Mux — lessons for Forge

Sources checked 2026-09-10:

• https://github.com/coder/mux
• https://github.com/coder/mux/blob/main/docs/config/policy-file.mdx

The upstream repository may rename/redirect; verify current location when implementing from source.

Observed source lessons

Mux policy configuration describes multiple runtime IDs such as local, worktree, SSH, Docker, and devcontainer. Its policy behavior is fail-closed in an important sense: when refreshed policy disallows a currently selected provider/model/runtime, it blocks rather than silently auto-switching.

Forge decisions influenced

• Agent Adapter and Execution Environment are independent axes;
• semantic policy/capability failures should be explicit;
• no silent fallback to a weaker provider strategy/runtime;
• future runtime extensibility can be designed as an internal interface before a public plugin system exists.