Fixed blob id emitted in job controller submission

[aylei]

Tested (run the relevant ones):

• Code formatting: install pre-commit (auto-check on commit) or bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: /smoke-test (CI) or pytest tests/test_smoke.py (local)
• Relevant individual tests: /smoke-test -k test_name (CI) or pytest tests/test_smoke.py::test_name (local)
• Backward compatibility: /quicktest-core (CI) or pytest tests/smoke_tests/test_backward_compat.py (local)

[gemini-code-assist]

Code Review

This pull request implements the propagation of file_mounts_blob_id through the task lifecycle to support server-internal task re-submissions, such as those used by the jobs controller. Key changes include updating the Task class to handle the new attribute during initialization and serialization, extending the task schema, and ensuring the blob ID is preserved when communicating with a local API server. A review comment identified a potential AttributeError in the server-side DAG processing logic when encountering nested DAGs, providing a suggestion to safely check for the attribute before assignment.