diff --git a/.gitignore b/.gitignore
index 2085f9df3..cb74e32ef 100644
--- a/.gitignore
+++ b/.gitignore
@@ -49,4 +49,15 @@ src/costrict/review/skill/builtin.ts
 
 # Review builtin cache
 packages/builtin-tools/bundled-review/
-bundled-review/
\ No newline at end of file
+
+# Upstream additions
+teach-me
+credentials.json
+
+# Session-scoped progress / state files written by agents and skills
+.claude-impl-state.md
+.claude-progress.md
+.claude-recovery.md
+.test-progress.md
+.squash-tmp/
+.git.*-backup
\ No newline at end of file
diff --git a/package.json b/package.json
index 08d0b027b..e52da4c7e 100644
--- a/package.json
+++ b/package.json
@@ -41,7 +41,6 @@
   ],
   "scripts": {
     "build": "bun run build.ts",
-    "build:builtin-review": "bun run scripts/generate-review-builtin.ts",
     "build:vite": "vite build && bun run scripts/post-build.ts",
     "build:vite:only": "vite build",
     "build:bun": "bun run build.ts",
@@ -207,6 +206,7 @@
     "turndown": "^7.2.2",
     "type-fest": "^5.5.0",
     "typescript": "^6.0.2",
+    "undici": "^7.24.6",
     "url-handler-napi": "workspace:*",
     "usehooks-ts": "^3.1.1",
     "vite": "^8.0.8",
diff --git a/scripts/generate-review-builtin.ts b/scripts/generate-review-builtin.ts
index a1607b37e..0af742575 100644
--- a/scripts/generate-review-builtin.ts
+++ b/scripts/generate-review-builtin.ts
@@ -293,26 +293,6 @@ export async function extractBundledSkill(skillName: string, targetDir: string,
     await writeFile(join(targetDir, relativePath), content, "utf-8")
   }
 }
-
-export async function extractBundledSkill(skillName: string, targetDir: string, locale: string): Promise<void> {
-  const localeData = SKILL_FILES[locale]
-  if (!localeData) {
-    throw new Error(\`Locale not found: \${locale}\`)
-  }
-
-  const skillFiles = localeData[skillName]
-  if (!skillFiles) {
-    throw new Error(\`Skill not found: \${skillName}\`)
-  }
-
-  const { mkdir: mkdirSync, writeFile: writeFileSync } = await import('fs/promises')
-  const { join: pathJoin, dirname: pathDirname } = await import('path')
-  await mkdirSync(targetDir, { recursive: true })
-  for (const [relativePath, fileContent] of Object.entries(skillFiles)) {
-    await mkdirSync(pathJoin(targetDir, pathDirname(relativePath)), { recursive: true })
-    await writeFileSync(pathJoin(targetDir, relativePath), fileContent, 'utf-8')
-  }
-}
 `
 
   await mkdir(path.dirname(builtinSkillsFile), { recursive: true })
diff --git a/src/commands/lang/lang.ts b/src/commands/lang/lang.ts
index e386ec726..8520d26f2 100644
--- a/src/commands/lang/lang.ts
+++ b/src/commands/lang/lang.ts
@@ -1,5 +1,4 @@
 import type { ToolUseContext } from '../../Tool.js'
-import { clearCommandsCache } from '../../commands.js'
 import type {
   LocalJSXCommandContext,
   LocalJSXCommandOnDone,
@@ -10,7 +9,6 @@ import {
   getLanguageDisplayName,
   getResolvedLanguage,
 } from '../../utils/language.js'
-import { Extension as ReviewExtension } from '../../costrict/review/index.js'
 
 const VALID_LANGS: readonly PreferredLanguage[] = ['en', 'zh', 'auto']
 
@@ -42,10 +40,6 @@ export async function call(
   const lang = arg as PreferredLanguage
   saveGlobalConfig(current => ({ ...current, preferredLanguage: lang }))
 
-  // Re-extract review skills for the new locale and refresh skill caches
-  await ReviewExtension.initializeBuiltinSkills().catch(() => {})
-  clearCommandsCache()
-
   const resolved = getResolvedLanguage()
   const suffix = lang === 'auto' ? ` → ${getLanguageDisplayName(resolved)}` : ''
   onDone(`Language set to ${getLanguageDisplayName(lang)}${suffix}`, {
diff --git a/src/costrict/command/locales/en/review.txt b/src/costrict/command/locales/en/review.txt
index 5fe8f59ab..e4a70121e 100644
--- a/src/costrict/command/locales/en/review.txt
+++ b/src/costrict/command/locales/en/review.txt
@@ -1,5 +1,5 @@
 # Code Review
 
