Gate ModuleSource provider

Date: 2026-06-10 Area: engine

JavaScript ModuleSource objects are now gated behind --experimental-js-module-source / "experimental-js-module-source" / cfExperimentalJSModuleSource. This keeps Stage 3 source-phase syntax enabled while requiring an explicit opt-in for the Stage 2.7 ESM Phase Imports JavaScript source-object provider; the test262 runner maps source-phase-imports-module-source tests to that flag instead of enabling it for all source-phase-imports tests. language.md. test262.md.