[zzwong]

Summary

• Select Go 1.27.4 using the module toolchain directive.
• Preserve the existing go language minimum and dependency graph.
• Update direct setup-go v5 calls to the shared automation's immutable v6.5.0 pin, which reads the toolchain directive.

Validation

• Passed git diff --check and static verification of the toolchain selection paths.
• Build, test, lint, and module-tidiness checks were not run locally: this execution environment has no Go compiler. CI must validate this draft before merge.
• No release, merge, deployment, or existing package-rollout PR changes.