-Please use the Skill tool to load the `review` skill to perform a code review on: $ARGUMENTS
+Please perform a code review on: $ARGUMENTS
 
 Please respond and write all files in English throughout the entire process.
diff --git a/src/costrict/command/locales/zh-CN/review.txt b/src/costrict/command/locales/zh-CN/review.txt
index fec845816..ed2871707 100644
--- a/src/costrict/command/locales/zh-CN/review.txt
+++ b/src/costrict/command/locales/zh-CN/review.txt
@@ -1,5 +1,5 @@
 # 代码审查
 
-请使用 Skill 工具加载 `review` 技能来对以下内容执行代码审查：$ARGUMENTS
+请对以下内容执行代码审查：$ARGUMENTS
 
 全程请使用中文进行回答与文件写入。
diff --git a/src/costrict/review/extension.ts b/src/costrict/review/extension.ts
index 54b26cfa2..99f7736c9 100644
--- a/src/costrict/review/extension.ts
+++ b/src/costrict/review/extension.ts
@@ -1,72 +1,87 @@
-import { mkdir, readFile, writeFile } from 'fs/promises'
-import { join } from 'path'
-import { getClaudeConfigHomeDir } from 'src/utils/envUtils.js'
+/**
+ * CoStrict Skill Extension
+ *
+ * Initializes builtin review skills by extracting them from embedded
+ * SKILL_FILES to a cache directory on disk.
+ *
+ * Version tracking uses commit SHA + locale in a .version file.
+ * Skills are re-extracted when version or locale changes.
+ */
+
+import path from 'path'
+import { writeFile, readFile, rm, mkdir, stat } from 'fs/promises'
 import { getResolvedLanguage } from 'src/utils/language.js'
-import {
-  extractBundledSkill,
-  getBuiltinSkillVersion,
-  listBuiltinSkillNames,
-} from './skill/builtin.js'
+import * as Builtin from './skill/builtin.js'
 
 const LOCALE_MAP: Record<string, string> = { zh: 'zh-CN', en: 'en' }
 
-function getLocale(): string {
-  const lang = getResolvedLanguage()
-  return LOCALE_MAP[lang] ?? 'zh-CN'
-}
-
-function getReviewSkillsDir(): string {
-  return join(getClaudeConfigHomeDir(), 'skills')
+function getSkillCacheDir(): string {
+  const home = process.env.HOME ?? process.env.USERPROFILE ?? ''
+  return path.join(home, '.claude', 'skills')
 }
 
 function getVersionFilePath(skillDir: string): string {
-  return join(skillDir, '.version')
+  return path.join(skillDir, '.version')
 }
 
 async function getInstalledVersion(skillDir: string): Promise<string | null> {
   try {
-    return await readFile(getVersionFilePath(skillDir), 'utf-8')
+    const content = await readFile(getVersionFilePath(skillDir), 'utf-8')
+    return content.trim()
   } catch {
     return null
   }
 }
 
-async function writeVersionFile(
-  skillDir: string,
-  skillName: string,
-  locale: string,
-): Promise<void> {
-  const builtinVersion = getBuiltinSkillVersion(skillName)
+async function needsUpdate(skillDir: string, skillName: string, locale: string): Promise<boolean> {
+  const builtinVersion = Builtin.getBuiltinSkillVersion(skillName)
+  if (!builtinVersion) return true
+
+  const installedVersion = await getInstalledVersion(skillDir)
+  const expectedVersion = `${builtinVersion}:${locale}`
+  return installedVersion !== expectedVersion
+}
+
+async function writeVersionFile(skillDir: string, skillName: string, locale: string): Promise<void> {
+  const builtinVersion = Builtin.getBuiltinSkillVersion(skillName)
   if (!builtinVersion) return
+
+  await mkdir(skillDir, { recursive: true })
   await writeFile(getVersionFilePath(skillDir), `${builtinVersion}:${locale}`, 'utf-8')
 }
 
