Replaces the salvaged tests' dict-config path (which required a
GatewayRunner.__init__ dict-coercion hack — dropped from this salvage;
the second commit on the PR branch existed only to support it) with the
established bare-runner test pattern. Also asserts full argument
passthrough to the inner task.
When multiplex_profiles is true, background tasks spawned by /background
command failed with UnscopedSecretError because _resolve_session_agent_runtime()
was called without a profile secret scope. This fix wraps the task in
_profile_runtime_scope, mirroring the pattern used by _run_agent.
Fixes#60726
Teknium