[variablenix]

Summary

• Raise the minimum Go toolchain and the CI/Docker build baseline to Go 1.26.10.
• Document Go 1.27.3 as the patched alternative for the Go 1.27 series.
• Address GO-2026-6809 in the standard library; existing deployments must rebuild and restart to receive the fix.

Validation

• Go 1.26.10: full race suite including offline Chrome fixtures passed.
• go vet ./... passed.
• govulncheck ./...: no vulnerabilities found.
• GitHub checks must pass before merge.
• No runtime configuration or application behavior changes.