Reject NUL bytes in reviewed terminal input (#41354)

## Why

Manual terminal-input approvals shell-quote the proposed input, which cannot
preserve NUL bytes for an accurate review.

## What changed

Reject terminal input containing a NUL byte before creating an approval request
or sending any of the input to the terminal.

## Testing

Extend the unreviewable-input integration test to cover both oversized input
and NUL-containing input, and verify that rejected input is not executed.

GitOrigin-RevId: e738c59ba5570012663bf6168ad052be237ca226

codex-rs/core/src/unified_exec/stdin_approval.rs

@@ -217,6 +217,12 @@ impl ProcessEntry {
         if sandbox_permissions == SandboxPermissions::UseDefault && !strict_auto_review {
             return Ok(None);
         }
+        // Manual approvals shell-quote the input, which cannot preserve NUL bytes.
+        if input.contains('\0') {
+            return Err(approval_error(
+                "terminal input contains a NUL byte and cannot be reviewed safely",
+            ));
+        }
         let reason = permissions
             .approval_reason(sandbox_permissions)
             .map_err(approval_error)?;