## Summary
Fixes a few things in our exec_policy handling of prefix_rules:
1. Correctly match redirects specifically for exec_policy parsing. i.e.
if you have `prefix_rule(["echo"], decision="allow")` then `echo hello >
output.txt` should match - this should fix#10321
2. If there already exists any rule that would match our prefix rule
(not just a prompt), then drop it, since it won't do anything.
## Testing
- [x] Updated unit tests, added approvals ScenarioSpecs
## Summary
This should rarely, if ever, happen in practice. But regardless, we
should never provide an empty list of `commands` to ExecPolicy. This PR
is almost entirely adding test around these cases.
## Testing
- [x] Adds a bunch of unit tests for this
