execution.backend: remote dispatches each experiment to a detached worker
with its own checkout, on a harness whose dispatch returns a receipt and
lands its work as a pushed ref or store file (the third capability
condition in the body's Execution Surface; without it the run uses
worktree). The worker verifies base_sha, implements inside scope.mutable,
measures baseline and candidate paired on its own machine, writes
result.yaml, and pushes optimize-exp/<spec>/exp-NNN. The orchestrator
accepts a result only when base_sha matches and the range touches only
mutable scope, runs decide.mjs on the worker's pair, and before any keep
obtains a confirmation pairing the candidate's author did not produce.
remote requires a paired or relative comparison; the parallel probe and
worktree budget do not apply to it. Log schema gains comparisons[].machine,
measured_by, and the result.yaml shape.
Co-authored-by: Kieran Klaassen <kieranklaassen@users.noreply.github.com>
