Validate env -S and --split-string escape syntax before shell scanning or
opaque fallback. Preserve literal single-quoted data and charge each
validation character against the shared input-proportional work budget.
Verified 787 focused cases and 290 real Git/config, harmless native env
and registered-routing controls. Keeps the prior paid-copy protection.
Co-authored-by: Nguyen Thanh Dat <ntdat812.dev@gmail.com>
Co-authored-by: Davemaina1 <dmain7015@gmail.com>