## Why
Multi-environment turns can run against different filesystems, so a single
thread-wide workspace-root list cannot accurately describe every selected
environment.
## What changed
- Add optional `runtimeWorkspaceRoots` to each app-server environment selection.
Omitted roots default to that environment's `cwd`, while an empty list selects
no roots.
- Carry environment-native roots through turn selection, model-visible context,
permission materialization, and tool sandboxing.
- Keep the top-level `runtimeWorkspaceRoots` field as a compatibility input when
constructing default environment selections; explicit selections use their
own roots.
## Testing
- Cover thread and turn API defaults, overrides, empty roots, and schema
round-tripping.
- Verify foreign roots remain model-visible and remote execution applies the
target environment's roots before sandbox selection.
GitOrigin-RevId: c6e7a62883c45c676c153055f46a55ee15a323a4