Fix WebGL reveal timing and flip texture readiness

public/js/book-pagination-module.js

@@ -353,6 +353,7 @@ class BookPaginationModule extends BaseModule {
                     lineHeightPx: layout.lineHeightPx,
                     fontStyle: layout.fontStyle,
                     blockWordStart: blockWordCursor,
+                    lineWordCount,
                     dropCapText: layoutLineIndex === 0 ? layout.dropCapText : '',
                     smallCaps: Boolean(layout.dropCap && layoutLineIndex === 0)
                 });

public/js/book-playback-timeline-module.js

@@ -208,9 +208,17 @@ class BookPlaybackTimelineModule extends BaseModule {
     }
 
     ensureAnimationTimings(sentence = {}) {
-        if (Array.isArray(sentence.animation?.wordTimings) && sentence.animation.wordTimings.length > 0) return;
+        const existingTimings = Array.isArray(sentence.animation?.wordTimings)
+            ? sentence.animation.wordTimings
+            : [];
+        const existingDuration = existingTimings.reduce((max, timing) => Math.max(
+            max,
+            Number(timing?.delay || 0) + Number(timing?.duration || 0)
+        ), Number(sentence.animation?.totalDuration || 0));
+        const ttsDuration = Number(sentence.tts?.duration || 0);
+        if (existingTimings.length > 0 && (existingDuration > 0 || ttsDuration <= 0)) return;
         const words = String(sentence.layoutText || sentence.text || '').match(/\S+/g) || [];
-        sentence.animation = this.calculateAnimationTiming(words, sentence.tts?.duration || 0, sentence.cueMarkers || []);
+        sentence.animation = this.calculateAnimationTiming(words, ttsDuration, sentence.cueMarkers || []);
     }
 
     calculateAnimationTiming(words = [], totalDuration = 0, cueMarkers = []) {

public/js/book-texture-renderer-module.js

@@ -119,6 +119,13 @@ class BookTextureRendererModule extends BaseModule {
             const latestRenderedBlockId = Math.max(0, Number(event.detail?.latestRenderedBlockId || 0));
             const visibility = event.detail?.visibility || 'current';
             this.currentSpread = spread || { left: [], right: [] };
+            if (document.documentElement.dataset.webglPageFlipActive === 'true' && this.activeAnimations.size === 0) {
+                this.markPipelineTiming('spreadUpdate:skip-during-flip', {
+                    spreadIndex,
+                    visibility
+                });
+                return;
+            }
             if (latestBlockId && Number(latestBlockId) > latestRenderedBlockId) {
                 this.markPendingReveal(latestBlockId);
                 const id = String(latestBlockId);
@@ -674,9 +681,16 @@ class BookTextureRendererModule extends BaseModule {
 
     collectRevealRegionCandidates() {
         const candidates = [];
-        const sourceSpreads = Array.isArray(this.pagination?.spreads) && this.pagination.spreads.length
-            ? this.pagination.spreads
-            : [this.currentSpread || { index: 0, left: [], right: [] }];
+        const sourceSpreads = [];
+        if (this.currentSpread) sourceSpreads.push(this.currentSpread);
+        if (Array.isArray(this.pagination?.spreads)) {
+            this.pagination.spreads.forEach((spread) => {
+                if (!spread) return;
+                if (this.currentSpread && Number(spread.index) === Number(this.currentSpread.index)) return;
+                sourceSpreads.push(spread);
+            });
+        }
+        if (!sourceSpreads.length) sourceSpreads.push({ index: 0, left: [], right: [] });
         sourceSpreads.forEach((spread) => {
             ['left', 'right'].forEach((side) => {
                 const spreadLines = Array.isArray(spread?.[side]) ? spread[side] : [];
@@ -707,7 +721,20 @@ class BookTextureRendererModule extends BaseModule {
         const fixedRegions = sortedRegions.filter(region => region.fixedDurationMs > 0);
         let fallbackDelay = 0;
         const totalArea = textRegions.reduce((sum, region) => sum + Math.max(1, region.area), 0);
+        const wordTimings = Array.isArray(animation.wordTimings) ? animation.wordTimings : [];
+        const canUseLineWordSpans = wordTimings.length > 0
+            && textRegions.every(region => Number.isFinite(Number(region.blockWordStart)) && Number(region.blockWordCount) > 0);
 
