Defeats split-and-substitute evasion where attackers split a destructive
command name across an assignment and a variable reference (X=rm; later
$X) so downstream regex gates miss the literal command name. T9 collects
prefix assignments (VAR=value at start of string or after ; & |) and
substitutes ${VAR} / $VAR forms with the captured value. One-level
forward-flow only — chained vars are not followed.
Documented limits in JSDoc:
- Quoted assignments (X="rm -rf") not parsed (whitespace stops capture)
- Substitution is global within string, not scoped. Acceptable because
T3 strips unknown ${VAR} to '' afterwards.
Single-quoted literals are masked before T9 runs, so legitimate
strings are preserved (FP probe in tests).
7 new tests in bash-normalize-t7-t9.test.mjs.
Closes E10 in critical-review-2026-04-20.md.
