Replace DagBag from global app state to with FastAPI dependency

[kaxil]

This change replaces the usage of app.state.dag_bag with a proper FastAPI dependency for better dependency injection and testability. The DagBag is now provided through a dependency that can be easily mocked in tests and follows FastAPI best practices as mentioned here.

• Explicit Dependencies: Using DagBagDep makes it clear in the function signature what each endpoint needs, rather than hiding the dependency in app.state.
• Better Testing: Dependencies can be easily mocked (via FastAPI's dependency_overrides) in tests without modifying app state, making unit testing simpler and more reliable.
• Request Isolation: Each request gets its own DagBag instance through the dependency, preventing any potential state leakage between requests.
• Type Safety: The dependency system provides better type checking and IDE support compared to accessing app.state.

This will help me have better dependency injection in #50300

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[bugraoz93]

Love it. Handling this with annotated depends is a great idea and follows the best practices. Not loading the request each time we need DagBag is already great for security measures and prevents leakage, as mentioned. Only CI and tests need some care

[kaxil]

Love it. Handling this with annotated depends is a great idea and follows the best practices. Not loading the request each time we need DagBag is already great for security measures and prevents leakage, as mentioned. Only CI and tests need some care

CI is green now 🎉

[jason810496]

Thanks! Having DagBag provided via FastAPI Depends is indeed much easier to trace than using the global app state.

[jason810496]

Follow up:

For the Auth Manager, should we also consider replacing the use of the global app state with FastAPI Depends?
Currently, init_auth_manager just sets the Auth Manager on the global app state.

[amoghrajesh]

Much cleaner, thank you!

[kaxil]

Follow up:

For the Auth Manager, should we also consider replacing the use of the global app state with FastAPI Depends? Currently, init_auth_manager just sets the Auth Manager on the global app state.

Yeah, go for it

[ashb]

cc @kaxil