+        if (canUseLineWordSpans) {
+            textRegions.forEach((region) => {
+                const timing = this.getLineTimingFromWords(region, wordTimings);
+                timedRegions.push({
+                    ...region,
+                    timing
+                });
+                fallbackDelay = Math.max(fallbackDelay, timing.delay + timing.duration);
+            });
+        } else {
             textRegions.forEach((region) => {
                 const duration = totalArea > 0
                     ? Math.max(1, totalDuration * (Math.max(1, region.area) / totalArea))
@@ -718,6 +745,7 @@ class BookTextureRendererModule extends BaseModule {
                 });
                 fallbackDelay += duration;
             });
+        }
 
         fixedRegions.forEach((region) => {
             timedRegions.push({
@@ -738,6 +766,23 @@ class BookTextureRendererModule extends BaseModule {
         });
     }
 
+    getLineTimingFromWords(region = {}, wordTimings = []) {
+        const start = Math.max(0, Math.floor(Number(region.blockWordStart || 0)));
+        const count = Math.max(1, Math.floor(Number(region.blockWordCount || 1)));
+        const first = wordTimings[Math.min(start, wordTimings.length - 1)] || { delay: 0, duration: 1 };
+        const lastIndex = Math.min(wordTimings.length - 1, start + count - 1);
+        const last = wordTimings[lastIndex] || first;
+        const delay = Math.max(0, Number(first.delay || 0));
+        const end = Math.max(
+            delay + 1,
+            Number(last.delay || 0) + Math.max(1, Number(last.duration || 1))
+        );
+        return {
+            delay,
+            duration: Math.max(1, end - delay)
+        };
+    }
+
     createRevealRegionForLine(side, lineRecord = {}, spreadIndex = null) {
         const blockId = String(lineRecord?.blockId ?? '');
         if (!blockId || !this.revealPublishBlockIds.has(blockId)) return null;
@@ -770,6 +815,8 @@ class BookTextureRendererModule extends BaseModule {
             spreadIndex: Math.max(0, Number((spreadIndex ?? Math.floor(Number(lineRecord.pageIndex || 0) / 2)) || 0)),
             blockId,
             lineIndex: Number(lineRecord.lineIndex ?? lineRecord.pageLine ?? 0),
+            blockWordStart: Number(lineRecord.blockWordStart ?? 0),
+            blockWordCount: Number(lineRecord.lineWordCount ?? 0),
             fixedDurationMs,
             area: rectWidth * rectHeight,
             pixelRect: { x: left, y: top, right, bottom },

public/js/loader.js

@@ -24,7 +24,7 @@ const ModuleState = {
     ERROR: 'ERROR'
 };
 
-const MODULE_CACHE_BUSTER = '20260610-book-timeline-d';
+const MODULE_CACHE_BUSTER = '20260610-book-timeline-j';
 window.MODULE_CACHE_BUSTER = MODULE_CACHE_BUSTER;
 
 /**

public/js/playback-coordinator-module.js

@@ -315,11 +315,22 @@ class PlaybackCoordinatorModule extends BaseModule {
         let cueTimings = Array.isArray(sentence.animation?.cueTimings)
             ? sentence.animation.cueTimings
             : [];
-        if (wordTimings.length === 0) {
+        const timingDuration = wordTimings.reduce((max, timing) => Math.max(
+            max,
+            Number(timing?.delay || 0) + Number(timing?.duration || 0)
+        ), Number(sentence.animation?.totalDuration || 0));
+        const ttsDuration = Number(sentence.tts?.duration || sentence.animation?.totalDuration || 0);
+        if (wordTimings.length === 0 || (timingDuration <= 0 && ttsDuration > 0)) {
             const words = String(sentence.text || '').match(/\S+/g) || [];
-            const calculated = this.calculateWordTimings(words, sentence.tts?.duration || sentence.animation?.totalDuration || 0);
+            const calculated = this.calculateWordTimings(words, ttsDuration);
             wordTimings = calculated.wordTimings;
             cueTimings = [];
+            sentence.animation = {
+                ...(sentence.animation || {}),
+                wordTimings,
+                cueTimings,
+                totalDuration: calculated.totalDuration
+            };
         }
 
