Go 1.27 allows promoted fields in composite literals, meaning that when a struct type embeds another, the embedding struct's fields can be set directly in the outer literal without nesting a redundant by-value wrapper. Several composite literals in the runtime and config packages were still using the old style — wrapping an embedded Config or SubSessionConfig with an explicit field name even though the fields it contains are directly promoted.

This change replaces those redundant wrapper layers with direct promoted-field assignment across five files: pkg/config/runtime_test.go, pkg/config/runtime_clone_test.go, pkg/runtime/agent_delegation.go, pkg/runtime/agent_delegation_test.go, and pkg/runtime/skill_runner.go. All expressions, evaluation order, nil and zero values are preserved exactly. No frozen versioned config packages (pkg/config/v0, pkg/config/v1, …) are touched.

This is a targeted, explicit migration of the five files identified in the Go 1.27 review, not a repository-wide go fix run. Lint settings are unchanged. Two test cases (TestLoadExamples/../../examples/dmr.yaml and unload_on_switch.yaml) were skipped during the final test run because Docker Model Runner is not running locally; the identical failures reproduce on the unmodified base commit 6929d9c13, confirming they are pre-existing environment constraints unrelated to this change.