Add require_approval preflight check to @task.llm_schema_compare

[ColtenOuO]

Sumarry

@task.llm, @task.llm_branch, and @task.llm_sql all reject a non-string Sequence[UserContent] prompt combined with require_approval=True before the LLM ever runs, raising a TypeError that names the decorator the caller actually used (e.g. @task.llm_branch: ...).

@task.llm_schema_compare was missing this decorator-level check. The same misuse still fails before any LLM call (the underlying operator has its own fallback guard), but the error instead names the internal _LLMSchemaCompareDecoratedOperator class -- an implementation detail the caller never wrote, which is confusing when debugging.

This adds the same reject_sequence_with_unsupported_feature preflight call that the other three decorators already use, so all four give a consistent, decorator-named error message.

Reproduce

Reproduced by running two tasks against the same misuse (require_approval=True with a Sequence[UserContent] prompt) -- one via @task.llm_branch, one via @task.llm_schema_compare -- and comparing the task logs.

from __future__ import annotations

from pydantic_ai.messages import ImageUrl

from airflow.providers.standard.operators.empty import EmptyOperator
from airflow.sdk import DAG, task

with DAG(
    dag_id="demo_require_approval_inconsistency",
    schedule=None,
    catchup=False,
):

    @task.llm_branch(
        llm_conn_id="demo_llm_conn",
        require_approval=True,
    )
    def branch_with_bad_prompt():
        return ["Compare these schemas:", ImageUrl(url="https://example.com/x.png")]

    @task.llm_schema_compare(
        llm_conn_id="demo_llm_conn",
        db_conn_ids=["demo_db_conn_a", "demo_db_conn_b"],
        table_names=["demo_table"],
        require_approval=True,
    )
    def schema_compare_with_bad_prompt():
        return ["Compare these schemas:", ImageUrl(url="https://example.com/x.png")]

    branch_with_bad_prompt() >> EmptyOperator(task_id="downstream_placeholder")
    schema_compare_with_bad_prompt()

Before this change:

INFO - Failure caused by _LLMSchemaCompareDecoratedOperator: require_approval=True is not supported with a non-string prompt (got list). The approval review body renders the prompt as text; passing a Sequence[UserContent] would expose object reprs (and any embedded bytes) in the human review UI. Return a str prompt, or disable require_approval.
INFO - Failure caused by @task.llm_branch: Sequence[UserContent] prompts are not supported with require_approval=True. Return a str prompt, or disable require_approval.

Note the first line names _LLMSchemaCompareDecoratedOperator -- an internal class the caller never wrote -- while the second names @task.llm_branch, the decorator actually used.

After this change:

The same misuse via @task.llm_schema_compare instead raises:

@task.llm_schema_compare: Sequence[UserContent] prompts are not supported with require_approval=True. Return a str prompt, or disable require_approval.

now consistent with the other three decorators.

[gopidesupavan]

no harm having this check, but does anyone really uses images to compare schema 🤔 :)

[ColtenOuO]

no harm having this check, but does anyone really uses images to compare schema 🤔 :)

Yeah... I don't think anyone would actually do this either, but since users can somehow pull off such crazy edge cases, I figured we might as well keep the error feedback consistent across all four decorators 🤣...