         if (typeof sentence.webglRevealController !== 'function') {

public/js/webgl-book-lab.js

@@ -4,7 +4,7 @@ import { RenderPass } from 'https://esm.sh/three@0.165.0/examples/jsm/postproces
 import { SSAOPass } from 'https://esm.sh/three@0.165.0/examples/jsm/postprocessing/SSAOPass.js';
 import { SMAAPass } from 'https://esm.sh/three@0.165.0/examples/jsm/postprocessing/SMAAPass.js';
 import { OutputPass } from 'https://esm.sh/three@0.165.0/examples/jsm/postprocessing/OutputPass.js';
-import { PROCEDURAL_BOOK, createProceduralBookModel, snapProceduralPageCount } from './procedural-book-model.js?v=20260610-book-timeline-d';
+import { PROCEDURAL_BOOK, createProceduralBookModel, snapProceduralPageCount } from './procedural-book-model.js?v=20260610-book-timeline-j';
 
 const canvas = document.getElementById('scene');
 canvas.style.cursor = 'grab';
@@ -278,6 +278,7 @@ const pageRevealState = {
 };
 let pageRevealFreezeAt = null;
 const pageRevealClearLog = [];
+let scheduledBookRebuildFrame = null;
 await reportLabStep(52, 'Generating leather texture set');
 const leatherTextures = createLeatherTextures();
 await reportLabStep(56, 'Generating spine cloth texture set');
@@ -1842,13 +1843,34 @@ function getCurrentPagePosition() {
     return spreadIndexToPagePosition(bookPaginationState.spreadIndex);
 }
 
-function syncReadingProgressToCurrentPage() {
-    const nextProgress = THREE.MathUtils.clamp(getCurrentPagePosition() / Math.max(1, bookPageCount), 0, 1);
-    if (Math.abs(nextProgress - readingProgress) < 0.0001) return;
-    readingProgress = nextProgress;
+function scheduleBookRebuild(reason = 'scheduled') {
+    if (scheduledBookRebuildFrame !== null) return;
+    const scheduler = typeof window.requestIdleCallback === 'function'
+        ? (callback) => window.requestIdleCallback(callback, { timeout: 180 })
+        : requestAnimationFrame;
+    scheduledBookRebuildFrame = scheduler(() => {
+        scheduledBookRebuildFrame = null;
+        markPageTextureTiming('bookRebuild:deferred', { reason });
         buildBook();
+        syncBookControls();
+    });
+}
+
+function syncReadingProgressToCurrentPage(options = {}) {
+    const nextProgress = THREE.MathUtils.clamp(getCurrentPagePosition() / Math.max(1, bookPageCount), 0, 1);
+    const changed = Math.abs(nextProgress - readingProgress) >= 0.0001;
+    if (changed) {
+        readingProgress = nextProgress;
         window.WebGLBookPreferenceBridge?.updateProgress?.(readingProgress);
     }
+    if (!changed && options.rebuild !== 'defer') return;
+    if (options.rebuild === 'defer') {
+        scheduleBookRebuild(options.reason || 'reading-progress-sync');
+        return;
+    }
+    if (options.rebuild === false) return;
+    buildBook();
+}
 
 function growBookIfWritableLimitReached() {
     const writtenLimit = Math.max(0, bookPaginationState.writtenPageLimit || 0);
@@ -2266,15 +2288,20 @@ function getPaginationPageMeta(pageIndex) {
     const index = Math.max(0, Math.round(Number(pageIndex || 0)));
     const spreadIndex = Math.floor(index / 2);
     const side = index % 2 === 0 ? 'left' : 'right';
-    const pagination = window.moduleRegistry?.getModule?.('book-pagination') || null;
-    const spread = typeof pagination?.getSpread === 'function'
-        ? pagination.getSpread(spreadIndex)
-        : Array.isArray(pagination?.spreads)
-            ? pagination.spreads[spreadIndex]
-            : null;
+    const spread = getPaginationSpread(spreadIndex);
     return spread?.pageMeta?.[side] || null;
 }
 
