Add airflow dags stability check CLI command

[202201142]

Add a new CLI command to detect non-deterministic DAG serialization by parsing and serializing DAGs twice and comparing the resulting hashes.

Non-deterministic DAG definitions can cause unnecessary dag_version changes, making deployments and code reviews harder. This command helps identify such DAGs and can be used in CI/CD to catch serialization instability before merging.

If the serialized hash differs between parses for the DAG, the command reports the differences between the serialized representations and exits with status code 1.

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[Copilot]

Pull request overview

This pull request introduces a new airflow dags stability CLI subcommand intended to detect unstable Dag serialization across repeated parses (a potential contributor to dag_version inflation). It wires the command into the CLI configuration, adds unit tests to validate pass/fail behavior, and updates the FAQ to mention the new workflow option.

Changes:

• Add dag_stability_check implementation that parses Dags twice and reports differing serialization via unified diffs.
• Register a new airflow dags stability [dag_folder] command and --fail-fast flag in the CLI.
• Add unit tests covering stable/unstable Dags and missing --dag-id handling, plus a small FAQ update.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
airflow-core/src/airflow/cli/commands/dag_command.py	Implements Dag stability check helpers and the new CLI action.
airflow-core/src/airflow/cli/cli_config.py	Adds CLI args and registers the new dags stability command.
airflow-core/tests/unit/cli/commands/test_dag_command.py	Adds unit tests validating stability check success/failure behavior.
airflow-core/docs/faq.rst	Mentions the new CLI command as an additional way to catch Dag version inflation issues.