CVE-2026-44266: Elo Ruby backend has Remote Code Execution via unescaped `#{...}` interpolation in emitted string literals and subtype-constraint labels

Elo’s Ruby backend emits attacker-controlled text into Ruby double-quoted strings without escaping the # character. Because # begins Ruby’s interpolation sequences — #{expr}, #@ivar, #@@cvar, #$gvar — and any expression wrapped in #{...} may use backticks for shell execution, an Elo program that contains a crafted string literal or a labelled subtype constraint compiles to Ruby that evaluates attacker-chosen Ruby, and through backticks runs attacker-chosen shell commands, at runtime.

The same Elo source compiled to JavaScript, Python, or SQL is benign, so the bug also breaks the cross-target portability guarantee the rest of the compiler honours.