fix(book): the auto layout's drawn templates no longer carry photos of the book they were drawn in

Three photo frames in the templates kept the photo ids of the journey the
templates were read out of (68 and 69). Only empty frames take an entry's
photos, so every book laid out on those templates pointed at those ids: a
broken picture on most installs, and on one where the id exists, someone
else's photo or an unrelated one of the user's own. The frames are empty
now and take the entry's photos like the others. The parity digests of the
five spreads that use them are written anew, as the spec asks for a
deliberate layout change.

client/src/components/Assistant/AssistantMessage.tsx

@@ -1,7 +1,7 @@
 import { ActionBarPrimitive, AuiIf, MessagePrimitive } from '@assistant-ui/react';
 import type { AssistantMessage as StoredMessage } from '@trek/shared';
 import { Check, Copy, FileText, LoaderCircle, Share2 } from 'lucide-react';
-import { useMemo } from 'react';
+import { Fragment, useMemo } from 'react';
 
 import { useTranslation } from '../../i18n';
 import { chatOf, useAssistantStore } from '../../store/assistantStore';
@@ -16,7 +16,7 @@ import AssistantShareDialog from './AssistantShareDialog';
 import AssistantSources from './AssistantSources';
 import AssistantToolSteps from './AssistantToolSteps';
 import AssistantWeatherStrip from './AssistantWeatherStrip';
-import { messageBlocks } from './assistantParts';
+import { type MessageBlock, messageBlocks, tailStart } from './assistantParts';
 import { useAssistantView } from './assistantViewContext';
 import AssistantCardBlock from './cards/AssistantCardBlock';
 import { useAssistantShare } from './useAssistantShare';
@@ -108,6 +108,28 @@ function Question({ message }: { message: StoredMessage }) {
   );
 }
 
+/** One block of an answer, in the shape its kind takes. */
+function AnswerBlock({
+  block,
+  message,
+  writing,
+  streaming,
+}: {
+  block: MessageBlock;
+  message: StoredMessage;
+  writing: boolean;
+  streaming: boolean;
+}) {
+  if (block.kind === 'text') return <AssistantMarkdown text={block.text} writing={streaming} />;
+  if (block.kind === 'steps') return <AssistantToolSteps steps={block.steps} />;
+  if (block.kind === 'places') return <AssistantPlaceStrip found={block.found} message={message} />;
+  if (block.kind === 'weather') return <AssistantWeatherStrip days={block.days} />;
+  if (block.kind === 'sources') return <AssistantSources sources={block.sources} />;
+  if (block.kind === 'remembered') return <AssistantRemembered note={block.note} live={writing} />;
+  if (block.kind === 'cards') return <AssistantCardBlock block={block} message={message} />;
+  return <AssistantChangeCard items={block.items} />;
+}
+
 function Answer({ message }: { message: StoredMessage }) {
   const { t } = useTranslation();
   const { tripId, variant } = useAssistantView();
@@ -119,25 +141,16 @@ function Answer({ message }: { message: StoredMessage }) {
   const share = useAssistantShare(tripId, message, writing);
   const last = blocks[blocks.length - 1];
   const hasText = blocks.some((b) => b.kind === 'text');
+  const tail = tailStart(blocks);
 
