bundle-source strips comments from type.js files?

[dckc]

Describe the bug

bundle-source reduces several types.js files to more or less an empty module.

@endo/marshal-v0.8.5/src/types.js
@endo/pass-style-v0.1.3/src/types.js
@endo/patterns-v0.2.2/src/types.js
@endo/promise-kit-v0.2.56/src/types.js
@endo/zip-v0.2.31/src/types.js

Steps to reproduce

1. bundle a file such as marshal/src/types.js using yarn bundle-source --cache-json /tmp/bx src/types.js x
2. Note that it has non-trivial type declarations in it: grep EncodingUnion src/types.js
3. Note that the bundled version does not:
   1. jq -r .endoZipBase64 /tmp/bx/bundle-x.json| base64 -d >,x.zip
   2. unzip ,x.zip
   3. grep EncodingUnion @endo/marshal-v0.8.8/src/types.js

Expected behavior

Contents of source files should be substantially preserved, including comments.

Platform environment

ubuntu linux 22.04.3 LTS
node v18.17.1
endo version 1e2be8eaa @endo/base64@0.2.34-129-g1e2be8eaa
which is the same as c2b3905 except for some unrelated files

also tested on master 877be98

Additional context

contents of the file as well as length (308 bytes) and sha512:

$ cat @endo/marshal-v0.8.8/src/types.js 
{"imports":[],"exports":[],"reexports":[],"__syncModuleProgram__":"(({   imports: $h‍_imports,   liveVar: $h‍_live,   onceVar: $h‍_once,   importMeta: $h‍____meta,  }) => {   $h‍_imports([]);   \n})\n","__liveExportMap__":{},"__reexportMap__":{},"__fixedExportMap__":{},"__needsImportMeta__":false}

$ wc -c @endo/marshal-v0.8.8/src/types.js 
308 @endo/marshal-v0.8.8/src/types.js

$ sha512sum @endo/marshal-v0.8.8/src/types.js 
98a851bdbf2f4dd09a13b521130e299f9d1955ae19291627cd28df4fb5d4878ecdf7ce2b22a5670b4397bf490b80d8982481db5ceb224b10afdefe5c44506265  @endo/marshal-v0.8.8/src/types.js

[dckc]

a bit more context: I'm prototyping bundleParts.js, a tool to exclude already-loaded parts of a bundle, as an exploration into...

• share Zoe/ERTP libraries among contracts Agoric/agoric-sdk#2391

See also:

• Bundle Explorer (prototype) shows modules, sizes from InstallBundle tx Agoric/agoric-sdk#8416