Malformed pyproject.toml crashes with a TOMLDecodeError traceback instead of a clear error #893

🤖 A pyproject.toml that doesn't parse produces an uncaught TOMLDecodeError traceback and Internal error, with no user-facing message.

Repro

mkdir p && cd p
printf 'from flask import Flask\napp = Flask(__name__)\n' > app.py
echo flask > requirements.txt
printf '[project\nname = "x"\n' > pyproject.toml
rsconnect write-manifest api .

tomllib.TOMLDecodeError: Expected ']' at the end of a table declaration (at line 1, column 9)
[ERROR]
Internal error: Expected ']' at the end of a table declaration (at line 1, column 9)

This happens even when pyproject.toml isn't the requirements source. The root file is parsed while detecting the Python version requirement (detect_python_version_requirement), before any code that would turn the parse error into a clear message.

Expected

An RSConnectException such as Error reading pyproject.toml: <reason>, with no traceback.

Found during live QA of #892 against Posit Connect. Reproduced on 1.32.0 and current main (0287aca3).