On macOS, Unix domain socket paths are capped at 104 bytes (sun_path).
SSH appends a 16-byte random suffix to the ControlPath when operating
in ControlMaster mode. With an IPv6 host embedded literally in the
filename and a deeply-nested macOS $TMPDIR like
/var/folders/XX/YYYYYYYYYYYY/T/, the full path reliably exceeds the
limit — every terminal/file-op tool call then fails immediately with
``unix_listener: path "…" too long for Unix domain socket``.
Swap the ``user@host:port.sock`` filename for a sha256-derived 16-char
hex digest. The digest is deterministic for a given (user, host, port)
triple, so ControlMaster reuse across reconnects is preserved, and the
full path fits comfortably under the limit even after SSH's random
suffix. Collision space is 2^64 — effectively unreachable for the
handful of concurrent connections any single Hermes process holds.
Regression tests cover: path length under realistic macOS $TMPDIR with
the IPv6 host from the issue report, determinism for reconnects, and
distinctness across different (user, host, port) triples.
Closes#11840
64a1368210