Extract step resource package from pkg/runner

Cameron Swordsrequested to merge
cswords/step-resource-package-design into main

Summary

Move step resource implementations from pkg/runner/ into a new pkg/runner/resource/ subpackage and drop the stuttering StepResource suffix from the type names (FileSystemStepResource → File, StepResourceParser → Parser, etc.). DI accessor renamed StepResourceParser() → ResourceParser(). pkg/runner now exposes only the runtime contract; the concrete loaders live in the subpackage. Behavior unchanged.

Split across three commits for reviewability: (1) relocate with filenames and type names preserved, (2) rename types and files, (3) update architecture doc.

Assumptions & Decisions
  • Struct literal → public constructor. In function.go, the old struct literal set FunctionDescriptor's unexported fields — unreachable from outside pkg/runner. Swapped for runner.NewFunctionDescriptor(spec, def, ""). Behaviorally identical.
  • pkg/testutil/bldr/fixed_step_resource_builder.go untouched — its internal duplicate of FixedStepResource is out of scope.

Merge request reports