Fix reader progress regressions found during release review

lib/src/engine/epub/epub_reader_engine.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:math' as math;
 
 import 'package:flutter/widgets.dart';
 
@@ -356,7 +357,10 @@ final class EpubReaderEngine extends ReaderEngine {
       await _goTo(
         _locatorFor(
           position.chapter,
-          local: progress == 1 ? 1 : 0,
+          local: progress == 1
+              ? 1
+              : position.offset /
+                    math.max(1, _progressIndex!.lengths[position.chapter]),
           textOffset: position.offset,
         ),
         seek: seek,

lib/src/engine/epub/epub_viewport.dart

@@ -522,7 +522,11 @@ final class _EpubViewportState extends State<EpubViewport> {
     return true;
   }
 
-  void _publishPage(int index, {int? restoredOffset}) {
+  void _publishPage(
+    int index, {
+    int? restoredOffset,
+    bool schedulePrefetch = true,
+  }) {
     if (_restoring || _busy || _pages.isEmpty) {
       return;
     }
@@ -558,7 +562,9 @@ final class _EpubViewportState extends State<EpubViewport> {
       coverageEnd: coverageEnd,
       atEnd: complete && after == _pages.length,
     );
-    _schedulePrefetch();
+    if (schedulePrefetch) {
+      _schedulePrefetch();
+    }
   }
 
   void _scrollChanged() {
@@ -835,7 +841,19 @@ final class _EpubViewportState extends State<EpubViewport> {
             wasComplete != current.complete) {
           setState(() {});
         }
-        _publishPageCount(current);
+        if (!wasComplete &&
+            current.complete &&
+            widget.engine.preferences.layoutMode ==
+                ReaderLayoutMode.paginated) {
+          _publishPage(
+            _pageIndex,
+            restoredOffset: widget.engine.locator.textOffset,
+            schedulePrefetch: false,
+          );
+        } else {
+          _publishPageCount(current);
+        }
+
         _warmImages(
           current.pages,
           (_pageIndex - _spreadsBehind) * _columns,

test/engine/epub_content_renderer_test.dart

@@ -1,8 +1,52 @@
-import 'package:flutter/widgets.dart';
+import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:papyrus_reader/papyrus_reader.dart';
 
+import '../support/in_process_epub_worker.dart';
+import '../support/synthetic_epub.dart';
+
 void main() {
+  testWidgets('progress seeks restore the custom renderer within a chapter', (
+    tester,
+  ) async {
+    final renderer = _TrackingRenderer();
+    final engine = EpubReaderEngine(
+      renderer: renderer,
+      workerFactory: () async => InProcessEpubWorker(),
+    );
+    addTearDown(engine.dispose);
+    await engine.load(
+      ReaderDocument(
+        id: 'custom-scroll',
+        format: ReaderFormat.epub,
+        loadBytes: () async => syntheticEpub(
+          singleSpine: true,
+          firstChapterBody:
+              '<p>${List.filled(200, "Scrollable text").join(" ")}</p>',
+        ),
+      ),
+      preferences: const ReaderPreferences(layoutMode: ReaderLayoutMode.scroll),
+    );
+    await tester.pumpWidget(
+      MaterialApp(
+        home: ListenableBuilder(
+          listenable: engine,
+          builder: (context, _) => engine.buildViewport(context),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    for (final progress in [.25, .75, 1.0]) {
+      await pumpReaderCommand(tester, engine.goToProgress(progress));
+      expect(
+        renderer.controller.offset /
+            renderer.controller.position.maxScrollExtent,
+        closeTo(progress, .01),
+      );
+      expect(engine.locator.totalProgression, closeTo(progress, .01));
+    }
+  });
+
   testWidgets('programmatic restoration does not publish progress', (
     tester,
   ) async {

test/presentation/epub_prefetch_test.dart

@@ -9,6 +9,33 @@ import '../support/in_process_epub_worker.dart';
 import '../support/synthetic_epub.dart';
 
 void main() {
+  testWidgets(
+    'prefetch reports completion when the entire book fits on one page',
+    (tester) async {
+      final engine = testEpubEngine();
+      await engine.load(
+        ReaderDocument(
+          id: 'one-page',
+          format: ReaderFormat.epub,
+          loadBytes: () async => syntheticEpub(
+            singleSpine: true,
+            firstChapterBody: '<p>A complete short book.</p>',
+          ),
+        ),
+        preferences: const ReaderPreferences(pageTurnAnimation: false),
+      );
+      await tester.pumpWidget(
+        MaterialApp(home: Builder(builder: engine.buildViewport)),
+      );
+      await tester.pumpAndSettle();
+      expect(engine.snapshot.contentReady, isTrue);
+      expect(engine.snapshot.atEnd, isTrue);
+      expect(engine.locator.totalProgression, 1);
+      expect(engine.snapshot.coverage.single.end, 1);
+      expect(engine.locator.textOffset, 0);
+    },
+  );
+
   testWidgets(
     'an immediate turn can use a page prepared before the viewport grows',
     (tester) async {