[muxx]

Summary

• update the pinned local and code generation toolchain from Node.js 22.18.0 to Node.js 26.12.1
• run CI, deterministic code generation, package builds, and npm publishing on Node.js 26
• keep the explicitly pinned npm 11.19.0 trusted-publishing client unchanged

Validation

• built agentbox-sdk-codegen and verified node --version reports v26.12.1
• make generate with no generated diff
• formatting, lint, type checking, and all JS/Python/CLI tests
• full Go checks, race tests, coverage, and consumer test
• release package build, public artifact validation, checksum validation, and clean npm/Python install smoke tests