* perf: scan diagnostic environment lines without repeated whitespace searches
* perf(observability): skip redundant terminator scans in environment-line redaction
After a successful match ENV_LINE.lastIndex already sits at end of input
or a line terminator, and a failed start's whitespace skip plus terminator
scan collapse into one LINE_CONTENT exec. Byte-identical output; verified
against the pre-change regex over 280k generated inputs.
* perf(observability): find environment-line ends without entering the regex engine
