feat: add ChapterContext and per-chapter line counts

packages/web/src/components/chapter/chapter-navigator.tsx

@@ -10,6 +10,7 @@ import {
 	Copy,
 	MoreHorizontal,
 } from "lucide-react";
+import { LineCounts } from "@/components/shared/line-counts";
 import { ShortcutTooltip } from "@/components/shared/shortcut-tooltip";
 import { StatusBadge } from "@/components/shared/status-badge";
 import { Button } from "@/components/ui/button";
@@ -19,28 +20,26 @@ import {
 	DropdownMenuItem,
 	DropdownMenuTrigger,
 } from "@/components/ui/dropdown-menu";
+import { useChapterContext } from "@/lib/chapter-context";
 import { SHORTCUT_KEY } from "@/lib/keyboard-shortcuts";
 import { cn } from "@/lib/utils";
 
 interface ChapterNavigatorProps {
-	runId: string;
 	chapter: Chapter;
 	chapterIndex: number;
-	allChapters: Chapter[];
 	viewedChapterIds: ReadonlySet<string>;
 	onToggleViewed: (externalId: string) => void;
 	onCopyChapter: () => void;
 }
 
 export function ChapterNavigator({
-	runId,
 	chapter,
 	chapterIndex,
-	allChapters,
 	viewedChapterIds,
 	onToggleViewed,
 	onCopyChapter,
 }: ChapterNavigatorProps) {
+	const { runId, chapters: allChapters, chapterLineCountsMap } = useChapterContext();
 	const isViewed = viewedChapterIds.has(chapter.externalId);
 	const canPrev = chapterIndex > 0;
 	const canNext = chapterIndex < allChapters.length - 1;
@@ -100,6 +99,7 @@ export function ChapterNavigator({
 						{allChapters.map((ch, index) => {
 							const isActive = index === chapterIndex;
 							const isChViewed = viewedChapterIds.has(ch.externalId);
+							const counts = chapterLineCountsMap.get(ch.id);
 							return (
 								<DropdownMenuItem key={ch.id} asChild className="gap-3 px-3 py-2.5">
 									<Link
@@ -127,6 +127,13 @@ export function ChapterNavigator({
 											</div>
 										</StatusBadge>
 										<span className="min-w-0 flex-1 truncate text-sm">{ch.title}</span>
+										{counts && (
+											<LineCounts
+												additions={counts.linesAdded}
+												deletions={counts.linesDeleted}
+												className="shrink-0 opacity-70"
+											/>
+										)}
 									</Link>
 								</DropdownMenuItem>
 							);

packages/web/src/components/chapter/chapter-side-panel.tsx

@@ -1,6 +1,8 @@
 import type { Chapter } from "@stage-cli/types/chapters";
 import { useCallback, useEffect, useRef, useState } from "react";
+import { LineCounts } from "@/components/shared/line-counts";
 import { Markdown } from "@/components/ui/markdown";
+import { useChapterContext } from "@/lib/chapter-context";
 import type { FileDiffEntry } from "@/lib/parse-diff";
 import { ChapterFileList } from "./chapter-file-list";
 import { ChapterNavigator } from "./chapter-navigator";
@@ -12,10 +14,8 @@ const MAX_WIDTH_FRACTION = 0.5;
 const SSR_FALLBACK_WIDTH = Math.round(1440 * DEFAULT_WIDTH_FRACTION);
 
 interface ChapterSidePanelProps {
-	runId: string;
 	chapter: Chapter;
 	chapterIndex: number;
-	allChapters: Chapter[];
 	chapterEntries: FileDiffEntry[];
 	viewedChapterIds: ReadonlySet<string>;
 	checkedKeyChangeIds: ReadonlySet<string>;
@@ -30,10 +30,8 @@ interface ChapterSidePanelProps {
 }
 
 export function ChapterSidePanel({
-	runId,
 	chapter,
 	chapterIndex,
-	allChapters,
 	chapterEntries,
 	viewedChapterIds,
 	checkedKeyChangeIds,
@@ -46,6 +44,8 @@ export function ChapterSidePanel({
 	onSelectFile,
 	onCopyChapter,
 }: ChapterSidePanelProps) {
+	const { chapterLineCountsMap } = useChapterContext();
+	const lineCounts = chapterLineCountsMap.get(chapter.id);
 	const [width, setWidth] = useState(SSR_FALLBACK_WIDTH);
 	const cleanupRef = useRef<(() => void) | null>(null);
 
