## Why
An unfamiliar executable can ignore its arguments, so trust in an apparent
inner command must not implicitly trust the executable that runs it.
## What changed
- Evaluate unfamiliar shell executables alongside their parsed commands when
determining unified exec approval requirements. Inner commands can add
restrictions, but cannot grant trust to the executable.
- Include the executable in reusable approval keys so approval for one custom
shell does not apply to another.
- Parse literal PowerShell scripts without launching the requested executable,
preserving command policy checks before approval.
## Testing
Add cross-platform coverage for spoofed shell paths, allowed and forbidden
inner commands, explicit custom-shell approval, and session approval isolation.
GitOrigin-RevId: 0dd2c7e9a2ac30965ef5fe5de1a8d2968bb5f9d0
## What changed
- Add a Tree-sitter-based lowerer that converts a conservative subset of literal PowerShell commands into argument vectors.
- Reject dynamic expressions, parse recovery, unsupported value conversions, directives, and source outside recognized command nodes instead of guessing their meaning.
- Keep the lowerer alongside the existing production parser for later adoption.
## Testing
- Add fixture-driven coverage for supported literal commands and unsupported or ambiguous syntax, including a dedicated `#requires` rejection test.
GitOrigin-RevId: a6e7acc264ca40df264db4b271e38ae7d89e1ec4