+function getPaginationSpread(spreadIndex) {
+    const index = Math.max(0, Math.round(Number(spreadIndex || 0)));
+    const pagination = window.moduleRegistry?.getModule?.('book-pagination') || null;
+    return typeof pagination?.getSpread === 'function'
+        ? pagination.getSpread(index)
+        : Array.isArray(pagination?.spreads)
+            ? pagination.spreads[index]
+            : null;
+}
+
 async function prewarmSpreadTextures(spreadIndex) {
     return pageTextureStore?.prewarmSpreadTextures?.(spreadIndex, makePageMetaForCache) || {
         spreadIndex: Math.max(0, Math.round(Number(spreadIndex || 0))),
@@ -2314,6 +2341,8 @@ async function prewarmFlipTextures(direction, targetSpread = null) {
     const nextSpread = Number.isFinite(Number(targetSpread))
         ? Math.max(0, Math.round(Number(targetSpread)))
         : Math.max(0, currentSpread + Math.sign(Number(direction || 0)));
+    prepareSpreadTextureRecordsForFlip(currentSpread);
+    prepareSpreadTextureRecordsForFlip(nextSpread);
     const windowMap = await prewarmNavigationTextureWindow('flip-prewarm', { targetSpread: nextSpread });
     const current = windowMap?.[currentSpread] || await prewarmSpreadTextures(currentSpread);
     const next = windowMap?.[nextSpread] || await prewarmSpreadTextures(nextSpread);
@@ -2323,6 +2352,25 @@ async function prewarmFlipTextures(direction, targetSpread = null) {
     };
 }
 
+function prepareSpreadTextureRecordsForFlip(spreadIndex) {
+    const spread = getPaginationSpread(spreadIndex);
+    if (!spread || typeof window.BookTextureRenderer?.drawSpread !== 'function') return false;
+    if (spreadTextureRecordsReady(spread)) return true;
+    window.BookTextureRenderer.drawSpread(spread, ['left', 'right'], {
+        phase: 'prepare'
+    });
+    return true;
+}
+
+function spreadTextureRecordsReady(spread = null) {
+    if (!spread?.pageMeta || !pageTextureStore) return false;
+    return ['left', 'right'].every((side) => {
+        const meta = spread.pageMeta?.[side] || null;
+        if (!meta || meta.kind === 'blank') return true;
+        return Boolean(pageTextureStore.getResidentTextureForMeta?.(meta));
+    });
+}
+
 function takePreparedPageTexture(side, revealDetail = {}) {
     const key = getRevealCacheKey(revealDetail);
     const prepared = pageTextureStore?.takePreparedPageTexture?.(side, key) || null;
@@ -3047,6 +3095,9 @@ function updateActiveFlips(now) {
             const targetSpread = Number.isFinite(Number(flip.targetSpread))
                 ? Math.max(0, Math.round(Number(flip.targetSpread)))
                 : null;
+            if (targetSpread !== null && !hasActivePageReveal()) {
+                applyResidentSpreadTextures(targetSpread, 'page-flip-near-end');
+            }
             document.dispatchEvent(new CustomEvent('webgl-book:page-flip-near-end', {
                 detail: {
                     direction: flip.direction,
@@ -3060,6 +3111,48 @@ function updateActiveFlips(now) {
     completed.forEach((flip) => finishActiveFlip(flip));
 }
 
