[BUG] Running a Flower app as a Flare job fails due to bad path to custom dir

[taleinat]

Describe the bug
When running a Flower app as a Flare job, the Flower subprocess fails to find required files (specifically pyproject.toml). This is due to the path to its custom directory being passed incorrectly to the Flower subprocess: The subprocess is run with the "app dir" as is CWD, but the "custom dir" is passed as a relative path which is relative to the Flare client's CWD.

To Reproduce
Steps to reproduce the behavior:

1. Create a project running a Flower app as a Flare job. (versions specified below)
2. Try running a job.
3. See the failure in the client logs.

Expected behavior
The job should initialize successfully rather than crash.

Screenshots
Following is an excerpt from the NVFlare client logs:

[FLWR-CA@my_client] ERROR:     ClientApp raised an exception
[FLWR-CA@my_client] Traceback (most recent call last):
[FLWR-CA@my_client]   File "/venv/lib/python3.12/site-packages/flwr/client/app.py", line 531, in start_client_internal
[FLWR-CA@my_client]     client_app: ClientApp = load_client_app_fn(
[FLWR-CA@my_client]                             ^^^^^^^^^^^^^^^^^^^
[FLWR-CA@my_client]   File "/venv/lib/python3.12/site-packages/flwr/client/clientapp/utils.py", line 67, in _load
[FLWR-CA@my_client]     config = get_project_config(runtime_app_dir)
[FLWR-CA@my_client]              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[FLWR-CA@my_client]   File "/venv/lib/python3.12/site-packages/flwr/common/config.py", line 73, in get_project_config
[FLWR-CA@my_client]     raise FileNotFoundError(
[FLWR-CA@my_client] FileNotFoundError: Cannot find pyproject.toml in /home/localuser/client/bdfbd400-da2f-4853-adf9-eb366e3164b4/app_my_client_1/startup/../bdfbd400-da2f-4853-adf9-eb366e3164b4/app_my_client/custom

Desktop (please complete the following information):

• OS: Ubuntu 22.04
• Python version: 3.12
• NVFlare version: 2.5.1

Additional context
Flower version: 1.12

[chesterxgchen]

thanks Tal