@@ -97,19 +97,26 @@ export function ChapterSidePanel({
 		>
 			<div className="shrink-0 border-border border-b">
 				<ChapterNavigator
-					runId={runId}
 					chapter={chapter}
 					chapterIndex={chapterIndex}
-					allChapters={allChapters}
 					viewedChapterIds={viewedChapterIds}
 					onToggleViewed={onToggleChapterViewed}
 					onCopyChapter={onCopyChapter}
 				/>
 				<Markdown
 					content={chapter.title}
 					inheritSize
-					className="pb-3 pl-6 pr-4 font-semibold text-base leading-snug [&_.md-p]:my-0 lg:pl-8"
+					className="pb-1 pl-6 pr-4 font-semibold text-base leading-snug [&_.md-p]:my-0 lg:pl-8"
 				/>
+				{lineCounts && (lineCounts.linesAdded > 0 || lineCounts.linesDeleted > 0) ? (
+					<LineCounts
+						additions={lineCounts.linesAdded}
+						deletions={lineCounts.linesDeleted}
+						className="pb-3 pl-6 pr-4 lg:pl-8"
+					/>
+				) : (
+					<div className="pb-2" />
+				)}
 			</div>
 			<div className="flex-1 overflow-y-auto">
 				<ChapterSummary

packages/web/src/components/chapter/file-header.tsx

@@ -8,6 +8,7 @@ import {
 } from "lucide-react";
 import type { MouseEvent } from "react";
 import { useCallback } from "react";
+import { LineCounts } from "@/components/shared/line-counts";
 import { Tooltip, TooltipContent, TooltipTrigger } from "@/components/ui/tooltip";
 import { FILE_STATUS, type PullRequestFile } from "@/lib/diff-types";
 import { FILE_STATUS_ICONS, FILE_STATUS_LABELS, FILE_STATUS_TEXT_COLORS } from "@/lib/file-status";
@@ -206,14 +207,11 @@ export function FileHeader({
 				</Tooltip>
 			)}
 			<div className="flex-1" />
-			<div className="relative z-10 flex shrink-0 items-center gap-1 font-medium text-[10px] tabular-nums">
-				{file.additions > 0 && (
-					<span className="text-green-600 dark:text-green-500">+{file.additions}</span>
-				)}
-				{file.deletions > 0 && (
-					<span className="text-red-600 dark:text-red-500">-{file.deletions}</span>
-				)}
-			</div>
+			<LineCounts
+				additions={file.additions}
+				deletions={file.deletions}
+				className="relative z-10 shrink-0"
+			/>
 			{onToggleViewed && (
 				<Tooltip>
 					<TooltipTrigger asChild>

packages/web/src/components/files/file-picker.tsx

@@ -1,5 +1,6 @@
 import { ChevronRight, CircleCheck, FileText, Folder, Search } from "lucide-react";
 import { useEffect, useMemo, useRef, useState } from "react";
+import { LineCounts } from "@/components/shared/line-counts";
 import { FILE_STATUS, type PullRequestFile } from "@/lib/diff-types";
 import { FILE_STATUS_ICONS, FILE_STATUS_TEXT_COLORS } from "@/lib/file-status";
 import { buildFileTree, collapseEmptyFolders, type FileNode, sortFileTree } from "@/lib/file-tree";
@@ -182,14 +183,7 @@ function FilePickerTreeItem({
 				>
 					{node.name}
 				</span>
-				<div className="flex items-center gap-1 font-medium text-[10px] tabular-nums opacity-70">
-					{file.additions > 0 && (
-						<span className="text-green-600 dark:text-green-500">+{file.additions}</span>
-					)}
-					{file.deletions > 0 && (
-						<span className="text-red-600 dark:text-red-500">-{file.deletions}</span>
-					)}
-				</div>
+				<LineCounts additions={file.additions} deletions={file.deletions} className="opacity-70" />
 				{isViewed && (
 					<CircleCheck
 						className="size-3 shrink-0 text-green-600 dark:text-green-500"

packages/web/src/components/shared/line-counts.tsx

@@ -0,0 +1,17 @@
+import { cn } from "@/lib/utils";
+
+interface LineCountsProps {
+	additions: number;
+	deletions: number;
+	className?: string;
+}
+
+export function LineCounts({ additions, deletions, className }: LineCountsProps) {
+	if (additions === 0 && deletions === 0) return null;
+	return (
+		<div className={cn("flex items-center gap-1 font-medium text-[10px] tabular-nums", className)}>
+			{additions > 0 && <span className="text-green-600 dark:text-green-500">+{additions}</span>}
+			{deletions > 0 && <span className="text-red-600 dark:text-red-500">-{deletions}</span>}
+		</div>
+	);
+}

