Keep strict parsers compatible with finite documented wire aliases

A strict parser can accept a finite set of documented wire aliases without weakening its trust boundary. Build fixtures independently from each endpoint's contract: reusing one handcrafted representation for both list and detail calls can hide a real compatibility failure. Normalize only the known optional marker, then compare against an exact closed allowlist; pair accepted aliases with near-match negatives. Documentation compatibility and synthetic tests still do not establish the representation returned by a live tenant.

Evidence/example — 2026-09-11: Microsoft's Graph list-attachments example uses microsoft.graph.fileAttachment, while its attachment-get example uses #microsoft.graph.fileAttachment. A synthetic parser check accepting only the latter rejected the former after the metadata read. Four list/detail alias pairs and three invalid near-matches exposed and bounded the correction. Public source provenance: https://learn.microsoft.com/en-us/graph/api/message-list-attachments?view=graph-rest-1.0 and https://learn.microsoft.com/en-us/graph/api/attachment-get?view=graph-rest-1.0. Live Graph behavior was not tested.