   return (
     <MessagePrimitive.Root className="trek-assistant-enter flex flex-col gap-2.5 py-2">
-      {blocks.map((block) => {
-        if (block.kind === 'text') {
-          return <AssistantMarkdown key={block.key} text={block.text} writing={writing && block === last} />;
-        }
-        if (block.kind === 'steps') return <AssistantToolSteps key={block.key} steps={block.steps} />;
-        if (block.kind === 'places') {
-          return <AssistantPlaceStrip key={block.key} found={block.found} message={message} />;
-        }
-        if (block.kind === 'weather') return <AssistantWeatherStrip key={block.key} days={block.days} />;
-        if (block.kind === 'sources') return <AssistantSources key={block.key} sources={block.sources} />;
-        if (block.kind === 'remembered') {
-          return <AssistantRemembered key={block.key} note={block.note} live={writing} />;
-        }
-        if (block.kind === 'cards') return <AssistantCardBlock key={block.key} block={block} message={message} />;
-        return <AssistantChangeCard key={block.key} items={block.items} />;
-      })}
+      {blocks.map((block, i) => (
+        <Fragment key={block.key}>
+          {i === tail && i > 0 && <span data-assistant-tail aria-hidden="true" className="-mb-2.5 block h-0" />}
+          <AnswerBlock block={block} message={message} writing={writing} streaming={writing && block === last} />
+        </Fragment>
+      ))}
       {/* Nothing below says the answer goes on: no words being written, no step running. */}
       {writing && last?.kind !== 'text' && last?.kind !== 'steps' && (
         <p role="status" className="m-0 text-caption">

client/src/components/Assistant/AssistantThread.tsx

@@ -1,6 +1,6 @@
 import { AuiIf, ThreadPrimitive } from '@assistant-ui/react';
 import { ArrowDown, FileUp, MapPin } from 'lucide-react';
-import { useMemo } from 'react';
+import { useMemo, useRef } from 'react';
 
 import { useTranslation } from '../../i18n';
 import { chatOf, useAssistantStore } from '../../store/assistantStore';
@@ -15,13 +15,15 @@ import { useAssistantAttach } from './useAssistantAttach';
 import { useFollowSelectedDay } from './useAssistantFocus';
 import { joinDropZones, useAssistantPlaceDrop } from './useAssistantPlaceDrop';
 import { useAssistantSuggestions } from './useAssistantSuggestions';
+import { useRevealAnswerTail } from './useRevealAnswerTail';
 
 /**
  * The chat itself: the messages, and under them the line that says what went
  * wrong, the privacy note and the composer, held at the bottom while the
  * messages scroll. A new question moves up to the top of the view, so its
- * answer reads from its first line instead of chasing the newest one. A
- * booking file or a place of the trip can be dropped anywhere on it.
+ * answer reads from its first line instead of chasing the newest one, and once
+ * the answer is written its end comes into view. A booking file or a place of
+ * the trip can be dropped anywhere on it.
  */
 export default function AssistantThread({ tripTitle }: { tripTitle: string }) {
   const { t } = useTranslation();
@@ -31,6 +33,8 @@ export default function AssistantThread({ tripTitle }: { tripTitle: string }) {
   const byId = useMemo(() => new Map(messages.map((m) => [m.id, m])), [messages]);
   const { suggestions, canEdit } = useAssistantSuggestions(tripId);
   useFollowSelectedDay(tripId);
+  const viewport = useRef<HTMLDivElement>(null);
+  useRevealAnswerTail(viewport, isRunning);
 
   const phone = variant === 'fullscreen';
   const attach = useAssistantAttach(tripId);
@@ -52,7 +56,11 @@ export default function AssistantThread({ tripTitle }: { tripTitle: string }) {
           </span>
         </div>
       )}
-      <ThreadPrimitive.Viewport turnAnchor="top" className="flex min-h-0 flex-1 flex-col overflow-y-auto px-4">
+      <ThreadPrimitive.Viewport
+        ref={viewport}
+        turnAnchor="top"
+        className="flex min-h-0 flex-1 flex-col overflow-y-auto px-4"
+      >
         <AuiIf condition={(s) => s.thread.isEmpty}>
           <AssistantWelcome suggestions={suggestions} canEdit={canEdit} withSuggestions={!phone} />
           {mentionable && (

client/src/components/Assistant/assistantParts.ts

@@ -61,7 +61,7 @@ export interface ChangeItem {
 /** The answer cards of one group, side by side. */
 export type CardsBlock = { kind: 'cards'; key: string; group: string; entries: CardEntry[] };
 
