Revert "Remove per-draw canvas clones; title nav cap + right-page-number labels"

This reverts commit 0f66dae4eb.

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

@@ -53,6 +53,7 @@ class BookTextureRendererModule extends BaseModule {
             'drawSpreadSerial',
             'rasterizeSpread',
             'getDrawSignature',
+            'cloneCanvas',
             'buildRevealRegions',
             'shouldFlipAfterSideReveal',
             'collectRevealRegionCandidates',
@@ -372,6 +373,15 @@ class BookTextureRendererModule extends BaseModule {
         }).join('|');
     }
 
+    cloneCanvas(canvas) {
+        if (!canvas) return null;
+        const clone = document.createElement('canvas');
+        clone.width = canvas.width;
+        clone.height = canvas.height;
+        const context = clone.getContext('2d');
+        if (context) context.drawImage(canvas, 0, 0);
+        return clone;
+    }
 
     getPageContent(side = 'left') {
         return this.metrics?.contentBySide?.[side] || this.metrics?.content || {
@@ -943,17 +953,19 @@ class BookTextureRendererModule extends BaseModule {
             pageMeta: this.buildPublishPageMeta(sidesToPublish),
             phase
         };
-        // The page-texture-records event is dispatched synchronously below, and its handler
+        if (sidesToPublish.includes('left')) {
-        // uploads the canvas to a GPU texture synchronously (renderer.initTexture). So the live
+            detail.left = phase === 'prepare' ? this.cloneCanvas(this.canvases.left) : this.canvases.left;
-        // page canvas (and the static cached base) are consumed before the next draw can touch
+        }
-        // them — no per-draw clones needed (those large canvas copies drove the GC stalls).
+        if (sidesToPublish.includes('right')) {
-        if (sidesToPublish.includes('left')) detail.left = this.canvases.left;
+            detail.right = phase === 'prepare' ? this.cloneCanvas(this.canvases.right) : this.canvases.right;
-        if (sidesToPublish.includes('right')) detail.right = this.canvases.right;
+        }
         const reveal = {};
         sidesToPublish.forEach((side) => {
             const sideReveal = this.buildRevealRegions(side);
             if (!sideReveal) return;
-            sideReveal.baseCanvas = this.revealBaseCanvases?.[side] || null;
+            sideReveal.baseCanvas = phase === 'prepare'
+                ? this.cloneCanvas(this.revealBaseCanvases?.[side])
+                : this.revealBaseCanvases?.[side] || null;
             regionCounts[side] = sideReveal.lineRects.length;
             reveal[side] = sideReveal;
         });

public/js/webgl-book-lab.js

@@ -1950,21 +1950,14 @@ function getCurrentPagePosition() {
 function getMaxNavigableSpread() {
     const spreadCount = Math.max(1, Math.round(Number(bookPaginationState.spreadCount || 1)));
     const visitedSpread = pageToSpreadIndex(maxVisitedPagePosition);
-    // Body content starts at page index 3 (after the blank/title/blank frontmatter). Until any
+    return Math.max(0, Math.min(visitedSpread, spreadCount - 1));
-    // content is written the book stays on the title spread — no flipping forward into blank
-    // leaves. Once content exists, cap navigation to the spread holding the last written page.
-    const writtenPageLimit = Math.max(0, Number(bookPaginationState.writtenPageLimit || 0));
-    const contentSpread = writtenPageLimit >= 3 ? pageToSpreadIndex(writtenPageLimit) : 0;
-    return Math.max(0, Math.min(visitedSpread, contentSpread, spreadCount - 1));
 }
 
-// Title spread reads 0; every other spread reads the printed page number of its right page.
+// The page-number readout shows the odd (right) page of the visible pair, or 0 at the
+// title spread.
 function spreadPageLabel(spreadIndex) {
     const spread = Math.max(0, Math.round(Number(spreadIndex || 0)));
-    if (spread <= 0) return '0';
+    return spread <= 0 ? '0' : String(spread * 2 + 1);
-    const rightPageIndex = spreadPageIndices(spread).right;
-    const pageNumber = getPaginationPageMeta(rightPageIndex)?.pageNumber;
-    return pageNumber != null ? String(pageNumber) : '0';
 }
 
 function scheduleBookRebuild(reason = 'scheduled') {
@@ -2137,16 +2130,6 @@ function ensureBottomNavigation() {
 }
 
 function navigateToSpread(targetSpread) {
-    if (isManualBookNavigationBusy()) {
-        markPageTextureTiming('navigation:blocked-busy', {
-            targetSpread,
-            activeFlips: activeFlips.length,
-            revealActive: hasActivePageReveal(),
-            playbackActive: document.documentElement.dataset.webglBookPlaybackActive === 'true'
-        });
-        syncBookControls();
-        return false;
-    }
     const maxSpread = getMaxNavigableSpread();
     const target = THREE.MathUtils.clamp(Math.round(Number(targetSpread || 0)), 0, maxSpread);
     const currentSpread = Math.max(0, Math.round(Number(bookPaginationState.spreadIndex || 0)));
@@ -2176,7 +2159,7 @@ function navigateByPageDelta(delta) {
 }
 
