Unhelpful error message when running Kontrol with invalid `FOUNDRY_PROFILE`

Like Foundry, Kontrol uses the FOUNDRY_PROFILE environment variable to select a profile from foundry.toml. However, if FOUNDRY_PROFILE is set to a profile that doesn't exist (for example, it might have been set for a different project and the user forgot to unset it), Kontrol throws an exception with an unhelpful error message (the example below has FOUNDRY_PROFILE=k):

Traceback (most recent call last):
  File "/nix/store/2crjmyp0v36djwj0bpg0q1mjqxj2iq34-python3.10-kontrol-0.1.76/bin/.kontrol-wrapped", line 9, in <module>
    sys.exit(main())
  File "/nix/store/2crjmyp0v36djwj0bpg0q1mjqxj2iq34-python3.10-kontrol-0.1.76/lib/python3.10/site-packages/kontrol/__main__.py", line 75, in main
    execute(**vars(args))
  File "/nix/store/2crjmyp0v36djwj0bpg0q1mjqxj2iq34-python3.10-kontrol-0.1.76/lib/python3.10/site-packages/kontrol/__main__.py", line 157, in exec_build
    foundry_kompile(
  File "/nix/store/2crjmyp0v36djwj0bpg0q1mjqxj2iq34-python3.10-kontrol-0.1.76/lib/python3.10/site-packages/kontrol/kompile.py", line 44, in foundry_kompile
    foundry_requires_dir = foundry.kompiled / 'requires'
  File "/nix/store/2crjmyp0v36djwj0bpg0q1mjqxj2iq34-python3.10-kontrol-0.1.76/lib/python3.10/site-packages/kontrol/foundry.py", line 84, in kompiled
    return self.out / 'kompiled'
  File "/nix/store/2crjmyp0v36djwj0bpg0q1mjqxj2iq34-python3.10-kontrol-0.1.76/lib/python3.10/site-packages/kontrol/foundry.py", line 72, in out
    return self._root / self.profile.get('out', '')
  File "/nix/store/2crjmyp0v36djwj0bpg0q1mjqxj2iq34-python3.10-kontrol-0.1.76/lib/python3.10/site-packages/kontrol/foundry.py", line 68, in profile
    return self._toml['profile'][profile_name]
  File "/nix/store/74rhjn329qvln8pqgqcrplj3hdp0xs6n-python3.10-tomlkit-0.11.8/lib/python3.10/site-packages/tomlkit/items.py", line 1484, in __getitem__
    return cast(Item, self._value[key])
  File "/nix/store/74rhjn329qvln8pqgqcrplj3hdp0xs6n-python3.10-tomlkit-0.11.8/lib/python3.10/site-packages/tomlkit/container.py", line 613, in __getitem__
    raise NonExistentKey(key)
tomlkit.exceptions.NonExistentKey: 'Key "k" does not exist.'

To fix this, the user needs to run unset FOUNDRY_PROFILE or export FOUNDRY_PROFILE=default to revert back to the default profile, or set it to a different existing profile. But this is not clear from the error message, and if the profile name is not particularly unique, the user might not even realize that this is what is causing the error. This exception should be caught within Kontrol and handled to return a more informative message.

Start in kontrol/foundry.py at the profile property and trace its use from kontrol/kompile.py and kontrol/main.py. Reproduce the failure with an invalid FOUNDRY_PROFILE; done means Kontrol reports that the selected profile does not exist and explains how to choose or restore an existing profile.