The per-PTY job already denies JOB_OBJECT_LIMIT_BREAKAWAY_OK for Cygwin/MSYS
shells (#19068), but nothing records why, and a conpty.node built before that
commit fails windows-msys-job.win32.test.ts in a way that reads as a source
defect. Measured on a real Windows 11 host: both the plain and the exec-
replacement Git Bash shapes leak, the escape is the MSYS runtime's own
spawn/exec (fork keeps membership), and a single-variable A/B on
usesCygwinRuntime flips the result 0/2 -> 4/4.
Also names the gap the failure hid behind: node-pty-job-ownership.cjs asserts
symbol presence, which cannot distinguish patch revisions.
Neil
0b37de7cd4