feat: add Codebase Intelligence — repo map with PageRank-ranked structural summaries

Add a new module that builds a structural map of the repository by parsing
source files with tree-sitter, building a cross-file reference graph
weighted by IDF, ranking files with PageRank, and rendering a
token-budgeted summary of the most important files and their signatures.

Stage 1 — Core module (src/context/repoMap/):
  Symbol extraction via web-tree-sitter WASM, IDF-weighted reference graph
  via graphology, PageRank ranking, token-budgeted rendering via js-tiktoken
  cl100k_base, disk cache with mtime invalidation. Supports TypeScript,
  JavaScript, and Python. 10 tests.

Stage 2 — RepoMap tool (src/tools/RepoMapTool/):
  buildTool wrapper registered in src/tools.ts. Read-only, concurrency-safe.
  Supports focus_files, focus_symbols, and max_tokens parameters. 9 tests.

Stage 3 — Integration:
  Auto-injection into session context behind REPO_MAP feature flag (off by
  default). /repomap slash command with --tokens, --focus, --stats, and
  --invalidate flags. User-facing docs in docs/repo-map.md. 13 tests.

With the flag off, the system context is byte-identical to previous behavior.

Dependencies: web-tree-sitter, tree-sitter-wasms, graphology,
graphology-pagerank, graphology-operators, js-tiktoken

Tests: 32 new, 621 total passing, 0 failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/context/repoMap/gitFiles.ts

@@ -0,0 +1,109 @@
+import { execFile } from 'child_process'
+import { readdirSync, statSync } from 'fs'
+import { join, relative } from 'path'
+import type { SupportedLanguage } from './types.js'
+
+const SUPPORTED_EXTENSIONS: Record<string, SupportedLanguage> = {
+  '.ts': 'typescript',
+  '.tsx': 'typescript',
+  '.js': 'javascript',
+  '.jsx': 'javascript',
+  '.mjs': 'javascript',
+  '.cjs': 'javascript',
+  '.py': 'python',
+}
+
+const EXCLUDED_DIRS = new Set([
+  'node_modules',
+  'dist',
+  '.git',
+  '.hg',
+  '.svn',
+  'build',
+  'out',
+  'coverage',
+  '__pycache__',
+  '.next',
+  '.nuxt',
+  'vendor',
+  '.worktrees',
+])
+
+const EXCLUDED_FILES = new Set([
+  'bun.lock',
+  'bun.lockb',
+  'package-lock.json',
+  'yarn.lock',
+  'pnpm-lock.yaml',
+])
+
+export function getLanguageForFile(filePath: string): SupportedLanguage | null {
+  const ext = filePath.substring(filePath.lastIndexOf('.'))
+  return SUPPORTED_EXTENSIONS[ext] ?? null
+}
+
+export function isSupportedFile(filePath: string): boolean {
+  return getLanguageForFile(filePath) !== null
+}
+
+/** List files using git ls-files. Returns relative paths. */
+function gitLsFiles(root: string): Promise<string[]> {
+  return new Promise((resolve, reject) => {
+    execFile(
+      'git',
+      ['ls-files', '--cached', '--others', '--exclude-standard'],
+      { cwd: root, maxBuffer: 10 * 1024 * 1024 },
+      (error, stdout) => {
+        if (error) {
+          reject(error)
+          return
+        }
+        const files = stdout
+          .split('\n')
+          .map(f => f.trim())
+          .filter(f => f.length > 0)
+        resolve(files)
+      },
+    )
+  })
+}
+
+/** Walk directory tree manually as fallback when git is unavailable. */
+function walkDirectory(root: string, currentDir: string = root): string[] {
+  const results: string[] = []
+  let entries: ReturnType<typeof readdirSync>
+  try {
+    entries = readdirSync(currentDir, { withFileTypes: true })
+  } catch {
+    return results
+  }
+
+  for (const entry of entries) {
+    const name = entry.name
+    if (entry.isDirectory()) {
+      if (!EXCLUDED_DIRS.has(name) && !name.startsWith('.')) {
+        results.push(...walkDirectory(root, join(currentDir, name)))
+      }
+    } else if (entry.isFile()) {
+      if (!EXCLUDED_FILES.has(name)) {
+        results.push(relative(root, join(currentDir, name)))
+      }
+    }
+  }
+  return results
+}
+
+/**
+ * Enumerate all supported source files in the repo.
+ * Tries git ls-files first, falls back to manual walk.
+ */
+export async function getRepoFiles(root: string): Promise<string[]> {
+  let files: string[]
+  try {
+    files = await gitLsFiles(root)
+  } catch {
+    files = walkDirectory(root)
+  }
+
+  return files.filter(isSupportedFile)
+}