 function syncBookControls() {
-    const busy = isManualBookNavigationBusy();
+    const busy = activeFlips.length > 0;
     if (progressInput) progressInput.value = readingProgress.toFixed(3);
     if (progressValue) progressValue.textContent = readingProgress.toFixed(2);
     if (pageCountInput) pageCountInput.value = String(bookPageCount);
@@ -2205,12 +2188,10 @@ function syncBottomNavigation() {
     bottomNavigation.root.style.setProperty('--book-nav-reserve-start', '1');
     bottomNavigation.root.dataset.bookSize = String(bookPageCount);
     bottomNavigation.root.dataset.pageReserve = String(pageReserve);
-    const busy = isManualBookNavigationBusy();
+    bottomNavigation.startButton.disabled = activeFlips.length > 0 || currentSpread <= 0;
-    bottomNavigation.slider.disabled = busy;
+    bottomNavigation.backButton.disabled = activeFlips.length > 0 || currentSpread <= 0;
-    bottomNavigation.startButton.disabled = busy || currentSpread <= 0;
+    bottomNavigation.forwardButton.disabled = activeFlips.length > 0 || currentSpread >= maxSpread;
-    bottomNavigation.backButton.disabled = busy || currentSpread <= 0;
+    bottomNavigation.endButton.disabled = activeFlips.length > 0 || currentSpread >= maxSpread;
-    bottomNavigation.forwardButton.disabled = busy || currentSpread >= maxSpread;
-    bottomNavigation.endButton.disabled = busy || currentSpread >= maxSpread;
 }
 
 function handlePageTextureRecords(event) {
@@ -3358,12 +3339,6 @@ function hasActivePageReveal() {
     });
 }
 
-function isManualBookNavigationBusy() {
-    return activeFlips.length > 0
-        || hasActivePageReveal()
-        || document.documentElement.dataset.webglBookPlaybackActive === 'true';
-}
-
 function applyResidentSpreadTextures(spreadIndex, reason = 'resident-spread', options = {}) {
     const skipSides = Array.isArray(options.skipSides) ? options.skipSides : [];
     const pageIndices = spreadPageIndices(spreadIndex);

scripts/check-webgl-book-lab.js

@@ -258,8 +258,7 @@ const checks = [
     ['book playback timeline flips at planned right-page fragment time without a stray commit timeout', /waitForPlannedRightReveal/.test(bookPlaybackTimelineSource) && /getRightRevealDurationMs/.test(bookPlaybackTimelineSource) && /segment\.revealStartedPromise/.test(bookPlaybackTimelineSource) && /const timer = setTimeout\(\(\) => finish\(true\), remaining\)/.test(bookPlaybackTimelineSource) && !/waitForRevealCommit/.test(bookPlaybackTimelineSource)],
     ['book playback timeline exposes reveal lifecycle benchmark entries', /benchmarkEntries/.test(bookPlaybackTimelineSource) && /markBenchmark\('reveal-start'/.test(bookPlaybackTimelineSource) && /markBenchmark\('reveal-committed'/.test(bookPlaybackTimelineSource) && /webglBookBenchmark/.test(bookPlaybackTimelineSource)],
     ['webgl scene records reveal start and slow-frame benchmark diagnostics', /revealState:created/.test(source) && /revealStart:applied/.test(source) && /slowFrameLog/.test(source) && /getBenchmarkState/.test(source) && /webglSlowFrames/.test(source)],
-    ['webgl navigation is spread-based and caps at the written-content spread (title-only before content)', /function navigateToSpread\(/.test(source) && /function navigateBySpreadDelta\(/.test(source) && /function getMaxNavigableSpread\(\)/.test(source) && /Math\.min\(visitedSpread, contentSpread, spreadCount - 1\)/.test(source) && /writtenPageLimit >= 3 \? pageToSpreadIndex\(writtenPageLimit\) : 0/.test(source) && /navigateBySpreadDelta\(1\)/.test(source) && /currentSpread < getMaxNavigableSpread\(\)/.test(source)],
+    ['webgl navigation is spread-based and caps at visited/written spread', /function navigateToSpread\(/.test(source) && /function navigateBySpreadDelta\(/.test(source) && /function getMaxNavigableSpread\(\)/.test(source) && /Math\.min\(visitedSpread, spreadCount - 1\)/.test(source) && /navigateBySpreadDelta\(1\)/.test(source) && /spread <= 0 \? '0' : String\(spread \* 2 \+ 1\)/.test(source) && /currentSpread < getMaxNavigableSpread\(\)/.test(source)],
-    ['webgl spread label reads 0 at the title and the right page number elsewhere', /function spreadPageLabel\(spreadIndex\)/.test(source) && /if \(spread <= 0\) return '0'/.test(source) && /spreadPageIndices\(spread\)\.right/.test(source) && /getPaginationPageMeta\(rightPageIndex\)\?\.pageNumber/.test(source)],
     ['webgl manual page navigation is blocked while reveal playback or flips are active', /function isManualBookNavigationBusy\(\) \{[\s\S]*activeFlips\.length > 0[\s\S]*hasActivePageReveal\(\)[\s\S]*webglBookPlaybackActive/.test(source) && /function navigateToSpread\(targetSpread\) \{[\s\S]*if \(isManualBookNavigationBusy\(\)\) \{[\s\S]*navigation:blocked-busy/.test(source) && /bottomNavigation\.slider\.disabled = busy/.test(source)],
     ['webgl fast-forward always reaches scene reveal state even without renderer-side active animations', /fastForwardAnimations\(\) \{[\s\S]*webgl-book:page-reveal-fast-forward[\s\S]*broad: !changed/.test(textureRendererSource) && /function fastForwardPageReveals\(blockIds = \[\]\) \{[\s\S]*const matches = ids\.size === 0/.test(source)],
     ['webgl save restore carries visited page limit for navigation', /maxVisitedPagePosition/.test(source) && /setMaxVisitedPagePosition/.test(source) && /state\.maxVisitedPagePosition \?\? state\.pagePosition/.test(webglSceneSource)],