Skipper: Incomplete fix for CVE-2026-50197: an oversized body can bypass OPA deny-on-presence Rego policies

### Summary A wrong policy can be an open door. You have to check `input.attributes.request.http.truncated_body` in your policy. ### Description Incomplete fix for CVE-2026-50197: an oversized declared-`Content-Length` body still hands OPA an empty `parsed_body`, so deny-on-presence Rego policies fail OPEN while the full payload reaches upstream. The CVE-2026-50197 fix (commit `3152f3b0`, PR #4041, v0.26.10) substituted `expectedSize = maxBodyBytes` only when `req.ContentLength < 0` (chunked / HTTP/2 without content-length). But when a request declares a `Content-Length` larger than `maxBodyBytes`, `expectedSize > maxBodyBytes`, the body-extraction `if` is skipped entirely, and `ExtractHttpBodyOptionally` returns `rawBodyBytes = nil` — so OPA evaluates an empty `parsed_body`, while the full forbidden payload still flows to the upstream. A deny-on-presence policy (`default allow = true; allow = false if input.parsed_body.`) — the exact Rego shape the advisory describes — fails OPEN. The fix's own comment reasons only about `ContentLength == -1`; the oversized branch was never considered, and the added PoC test only covers small bodies. ### Affected code - `filters/openpolicyagent/openpolicyagent.go` `ExtractHttpBodyOptionally`: the `expectedSize <= maxBodyBytes` gate lets an oversized declared body fall through to `return req.Body, nil, func() {}, nil` (OPA sees an empty document). - Corroborated by Skipper's own unit test "Read body exhausting max bytes" (`{ "welcome": "world