+function hasActivePageReveal() {
+    return ['left', 'right'].some((side) => {
+        const state = pageRevealState[side];
+        if (!state) return false;
+        if (state.startedAt != null) return true;
+        return Array.isArray(state.blockIds) && state.blockIds.length > 0;
+    });
+}
+
+function applyResidentSpreadTextures(spreadIndex, reason = 'resident-spread') {
+    const pageIndices = spreadPageIndices(spreadIndex);
+    ['left', 'right'].forEach((side) => {
+        const pageIndex = pageIndices[side];
+        const pageMeta = getPaginationPageMeta(pageIndex) || makeBlankPageMeta(pageIndex);
+        const texture = pageMeta.kind === 'blank'
+            ? getBlankPageTexture()
+            : pageTextureStore?.getResidentTextureForMeta?.(pageMeta);
+        if (!texture) {
+            pageTextureStore?.recordProblem?.({
+                type: 'resident-spread-texture-missing',
+                reason,
+                side,
+                spreadIndex,
+                pageIndex,
+                pageKind: pageMeta.kind
+            });
+            return;
+        }
+        const material = side === 'left' ? materials.leftPage : materials.rightPage;
+        clearPageReveal(side, reason);
+        if (material.map !== texture) {
+            material.map = texture;
+            material.needsUpdate = true;
+        }
+    });
+    markStaticSceneBuffersDirty();
+    markPageTextureTiming('residentSpreadTextures:applied', {
+        reason,
+        spreadIndex
+    });
+}
+
 function buildFlippingPageSurface(sourceLine, destinationLine, direction, t, pageOffset = 0) {
     const widthSegments = sourceLine.points.length - 1;
     const depthSegments = 18;
@@ -3208,6 +3301,10 @@ function createFlippingPageGeometry(surface, direction = 1) {
     const depthSegments = surface[0].length - 1;
     const sourceSide = direction > 0 ? 1 : -1;
     const targetSide = -sourceSide;
+    const topPageSide = direction > 0 ? targetSide : sourceSide;
+    const bottomPageSide = direction > 0 ? sourceSide : targetSide;
+    const topMaterialIndex = direction > 0 ? 1 : 0;
+    const bottomMaterialIndex = direction > 0 ? 0 : 1;
     const push = (point, yOffset, uv) => {
         const index = positions.length / 3;
         positions.push(point.x, point.y + yOffset, point.z);
@@ -3221,8 +3318,8 @@ function createFlippingPageGeometry(surface, direction = 1) {
         const u = widthSegments <= 0 ? 0 : widthIndex / widthSegments;
         rowPoints.forEach((point, depthIndex) => {
             const v = depthSegments <= 0 ? 0 : depthIndex / depthSegments;
-            topRow.push(push(point, pageThickness, pageUvForSide(sourceSide, u, v)));
-            bottomRow.push(push(point, 0, pageUvForSide(targetSide, u, v)));
+            topRow.push(push(point, pageThickness, pageUvForSide(topPageSide, u, v)));
+            bottomRow.push(push(point, 0, pageUvForSide(bottomPageSide, u, v)));
         });
         topGrid.push(topRow);
         bottomGrid.push(bottomRow);
@@ -3257,8 +3354,8 @@ function createFlippingPageGeometry(surface, direction = 1) {
     geometry.setAttribute('position', new THREE.Float32BufferAttribute(positions, 3));
     geometry.setAttribute('uv', new THREE.Float32BufferAttribute(uvs, 2));
     geometry.clearGroups();
-    geometry.addGroup(0, topIndices.length, 0);
-    geometry.addGroup(topIndices.length, bottomIndices.length, 1);
+    geometry.addGroup(0, topIndices.length, topMaterialIndex);
+    geometry.addGroup(topIndices.length, bottomIndices.length, bottomMaterialIndex);
     geometry.addGroup(topIndices.length + bottomIndices.length, wallIndices.length, 2);
     geometry.computeVertexNormals();
     return geometry;
@@ -3271,7 +3368,7 @@ function createFlippingPageGeometry(surface, direction = 1) {
 function pageUvForSide(side, u, v) {
     return {
         x: side < 0 ? 1 - u : u,
-        y: 1 - v
+        y: v
     };
 }
 
