+sub ibx_async_cat ($$$$) {
+ my ($ibx, $oid, $cb, $arg) = @_;
+ my $git = $ibx->{git} // $ibx->git;
+ # {topdir} means ExtSearch (likely [extindex "all"]) with potentially
+ # 100K alternates. git(1) has a proposed patch for 100K alternates:
+ # <https://lore.kernel.org/git/20210624005806.12079-1-e@80x24.org/>
+ if (!defined($ibx->{topdir}) && !defined($git->{-tmp}) &&
+ ($GCF2C //= eval {
+ require PublicInbox::Gcf2Client;
+ PublicInbox::Gcf2Client::new();
+ } // 0)) { # 0: do not retry if libgit2 or Inline::C are missing
+ $GCF2C->gcf2_async(\"$oid $git->{git_dir}\n", $cb, $arg);
+ \undef;
+ } else { # read-only end of git-cat-file pipe
+ $git->cat_async($oid, $cb, $arg);
+ watch_cat($git);
+ }
+}
+