feat(config): add validation for config file paths and improve error …

[wakonig]

Description

A typo while loading the config can lead to a confusing "NotImplementedError" as the system first checks against the suffix. This PR changes the config loading by verifying that file exists before checking for compatibility. Moreover, it tries to give a more helpful error message by checking yaml and yml files that the user may have wanted to use instead.

Potential side effects

I decided to not automatically load the found config as this could be quite nasty to debug and lead to unexpected results.

Screenshots / GIFs (if applicable)

Examples:

bec.config.update_session_with_file("./bec_lib/bec_lib/tests/test_confi")
>>> DeviceConfigError: Config file 'bec_lib/bec_lib/tests/test_confi' does not exist.

bec.config.update_session_with_file("./bec_lib/bec_lib/tests/test_config")
>>> DeviceConfigError: Config file 'bec_lib/bec_lib/tests/test_config' does not exist. Did you mean 'bec_lib/bec_lib/tests/test_config.yaml'?

bec.config.update_session_with_file("./bec_lib/bec_lib/tests/test_config.yml")
>>> DeviceConfigError: Config file 'bec_lib/bec_lib/tests/test_config.yml' does not exist. Did you mean 'bec_lib/bec_lib/tests/test_config.yaml'?

bec.config.update_session_with_file("./bec_lib/bec_lib/tests/test_confg.yaml")
>>> DeviceConfigError: Config file 'bec_lib/bec_lib/tests/test_confg.yaml' does not exist. Did you mean 'bec_lib/bec_lib/tests/test_config.yaml'?

[Copilot]

🟡 Changes recommended

The new path validation does not ensure the path is a regular file, so a directory named *.yaml/*.yml can slip through and later fail with an unexpected IsADirectoryError instead of a DeviceConfigError.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR improves bec_lib configuration loading error handling by validating config file paths before checking YAML compatibility, and by suggesting likely .yaml/.yml alternatives when the provided path is missing—avoiding the previously confusing NotImplementedError behavior.

Changes:

• Add explicit config-path validation that raises DeviceConfigError with clearer messages (and optional “Did you mean …?” suggestions).
• Add comprehensive unit tests covering unsupported extensions, missing files, suggestion ordering/limits, and error-tolerant directory scanning.

File summaries

File	Description
bec_lib/bec_lib/config_helper.py	Adds path validation + alternative suggestion logic for missing config files.
bec_lib/tests/test_config_helper.py	Adds/extends tests for missing/unsupported config path handling and suggestion behavior.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[Copilot]

🟢 Approval recommended

The changes are coherent, well-tested, and align with the PR’s stated goal of improving config-loading validation and error reporting without introducing breaking cross-service contract changes.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 0 new
• Review effort level: Lite