-type MessageBlock =
+export type MessageBlock =
   | { kind: 'text'; key: string; text: string }
   | { kind: 'steps'; key: string; steps: ToolStep[] }
   | { kind: 'change'; key: string; items: ChangeItem[] }
@@ -464,3 +464,14 @@ export const CHANGE_LABELS: Record<AssistantChangeLabelKey, { labelKey: string }
   packing: { labelKey: 'assistant.change.label.packing' },
   breaks: { labelKey: 'assistant.change.label.breaks' },
 };
+
+/**
+ * Where an answer's closing words and changes begin: the block after its last
+ * step, strip or card. That end is what the thread brings into view once the
+ * answer is written.
+ */
+export function tailStart(blocks: MessageBlock[]): number {
+  let i = blocks.length;
+  while (i > 0 && (blocks[i - 1].kind === 'text' || blocks[i - 1].kind === 'change')) i -= 1;
+  return i;
+}

client/src/components/Assistant/useRevealAnswerTail.test.tsx

@@ -0,0 +1,109 @@
+/**
+ * FE-AI-REVEAL-001 to FE-AI-REVEAL-007
+ *
+ * Once an answer is written, its closing words and changes come into view,
+ * unless the user scrolled the thread themselves while it was written; and
+ * where that end begins in an answer's blocks.
+ */
+import { useRef } from 'react';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { fireEvent, render } from '../../../tests/helpers/render';
+import { type MessageBlock, tailStart } from './assistantParts';
+import { tailScrollTop, useRevealAnswerTail } from './useRevealAnswerTail';
+
+/** A viewport of 400px holding 1200px, its tail mark 900px down, scrolled to `scrollTop`. */
+function lay(viewport: HTMLElement, { tailAt = 900, scrollTop = 0, height = 1200 } = {}) {
+  Object.defineProperty(viewport, 'clientHeight', { configurable: true, value: 400 });
+  Object.defineProperty(viewport, 'scrollHeight', { configurable: true, value: height });
+  viewport.scrollTop = scrollTop;
+  viewport.getBoundingClientRect = () => ({ top: 100 }) as DOMRect;
+  const tail = viewport.querySelector('[data-assistant-tail]') as HTMLElement | null;
+  if (tail) tail.getBoundingClientRect = () => ({ top: 100 + tailAt - scrollTop }) as DOMRect;
+}
+
+function Thread({ running }: { running: boolean }) {
+  const ref = useRef<HTMLDivElement>(null);
+  useRevealAnswerTail(ref, running);
+  return (
+    <div ref={ref} data-testid="viewport" tabIndex={0}>
+      <span data-assistant-tail />
+    </div>
+  );
+}
+
+const block = (kind: MessageBlock['kind']) => ({ kind, key: kind }) as MessageBlock;
+
+describe('useRevealAnswerTail', () => {
+  let scrollTo: ReturnType<typeof vi.fn>;
+
+  beforeEach(() => {
+    scrollTo = vi.fn();
+    HTMLElement.prototype.scrollTo = scrollTo as unknown as HTMLElement['scrollTo'];
+    vi.spyOn(window, 'requestAnimationFrame').mockImplementation((cb) => {
+      cb(0);
+      return 1;
+    });
+  });
+  afterEach(() => vi.restoreAllMocks());
+
+  it('FE-AI-REVEAL-001: brings the end of the answer into view once it is written', () => {
+    const view = render(<Thread running />);
+    lay(view.getByTestId('viewport'), { height: 2000 });
+    view.rerender(<Thread running={false} />);
+    expect(scrollTo).toHaveBeenCalledWith(expect.objectContaining({ top: 888 }));
+  });
+
+  it('FE-AI-REVEAL-002: leaves the thread where the user scrolled it while the answer was written', () => {
+    const view = render(<Thread running />);
+    const viewport = view.getByTestId('viewport');
+    lay(viewport);
+    fireEvent.wheel(viewport, { deltaY: 120 });
+    view.rerender(<Thread running={false} />);
+    expect(scrollTo).not.toHaveBeenCalled();
+  });
+
+  it('FE-AI-REVEAL-003: does nothing on the first render or while nothing runs', () => {
+    const view = render(<Thread running={false} />);
+    lay(view.getByTestId('viewport'));
+    view.rerender(<Thread running={false} />);
+    expect(scrollTo).not.toHaveBeenCalled();
+  });
+
+  it('FE-AI-REVEAL-004: a new answer reveals its end again after an earlier one was scrolled by hand', () => {
+    const view = render(<Thread running />);
+    const viewport = view.getByTestId('viewport');
+    lay(viewport);
+    fireEvent.wheel(viewport, { deltaY: 120 });
+    view.rerender(<Thread running={false} />);
+    view.rerender(<Thread running />);
+    view.rerender(<Thread running={false} />);
+    expect(scrollTo).toHaveBeenCalledTimes(1);
+  });
+});
+
+describe('tailScrollTop', () => {
+  it('FE-AI-REVEAL-005: stops at the bottom when the end is shorter than the view, and never scrolls up', () => {
+    const viewport = document.createElement('div');
+    viewport.innerHTML = '<span data-assistant-tail></span>';
+    lay(viewport, { tailAt: 1100 });
+    expect(tailScrollTop(viewport)).toBe(800);
+    lay(viewport, { tailAt: 300, scrollTop: 500 });
+    expect(tailScrollTop(viewport)).toBeNull();
+  });
+
+  it('FE-AI-REVEAL-006: without a mark there is nothing to reveal', () => {
+    const viewport = document.createElement('div');
+    lay(viewport);
+    expect(tailScrollTop(viewport)).toBeNull();
+  });
+});
+
+describe('tailStart', () => {
+  it('FE-AI-REVEAL-007: the end begins after the last step, strip or card', () => {
+    expect(tailStart([block('steps'), block('places'), block('text'), block('change')])).toBe(2);
+    expect(tailStart([block('text'), block('places')])).toBe(2);
+    expect(tailStart([block('text'), block('change')])).toBe(0);
+    expect(tailStart([])).toBe(0);
+  });
+});

