#2307 Multi-pass: copy feedback dir between passes (but remove nextpass.in)

This commit has been used in NWERC 2024 (d7cc716),
as well as GCPC 2025 and BAPC 2025.
It follows the latest release-candidate specification of multi-pass validation:
https://www.kattis.com/problem-package-format/spec/2025-09.html#multi-pass-validation
(the mirror at https://icpc.io/problem-package-format/spec/2025-09.html
should be deployed "soon™").
Copying the feedback directory to the next pass is an implementation of
"All other files inside the feedback directory are guaranteed to persist between passes."
Additionally, "Note that the `nextpass.in` will be removed before the next pass."

See also Kattis/problem-package-format#446 (comment)

Author: mpsijm

judge/judgedaemon.main.php

@@ -1451,6 +1451,16 @@ function judge(array $judgeTask): bool
         $passdir = $testcasedir . '/' . $passCnt;
         mkdir($passdir, 0755, true);
 
+        // In multi-pass problems, all files in the feedback directory
+        // are guaranteed to persist between passes, except `nextpass.in`.
+        // So, we recursively copy the feedback directory for every pass
+        // after the first (note that $passCnt starts at 1).
+        if ($passCnt > 1) {
+            $prevPassdir = $testcasedir . '/' . ($passCnt - 1) . '/feedback';
+            system('cp -R ' . dj_escapeshellarg($prevPassdir) . ' ' . dj_escapeshellarg($passdir . '/'));
+            system('rm ' . dj_escapeshellarg($passdir . '/feedback/nextpass.in'));
+        }
+
         // Copy program with all possible additional files to testcase
         // dir. Use hardlinks to preserve space with big executables.
         $programdir = $passdir . '/execdir';

judge/testcase_run.sh

@@ -197,7 +197,7 @@ if [ $COMBINED_RUN_COMPARE -eq 1 ]; then
 	# A combined run and compare script may now already need the
 	# feedback directory, and perhaps access to the test answers (but
 	# only the original that lives outside the chroot).
-	mkdir feedback
+	mkdir -p feedback
 	RUNARGS="$RUNARGS $TESTOUT compare.meta feedback"
 fi
 
@@ -234,8 +234,8 @@ if [ $COMBINED_RUN_COMPARE -eq 0 ]; then
 
 	exitcode=0
 	# Create dir for feedback files and make it writable for $RUNUSER
-	mkdir feedback
-	chmod a+w feedback
+	mkdir -p feedback
+	chmod -R a+w feedback
 
 	runcheck $GAINROOT "$RUNGUARD" ${DEBUG:+-v} $CPUSET_OPT -u "$RUNUSER" -g "$RUNGROUP" \
 		-m $SCRIPTMEMLIMIT -t $SCRIPTTIMELIMIT --no-core \