html-wasm export gives unhelpful error when output is current directory and public/ is non empty

[astrojuanlu]

Describe the bug

As per title.

Environment

{
  "marimo": "0.10.19",
  "OS": "Linux",
  "OS Version": "6.8.0-51-generic",
  "Processor": "x86_64",
  "Python Version": "3.12.3",
  "Binaries": {
    "Browser": "--",
    "Node": "v20.16.0"
  },
  "Dependencies": {
    "click": "8.1.8",
    "docutils": "0.21.2",
    "itsdangerous": "2.2.0",
    "jedi": "0.19.2",
    "markdown": "3.7",
    "narwhals": "1.24.2",
    "packaging": "24.2",
    "psutil": "6.1.1",
    "pygments": "2.19.1",
    "pymdown-extensions": "10.14.3",
    "pyyaml": "6.0.2",
    "ruff": "0.9.4",
    "starlette": "0.45.3",
    "tomlkit": "0.13.2",
    "typing-extensions": "4.12.2",
    "uvicorn": "0.34.0",
    "websockets": "14.2"
  },
  "Optional Dependencies": {},
  "Experimental Flags": {}
}

Code to reproduce

uv venv -p 3.12 && source .venv/bin/activate
uv pip install marimo
marimo edit slides.py

Slides content:

$ cat slides.py
import marimo

__generated_with = "0.10.19"
app = marimo.App(width="medium")


@app.cell
def _():
    import marimo as mo
    return (mo,)


@app.cell
def _(mo):
    mo.md("""# Hello, world!""")
    return


if __name__ == "__main__":
    app.run()

Works:

marimo export html slides.py -o slides.html
marimo export html-wasm slides.py -o slides.wasm.html

Cleanup:

rm -rf *.png *.ico *.json *.webmanifest slides.html slides.wasm.html assets/

Still works:

mkdir public
touch public/foo.txt
mkdir out
marimo export html-wasm slides.py -o out/slides.wasm.html
# Cleanup
rm -r out

Fails:

$ marimo export html-wasm slides.py -o slides.wasm.html
Assets copied to . These assets are required for the notebook to run in the browser.
Traceback (most recent call last):
  File "/tmp/test-marimo-bug/.venv/bin/marimo", line 10, in <module>
    sys.exit(main())
             ^^^^^^
  File "/tmp/test-marimo-bug/.venv/lib/python3.12/site-packages/click/core.py", line 1161, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/test-marimo-bug/.venv/lib/python3.12/site-packages/click/core.py", line 1082, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/tmp/test-marimo-bug/.venv/lib/python3.12/site-packages/click/core.py", line 1697, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/test-marimo-bug/.venv/lib/python3.12/site-packages/click/core.py", line 1697, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/test-marimo-bug/.venv/lib/python3.12/site-packages/click/core.py", line 1443, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/test-marimo-bug/.venv/lib/python3.12/site-packages/click/core.py", line 788, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/test-marimo-bug/.venv/lib/python3.12/site-packages/marimo/_cli/export/commands.py", line 471, in html_wasm
    did_export_public = Exporter().export_public_folder(out_dir, marimo_file)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/test-marimo-bug/.venv/lib/python3.12/site-packages/marimo/_server/export/exporter.py", line 396, in export_public_folder
    shutil.copytree(
  File "/usr/lib/python3.12/shutil.py", line 600, in copytree
    return _copytree(entries=entries, src=src, dst=dst, symlinks=symlinks,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/shutil.py", line 554, in _copytree
    raise Error(errors)
shutil.Error: ['<', 'D', 'i', 'r', 'E', 'n', 't', 'r', 'y', ' ', "'", 'f', 'o', 'o', '.', 't', 'x', 't', "'", '>', ' ', 'a', 'n', 'd', ' ', "'", 'p', 'u', 'b', 'l', 'i', 'c', '/', 'f', 'o', 'o', '.', 't', 'x', 't', "'", ' ', 'a', 'r', 'e', ' ', 't', 'h', 'e', ' ', 's', 'a', 'm', 'e', ' ', 'f', 'i', 'l', 'e']