fix: let the learner retry a turn whose model call failed

components/chat.tsx

@@ -65,9 +65,11 @@ import {
 	type CompactionDividerData,
 } from "@/components/compaction-divider";
 import { CoverageRing } from "@/components/extraction-coverage";
+import { Button } from "@/components/ui/button";
 import {
 	activeProblemOf,
 	dismissedAnswer,
+	endsInFailedTurn,
 	findPendingToolCall,
 	phaseAt3,
 	phaseTimeline,
@@ -458,6 +460,12 @@ export function Chat({
 	const busy = localStream || turnInFlight;
 	const busyRef = useRef(busy);
 	busyRef.current = busy;
+	// A failed model call (issue #110): the banner offers Retry, which
+	// re-runs the turn from the saved input — the only path back, since an
+	// answered question cannot be answered again. Offered from "error" too:
+	// a dropped stream leaves the model there, and send() recovers from it.
+	const retryable = (status === "ready" || status === "error") && !busy && endsInFailedTurn(nativeMessages);
+	const retryFailedTurn = () => void send({ type: "retry" });
 
 	// The attach handoff (stream-reattach wave): the moment a resumed
 	// stream takes over the rendering — the SDK left "ready", so
@@ -1577,8 +1585,13 @@ export function Chat({
 								</span>
 							)}
 							{error && (
-								<div className="rounded-lg border border-destructive/50 bg-destructive/10 px-3 py-2 text-sm">
-									Something went wrong: {error.message}
+								<div className="flex items-center justify-between gap-3 rounded-lg border border-destructive/50 bg-destructive/10 px-3 py-2 text-sm">
+									<span>Something went wrong: {error.message}</span>
+									{retryable && (
+										<Button variant="outline" size="xs" data-testid="retry-failed-turn" onClick={retryFailedTurn}>
+											Retry
+										</Button>
+									)}
 								</div>
 							)}
 						</div>