## Why
Extension calls omitted environments whose working directories could not be converted to host-native paths, preventing extensions from receiving those environments.
## What changed
Store `ToolEnvironment.cwd` as `PathUri` and pass all turn environments to extension tools without requiring host-native path conversion. Keep image generation's existing path requirements by selecting the first environment with a convertible working directory when reading referenced images or saving generated images.
GitOrigin-RevId: b4320c6e07d27ef59885cd0013e5d1c535f69659