refactor(dlx): split main.ts into focused modules

Split dlx/main.ts into smaller, focused modules for better organization
and maintainability.

Changes:
- Create dlx/cache.ts for cache key generation (generateCacheKey)
- Create dlx/paths.ts for path utilities (getDlxPackageDir, getDlxInstalledPackageDir, getDlxPackageJsonPath, getDlxPackageNodeModulesDir, isInSocketDlx)
- Create dlx/dir.ts for directory management (clearDlx, clearDlxSync, dlxDirExists, dlxDirExistsAsync, ensureDlxDir, ensureDlxDirSync)
- Create dlx/packages.ts for package management (isDlxPackageInstalled, isDlxPackageInstalledAsync, listDlxPackages, listDlxPackagesAsync, removeDlxPackage, removeDlxPackageSync)
- Remove old dlx/main.ts file
- Update imports in dlx/binary.ts and dlx/package.ts to use dlx/cache
- Update package.json exports:
  - Remove ./dlx/main
  - Add ./dlx/cache, ./dlx/dir, ./dlx/packages, ./dlx/paths
- Update test imports in test/unit/dlx/main.test.ts to use split modules
- All tests passing (182 tests, 179 passed, 3 skipped)

Author: jdalton

package.json

@@ -223,9 +223,13 @@
       "types": "./dist/dlx/binary.d.ts",
       "default": "./dist/dlx/binary.js"
     },
-    "./dlx/main": {
-      "types": "./dist/dlx/main.d.ts",
-      "default": "./dist/dlx/main.js"
+    "./dlx/cache": {
+      "types": "./dist/dlx/cache.d.ts",
+      "default": "./dist/dlx/cache.js"
+    },
+    "./dlx/dir": {
+      "types": "./dist/dlx/dir.d.ts",
+      "default": "./dist/dlx/dir.js"
     },
     "./dlx/manifest": {
       "types": "./dist/dlx/manifest.d.ts",
@@ -235,6 +239,14 @@
       "types": "./dist/dlx/package.d.ts",
       "default": "./dist/dlx/package.js"
     },
+    "./dlx/packages": {
+      "types": "./dist/dlx/packages.d.ts",
+      "default": "./dist/dlx/packages.js"
+    },
+    "./dlx/paths": {
+      "types": "./dist/dlx/paths.d.ts",
+      "default": "./dist/dlx/paths.js"
+    },
     "./effects/pulse-frames": {
       "types": "./dist/effects/pulse-frames.d.ts",
       "default": "./dist/effects/pulse-frames.js"

src/dlx/binary.ts

@@ -9,7 +9,7 @@ import path from 'path'
 import { WIN32 } from '../constants/platform'
 import { DLX_BINARY_CACHE_TTL } from '../constants/time'
 
-import { generateCacheKey } from './main'
+import { generateCacheKey } from './cache'
 import { dlxManifest } from './manifest'
 import { httpDownload } from '../http-request'
 import { isDir, readJson, safeDelete, safeMkdir } from '../fs'

src/dlx/cache.ts

@@ -0,0 +1,31 @@
+/** @fileoverview Cache key generation utilities for DLX package installations. */
+
+import { createHash } from 'node:crypto'
+
+/**
+ * Generate a cache directory name using npm/npx approach.
+ * Uses first 16 characters of SHA-512 hash (like npm/npx).
+ *
+ * Rationale for SHA-512 truncated (vs full SHA-256):
+ * - Matches npm/npx ecosystem behavior
+ * - Shorter paths for Windows MAX_PATH compatibility (260 chars)
+ * - 16 hex chars = 64 bits = acceptable collision risk for local cache
+ * - Collision probability ~1 in 18 quintillion with 1000 entries
+ *
+ * Input strategy (aligned with npx):
+ * - npx uses package spec strings (e.g., '@scope/pkg@1.0.0', 'prettier@3.0.0')
+ * - Caller provides complete spec string with version for accurate cache keying
+ * - For package installs: Use PURL-style spec with version
+ *   Examples: 'npm:prettier@3.0.0', 'pypi:requests@2.31.0', 'gem:rails@7.0.0'
+ *   Note: Socket uses shorthand format without 'pkg:' prefix
+ *   (handled by @socketregistry/packageurl-js)
+ * - For binary downloads: Use URL:name for uniqueness
+ *
+ * Reference: npm/cli v11.6.2 libnpmexec/lib/index.js#L233-L244
+ * https://github.com/npm/cli/blob/v11.6.2/workspaces/libnpmexec/lib/index.js#L233-L244
+ * Implementation: packages.map().sort().join('\n') → SHA-512 → slice(0,16)
+ * npx hashes the package spec (name@version), not just name
+ */
+export function generateCacheKey(spec: string): string {
+  return createHash('sha512').update(spec).digest('hex').substring(0, 16)
+}

src/dlx/dir.ts

@@ -0,0 +1,82 @@
+/** @fileoverview Directory management utilities for DLX installations. */
+
+import { safeMkdir, safeMkdirSync } from '../fs'
+import { getSocketDlxDir } from '../paths/socket'
+import { pEach } from '../promises'
+import {
+  listDlxPackages,
+  listDlxPackagesAsync,
+  removeDlxPackage,
+  removeDlxPackageSync,
+} from './packages'
+
+let _fs: typeof import('fs') | undefined
+/**
+ * Lazily load the fs module to avoid Webpack errors.
+ * Uses non-'node:' prefixed require to prevent Webpack bundling issues.
+ *
+ * @returns The Node.js fs module
+ * @private
+ */
+/*@__NO_SIDE_EFFECTS__*/
+function getFs() {
+  if (_fs === undefined) {
+    // Use non-'node:' prefixed require to avoid Webpack errors.
+
+    _fs = /*@__PURE__*/ require('node:fs')
+  }
+  return _fs as typeof import('fs')
+}
+
+/**
+ * Clear all DLX package installations.
+ */
+export async function clearDlx(): Promise<void> {
+  const packages = await listDlxPackagesAsync()
+  await pEach(packages, pkg => removeDlxPackage(pkg))
+}
+
+/**
+ * Clear all DLX package installations synchronously.
+ */
+export function clearDlxSync(): void {
+  const packages = listDlxPackages()
+  for (const pkg of packages) {
+    removeDlxPackageSync(pkg)
+  }
+}
+
+/**
+ * Check if the DLX directory exists.
+ */
+export function dlxDirExists(): boolean {
+  const fs = getFs()
+  return fs.existsSync(getSocketDlxDir())
+}
+
+/**
+ * Check if the DLX directory exists asynchronously.
+ */
+export async function dlxDirExistsAsync(): Promise<boolean> {
+  const fs = getFs()
+  try {
+    await fs.promises.access(getSocketDlxDir())
+    return true
+  } catch {
+    return false
+  }
+}
+
+/**
+ * Ensure the DLX directory exists, creating it if necessary.
+ */
+export async function ensureDlxDir(): Promise<void> {
+  await safeMkdir(getSocketDlxDir())
+}
+
+/**
+ * Ensure the DLX directory exists synchronously, creating it if necessary.
+ */
+export function ensureDlxDirSync(): void {
+  safeMkdirSync(getSocketDlxDir())
+}