@@ -3313,7 +3410,10 @@ function finishActiveFlip(flip) {
             spreadIndex: Math.max(0, Math.round(Number(flip.targetSpread)))
         };
         maxVisitedPagePosition = Math.max(maxVisitedPagePosition, getCurrentPagePosition());
-        syncReadingProgressToCurrentPage();
+        syncReadingProgressToCurrentPage({
+            rebuild: 'defer',
+            reason: 'page-flip-finished'
+        });
     }
     document.dispatchEvent(new CustomEvent('webgl-book:page-flip-finished', {
         detail: {

scripts/check-webgl-book-lab.js

@@ -190,10 +190,11 @@ const checks = [
     ['texture renderer marks page canvases with content versions before cache writes', /pageContentVersions/.test(textureRendererSource) && /buildPublishPageMeta/.test(textureRendererSource) && /completenessScore: \(maxBlockId \* 1000\) \+ lineCount/.test(textureRendererSource)],
     ['texture store queues newer same-page cache writes instead of dropping them', /storePageCanvas/.test(webglPageCacheSource) && /isOlderPageMeta/.test(webglPageCacheSource) && /const previousWrite = pending\?\.promise \|\| Promise\.resolve\(\)/.test(webglPageCacheSource) && /pendingPageWrites\.set\(key, \{[\s\S]*pageMeta: \{ \.\.\.\(pageMeta \|\| \{\}\) \}/.test(webglPageCacheSource)],
     ['webgl texture store resident cache reuses newest page version for older readiness requests', /isOlderPageMeta/.test(webglPageCacheSource) && /getResidentTextureForMeta/.test(webglPageCacheSource) && /if \(!resident\) return null/.test(webglPageCacheSource) && !/if \(!resident \|\| this\.isOlderPageMeta\(pageMeta, resident\.pageMeta\)\) return null/.test(webglPageCacheSource)],
-    ['webgl flip page is a two-sided body using paper-thickness constants', /flipPageBackSurface/.test(source) && /flipPageEdge/.test(source) && /new THREE\.Mesh\(geometry, \[\s*materials\.flipPageSurface,\s*materials\.flipPageBackSurface,\s*materials\.flipPageEdge\s*\]\)/.test(source) && /PROCEDURAL_BOOK\.SHEET_THICKNESS_MODEL/.test(source) && /geometry\.addGroup\(0, topIndices\.length, 0\)/.test(source)],
+    ['webgl flip page is a two-sided body using paper-thickness constants', /flipPageBackSurface/.test(source) && /flipPageEdge/.test(source) && /new THREE\.Mesh\(geometry, \[\s*materials\.flipPageSurface,\s*materials\.flipPageBackSurface,\s*materials\.flipPageEdge\s*\]\)/.test(source) && /PROCEDURAL_BOOK\.SHEET_THICKNESS_MODEL/.test(source) && /const topMaterialIndex = direction > 0 \? 1 : 0/.test(source) && /const bottomMaterialIndex = direction > 0 \? 0 : 1/.test(source) && /geometry\.addGroup\(0, topIndices\.length, topMaterialIndex\)/.test(source) && /geometry\.addGroup\(topIndices\.length, bottomIndices\.length, bottomMaterialIndex\)/.test(source)],
     ['webgl animated page front and back maps are independently switchable before animation starts', /materials\.flipPageBackSurface = materials\.flipPageSurface\.clone\(\)/.test(source) && /materials\.flipPageSurface\.map = sourceTexture/.test(source) && /materials\.flipPageBackSurface\.map = backTexture \|\| getBlankPageTexture\(\)/.test(source) && /flip\.sourceTexture = sourceTexture/.test(source) && /flip\.backTexture = backTexture \|\| getBlankPageTexture\(\)/.test(source)],
     ['webgl flip preflight exposes texture side and orientation invariants for browser tests', /lastFlipTexturePreflight/.test(source) && /sourceTextureMatchesBackTexture/.test(source) && /targetBackSide/.test(source) && /getRuntimeInvariants/.test(source)],
-    ['webgl animated page back face uses destination-side page UV orientation', /pageUvForSide\(targetSide, u, v\)/.test(source) && /pageUvForSide\(sourceSide, u, v\)/.test(source) && /side < 0 \? 1 - u : u/.test(source)],
