fix(ssh): keep the github.com connection alive through slow pre-push hooks (#59)

git push opens the SSH connection to github.com before running the
pre-push hook, then leaves it fully idle for the hook's entire duration.
Under heavy concurrent machine load, hooks routinely took long enough
that GitHub's idle-connection timeout closed the SSH session mid-hook —
the push then silently failed to transfer after printing "Safe to
push," with only a stray "Connection to github.com closed by remote
host." to explain it. Reproduced 4x in one session before diagnosing
via GIT_TRACE=1. ServerAliveInterval/CountMax keep the connection alive
during that idle window.

Co-authored-by: Mao Nakamoto <41178744+maonakamoto@users.noreply.github.com>

Author: catomean

.ssh/config

@@ -4,3 +4,13 @@ Host github.com
     User git
     IdentityFile ~/.ssh/github_ed25519
     IdentitiesOnly yes
+    # git push opens this connection BEFORE running the pre-push hook, then
+    # leaves it fully idle for the hook's entire duration. Found 2026-08-29:
+    # under heavy concurrent machine load (~80 sessions), hooks routinely ran
+    # long enough that GitHub's idle-connection timeout killed the SSH session
+    # while the hook was still running — the push then silently failed to
+    # transfer after printing "Safe to push," with only a stray "Connection to
+    # github.com closed by remote host." in the log to explain it. Active
+    # keepalives during that idle window prevent the drop.
+    ServerAliveInterval 30
+    ServerAliveCountMax 10