Validate Mcp-Param-* headers server-side on the 2026-07-28 HTTP path (SEP-2243) (#3033)

.github/actions/conformance/expected-failures.2026-07-28.yml

@@ -26,6 +26,3 @@ server:
   # SEP-2575 subscriptions/listen is not implemented yet; see the matching
   # entry in expected-failures.yml for the full rationale.
   - server-stateless
-  # SEP-2243 Mcp-Param-* server-side validation is not implemented yet; see
-  # the matching entry in expected-failures.yml for the full rationale.
-  - http-custom-header-server-validation

.github/actions/conformance/expected-failures.yml

@@ -23,13 +23,6 @@ server:
   # failures in the scenario's other 25 (currently passing) checks — the
   # baseline is per-scenario, not per-check.
   - server-stateless
-  # SEP-2243 Mcp-Param-* server-side validation is not implemented yet. The
-  # everything-server's `test_x_mcp_header` tool arms these checks (without an
-  # x-mcp-header-annotated tool the harness skips all of them silently); the
-  # accept-path checks pass, the reject-path checks fail until the server
-  # validates Mcp-Param headers against body params. Read by the draft leg and
-  # the bare `--suite all` leg; the 2026-07-28 leg carries its own entry.
-  - http-custom-header-server-validation
   # SEP-2663 (io.modelcontextprotocol/tasks): the SDK does not implement the
   # tasks extension yet. These extension-tagged scenarios are selected only by
   # the bare `--suite all` leg — extension scenarios never match a