Phase 3: Check my work, follow-ups and turn-into-deck

Check my work (third homework mode)
- One model call with its own system prompt marks the student's own
  attempt: verdict, what's right, each issue with why + fix, and the
  corrected version that keeps everything the student got right.
  Unasked-for extras are never errors. The attempt is typed/pasted
  (photos of handwriting are documented as unsupported) and stored in
  the record so Redo re-checks the same work.
- Server: mode "check" + solution on POST /api/homework (zod, 400
  server.needSolution without one) and the same NDJSON stream; new
  checkHomework() pipeline with repair-once validation.

Follow-ups
- New POST /api/homework/refine (plain JSON, RATE_LIMIT_REFINE, zod,
  auth before body): shorter / more detail / explain, plain text back,
  language preserved.
- Shorter + More detail + Original rewrite the finished answer and the
  corrected version in place (FollowUpBar); every guide step has
  Explain step N differently; failed calls say so without losing text.

Turn into a study deck
- Any result hands its content (answer, corrected version or assembled
  guide) to New deck through a one-shot sessionStorage seed with the
  options step pre-filled.

UI
- Phone step 2 gains the third card: tapping it reveals the solution
  field + submit; desktop has three cards and the solution field shows
  with the mode. Homework history labels and share/card previews cover
  the new mode.

Verified: new phase-3 suite 20/20 against a stub Ollama (check payload,
missing-solution 400, refine validation, phone + desktop check flows,
shorter follow-up with restore, guide explain, deck hand-off) plus
regression 74/74, mobile 52/52, declutter 116/116, wizard 80/80,
animation 8/8, native 35/35, phase1 38/38, phase2 43/43, i18n 25/25.
Key parity 734/734. Lint + build clean. SW freezmo-v27.

components/homework/HomeworkResult.tsx

@@ -1,25 +1,31 @@
 "use client";
 
+import { useState } from "react";
+
 import { Button } from "@/components/ui";
 import { useI18n } from "@/lib/i18n";
 import type { HomeworkMakeRecord } from "@/lib/schemas";
 import { shareHomework } from "@/lib/share";
 
 import { CopyButton } from "./CopyButton";
+import { FollowUpBar } from "./FollowUpBar";
 
 /** Mode 1 result: the finished homework, nothing else. */
 export function HomeworkResult({
   record,
   onAgain,
   onNew,
+  onToDeck,
   againLoading,
 }: {
   record: HomeworkMakeRecord;
   onAgain: () => void;
   onNew: () => void;
+  onToDeck: () => void;
   againLoading: boolean;
 }) {
   const { t } = useI18n();
+  const [answer, setAnswer] = useState(record.answer);
 
   return (
     <div className="space-y-5">
@@ -32,24 +38,33 @@ export function HomeworkResult({
         </h1>
       </header>
 
-      <article className="card p-4 sm:p-5">
-        <p className="whitespace-pre-wrap break-words text-[15px] leading-relaxed text-[var(--text)]">
-          {record.answer}
-        </p>
+      <article className="card space-y-3 p-4 sm:p-5">
+        <p className="whitespace-pre-wrap break-words text-[15px] leading-relaxed text-[var(--text)]">{answer}</p>
+        <FollowUpBar
+          text={answer}
+          context={record.sourceText}
+          onReplace={setAnswer}
+          onRestore={() => setAnswer(record.answer)}
+          canRestore={answer !== record.answer}
+        />
       </article>
 
       <div className="flex flex-wrap items-start gap-2">
-        <CopyButton text={record.answer} />
-        <Button variant="secondary" className="touch-target" onClick={() => void shareHomework(record)}>
+        <CopyButton text={answer} />
+        <Button variant="secondary" className="touch-target" onClick={() => void shareHomework({ ...record, answer })}>
           {t("deck.share")}
         </Button>
         <Button variant="secondary" className="touch-target" onClick={onAgain} loading={againLoading}>
-          {t("homework.result.again")}
+          {t("homework.followup.redo")}
+        </Button>
+        <Button variant="secondary" className="touch-target" onClick={onToDeck}>
+          {t("homework.toDeck")}
         </Button>
         <Button variant="ghost" className="touch-target" onClick={onNew}>
           {t("homework.result.new")}
         </Button>
       </div>
+      <p className="text-[11.5px] text-[var(--text-subtle)]">{t("homework.toDeckNote")}</p>
     </div>
   );
 }