feat: implement granular section visibility control

Introduce the ability to reveal specific sections of a document
rather than entire files. This includes:

- Updating `revealedPaths` to map normalized file paths to sets of
  revealed section slugs.
- Adding `isPathRevealed` to handle visibility logic for connected
  clients and GMs.
- Enhancing `extractHeadings` to calculate `startLine` and `endLine`
  for each TOC node to support precise section identification.

src/data-loader/toc.ts

@@ -8,6 +8,10 @@ export interface TocNode {
   id?: string;
   path?: string;
   level: number;
+  /** 1-based line index where the heading starts */
+  startLine: number;
+  /** 1-based line index where this heading's section ends (exclusive) */
+  endLine: number;
   children?: TocNode[];
 }
 
@@ -21,26 +25,58 @@ export interface FileNode {
 }
 
 /**
- * 从 markdown 内容提取标题结构
+ * 从 markdown 内容提取标题结构（含行号范围）
  */
 export function extractHeadings(content: string): TocNode[] {
   const headings: TocNode[] = [];
   const lines = content.split("\n");
   const stack: { node: TocNode; level: number }[] = [];
   const slugger = new Slugger();
+  const totalLines = lines.length;
 
-  for (const line of lines) {
-    const match = line.trim().match(/^(#{1,6})\s+(.+)$/);
+  // First pass: collect heading positions
+  interface HeadingPos {
+    lineIndex: number; // 0-based line index
+    level: number;
+    title: string;
+    id: string;
+  }
+  const positions: HeadingPos[] = [];
+
+  for (let i = 0; i < totalLines; i++) {
+    const match = lines[i].trim().match(/^(#{1,6})\s+(.+)$/);
     if (!match) continue;
-
     const level = match[1].length;
     const title = match[2].trim();
     // 使用 github-slugger 生成 ID，与 marked-gfm-heading-id 保持一致
     const id = slugger.slug(title.toLowerCase());
-    const node: TocNode = { title, id, level };
+    positions.push({ lineIndex: i, level, title, id });
+  }
+
+  // Compute endLine for each heading: endLine is the 1-based line index of
+  // the next heading of same or higher level (or EOF+1).
+  for (let pi = 0; pi < positions.length; pi++) {
+    const pos = positions[pi];
+    let endLine = totalLines + 1; // default: end of file (1-based, exclusive)
+    for (let pj = pi + 1; pj < positions.length; pj++) {
+      if (positions[pj].level <= pos.level) {
+        endLine = positions[pj].lineIndex + 1; // 1-based
+        break;
+      }
+    }
+
+    const node: TocNode = {
+      title: pos.title,
+      id: pos.id,
+      level: pos.level,
+      startLine: pos.lineIndex + 1,
+      endLine,
+    };
 
     // 找到合适的父节点
-    while (stack.length > 0 && stack[stack.length - 1].level >= level) {
+    while (stack.length > 0 && stack[stack.length - 1].level >= node.level) {
+      // Close out the current parent's endLine at this heading's start
+      stack[stack.length - 1].node.endLine = node.startLine;
       stack.pop();
     }
 
@@ -52,7 +88,13 @@ export function extractHeadings(content: string): TocNode[] {
       parent.children.push(node);
     }
 
-    stack.push({ node, level });
+    stack.push({ node, level: node.level });
+  }
+
+  // Close remaining stack entries at EOF
+  while (stack.length > 0) {
+    stack[stack.length - 1].node.endLine = totalLines + 1;
+    stack.pop();
   }
 
   return headings;
@@ -136,7 +178,7 @@ export function extractSection(content: string, sectionTitle: string): string {
   // 匹配标题（支持 1-6 级标题）
   const sectionRegex = new RegExp(
     `^(#{1,6})\\s*${escapeRegExp(sectionTitle)}\\s*$`,
-    "im"
+    "im",
   );
 
   const match = content.match(sectionRegex);
@@ -149,10 +191,7 @@ export function extractSection(content: string, sectionTitle: string): string {
   const startIndex = match.index!;
 
   // 查找下一个同级或更高级别的标题
-  const nextHeaderRegex = new RegExp(
-    `^#{1,${headerLevel}}\\s+.+$`,
-    "gm"
-  );
+  const nextHeaderRegex = new RegExp(`^#{1,${headerLevel}}\\s+.+$`, "gm");
 
   // 从标题后开始搜索
   nextHeaderRegex.lastIndex = startIndex + match[0].length;