Revert per-line reveal timing to area-weighting

The previous commit changed per-line reveal-duration distribution from ink-area to
word-count. That dropped a deliberate precision decision (area gives sub-line
granularity) and, verified live on a spanning paragraph, it was what made the
continuation page fail to animate. Restore area-weighting for the per-line split.

The word-share scaling of the *total* duration for partial (spanning) blocks and the
timeline-module timing snapshot/restore are kept — they only preserve existing
word-timings, they do not change the area-based per-line distribution.

Verified: on a real spanning block the right line reveals over its area share (~3.3s),
the page flips, and the continuation animates progressively across the next spread
over the full TTS (no fast-forward, no reveal-all-at-once).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/check-webgl-book-lab.js

@@ -165,7 +165,7 @@ const checks = [
     ['webgl page text textures avoid mipmap generation', /function configurePageCanvasTexture/.test(source) && /texture\.minFilter = THREE\.LinearFilter/.test(source) && /texture\.generateMipmaps = false/.test(source)],
     ['webgl reveal shader masks against a base-page texture instead of flat color blocks', /bookRevealBaseMap/.test(source) && /bookRevealUseBaseMap/.test(source) && /revealBaseColor/.test(source) && /baseCanvas/.test(textureRendererSource)],
     ['webgl reveal shader masks antialiased ink and uses smooth line-dominant scan', /smoothstep\(0\.52, 0\.9, luminance\)/.test(source) && /local\.x \* 0\.96/.test(source) && /bookRevealSoftness = \{ value: 0\.025 \}/.test(source)],
-    ['webgl reveal line timings use global word-weighted timing across split-page spreads', /assignRevealTiming/.test(textureRendererSource) && /sourceSpreads/.test(textureRendererSource) && /this\.pagination\?\.spreads/.test(textureRendererSource) && /spreadIndex/.test(textureRendererSource) && /totalDuration \* \(weight \/ totalWeight\)/.test(textureRendererSource) && /durationMs: sideRegions\.reduce/.test(textureRendererSource)],
+    ['webgl reveal line timings use global area-weighted timing across split-page spreads', /assignRevealTiming/.test(textureRendererSource) && /sourceSpreads/.test(textureRendererSource) && /this\.pagination\?\.spreads/.test(textureRendererSource) && /spreadIndex/.test(textureRendererSource) && /totalDuration \* \(Math\.max\(1, region\.timingArea \|\| region\.area\) \/ totalArea\)/.test(textureRendererSource) && /durationMs: sideRegions\.reduce/.test(textureRendererSource)],
     ['webgl page format reduces only outer margins from previous value', /outerBaseIn: 0\.27/.test(pageFormatSource) && /outerThicknessFactor: 0\.015/.test(pageFormatSource) && /outerMaxIn: 0\.315/.test(pageFormatSource) && /innerBaseIn: 0\.42/.test(pageFormatSource)],
     ['webgl mode enlarges and inverts DOM overlay text without touching 2D mode', /body\.webgl-mode \{[\s\S]*font-size: 18px;/.test(styleSource) && /body\.webgl-mode \.choice-list \.choice-button/.test(styleSource) && /rgba\(246, 231, 201/.test(styleSource)],
     ['webgl choice overlay hides title clutter and prevents horizontal scrollbar', /body\.webgl-mode #page_left #game_title/.test(styleSource) && /body\.webgl-mode #page_left #start_prompt/.test(styleSource) && /overflow-x: hidden/.test(styleSource) && /book\.style\.width = 'min\(44rem/.test(webglSceneSource)],
@@ -213,7 +213,7 @@ 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 flips are owned by the timeline, not the scene', !/pendingRightPageFlip/.test(source) && !/handleRevealCommittedForPageFlip/.test(source) && /waitForVisualCompletion/.test(bookPlaybackTimelineSource) && /reason: 'timeline-right-page-filled'/.test(bookPlaybackTimelineSource) && /requiresRightPageFlipAfterReveal/.test(bookPlaybackTimelineSource) && /isChoiceAwaitingPlayer/.test(bookPlaybackTimelineSource)],
     ['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 is word-weighted (reliable for 0-area continuation lines) with area fallback', /lineWordCount/.test(bookPaginationSource) && /blockWordStart/.test(textureRendererSource) && /blockWordCount/.test(textureRendererSource) && /timingArea/.test(textureRendererSource) && /const useWordWeights = collectedWords > 0/.test(textureRendererSource) && /totalDuration \* \(weight \/ totalWeight\)/.test(textureRendererSource) && !/const canUseLineWordSpans/.test(textureRendererSource)],
+    ['webgl line reveal timing scales total by word-share for partial blocks and splits per-line by area', /lineWordCount/.test(bookPaginationSource) && /blockWordStart/.test(textureRendererSource) && /blockWordCount/.test(textureRendererSource) && /timingArea/.test(textureRendererSource) && /const useWordShare = totalBlockWords > 0 && collectedWords > 0 && collectedWords < totalBlockWords/.test(textureRendererSource) && /totalDuration \* \(Math\.max\(1, region\.timingArea \|\| region\.area\) \/ totalArea\)/.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 and defers revealing sides', /applyResidentSpreadTextures\(targetSpread, 'page-flip-near-end', \{ skipSides: flip\.deferRevealSides \}\)/.test(source) && /function applyResidentSpreadTextures\(spreadIndex, reason = 'resident-spread', options = \{\}\)/.test(source) && /const skipSides = Array\.isArray\(options\.skipSides\)/.test(source) && /residentSpreadTextures:applied/.test(source) && /spreadUpdate:state-only/.test(source)],
     ['webgl autoplay flip source prefers currently revealing visible material over resident cache', /if \(revealStateMatchesPage\(side, pageMeta\)\) return material\?\.map \|\| null/.test(source) && /revealStateMatchesPage\(sourceSide, sourcePageMeta\) \? sourceSide : null/.test(source)],