Path shape: literals kept, variables erased to {} (keys on shape, not on var spelling).
Sorted query key-set (order/repetition-insensitive).
Canonical media type, or "*" if absent (does-not-participate).
Participating header names (lowercased, sorted); "*" sentinel if none (best-effort, #108).
Stable id of the request-body schema: its $ref, the "#inline" SENTINEL (inline shape stays OUT of the key — D1/§A.2), or "*".
Canonical signature tuple (C019 §A.2). The ADA's identity of a request; the matcher/collision key.