Function compile_streaming_query 

pub fn compile_streaming_query(
    sql: &str,
    plan: &LogicalPlan,
    cache: &mut CompilerCache,
    config: &QueryConfig,
) -> Result<Option<CompiledStreamingQuery>, CompileError>

Attempts to compile a DataFusion [LogicalPlan] into a StreamingQuery.

Returns Ok(None) when the plan contains stateful operators (aggregations, sorts, joins) that cannot be compiled — the caller should fall back to DataFusion interpreted execution.

Returns Ok(Some(compiled)) with a ready-to-start StreamingQuery, the source scan plan for DataFusion to execute, and the input/output schemas for RecordBatch ↔ EventRow conversion.

Errors

Returns CompileError only on hard failures (e.g., Cranelift context initialization failure, or the plan has no source scan). Soft failures (unsupported expressions) result in fallback pipelines within the query.