add comment explaining inline esbuild plugin

Signed-off-by: Karthik Ganeshram <[email protected]>

Author: karthik2804

packages/build-tools/src/precompile.js

@@ -62,7 +62,6 @@ export function precompile(source, filename = '<input>', moduleMode = false, pre
 
     const precompiledSource = magicString.toString() + `\n//# sourceMappingURL=${precompiledFileName}.map\n`;
 
-    // When we're ready to pipe in source maps:
     const map = magicString.generateMap({
         source: filename,
         file: `${precompiledFileName}.map`,

test/test-app/build.mjs

@@ -6,6 +6,10 @@ import fs from 'fs';
 
 const spinPlugin = await SpinEsbuildPlugin();
 
+// plugin to handle vendor files in node_modules that may not be bundled.
+// Instead of generating a real source map for these files, it appends a minimal
+// inline source map pointing to an empty source. This avoids errors and ensures
+// source maps exist even for unbundled vendor code.
 let SourceMapPlugin = {
     name: 'excludeVendorFromSourceMap',
     setup(build) {