Adds BLOCK_RULE for the malware-loader pattern:
echo|cat|printf <base64-blob> | base64 -d | <shell>
This is a common RCE delivery shape that bypasses static name-matching
gates by encoding the destructive command as a base64 blob. The new
rule fires only when the final pipe target is a shell interpreter
(bash, sh, zsh, dash, ksh) — base64 decoded into jq or any non-shell
consumer remains allowed.
5 new tests in pre-bash-destructive.test.mjs:
- 3 BLOCK cases (echo|base64|bash, printf|base64|sh, cat|base64|zsh)
- 2 FP probes (base64 -d -> jq passes; base64 -d alone passes)
Closes E9 in critical-review-2026-04-20.md.
