[ndonkoHenri]

When a command run by package failed, serious_python printed only that command's stderr, and its stdout was shown only with --verbose. Some tools report errors on stdout: python -m compileall prints a file's SyntaxError there and leaves stderr empty. So when an app had a .py file that doesn't compile, flet build failed with "Error building Flet app - see the log of failed command above." and nothing above it, unless it ran with -vv, the only level at which it passes --verbose. Dependencies hadn't been installed yet at that point, which is what flet-dev/flet#7029 reported as an empty site-packages.

Change

runExec now keeps the command's stdout when --verbose is off. If the command fails, it writes that stdout to stderr, then the command's stderr, then flushes before exit(1), which doesn't wait for pending writes.

• Successful commands: their output still isn't printed, so builds are as quiet as before.
• --verbose: unchanged; stdout is still shown as it arrives.
• The failing command line isn't printed: pip index URLs can carry credentials.

flet build already prints the package command's stderr when it fails, at every verbosity, so on the Flet side only the template's serious_python pin needs bumping.

Bumps every package to 6.1.3.

Testing

On macOS, dart run serious_python:main package on a Flet app whose helper.py contains def broken(::

• Before (via flet build macos -v with flet 1.0.5 / serious_python 5.0.0): the log ends at the compileall line; no error is shown.
• After, without --verbose: stderr shows the file, line 1 and SyntaxError: invalid syntax.
• After, with --verbose: same output as before.
• After, valid app: compileall and pip write nothing to stderr.
• dart analyze bin reports no issues; dart format makes no changes.

Fixes flet-dev/flet#7029