fix(pdf): readd source unit extraction for TTS integration in page parsing

Introduce sourceUnitsFromParsedPage helper to extract CanonicalTtsSourceUnit
objects from parsed PDF pages, filtering by block kind and text content. Update
TTS state setter to include extracted source units when available, enabling
improved TTS segment mapping and future extensibility.

src/app/(app)/pdf/[id]/usePdfDocument.ts

@@ -37,6 +37,7 @@ import {
   highlightWordIndex,
 } from '@/lib/client/pdf';
 import { buildPageTextFromBlocks } from '@/lib/client/pdf-block-text';
+import type { CanonicalTtsSourceUnit } from '@/lib/shared/tts-segment-plan';
 import {
   DEFAULT_DOCUMENT_SETTINGS,
   type DocumentSettings,
@@ -263,6 +264,24 @@ export function usePdfDocument(): PdfDocumentState {
         return;
       }
 
+      const sourceUnitsFromParsedPage = (pageNum: number): CanonicalTtsSourceUnit[] => {
+        const page = pageFromParsed(pageNum);
+        if (!page) return [];
+        const skipKinds = new Set(documentSettings.pdf?.skipBlockKinds ?? []);
+        return page.blocks
+          .filter((block) => !skipKinds.has(block.kind))
+          .map((block) => ({
+            sourceKey: `pdf:${pageNum}:${block.id}`,
+            text: block.text,
+            locator: {
+              readerType: 'pdf',
+              page: block.fragments[0]?.page ?? pageNum,
+              blockId: block.id,
+            } as TTSSegmentLocator,
+          }))
+          .filter((unit) => unit.text.trim().length > 0);
+      };
+
       const getPageText = async (pageNumber: number, shouldCache = false): Promise<string> => {
         // Ignore stale/in-flight work if the document or worker changed.
         if (generation !== pdfDocGenerationRef.current || pdfDocumentRef.current !== currentPdf) {
@@ -326,12 +345,14 @@ export function usePdfDocument(): PdfDocumentState {
 
       if (text !== currDocText || text === '') {
         setCurrDocText(text);
+        const sourceUnits = sourceUnitsFromParsedPage(currDocPageNumber);
         setTTSText(text, {
           location: currDocPageNumber,
           previousText: prevText,
           nextLocation: nextPageNumber,
           nextText: nextText,
           upcomingLocations: additionalUpcoming,
+          ...(sourceUnits.length > 0 ? { sourceUnits } : {}),
         });
       }
     } catch (error) {