## Why
Filesystem policies for remote execution need to interpret paths, home directories, and temporary directories using the execution host's context.
## What changed
- Add context-based read-denial matching, read-access checks, glob resolution, and `PathUri` workspace-write constructors without consulting local paths or environment variables.
- Share managed read-denial validation through `DenyReadValidator` and use it in core configuration, preserving required-entry checks, concrete grant validation, and constraint diagnostics.
- Reject invalid or unresolvable denial paths when constructing a context-based matcher, and apply `/tmp` denials according to the execution host's path convention.
- Preserve workspace-root symbols and protected metadata entries when materializing URI-based writable roots.
## Testing
Add regression tests for POSIX, Windows, and UNC path matching; conflicting read and write grants; malformed or unresolvable denials; `/tmp` handling; and workspace metadata protection.
GitOrigin-RevId: aa2b174288d1172ab52ff485f58d306236d27652
c53f342fec