+    ['webgl animated page maps source and destination textures to direction-aware physical sides', /const topPageSide = direction > 0 \? targetSide : sourceSide/.test(source) && /const bottomPageSide = direction > 0 \? sourceSide : targetSide/.test(source) && /topRow\.push\(push\(point, pageThickness, pageUvForSide\(topPageSide, u, v\)\)\)/.test(source) && /bottomRow\.push\(push\(point, 0, pageUvForSide\(bottomPageSide, u, v\)\)\)/.test(source) && /side < 0 \? 1 - u : u/.test(source) && /y: v/.test(source)],
+    ['webgl flip prewarm prepares current and target spread texture records before cache lookup', /prepareSpreadTextureRecordsForFlip\(currentSpread\)/.test(source) && /prepareSpreadTextureRecordsForFlip\(nextSpread\)/.test(source) && /function prepareSpreadTextureRecordsForFlip/.test(source) && /spreadTextureRecordsReady\(spread\)/.test(source) && /window\.BookTextureRenderer\.drawSpread\(spread, \['left', 'right'\], \{[\s\S]*phase: 'prepare'/.test(source)],
     ['webgl animated page reuses geometry buffers during flips', /function updateFlippingPageGeometry/.test(source) && /position\.needsUpdate = true/.test(source) && /updateFlippingPageGeometry\(flip\.mesh\.geometry, surface\)/.test(source) && !/flip\.mesh\.geometry\.dispose\(\);\s*flip\.mesh\.geometry = geometry;/.test(methodBody(source, 'setActivePageGeometry'))],
     ['webgl scene targets 60fps with browser-frame scheduling live mirror and static heavy refresh', /const targetFrameDurationMs = 1000 \/ 60/.test(source) && /this\.targetFrameDurationMs = 1000 \/ 60/.test(textureRendererSource) && /requestAnimationFrame\(animate\)/.test(source) && /const refreshStaticSceneBuffers = staticSceneBuffersDirty \|\| activeFlips\.length > 0/.test(source) && /updateTableReflection\(\);/.test(source) && /mirrorRefreshesEveryFrame: true/.test(source) && !/setTimeout\(animate/.test(source)],
     ['webgl scene lowers mirror target and caps table film maps to 2k', /const reflectionPixelRatio = 1/.test(source) && /const tableReflectionBaseWidth = 2048/.test(source) && /const tableReflectionBaseHeight = 1152/.test(source) && /tableDustTexture = loadUtilityTexture\('\/assets\/webgl\/table_dust_4k\.png', \{ maxSize: 2048 \}\)/.test(source) && /tableGreaseTexture = loadUtilityTexture\('\/assets\/webgl\/table_grease_4k\.png', \{ maxSize: 2048 \}\)/.test(source)],
@@ -209,6 +210,12 @@ const checks = [
     ['game loop persists webgl book state in save slots', /webglBookState: this\.getWebGLBookState\(\)/.test(fs.readFileSync(path.join(__dirname, '..', 'public', 'js', 'game-loop-module.js'), 'utf8')) && /applyWebGLBookState\(browserSave\.webglBookState\)/.test(fs.readFileSync(path.join(__dirname, '..', 'public', 'js', 'game-loop-module.js'), 'utf8'))],
     ['webgl right-page reveal records arm a durable autoplay-targeted flip without bypassing choices', /handleRevealCommittedForPageFlip/.test(source) && /pageFlipAfterReveal/.test(textureRendererSource) && /tryStartPendingRightPageFlip/.test(source) && /pendingRightPageFlipAutoplay/.test(source) && /const targetSpread = Math\.max\(0, Math\.round\(Number\(bookPaginationState\.spreadIndex \|\| 0\)\) \+ 1\)/.test(source) && /force: options\.force === true \|\| pendingRightPageFlipAutoplay/.test(source) && /isChoiceAwaitingPlayer/.test(source) && /pendingRightPageFlip = true/.test(source)],