client/src/components/Assistant/useRevealAnswerTail.ts

@@ -0,0 +1,61 @@
+import { type RefObject, useEffect, useRef } from 'react';
+
+import { prefersReducedMotion } from '../../utils/reducedMotion';
+
+/** Room left above the tail, so its first line does not sit flush on the edge. */
+const TAIL_GAP = 12;
+/** What reading the thread by hand looks like while the answer is written. */
+const OWN_SCROLL = ['wheel', 'touchmove', 'keydown'] as const;
+
+/**
+ * Where to scroll so the end of the latest answer is in view: the start of its
+ * closing text and proposed changes (the `data-assistant-tail` mark), or the
+ * very bottom when that tail is shorter than the view. Null when it is in view
+ * already, so the thread never moves up.
+ */
+export function tailScrollTop(viewport: HTMLElement): number | null {
+  const marks = viewport.querySelectorAll('[data-assistant-tail]');
+  const tail = marks[marks.length - 1];
+  if (!tail) return null;
+  const offset = tail.getBoundingClientRect().top - viewport.getBoundingClientRect().top + viewport.scrollTop;
+  const target = Math.min(offset - TAIL_GAP, viewport.scrollHeight - viewport.clientHeight);
+  return target > viewport.scrollTop + 1 ? target : null;
+}
+
+/**
+ * A new question moves to the top of the view, so its answer reads from the
+ * first line. A long answer (steps, a strip of places found, cards) then ends
+ * below the view, and its closing words and the changes to apply were never
+ * seen. Once the answer is written, this brings that end into view, unless the
+ * user scrolled the thread themselves while it was written.
+ */
+export function useRevealAnswerTail(viewport: RefObject<HTMLElement | null>, isRunning: boolean): void {
+  const scrolledByHand = useRef(false);
+  const wasRunning = useRef(isRunning);
+
+  useEffect(() => {
+    const el = viewport.current;
+    if (!el || !isRunning) return;
+    scrolledByHand.current = false;
+    const mark = () => {
+      scrolledByHand.current = true;
+    };
+    for (const type of OWN_SCROLL) el.addEventListener(type, mark, { passive: true });
+    return () => {
+      for (const type of OWN_SCROLL) el.removeEventListener(type, mark);
+    };
+  }, [viewport, isRunning]);
+
+  useEffect(() => {
+    const ended = wasRunning.current && !isRunning;
+    wasRunning.current = isRunning;
+    const el = viewport.current;
+    if (!ended || !el || scrolledByHand.current) return;
+    // A frame later, so the answer's last blocks have their height.
+    const frame = requestAnimationFrame(() => {
+      const top = tailScrollTop(el);
+      if (top !== null) el.scrollTo({ top, behavior: prefersReducedMotion() ? 'auto' : 'smooth' });
+    });
+    return () => cancelAnimationFrame(frame);
+  }, [viewport, isRunning]);
+}