-async function needsUpdate(
-  skillDir: string,
-  skillName: string,
-  locale: string,
-): Promise<boolean> {
-  const builtinVersion = getBuiltinSkillVersion(skillName)
-  if (!builtinVersion) return true
-  const installed = await getInstalledVersion(skillDir)
-  return installed !== `${builtinVersion}:${locale}`
-}
-
 export async function initializeBuiltinSkills(): Promise<void> {
-  const locale = getLocale()
-  const skillsDir = getReviewSkillsDir()
-  const skillNames = listBuiltinSkillNames()
+  const lang = getResolvedLanguage()
+  const locale = LOCALE_MAP[lang] ?? 'zh-CN'
 
-  for (const skillName of skillNames) {
-    const skillDir = join(skillsDir, skillName)
-    if (!(await needsUpdate(skillDir, skillName, locale))) continue
+  const cacheDir = getSkillCacheDir()
+  const skillNames = Builtin.listBuiltinSkills()
 
-    await mkdir(skillDir, { recursive: true })
-    await extractBundledSkill(skillName, skillDir, locale)
-    await writeVersionFile(skillDir, skillName, locale)
+  for (const name of skillNames) {
+    const skillDir = path.join(cacheDir, name)
+
+    const dirExists = await stat(skillDir).then(s => s.isDirectory()).catch(() => false)
+
+    if (dirExists) {
+      const updateNeeded = await needsUpdate(skillDir, name, locale)
+      if (!updateNeeded) continue
+
+      try {
+        await rm(skillDir, { recursive: true, force: true })
+      } catch {
+        // Continue with copy over existing files
+      }
+    }
+
+    await Builtin.extractBundledSkill(name, skillDir, locale)
+    await writeVersionFile(skillDir, name, locale)
+
+    const skillFiles = Builtin.listSkillFiles(name, locale)
+    const builtinVersion = Builtin.getBuiltinSkillVersion(name)
+    console.log(`  [review] initialized skill "${name}" (${locale}, ${skillFiles.length} files, v${builtinVersion?.slice(0, 7)})`)
   }
 }
 
 export function getBuiltinSkillsDir(): string {
-  return getReviewSkillsDir()
+  return getSkillCacheDir()
 }
diff --git a/src/costrict/review/index.ts b/src/costrict/review/index.ts
index 01f347fbb..09d86b8a2 100644
--- a/src/costrict/review/index.ts
+++ b/src/costrict/review/index.ts
@@ -1,9 +1,15 @@
 /**
  * CoStrict Review Module
  *
- * Provides builtin review skills that are extracted to disk at runtime
- * and discovered by the standard skill scanner.
+ * Provides builtin review skills and agents that are embedded
+ * in the binary and extracted to cache on first run.
  */
 
-export * as SkillBuiltin from './skill/builtin.js'
 export * as Extension from './extension.js'
+export * as SkillBuiltin from './skill/builtin.js'
+export {
+  REVIEW_AGENTS,
+  AGENT_VERSIONS,
+  PRIMARY_REVIEW_AGENT,
+  SUB_REVIEW_AGENT,
+} from './agent/builtin.js'
diff --git a/src/skills/bundled/index.ts b/src/skills/bundled/index.ts
index a082c2a6e..38b7edb75 100644
--- a/src/skills/bundled/index.ts
+++ b/src/skills/bundled/index.ts
@@ -1,6 +1,6 @@
 import { feature } from 'bun:bundle'
 import { shouldAutoEnableClaudeInChrome } from 'src/utils/claudeInChrome/setup.js'
-import { Extension as ReviewExtension } from 'src/costrict/review/index.js'
+import { initializeBuiltinSkills } from 'src/costrict/review/extension.js'
 import { registerBatchSkill } from './batch.js'
 import { registerClaudeInChromeSkill } from './claudeInChrome.js'
 import { registerDebugSkill } from './debug.js'
@@ -30,8 +30,8 @@ import { registerTddSkill } from 'src/costrict/skills/tdd.js'
  * 3. Import and call that function here
  */
 export function initBundledSkills(): void {
-  // Extract review skills to disk for standard scanner discovery
-  ReviewExtension.initializeBuiltinSkills().catch(() => {})
+  // Initialize builtin review skills (extract to cache if needed)
+  initializeBuiltinSkills().catch(() => {})
 
   registerUpdateConfigSkill()
   registerProjectWikiSkill()