Constant MAX_RETICLE_DOCUMENT_BYTES 

pub const MAX_RETICLE_DOCUMENT_BYTES: usize = _; // 524_288usize

Largest reticle document reticle.import will parse.

The envelope cap (MAX_REQUEST_BYTES) already bounds the whole request, but a document-specific cap gives a caller a message naming the document rather than the envelope, and bounds the parse before it starts. Both formats are TEXT and travel inline — unlike .a7p, which is binary and needs base64 — so there is no inflation factor to leave headroom for.