Android also keeps the growing interim states of
+ * the same phrase as results of their own ("Test", "Test", "Test 1 2 3"). A result that only
+ * continues the one before it therefore replaces it instead of being appended.
+ */
+export function joinSpeechResults(transcripts: string[]): string {
+  const norm = (s: string) => s.trim().toLowerCase();
+  let text = '';
+  let last = '';
+  for (const t of transcripts) {
+    if (!t) continue;
+    if (last && norm(t).startsWith(norm(last))) {
+      text = text.slice(0, text.length - last.length) + t; // grown version of the same phrase
+    } else if (last && norm(last).startsWith(norm(t))) {
+      continue; // an earlier, shorter state of it
+    } else {
+      text += t;
+    }
+    last = t;
+  }
+  return text;
+}