chore: checkpoint current milestone work

Sources/RDReaderView/EPUBTextRendering/RDPlainTextBookBuilder.swift

@@ -24,25 +24,40 @@ public final class RDPlainTextBookBuilder {
             let rendered = try renderer.renderChapter(html: html, baseURL: nil, style: style)
 
             let content = NSMutableAttributedString(attributedString: rendered.attributedString)
-            let pageRanges = content.length > 0 ? content.ss_pageRanges(size: pageSize) : []
-            let effectivePageRanges = pageRanges.isEmpty && content.length > 0
-                ? [NSRange(location: 0, length: content.length)]
-                : pageRanges
+            let layoutFrames = content.length > 0 ? content.rd_paginatedFrames(size: pageSize) : []
+            let effectiveFrames = layoutFrames.isEmpty && content.length > 0
+                ? [
+                    RDEPUBTextLayoutFrame(
+                        contentRange: NSRange(location: 0, length: content.length),
+                        breakReason: .chapterEnd,
+                        blockRange: nil,
+                        attachmentRanges: [],
+                        attachmentKinds: [],
+                        trailingFragmentID: nil,
+                        diagnostics: [
+                            "page break: chapterEnd",
+                            "page range: \(NSStringFromRange(NSRange(location: 0, length: content.length)))"
+                        ]
+                    )
+                ]
+                : layoutFrames
 
             let href = "chapter_\(index).xhtml"
-            let pages = effectivePageRanges.enumerated().map { localPageIndex, range in
-                RDEPUBTextPage(
+            let pages = effectiveFrames.enumerated().map { localPageIndex, frame in
+                let range = frame.contentRange
+                return RDEPUBTextPage(
                     absolutePageIndex: flatPages.count + localPageIndex,
                     chapterIndex: index,
                     spineIndex: index,
                     href: href,
                     chapterTitle: spec.title ?? "第 \(index + 1) 章",
                     pageIndexInChapter: localPageIndex,
-                    totalPagesInChapter: effectivePageRanges.count,
+                    totalPagesInChapter: effectiveFrames.count,
                     content: content.attributedSubstring(from: range),
                     contentRange: range,
                     pageStartOffset: range.location,
-                    pageEndOffset: range.location + max(range.length - 1, 0)
+                    pageEndOffset: range.location + max(range.length - 1, 0),
+                    metadata: frame.metadata
                 )
             }
 
@@ -54,6 +69,7 @@ public final class RDPlainTextBookBuilder {
                     title: spec.title ?? "第 \(index + 1) 章",
                     attributedContent: content.copy() as! NSAttributedString,
                     fragmentOffsets: [:],
+                    pageBreakReasons: pages.map(\.metadata.breakReason),
                     pages: pages
                 )
             )