Add build infrastructure and QUICKSTART guide

- Build script (scripts/build.mjs) using esbuild with iterative stub creation
- Stubs for Bun compile-time intrinsics (feature(), MACRO, bun:bundle)
- Stub modules for feature-gated internal code paths
- QUICKSTART.md with 3 build options (pre-built, esbuild, Bun)
- tsconfig.json, package.json for build tooling

Build reaches ~95% — 108 remaining feature-gated modules need Bun runtime
for full dead code elimination. See QUICKSTART.md for details.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/prepare-src.mjs

@@ -0,0 +1,115 @@
+#!/usr/bin/env node
+/**
+ * prepare-src.mjs — Pre-build source transformation
+ *
+ * This script patches the source tree to make it compilable without Bun:
+ *   1. Replace `import { feature } from 'bun:bundle'` with our stub
+ *   2. Replace `MACRO.X` references with runtime values
+ *   3. Create missing type declarations
+ */
+
+import fs from 'node:fs'
+import path from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+const ROOT = path.resolve(__dirname, '..')
+const SRC = path.join(ROOT, 'src')
+
+const VERSION = '2.1.88'
+
+// ── Helpers ──────────────────────────────────────────────────────────────────
+
+function walk(dir, ext = '.ts') {
+  const results = []
+  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+    const full = path.join(dir, entry.name)
+    if (entry.isDirectory() && entry.name !== 'node_modules') {
+      results.push(...walk(full, ext))
+    } else if (entry.name.endsWith(ext) || entry.name.endsWith('.tsx')) {
+      results.push(full)
+    }
+  }
+  return results
+}
+
+function patchFile(filePath) {
+  let src = fs.readFileSync(filePath, 'utf8')
+  let changed = false
+
+  // 1. Replace `import { feature } from 'bun:bundle'` / `"bun:bundle"`
+  if (src.includes("from 'bun:bundle'") || src.includes('from "bun:bundle"')) {
+    src = src.replace(/import\s*\{\s*feature\s*\}\s*from\s*['"]bun:bundle['"]/g,
+      "import { feature } from '../stubs/bun-bundle.js'")
+    // Fix relative depth based on file location
+    const rel = path.relative(SRC, path.dirname(filePath))
+    const depth = rel ? '../'.repeat(rel.split('/').length) : ''
+    if (depth) {
+      src = src.replace("from '../stubs/bun-bundle.js'", `from '${depth}stubs/bun-bundle.js'`)
+    }
+    changed = true
+  }
+
+  // 2. Replace MACRO.X with string literals
+  const macroReplacements = {
+    'MACRO.VERSION': `'${VERSION}'`,
+    'MACRO.BUILD_TIME': `'${new Date().toISOString()}'`,
+    'MACRO.FEEDBACK_CHANNEL': `'https://github.com/anthropics/claude-code/issues'`,
+    'MACRO.ISSUES_EXPLAINER': `'https://github.com/anthropics/claude-code/issues/new/choose'`,
+    'MACRO.NATIVE_PACKAGE_URL': `'@anthropic-ai/claude-code'`,
+    'MACRO.PACKAGE_URL': `'@anthropic-ai/claude-code'`,
+    'MACRO.VERSION_CHANGELOG': `''`,
+  }
+
+  for (const [macro, replacement] of Object.entries(macroReplacements)) {
+    if (src.includes(macro)) {
+      // Don't replace inside strings
+      src = src.replace(new RegExp(`(?<![\\w'"])${macro.replace('.', '\\.')}(?![\\w'" ])`, 'g'), replacement)
+      changed = true
+    }
+  }
+
+  if (changed) {
+    fs.writeFileSync(filePath, src, 'utf8')
+    return true
+  }
+  return false
+}
+
+// ── Main ─────────────────────────────────────────────────────────────────────
+
+console.log('🔧 Preparing source files...\n')
+
+const files = walk(SRC)
+let patched = 0
+
+for (const file of files) {
+  if (patchFile(file)) {
+    patched++
+    console.log(`  patched: ${path.relative(ROOT, file)}`)
+  }
+}
+
+// Create stub for bun:ffi (only used in upstreamproxy)
+const ffiStub = path.join(ROOT, 'stubs', 'bun-ffi.ts')
+if (!fs.existsSync(ffiStub)) {
+  fs.writeFileSync(ffiStub, `// Stub for bun:ffi — not available outside Bun runtime\nexport const ffi = {} as any\nexport function dlopen() { return {} }\n`)
+  console.log('  created: stubs/bun-ffi.ts')
+}
+
+// Create global MACRO type declaration
+const macroDecl = path.join(ROOT, 'stubs', 'global.d.ts')
+fs.writeFileSync(macroDecl, `// Global compile-time macros (normally injected by Bun bundler)
+declare const MACRO: {
+  VERSION: string
+  BUILD_TIME: string
+  FEEDBACK_CHANNEL: string
+  ISSUES_EXPLAINER: string
+  NATIVE_PACKAGE_URL: string
+  PACKAGE_URL: string
+  VERSION_CHANGELOG: string
+}
+`)
+console.log('  created: stubs/global.d.ts')
+
+console.log(`\n✅ Patched ${patched} / ${files.length} source files`)