Summary

• Skip the DECRQM mode 2027 probe in probeGraphemeClusterMode() on Windows to prevent escape sequence leakage into process output

Problem

On Windows with Cygwin/MSYSTEM (Git Bash), the ExecTerminalProvider creates a PosixSysTerminal whose ExecPty slave output goes to a raw FileDescriptor (stdout/stderr) rather than a real PTY device. When probeGraphemeClusterMode() writes the DECRQM query (\e[?2027$p) to this raw fd, it contaminates the process output.

This was discovered via the Maven JLine 4.0.2 upgrade where all Windows CI jobs fail with:

java.nio.file.InvalidPathException: Illegal char <> at index 0: [?2027$pD:\a\maven\maven\...\localRepository4\.m2\repository

The [?2027$p escape sequence leaks into stdout and gets prepended to paths that Maven parses.

Fix

Added a guard in AbstractTerminal.probeGraphemeClusterMode() to return false on Windows. This is safe because:

1. AbstractWindowsTerminal already overrides supportsGraphemeClusterMode() to return false — native Windows terminals are unaffected
2. The only path to probeGraphemeClusterMode() on Windows is through the Cygwin/MSYSTEM PosixSysTerminal, where the probe output goes to a raw FileDescriptor rather than a real PTY device

Does not apply to jline-3.x — the grapheme cluster mode 2027 feature was introduced only in the 4.x line.

Test plan

• Existing GraphemeClusterModeTest passes (uses LineDisciplineTerminal, not affected)
• All terminal module tests pass
• Verify Maven Windows CI passes with the fix