Writing passport: evidence of process instead of an AI score

She's submitting work that gets run through an AI detector and wants to
pre-check she won't be wrongly flagged. Petal should not answer that with
a detector of its own: they misfire badly on non-native English (Stanford
2023 found >50% of TOEFL essays flagged as AI vs. near-zero for native
writers), so a percentage aimed at an ESL writer is worse than nothing —
it either scares her off her own voice or gives false comfort.

So the artifact is provenance, not a verdict. Petal already snapshots
every ~3 minutes; this turns that history into a standalone printable
report: session breakdown, word-count growth, span, active time. No score
is emitted anywhere.

Two schema additions back it. preserve_history opts a document out of the
40-snapshot prune cap — right for recovery, wrong for provenance, where
you want the whole span including the oldest rows. content_hash/prev_hash
chain each snapshot to the one before it, so a history edited or thinned
after the fact fails verification. Pruning legitimately severs links, so a
link break reports as "gaps" unless preserve_history is on; only a hash
that fails against its own contents is unconditionally "broken".

The chart's x axis is snapshot order, not wall-clock, and that is the load
-bearing decision. On a linear time axis an essay written in three
sittings across three days renders as three vertical cliffs separated by
empty space — visually identical to text pasted in three chunks, i.e. the
report would have argued the opposite of the truth. Breaks are compressed
into explicitly labelled gutters instead. TestChartGivesWidthToWriting
pins it.

The report volunteers its largest single word-count jump and states its
own limits: it cannot show who was at the keyboard, or whether typed text
was composed or copied in. Overclaiming would be self-defeating — a reader
who catches it overstating discounts all of it.

HTML rather than server-rendered PDF, as with the other exports: a CJK-safe
PDF needs an embedded Unicode font or a headless browser. Print styles are
there so the browser's Save as PDF is the handoff path.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

web/src/api/client.ts

@@ -41,6 +41,9 @@ export interface Document {
   word_count: number
   created_at: string
   updated_at: string
+  // When true, this document's automatic snapshots are never pruned, so its
+  // full writing trail survives as authorship evidence (see the passport).
+  preserve_history: boolean
 }
 
 // Fields the editor sends on auto-save. All optional so a rename can send title
@@ -51,6 +54,7 @@ export interface DocUpdate {
   content_text?: string
   tone?: string
   word_count?: number
+  preserve_history?: boolean
 }
 
 // One sense of a word from the offline dictionary.
@@ -219,6 +223,11 @@ export const api = {
   // the given format. A one-click "download all my writing" safety net.
   exportAllUrl: (format: ExportFormat) => `/api/docs/export-all?format=${format}`,
 
+  // Download URL for the writing passport: a standalone HTML report of how this
+  // document was written (timeline, growth, sessions), for showing someone who
+  // questions its authorship. Print to PDF from the browser to hand it over.
+  passportUrl: (id: string) => `/api/docs/${id}/passport`,
+
   // Offline word lookup (gloss + definition + synonyms) for the right-click popover.
   lookupWord: (word: string) => req<WordInfo>(`/word/${encodeURIComponent(word)}`),
   // Lightweight Chinese-only gloss for the inline hover/select tooltip — instant

web/src/components/History/HistoryPanel.tsx

@@ -42,6 +42,8 @@ export function HistoryPanel({ docId, onClose, onRestored }: Props) {
   const [selected, setSelected] = useState<DocumentVersion | null>(null)
   const [preview, setPreview] = useState<DocumentVersion | null>(null)
   const [busy, setBusy] = useState(false)
+  // Null until the document loads; the passport controls stay inert until then.
+  const [preserve, setPreserve] = useState<boolean | null>(null)
   const panelRef = useFocusTrap<HTMLElement>()
 
   const load = useCallback(async () => {
@@ -57,6 +59,25 @@ export function HistoryPanel({ docId, onClose, onRestored }: Props) {
     void load()
   }, [load])
 
+  // The keep-full-history flag lives on the document, not on its snapshots.
+  useEffect(() => {
+    void api
+      .getDoc(docId)
+      .then((d) => setPreserve(d.preserve_history))
+      .catch(() => setPreserve(null))
+  }, [docId])
+
+  const togglePreserve = useCallback(async () => {
+    if (preserve === null) return
+    const next = !preserve
+    setPreserve(next) // optimistic; revert if the save fails
+    try {
+      await api.updateDoc(docId, { preserve_history: next })
+    } catch {
+      setPreserve(!next)
+    }
+  }, [docId, preserve])
+
   // Escape closes the drawer.
   useEffect(() => {
     const onKey = (e: KeyboardEvent) => {
@@ -231,6 +252,51 @@ export function HistoryPanel({ docId, onClose, onRestored }: Props) {
             </div>
           </div>
         )}
+
+        {/* Writing passport: turn this history into something you can show
+            someone who doubts you wrote this yourself. */}
+        <div
+          className="shrink-0 px-4 py-3"
+          style={{ borderTop: '1px solid var(--color-border)' }}
+        >
+          <a
+            href={api.passportUrl(docId)}
+            download
+            className="flex w-full items-center justify-center gap-1.5 rounded-full py-2.5 text-sm font-extrabold"
+            style={{
+              border: '1.5px solid var(--color-accent)',
+              color: 'var(--color-accent)',
+            }}
+            onMouseEnter={(e) => (e.currentTarget.style.background = 'var(--color-surface-alt)')}
+            onMouseLeave={(e) => (e.currentTarget.style.background = 'transparent')}
+          >
+            📜 写作证明 · Writing passport
+          </a>
+          <div className="mt-1.5 text-center text-[11px]" style={{ color: 'var(--color-muted)' }}>
+            A report showing how this draft grew, session by session.
+          </div>
+
+          <label
+            className="mt-3 flex cursor-pointer items-start gap-2 text-[11px]"
+            style={{ color: 'var(--color-muted)' }}
+          >
+            <input
+              type="checkbox"
+              checked={preserve ?? false}
+              disabled={preserve === null}
+              onChange={togglePreserve}
+              className="mt-0.5 shrink-0"
+              style={{ accentColor: 'var(--color-accent)' }}
+            />
+            <span>
+              <span className="font-bold" style={{ color: 'var(--color-plum)' }}>
+                保留完整历史 · Keep full history
+              </span>
+              <br />
+              Never delete old snapshots of this document, so the record stays complete.
+            </span>
+          </label>
+        </div>
       </aside>
     </div>
   )