     ['webgl reveal clock follows absolute playback time and continues across page flips', /activeRevealBlockStarts/.test(source) && /state\.visualElapsedMs = Math\.max\(0, now - state\.startedAt\)/.test(source) && !/Math\.min\(revealFrameDeltaMs, targetFrameDurationMs\)/.test(source) && /prewarmFlipTextures\(1, targetSpread\)/.test(source)],
+    ['webgl line reveal timing uses TTS word spans instead of stretching split page fragments', /lineWordCount/.test(bookPaginationSource) && /blockWordStart/.test(textureRendererSource) && /blockWordCount/.test(textureRendererSource) && /getLineTimingFromWords/.test(textureRendererSource) && /const canUseLineWordSpans/.test(textureRendererSource)],
+    ['webgl flip completion defers book rebuild out of the final animation frame', /scheduledBookRebuildFrame/.test(source) && /function scheduleBookRebuild/.test(source) && /syncReadingProgressToCurrentPage\(\{[\s\S]*rebuild: 'defer'[\s\S]*reason: 'page-flip-finished'/.test(source)],
+    ['webgl ordinary flip near-end uses resident target textures instead of renderer redraw', /applyResidentSpreadTextures\(targetSpread, 'page-flip-near-end'\)/.test(source) && /function applyResidentSpreadTextures/.test(source) && /residentSpreadTextures:applied/.test(source) && /spreadUpdate:skip-during-flip/.test(textureRendererSource)],
+    ['webgl timeline recalculates placeholder zero-duration reveal timings from TTS duration', /existingTimings/.test(bookPlaybackTimelineSource) && /existingDuration/.test(bookPlaybackTimelineSource) && /ttsDuration/.test(bookPlaybackTimelineSource) && /existingTimings\.length > 0 && \(existingDuration > 0 \|\| ttsDuration <= 0\)/.test(bookPlaybackTimelineSource)],
+    ['webgl playback coordinator rejects placeholder zero-duration reveal timings', /timingDuration/.test(playbackCoordinatorSource) && /ttsDuration/.test(playbackCoordinatorSource) && /timingDuration <= 0 && ttsDuration > 0/.test(playbackCoordinatorSource) && /sentence\.animation = \{[\s\S]*wordTimings,[\s\S]*totalDuration: calculated\.totalDuration/.test(playbackCoordinatorSource)],
+    ['texture renderer derives reveal regions from the just-drawn preview spread before committed pagination', /if \(this\.currentSpread\) sourceSpreads\.push\(this\.currentSpread\)/.test(textureRendererSource) && /this\.pagination\.spreads\.forEach/.test(textureRendererSource) && /Number\(spread\.index\) === Number\(this\.currentSpread\.index\)/.test(textureRendererSource)],
     ['texture renderer preloads every spread touched by an active reveal block', /preloadAdditionalRevealSpreads/.test(textureRendererSource) && /spreadContainsBlock/.test(textureRendererSource) && /this\.drawSpread\(spread, \['left', 'right'\], \{ phase: 'prepare' \}\)/.test(textureRendererSource) && /this\.activeAnimations\.has\(id\)/.test(textureRendererSource)],
     ['webgl visible spread state ignores future prepared publishes before flip', /spreadUpdate:deferred-future-unrendered/.test(source) && /incomingSpreadIndex > Math\.max\(0, Number\(bookPaginationState\.spreadIndex/.test(source) && /this\.drawSpread\(this\.currentSpread, \['left', 'right'\], \{ phase: 'prepare' \}\)/.test(textureRendererSource)],
     ['3D overflow reveal preloads target spread before forced page flip', /createRevealDetail\(sentence, previewSpread, 'prepare'\)/.test(bookPlaybackTimelineSource) && /this\.textureRenderer\.prepareRevealBlock\(revealDetail, \{[\s\S]*phase: 'prepare'[\s\S]*publishEvent: false/.test(bookPlaybackTimelineSource) && /this\.prewarmSegmentTextures\(segment\)/.test(bookPlaybackTimelineSource) && /this\.assertSegmentReady\(segment, 'prepare'\)/.test(bookPlaybackTimelineSource) && /reason: 'timeline-preplay-spread-transition'/.test(bookPlaybackTimelineSource)],