The synchronous harness binds mocks as plain NativeFns, so no harness test
could exercise the real CEK perform/suspend/resume path — the HO+perform
element-drop class (S10) was structurally invisible (hosts.md C21).
Add harness-run-perform to spec/harness.sx: drives make-cek-state/
cek-step-loop, services each (perform {:op X :args L}) suspension from the
session's platform mocks (entry logged before invocation, C22-consistent),
cek-resumes with the mock value, loops to terminal; clear error on an
unmocked op. Shared arity dispatch extracted as harness-invoke-mock.
Pins (gate-C21-perform-mode-harness): single suspension, arithmetic-frame
resume, sequential performs, unmocked-op error, and the S10 probe — map
over a perform-suspending lambda keeps ALL 3 elements through 3
suspensions on the CEK path (localizing the drop class to serving-JIT).
290/0 under OCaml run_tests; harness self-suite green.
Caveat (documented): requires the runner's cek-* driver bindings — absent
on bare sx_server/MCP, the same runner-only-binding theme as section B.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
giles
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