Keep @inc hooks across the dev-lib re-exec

A dev-lib flag makes the script re-exec itself, carrying @inc across in
T2_HARNESS_INCLUDES. That variable can only hold paths, so a hook was
serialized as "Foo=HASH(0x...)" and came back as a nonexistent directory,
while the real hook PERL5OPT had already reinstalled in the new process was
thrown away by the script and inject_includes() both replacing @inc outright.

Under Carmel that is fatal: its modules are reachable through nothing but
its hook, so the re-exec'd yath could not load its own plugins.

Serialize only paths, and keep any hook the new process already has. The
script needs its own copy of the logic because it sets @inc up before
App::Yath::Script can be loaded, which also means an installed yath script
must be replaced for the fix to take effect.

Written with AI assistance.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: exodist

Changes

@@ -2,6 +2,7 @@
 
     - Replace AI_AND_LLM_POLICY.txt with a rewritten AI_AND_LLM_POLICY.md.
     - Keep internal docs, agent tooling and TEMPLATE.pod out of the tarball.
+    - Keep @INC hooks, such as Carmel's, working when the script re-execs itself for dev-libs.
 
 2.000016  2026-04-28 22:01:21-07:00 America/Los_Angeles
 

lib/App/Yath/Script.pm

@@ -81,7 +81,10 @@ sub do_runtime { $MOD->do_runtime(@_) }
 
 sub do_exec {
     my ($argv) = @_;
-    $ENV{T2_HARNESS_INCLUDES} = join ';' => @INC;
+    # Hooks (coderef, arrayref, blessed object) cannot be serialized. Anything
+    # that installed one via PERL5OPT installs it again in the new process, so
+    # only the paths need to survive the exec.
+    $ENV{T2_HARNESS_INCLUDES} = join ';' => grep { !ref $_ } @INC;
     exec($^X, $SCRIPT, @$argv);
 }
 
@@ -279,7 +282,10 @@ sub load_latest_yath_module {
 
 sub inject_includes {
     return unless $ENV{T2_HARNESS_INCLUDES};
-    @INC = split /;/, $ENV{T2_HARNESS_INCLUDES};
+    # Keep any hooks this process already has. PERL5OPT runs before us, so a
+    # tool like Carmel has already reinstalled the hook that makes its modules
+    # findable, and replacing @INC outright would throw it away.
+    @INC = (grep({ ref $_ } @INC), split(/;/, $ENV{T2_HARNESS_INCLUDES}));
 }
 
 # Scan ./lib/App/Yath/Script for V#.pm modules and return the highest
@@ -527,6 +533,8 @@ Returns the name of the currently loaded C<App::Yath::Script::V{X}> module.
 
 Re-executes the current script with the given arguments. Sets the
 C<T2_HARNESS_INCLUDES> environment variable to preserve the current C<@INC>.
+Only paths are preserved; C<@INC> hooks cannot cross an C<exec> and are
+reinstalled in the new process by whatever added them.
 
 =item $clean_path = clean_path($path)
 

scripts/yath

@@ -7,7 +7,10 @@ our $VERSION = '2.000017';
 BEGIN {
     return if $^C;
 
-    @INC = split /;/, $ENV{T2_HARNESS_INCLUDES} if $ENV{T2_HARNESS_INCLUDES};
+    # Same as App::Yath::Script::inject_includes(), which cannot run yet: any
+    # @INC hook in this process was installed by PERL5OPT and must be kept.
+    @INC = (grep({ ref $_ } @INC), split(/;/, $ENV{T2_HARNESS_INCLUDES}))
+        if $ENV{T2_HARNESS_INCLUDES};
 
     require App::Yath::Script;
 

t/acceptance/yath.t

@@ -205,4 +205,48 @@ subtest 'CLI V# finds uppercase V rc filename' => sub {
     is($exit, 0, 'exit code is 0');
 };
 
+subtest 'an @INC hook survives the dev-lib re-exec' => sub {
+    my $tdir = tempdir(CLEANUP => 1);
+
+    # A dev-lib flag in the rc file makes the script re-exec itself. PERL5OPT
+    # reinstalls the hook in the new process, so it must still be in @INC once
+    # the script has finished setting @INC up. Carmel works exactly this way,
+    # and its modules are reachable through nothing else.
+    my $rcfile = File::Spec->catfile($tdir, '.yath.v0.rc');
+    open(my $rcfh, '>', $rcfile) or die "Cannot write $rcfile: $!";
+    print $rcfh "-D\n";
+    close($rcfh) or die "Cannot close $rcfile: $!";
+
+    my $probe = File::Spec->catfile($tdir, 'HookProbe.pm');
+    open(my $pfh, '>', $probe) or die "Cannot write $probe: $!";
+    print $pfh <<'EOT';
+package HookProbe;
+use strict;
+use warnings;
+
+# Fully qualified on purpose: perl compiles a bare `sub INC` into main::
+# no matter which package is current, so the method would never be found.
+sub HookProbe::INC { return }
+
+unshift @INC, bless({}, __PACKAGE__);
+
+END {
+    print "HOOKS: " . scalar(grep { ref $_ } @INC) . "\n";
+    print "CORPSES: " . scalar(grep { !ref($_) && m/HookProbe=HASH\(/ } @INC) . "\n";
+}
+
+1;
+EOT
+    close($pfh) or die "Cannot close $probe: $!";
+
+    local $ENV{PERL5OPT} = "-I$tdir -MHookProbe";
+    my ($output, $exit) = run_yath_in($tdir, 'hook_arg');
+
+    like($output, qr/^RUNTIME: hook_arg$/m, 'runtime arg processed');
+    like($output, qr/^HOOKS: 1$/m,          'hook is still in @INC after the re-exec');
+    like($output, qr/^CORPSES: 0$/m,        'no stringified hook was put into @INC');
+
+    is($exit, 0, 'exit code is 0');
+};
+
 done_testing;

t/unit/Script.t

@@ -86,6 +86,13 @@ subtest 'inject_includes' => sub {
     App::Yath::Script::inject_includes();
     is(\@INC, ['/fake/path1', '/fake/path2'], 'replaces @INC from env var');
 
+    # A hook installed by PERL5OPT must survive. Only paths come from the env
+    # var; it cannot carry a ref.
+    my $hook = sub { return };
+    @INC = ($hook, '/whatever');
+    App::Yath::Script::inject_includes();
+    is(\@INC, [exact_ref($hook), '/fake/path1', '/fake/path2'], 'keeps @INC hooks, replaces paths');
+
     # Restore
     @INC = @orig_inc;
 };