shared/src/book/auto/auto-layout.parity.json

@@ -65,7 +65,7 @@
  "B/full/spread/0": "ac843317bb8d097c",
  "B/full/spread/1": "bf4b62404c36aa0e",
  "B/full/spread/2": "1af653e4557c90b9",
- "B/full/spread/3": "f766c7b6a3cad0fa",
+ "B/full/spread/3": "b094a0b5aa67b2c0",
  "B/full/relayout/3": "c0f3d2e84826b420",
  "B/full/spread/4": "8563f01a381c3b8b",
  "B/full/spread/5": "2458025780d8cbf3",
@@ -85,14 +85,14 @@
  "C/full/head": "0ffba0f701b7ccaa",
  "C/full/spread/0": "ee87e9e195e1edde",
  "C/full/spread/1": "bf4b62404c36aa0e",
- "C/full/spread/2": "973ed5d0aacb1063",
- "C/full/relayout/2": "973ed5d0aacb1063",
+ "C/full/spread/2": "b40cfdb0e5bea780",
+ "C/full/relayout/2": "b40cfdb0e5bea780",
  "C/full/spread/3": "8eb39a4e9d726f5e",
  "C/full/relayout/3": "8eb39a4e9d726f5e",
  "C/full/spread/4": "5a037193ef347c07",
  "C/full/relayout/4": "5a037193ef347c07",
- "C/full/spread/5": "71c9f776ce8ffc87",
- "C/full/relayout/5": "71c9f776ce8ffc87",
+ "C/full/spread/5": "b6dedb14199ad559",
+ "C/full/relayout/5": "b6dedb14199ad559",
  "C/full/spread/6": "0debcd2babd7ee6b",
  "C/full/relayout/6": "0debcd2babd7ee6b",
  "C/full/spread/7": "2458025780d8cbf3",

shared/src/book/auto/auto-templates.data.ts

@@ -281,7 +281,7 @@ export const AUTO_TEMPLATES: readonly AutoTemplate[] = [
         opacity: 1,
         locked: false,
         kind: 'photo',
-        photoId: 69,
+        photoId: null,
         fit: 'cover',
         focalX: 0.42168673729754674,
         focalY: 0.23833399057977409,
@@ -436,7 +436,7 @@ export const AUTO_TEMPLATES: readonly AutoTemplate[] = [
         opacity: 1,
         locked: false,
         kind: 'photo',
-        photoId: 68,
+        photoId: null,
         fit: 'cover',
         focalX: 0.5,
         focalY: 0.5,
@@ -457,7 +457,7 @@ export const AUTO_TEMPLATES: readonly AutoTemplate[] = [
         opacity: 1,
         locked: false,
         kind: 'photo',
-        photoId: 69,
+        photoId: null,
         fit: 'cover',
         focalX: 0.5,
         focalY: 0.5,