header_regexp does not behave as expected in an expression

[mininmobile]

something is different in the way header_regexp is parsed when in a CEL expression than as a regular matcher. this may be the case for path_regexp as well

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i used to have a matcher like this to detect bots. note the \b in the regex

@badbot header_regexp User-Agent (?i).*(bot\b|-ai\b|google|copilot|baidu|...).*
abort @badbot

it worked great! it matched everything i specified, and everything else that reported as a bot (eg. discordbot matches, despite not having discord explicitly in my regex)

⇒ curl -A "bot" aborts, but curl -A "bottom" does not

this fell apart when i had to combine it with other matchers. since there is no or { ... } matcher, i had to convert it to an expression. though, even if i do not OR it with anything, the same header_regexp does not work as expected

@badbot `header_regexp('User-Agent','(?i).*(bot\b|-ai\b|google|copilot|baidu|...).*'`
abort @badbot

⇒ curl -A "bot" does not get aborted!!???!??

the workaround is to have a normal matcher just for my regex with a word boundary, and then duplicate my abort @bot directive, but this is the exact thing expressions are supposed to help avoid!!