Errors column shows "12:5: error: 'x' undeclared" instead of "'x' undeclared" when the file path contains "error" #415

What's wrong

In ParseLogForErrors (BuildMonitor/Providers/GitHub.cs:725-728, main @ 561fdb3) a line is selected by ErrorPatternRegex() ((?:^|\s)error\s*:), but the message is then cut at the first : after trimmedLine.IndexOf("error", OrdinalIgnoreCase) — the first "error" anywhere in the line, not where the regex matched. A path or repo name containing "error" moves the cut to the first colon after the path.

Repro

Calling the method (via reflection) on GCC/clang-style log lines:

"...Z /home/runner/work/error-codes/error-codes/src/parse.c:12:5: error: 'x' undeclared (first use in this function)"
  -> "12:5: error: 'x' undeclared (first use in this function)"
"...Z src/errors.c:40:1: error: expected ';' before '}' token"
  -> "40:1: error: expected ';' before '}' token"
"...Z /home/runner/work/app/app/src/parse.c:12:5: error: 'y' undeclared"
  -> "'y' undeclared"   (control)

Expected 'x' undeclared ... and expected ';' before '}' token.

Why it matters

Low impact, but the Errors column shows location-prefixed noise for any repo/file named like errors.c, error-codes, ErrorHandling/..., and the seenErrors de-duplication treats the same compiler error at different locations as distinct messages.

Suggested fix

Use the regex match itself:

Match m = ErrorPatternRegex().Match(trimmedLine);
if (m.Success) { string errorMessage = trimmedLine[(m.Index + m.Length)..].Trim(); ... }

Acceptance: a test with the first two lines above yields the bare messages; existing log-parsing tests still pass.