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

internal/docs/handlers.go

@@ -139,6 +139,10 @@ type updateRequest struct {
 	ContentText *string `json:"content_text"`
 	Tone        *string `json:"tone"`
 	WordCount   *int    `json:"word_count"`
+
+	// PreserveHistory toggles the passport's keep-everything mode. Sent alone
+	// by the History panel's toggle, never by the auto-save path.
+	PreserveHistory *bool `json:"preserve_history"`
 }
 
 // update applies the provided fields to a document and returns the saved row.
@@ -159,9 +163,11 @@ func (h *Handler) update(w http.ResponseWriter, r *http.Request) {
 		        content_text = COALESCE(?, content_text),
 		        tone         = COALESCE(?, tone),
 		        word_count   = COALESCE(?, word_count),
+		        preserve_history = COALESCE(?, preserve_history),
 		        updated_at   = CURRENT_TIMESTAMP
 		  WHERE id = ? AND user_id = ?`,
-		req.Title, req.Content, req.ContentText, req.Tone, req.WordCount, id, db.LocalUserID,
+		req.Title, req.Content, req.ContentText, req.Tone, req.WordCount,
+		req.PreserveHistory, id, db.LocalUserID,
 	)
 	if err != nil {
 		httputil.ServerError(w, err)
@@ -211,13 +217,14 @@ func (h *Handler) delete(w http.ResponseWriter, r *http.Request) {
 func (h *Handler) fetch(id string) (db.Document, error) {
 	var doc db.Document
 	err := h.DB.QueryRow(
-		`SELECT id, user_id, title, content, content_text, tone, word_count, created_at, updated_at
+		`SELECT id, user_id, title, content, content_text, tone, word_count,
+		        created_at, updated_at, preserve_history
 		   FROM documents
 		  WHERE id = ? AND user_id = ?`,
 		id, db.LocalUserID,
 	).Scan(
 		&doc.ID, &doc.UserID, &doc.Title, &doc.Content, &doc.ContentText,
-		&doc.Tone, &doc.WordCount, &doc.CreatedAt, &doc.UpdatedAt,
+		&doc.Tone, &doc.WordCount, &doc.CreatedAt, &doc.UpdatedAt, &doc.PreserveHistory,
 	)
 	return doc, err
 }