Constant TEST_BODY_READ_CAP 

pub const TEST_BODY_READ_CAP: usize = HTTP_BODY_LIMIT_BYTES; // 2_097_152usize

F-B6 — test-side body read cap; pinned equal to the production limit so tests exercise the full 0..=2 MiB envelope production accepts (was an asymmetric 1 MiB across 90+ to_bytes(.., 1024 * 1024) call sites).