Let admins hear a voice sample before picking it

The Speech section of every model settings form now has "Hear a
sample", which streams a short sentence (AppData.VoicePreviewText) in
the form's model and voice before they're saved, through
GET api/admin/harness/preview-voice (super admins and admins, that
model only via grabModelCandidate). pickVoice is shared with
speakText, and explainAudioError reads why a streamed player failed
for both read-aloud and the sample.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/pages/admin/settings/models/(partials)/harness-setting-group.tsx

@@ -4,6 +4,7 @@ import SettingsGroup from "../../(partials)/settings-group";
 import HarnessCurrentModel from "./harness-current-model";
 import HarnessModelSelect from "./harness-model-select";
 import HarnessProviderSelect from "./harness-provider-select";
+import HarnessVoicePreview from "./harness-voice-preview";
 import HarnessVoiceSelect from "./harness-voice-select";
 
 type Props = {
@@ -15,8 +16,8 @@ type Props = {
 /**
  * One harness: its provider, then its model (narrowed to that provider),
  * whether it falls back to the automatic picks (for a harness that has
- * them), whether it's on, and its
- * voice for speech. On a bot's page the provider select can also use the
+ * them), whether it's on, and its voice for speech, with a sample to hear
+ * it before saving. On a bot's page the provider select can also use the
  * default, which hides the rest.
  */
 export default function HarnessSettingGroup({ harness, value, onChange }: Props) {
@@ -86,6 +87,9 @@ export default function HarnessSettingGroup({ harness, value, onChange }: Props)
                     onChange={(voice) => onChange({ ...value, voice: voice || undefined })}
                 />
             ) : null}
+            {!value.inherit && harness.harness == "speech" && picked ? (
+                <HarnessVoicePreview model_id={picked.id} voice={value.voice} />
+            ) : null}
             {value.inherit || harness.required ? null : (
                 <Checkbox
                     title={`Turn ${harness.title.toLowerCase()} on`}

src/pages/admin/settings/models/(partials)/harness-voice-preview.tsx

@@ -0,0 +1,91 @@
+import { useEffect, useRef, useState } from "react";
+import Button from "@moduletrace/twui/layout/Button";
+import Row from "@moduletrace/twui/layout/Row";
+import Span from "@moduletrace/twui/layout/Span";
+import { Square, Volume2 } from "lucide-react";
+import explainAudioError from "@/src/functions/frontend/explain-audio-error";
+
+type Props = {
+    /**
+     * The speech model picked in the form, saved or not.
+     */
+    model_id: number;
+    voice?: string;
+};
+
+/**
+ * Plays a short sample in the form's speech model and voice, before
+ * they're saved (`api/admin/harness/preview-voice`, streamed). Stops when
+ * clicked again or when the pick changes.
+ */
+export default function HarnessVoicePreview({ model_id, voice }: Props) {
+    const [state, setState] = useState<"idle" | "loading" | "playing">("idle");
+    const [error, setError] = useState<string>();
+    const audio_ref = useRef<HTMLAudioElement | null>(null);
+
+    function stop() {
+        const audio = audio_ref.current;
+
+        if (audio) {
+            audio.onerror = null;
+            audio.pause();
+            audio.removeAttribute("src");
+            audio.load();
+        }
+
+        setState("idle");
+    }
+
+    useEffect(() => {
+        setError(undefined);
+        return stop;
+    }, [model_id, voice]);
+
+    function play() {
+        stop();
+        setError(undefined);
+        setState("loading");
+
+        const src = `/api/admin/harness/preview-voice?${new URLSearchParams({
+            model_id: String(model_id),
+            ...(voice ? { voice } : {}),
+        })}`;
+        const audio = audio_ref.current || new Audio();
+
+        audio_ref.current = audio;
+        audio.onplaying = () => setState("playing");
+        audio.onended = () => setState("idle");
+        audio.onerror = () => {
+            setState("idle");
+            explainAudioError({ src, fallback: "Couldn't play the sample. Try again." }).then(setError);
+        };
+        audio.src = src;
+        audio.play().catch(() => {});
+    }
+
+    const playing = state == "playing";
+
+    return (
+        <Row className="gap-2! flex-nowrap items-center">
+            <Button
+                title={playing ? "Stop the sample" : "Hear a short sample in this voice"}
+                type="button"
+                variant="ghost"
+                color="gray"
+                size="small"
+                loading={state == "loading"}
+                beforeIcon={
+                    playing ? <Square size={13} fill="currentColor" /> : <Volume2 size={15} />
+                }
+                onClick={playing ? stop : play}
+            >
+                {playing ? "Stop" : "Hear a sample"}
+            </Button>
+            {error ? (
+                <Span role="status" className="text-[13px] leading-[18px] text-ink-secondary">
+                    {error}
+                </Span>
+            ) : null}
+        </Row>
+    );
+}