fix: add .js extensions to declaration file imports to resolve type re-export issue

Fixes type re-export issue where types exported from this package could not be
re-exported by consuming packages when package.json has "type": "module".

## Root Cause

When `package.json` has `"type": "module"`, TypeScript treats `.d.ts` files as
ESM modules, which require explicit file extensions (`.js`) for relative imports.
The generated declaration files had imports like `from './twist-api'` instead of
`from './twist-api.js'`, causing module resolution to fail when other packages
tried to re-export types.

## Changes

- **Added `scripts/fix-dts-imports.cjs`**: Post-build script that adds `.js`
  extensions to all relative imports in generated `.d.ts` files
  - Handles `import` statements
  - Handles `export` statements
  - Handles dynamic `import()` type expressions
- **Updated `package.json`**:
  - Added `build:fix-dts` script to run the DTS fixer
  - Updated `build` script to include the fix-dts step
  - Added `attw` script for type validation using `@arethetypeswrong/cli`
  - Updated `integrity-checks` to include `attw` validation

## Verification

**Before fix** (using `@arethetypeswrong/cli --pack`):
- ❌ **InternalResolutionError** - Module resolution failed (breaking bug)

**After fix**:
- ✅ **No problems found** - All module resolution working correctly ⭐
- ✅ Declaration files now have `.js` extensions on all relative imports
- ✅ Type validation passes with `@arethetypeswrong/cli`

## Test Plan

- [x] Build completes successfully with new fix-dts step
- [x] Declaration files now have `.js` extensions on all relative imports
- [x] `@arethetypeswrong/cli` validation passes (no problems found)
- [x] All 166 tests pass without modification
- [x] TypeScript compilation succeeds without errors

Applies same fix as:
- Doist/todoist-api-typescript#410

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: scottlovegrove

package.json

@@ -29,8 +29,9 @@
         "build:cjs": "npx tsc -p tsconfig.cjs.json",
         "build:esm": "npx tsc -p tsconfig.esm.json",
         "build:fix-esm": "node scripts/fix-esm-imports.cjs",
+        "build:fix-dts": "node scripts/fix-dts-imports.cjs",
         "build:post": "echo '{\"type\":\"commonjs\"}' > dist/cjs/package.json",
-        "build": "npm-run-all clean build:cjs build:esm build:fix-esm build:post",
+        "build": "npm-run-all clean build:cjs build:esm build:fix-esm build:fix-dts build:post",
         "type-check": "npx tsc --noEmit",
         "biome:sort-imports": "biome check --formatter-enabled=false --linter-enabled=false --organize-imports-enabled=true --write .",
         "lint:check": "biome lint",
@@ -39,8 +40,9 @@
         "format:write": "biome format --write",
         "check": "biome check",
         "check:fix": "biome check --fix --unsafe",
+        "attw": "npx @arethetypeswrong/cli --pack --ignore-rules fallback-condition false-esm",
         "audit": "npm audit --audit-level=moderate",
-        "integrity-checks": "npm-run-all clean check test build",
+        "integrity-checks": "npm-run-all clean check test build attw",
         "prepublishOnly": "npm run integrity-checks",
         "prepare": "npm run build"
     },

scripts/fix-dts-imports.cjs

@@ -0,0 +1,125 @@
+#!/usr/bin/env node
+
+const fs = require('node:fs')
+const path = require('node:path')
+
+/**
+ * Post-build script to fix TypeScript declaration file imports by adding .js extensions.
+ * This is required because when package.json has "type": "module", TypeScript treats
+ * .d.ts files as ESM modules, which require explicit file extensions for relative imports.
+ */
+
+const TYPES_DIR = path.join(__dirname, '../dist/types')
+
+function fixImportsInFile(filePath) {
+    let content = fs.readFileSync(filePath, 'utf8')
+    let modified = false
+
+    // Fix relative imports - add .js extension if missing
+    content = content.replace(
+        /from\s+['"](\.[^'"]*?)['"];?/g,
+        (match, importPath) => {
+            // Skip if already has extension or is directory import
+            if (path.extname(importPath) || importPath.endsWith('/')) {
+                return match
+            }
+
+            // Check if this is a directory import (look for index file)
+            const fullPath = path.resolve(path.dirname(filePath), importPath)
+            const indexPath = path.join(fullPath, 'index.d.ts')
+
+            if (fs.existsSync(indexPath)) {
+                // Directory import - add /index.js
+                modified = true
+                return match.replace(importPath, importPath + '/index.js')
+            } else {
+                // File import - add .js
+                modified = true
+                return match.replace(importPath, importPath + '.js')
+            }
+        }
+    )
+
+    // Fix export statements as well
+    content = content.replace(
+        /export\s+(?:\*|\{[^}]*\})\s+from\s+['"](\.[^'"]*?)['"];?/g,
+        (match, importPath) => {
+            // Skip if already has extension or is directory import
+            if (path.extname(importPath) || importPath.endsWith('/')) {
+                return match
+            }
+
+            // Check if this is a directory import (look for index file)
+            const fullPath = path.resolve(path.dirname(filePath), importPath)
+            const indexPath = path.join(fullPath, 'index.d.ts')
+
+            if (fs.existsSync(indexPath)) {
+                // Directory import - add /index.js
+                modified = true
+                return match.replace(importPath, importPath + '/index.js')
+            } else {
+                // File import - add .js
+                modified = true
+                return match.replace(importPath, importPath + '.js')
+            }
+        }
+    )
+
+    // Fix dynamic import() type expressions
+    content = content.replace(
+        /import\(['"](\.[^'"]*?)['"]\)/g,
+        (match, importPath) => {
+            // Skip if already has extension or is directory import
+            if (path.extname(importPath) || importPath.endsWith('/')) {
+                return match
+            }
+
+            // Check if this is a directory import (look for index file)
+            const fullPath = path.resolve(path.dirname(filePath), importPath)
+            const indexPath = path.join(fullPath, 'index.d.ts')
+
+            if (fs.existsSync(indexPath)) {
+                // Directory import - add /index.js
+                modified = true
+                return match.replace(importPath, importPath + '/index.js')
+            } else {
+                // File import - add .js
+                modified = true
+                return match.replace(importPath, importPath + '.js')
+            }
+        }
+    )
+
+    if (modified) {
+        fs.writeFileSync(filePath, content, 'utf8')
+        console.log(`Fixed imports in: ${path.relative(process.cwd(), filePath)}`)
+    }
+}
+
+function walkDirectory(dir) {
+    const files = fs.readdirSync(dir)
+
+    for (const file of files) {
+        const filePath = path.join(dir, file)
+        const stat = fs.statSync(filePath)
+
+        if (stat.isDirectory()) {
+            walkDirectory(filePath)
+        } else if (file.endsWith('.d.ts')) {
+            fixImportsInFile(filePath)
+        }
+    }
+}
+
+function main() {
+    if (!fs.existsSync(TYPES_DIR)) {
+        console.log('Types directory does not exist, skipping declaration file fixing')
+        return
+    }
+
+    console.log('Fixing TypeScript declaration file imports by adding .js extensions...')
+    walkDirectory(TYPES_DIR)
+    console.log('Declaration file import fixing completed')
+}
+
+main()