[approval_policy] Add OnRequest approval_policy (#1865)

## Summary
A split-up PR of #1763 , stacked on top of a tools refactor #1858 to
make the change clearer. From the previous summary:

> Let's try something new: tell the model about the sandbox, and let it
decide when it will need to break the sandbox. Some local testing
suggests that it works pretty well with zero iteration on the prompt!

## Testing
- [x] Added unit tests
- [x] Tested locally and it appears to work smoothly!

codex-rs/core/src/safety.rs

@@ -11,7 +11,7 @@ use crate::is_safe_command::is_known_safe_command;
 use crate::protocol::AskForApproval;
 use crate::protocol::SandboxPolicy;
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq)]
 pub enum SafetyCheck {
     AutoApprove { sandbox_type: SandboxType },
     AskUser,
@@ -31,7 +31,7 @@ pub fn assess_patch_safety(
     }
 
     match policy {
-        AskForApproval::OnFailure | AskForApproval::Never => {
+        AskForApproval::OnFailure | AskForApproval::Never | AskForApproval::OnRequest => {
             // Continue to see if this can be auto-approved.
         }
         // TODO(ragona): I'm not sure this is actually correct? I believe in this case
@@ -76,6 +76,7 @@ pub fn assess_command_safety(
     approval_policy: AskForApproval,
     sandbox_policy: &SandboxPolicy,
     approved: &HashSet<Vec<String>>,
+    with_escalated_permissions: bool,
 ) -> SafetyCheck {
     // A command is "trusted" because either:
     // - it belongs to a set of commands we consider "safe" by default, or
@@ -96,12 +97,13 @@ pub fn assess_command_safety(
         };
     }
 
-    assess_safety_for_untrusted_command(approval_policy, sandbox_policy)
+    assess_safety_for_untrusted_command(approval_policy, sandbox_policy, with_escalated_permissions)
 }
 
 pub(crate) fn assess_safety_for_untrusted_command(
     approval_policy: AskForApproval,
     sandbox_policy: &SandboxPolicy,
+    with_escalated_permissions: bool,
 ) -> SafetyCheck {
     use AskForApproval::*;
     use SandboxPolicy::*;
@@ -113,9 +115,23 @@ pub(crate) fn assess_safety_for_untrusted_command(
             // commands.
             SafetyCheck::AskUser
         }
-        (OnFailure, DangerFullAccess) | (Never, DangerFullAccess) => SafetyCheck::AutoApprove {
+        (OnFailure, DangerFullAccess)
+        | (Never, DangerFullAccess)
+        | (OnRequest, DangerFullAccess) => SafetyCheck::AutoApprove {
             sandbox_type: SandboxType::None,
         },
+        (OnRequest, ReadOnly) | (OnRequest, WorkspaceWrite { .. }) => {
+            if with_escalated_permissions {
+                SafetyCheck::AskUser
+            } else {
+                match get_platform_sandbox() {
+                    Some(sandbox_type) => SafetyCheck::AutoApprove { sandbox_type },
+                    // Fall back to asking since the command is untrusted and
+                    // we do not have a sandbox available
+                    None => SafetyCheck::AskUser,
+                }
+            }
+        }
         (Never, ReadOnly)
         | (Never, WorkspaceWrite { .. })
         | (OnFailure, ReadOnly)
@@ -264,4 +280,47 @@ mod tests {
             &cwd,
         ))
     }
+
+    #[test]
+    fn test_request_escalated_privileges() {
+        // Should not be a trusted command
+        let command = vec!["git commit".to_string()];
+        let approval_policy = AskForApproval::OnRequest;
+        let sandbox_policy = SandboxPolicy::ReadOnly;
+        let approved: HashSet<Vec<String>> = HashSet::new();
+        let request_escalated_privileges = true;
+
+        let safety_check = assess_command_safety(
+            &command,
+            approval_policy,
+            &sandbox_policy,
+            &approved,
+            request_escalated_privileges,
+        );
+
+        assert_eq!(safety_check, SafetyCheck::AskUser);
+    }
+
+    #[test]
+    fn test_request_escalated_privileges_no_sandbox_fallback() {
+        let command = vec!["git".to_string(), "commit".to_string()];
+        let approval_policy = AskForApproval::OnRequest;
+        let sandbox_policy = SandboxPolicy::ReadOnly;
+        let approved: HashSet<Vec<String>> = HashSet::new();
+        let request_escalated_privileges = false;
+
+        let safety_check = assess_command_safety(
+            &command,
+            approval_policy,
+            &sandbox_policy,
+            &approved,
+            request_escalated_privileges,
+        );
+
+        let expected = match get_platform_sandbox() {
+            Some(sandbox_type) => SafetyCheck::AutoApprove { sandbox_type },
+            None => SafetyCheck::AskUser,
+        };
+        assert_eq!(safety_check, expected);
+    }
 }