packages/web/src/lib/chapter-context.tsx

@@ -0,0 +1,67 @@
+import type { Chapter } from "@stage-cli/types/chapters";
+import { createContext, type ReactNode, use, useMemo } from "react";
+import { filterFilesForChapter } from "./filter-files-for-chapter";
+import { useChapters } from "./use-chapters";
+import { useDiffPatch } from "./use-diff-patch";
+
+export interface ChapterLineCounts {
+	linesAdded: number;
+	linesDeleted: number;
+}
+
+interface ChapterContextValue {
+	runId: string;
+	chapters: readonly Chapter[];
+	chapterLineCountsMap: ReadonlyMap<string, ChapterLineCounts>;
+}
+
+const ChapterContext = createContext<ChapterContextValue | null>(null);
+
+function buildChapterLineCountsMap(
+	chapters: readonly Chapter[],
+	patch: string | undefined,
+): ReadonlyMap<string, ChapterLineCounts> {
+	const map = new Map<string, ChapterLineCounts>();
+	if (!patch) return map;
+	for (const chapter of chapters) {
+		const entries = filterFilesForChapter(patch, chapter.hunkRefs);
+		let linesAdded = 0;
+		let linesDeleted = 0;
+		for (const entry of entries) {
+			linesAdded += entry.file.additions;
+			linesDeleted += entry.file.deletions;
+		}
+		map.set(chapter.id, { linesAdded, linesDeleted });
+	}
+	return map;
+}
+
+export function ChapterProvider({ runId, children }: { runId: string; children: ReactNode }) {
+	const { data: chaptersData } = useChapters(runId);
+	const { data: patch } = useDiffPatch(runId);
+
+	const chapters = useMemo<readonly Chapter[]>(() => {
+		if (!chaptersData?.chapters) return [];
+		return [...chaptersData.chapters].sort((a, b) => a.order - b.order);
+	}, [chaptersData?.chapters]);
+
+	const chapterLineCountsMap = useMemo(
+		() => buildChapterLineCountsMap(chapters, patch),
+		[chapters, patch],
+	);
+
+	const value = useMemo<ChapterContextValue>(
+		() => ({ runId, chapters, chapterLineCountsMap }),
+		[runId, chapters, chapterLineCountsMap],
+	);
+
+	return <ChapterContext value={value}>{children}</ChapterContext>;
+}
+
+export function useChapterContext(): ChapterContextValue {
+	const ctx = use(ChapterContext);
+	if (!ctx) {
+		throw new Error("useChapterContext must be used within a ChapterProvider");
+	}
+	return ctx;
+}

packages/web/src/routes/chapter-detail-page.tsx

@@ -11,6 +11,7 @@ import {
 } from "@/components/files";
 import { Button } from "@/components/ui/button";
 import { Skeleton } from "@/components/ui/skeleton";
+import { useChapterContext } from "@/lib/chapter-context";
 import { FILE_STATUS } from "@/lib/diff-types";
 import { filterFilesForChapter } from "@/lib/filter-files-for-chapter";
 import { formatChapterAsMarkdown } from "@/lib/format-chapter-markdown";
@@ -35,23 +36,13 @@ interface ChapterDetailPageProps {
 }
 
 export function ChapterDetailPage({ runId, chapterNumber }: ChapterDetailPageProps) {
-	const {
-		data: chaptersData,
-		isLoading: chaptersLoading,
-		error: chaptersError,
-	} = useChapters(runId);
+	const { chapters } = useChapterContext();
+	const { isLoading: chaptersLoading, error: chaptersError } = useChapters(runId);
 	const { data: patch, isLoading: patchLoading, error: patchError } = useDiffPatch(runId);
 
-	const allChapters = useMemo<Chapter[]>(() => {
-		if (!chaptersData?.chapters) return [];
-		return [...chaptersData.chapters].sort((a, b) => a.order - b.order);
-	}, [chaptersData?.chapters]);
-	// Look up by `order` rather than indexing — the schema only requires
-	// positive ints, so chapters can have gaps (1, 3, 5) and array position
-	// won't match the URL chapter number.
 	const chapter =
-		chapterNumber === null ? undefined : allChapters.find((c) => c.order === chapterNumber);
-	const chapterIndex = chapter ? allChapters.indexOf(chapter) : -1;
+		chapterNumber === null ? undefined : chapters.find((c) => c.order === chapterNumber);
+	const chapterIndex = chapter ? chapters.indexOf(chapter) : -1;
 
 	const isLoading = chaptersLoading || patchLoading;
 	const error = chaptersError ?? patchError;
@@ -67,32 +58,17 @@ export function ChapterDetailPage({ runId, chapterNumber }: ChapterDetailPagePro
 		return <ErrorState runId={runId} error={new Error("Diff patch unavailable")} />;
 	}
 
-	return (
-		<ChapterDetailContent
-			runId={runId}
-			chapter={chapter}
-			chapterIndex={chapterIndex}
-			allChapters={allChapters}
-			patch={patch}
-		/>
-	);
+	return <ChapterDetailContent chapter={chapter} chapterIndex={chapterIndex} patch={patch} />;
 }
 
 interface ChapterDetailContentProps {
-	runId: string;
 	chapter: Chapter;
 	chapterIndex: number;
-	allChapters: Chapter[];
 	patch: string;
 }
 
-function ChapterDetailContent({
-	runId,
-	chapter,
-	chapterIndex,
-	allChapters,
-	patch,
-}: ChapterDetailContentProps) {
+function ChapterDetailContent({ chapter, chapterIndex, patch }: ChapterDetailContentProps) {
+	const { runId, chapters: allChapters } = useChapterContext();
 	const view = useViewState(runId);
 	const [focusedKeyChangeId, setFocusedKeyChangeId] = useState<string | null>(null);
 
@@ -253,10 +229,8 @@ function ChapterDetailContent({
 		<SidebarLayout
 			sidebar={
 				<ChapterSidePanel
-					runId={runId}
 					chapter={chapter}
 					chapterIndex={chapterIndex}
-					allChapters={allChapters}
 					chapterEntries={chapterEntries}
 					viewedChapterIds={view.chapterIdSet}
 					checkedKeyChangeIds={view.keyChangeIdSet}