Fix round 2 for task 1: store-codegen.ts stopped emitting runtime:
"legacy" actions in round 1, making the StoreRuntime variant and its
resolution fallback dead. Narrows StoreRuntime to three variants and
adds a regression test for the remaining options.runtime -> shared
fallback chain.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>