`direnv` / `flake.nix` environment is not propagated to agent sessions

[sgiath]

I’m using direnv together with flake.nix to provide project-local dependencies automatically when entering a directory.

This setup works as expected in:

• terminal-based agents
• Cursor
• Zed

But when I run t3code, the agent behaves as if those dependencies are not available in the project environment.

For example, tools/binaries made available through direnv are visible in my shell, but the T3 Code agent reports that they are missing:

Expected behavior

• T3 Code should use the environment for the target project/worktree directory
• if a project relies on direnv + flake.nix, the agent should see the same dependencies that are available in a normal shell inside that directory

Actual behavior

• T3 Code appears to inherit only the parent process environment
• workspace-local environment activation does not seem to happen for the agent session

Notes

• My guess is that this may also affect other environment managers with similar behavior, such as asdf, mise, nix develop, etc.
• I suspect the issue is that changing cwd alone is not enough; tools like direnv require explicit environment activation for that directory

Example project

Here is one of my projects that uses this setup: https://github.com/sgiath/nostr

[Eriyc]

+1 on this. I have exactly this use case as well

[sgiath]

@Eriyc I have added this to my global Codex AGENTS.md and it mostly solved any problems with this kind of setup:

## NixOS

This is a NixOS system. Many projects use `flake.nix`; when project-specific tools are missing, prefer `nix develop -c <command>`. If `direnv` has already loaded the dev shell, run commands normally.