Improve dag error handling

[Yusin0903]

Improve error handling for DAG access in API endpoints

This PR improves error handling when accessing DAGs via API endpoints:

• Add consistent error handling for DAG access across API endpoints
• Handle ImportError and SyntaxError with 422 status code and clear error messages
• Handle generic exceptions with 500 status code
• Provide clear error messages for different failure scenarios
• Update API documentation to include new error response codes
• Add comprehensive tests for error handling scenarios

This change ensures users get clear feedback when DAGs fail to load due to import errors, syntax errors, or other unexpected issues.

closes: #48960

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[pierrejeambrun]

Don't hesitate to directly resolve comments you've addressed so we know easily what's left to focus on.

[Yusin0903]

The main problem of this is it will really handle only a precise deserialization errror => dag_id is missing from the encoded dag.

Any other undexpected error in the deserialization process, will just crash and not provide any specific feedback.

I think we shoul catch everything in SerializedDAG.deserialize_dag and raise based on the exception a new custom DeserializationError.

Then all those deserialization errors can be catch on the API side and provide a relevant feedback.

Hi @pierrejeambrun, Thanks for the review. I’ve raised a custom DeserializationError and handled it in SerializedDAG.deserialize_dag. I also noticed the new dependency DagBagDep, and I’ve merged it into get_dag_from_dag_bag.

[Yusin0903]

Hi @pierrejeambrun, Thanks for the review and suggestion. I have catched all the Runtime error in the DeserializationError and simplify the dag_bag.get_dag handle.

[phanikumv]

@Yusin0903 just checking to see if you got a chance to work on the review comments?

[Yusin0903]

@phanikumv Thanks for the reminder! I’ve been a bit tied up, but I’ll make sure to complete the review comments shortly.

[uranusjr]

Looks good to me except for one question above

[Lee-W]

mostly good, a few minor improvements left

[Lee-W]

some changes have been made in the main branches. During fixing those, I also rewrote the test cases. no need for a new PR

[boring-cyborg[bot]]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.