Function decide 

pub fn decide(
    policy: &Compression,
    types: &CompiledContentTypeFilter,
    status: StatusCode,
    headers: &HeaderMap,
    body_size: Option<u64>,
    accept_encoding: Option<&str>,
) -> Option<CompressionPlan>

Decide whether THIS response gets compressed under the policy (DW-027): status, existing encoding, known size, content type, and negotiation all have to line up. None = pass through (the caller still adds Vary: Accept-Encoding for cache correctness).

types is the policy’s snapshot-compiled content-type filter (see crate::snapshot::RouteTable::compression_types); body_size is the response body’s exact size when known (size_hint().exact() — exact for the gateway’s fully-buffered bodies) so min_size gates bodies that carry no Content-Length header too (respond-action and redirect bodies). None = length unknown (streaming).