docs: clarify single package build instructions in CLAUDE.md

Author: marcj

CLAUDE.md

@@ -94,29 +94,27 @@ npm run clean        # Clean artifacts
 
 **Important:** After modifying TypeScript source files, run `tsc --build` (or `npm run tsc`) to compile the changes before running tests. Tests execute the compiled JavaScript in `dist/`, not the TypeScript source directly.
 
-### Package Build Structure
+### Building a Single Package
 
-Each package has a dual build output:
+To build a specific package (e.g., `@deepkit/bson`) from the repo root:
 
-- `dist/cjs/` - CommonJS build (from `tsconfig.json`)
-- `dist/esm/` - ES Modules build (from `tsconfig.esm.json`)
+```bash
+npx tsc --build packages/bson/tsconfig.json packages/bson/tsconfig.esm.json
+cd packages/bson && npm run build
+```
 
-**CRITICAL:** Each package's `npm run build` script creates a `dist/esm/package.json` with `{"type": "module"}` to enable ES modules. If you delete `dist/` manually, you MUST run `npm run build` in that package to recreate this file, otherwise ES module imports will fail.
+The order matters:
+1. `tsc --build` compiles TypeScript and creates the `dist/` directories
+2. `npm run build` creates `dist/esm/package.json` for ES module support
 
-```bash
-# If you deleted dist/ in a package, run:
-cd packages/<package-name> && npm run build
+### Package Build Structure
 
-# Or rebuild everything:
-npm run build
-```
+Each package has a dual build output:
 
-**When rebuilding a single package:** Always build both tsconfig files:
+- `dist/cjs/` - CommonJS build (from `tsconfig.json`)
+- `dist/esm/` - ES Modules build (from `tsconfig.esm.json`)
 
-```bash
-npm run tsc -- --build packages/core/tsconfig.json packages/core/tsconfig.esm.json
-cd packages/core && npm run build  # Creates dist/esm/package.json
-```
+**CRITICAL:** The `npm run build` script in each package creates `dist/esm/package.json` with `{"type": "module"}`. This file is required for ES module imports to work. If you delete `dist/` manually, you MUST run `npm run build` to recreate it.
 
 ## Architecture Overview