test(seed): pin reader_lock_acquire in hardlink_clone_into (#12)

Co-authored-by: Claude <claude@gitdan.com>
Co-committed-by: Claude <claude@gitdan.com>

scripts/seed-target-dir-selftest.sh

@@ -74,6 +74,17 @@
 #      onto one set of fingerprints. That is the silent stale-reuse bug the
 #      whole scheme exists to prevent, so the failure has to abort the clone
 #      rather than be swallowed.
+#  11. THE CONSUMER'S MARKER ACTUALLY STOPS THE PUBLISHER — reader_lock_acquire
+#      is exercised (not faked, unlike publish-snapshot-selftest.sh's scenario
+#      6) by a real hardlink_clone_into racing a real, concurrent
+#      publish-snapshot.sh republish of the exact snapshot being cloned. Pins
+#      that the publisher OBSERVABLY WAITS on this consumer's marker — its own
+#      log reports entering the drain wait — rather than only that the run
+#      succeeds, which stayed green with the marker call deleted (issue #10).
+#      Kept as its own scenario, not folded into 8a, because 8a already pins
+#      exactly one property (the identity check) for exactly one mutant, and
+#      the suite's one-scenario-one-mutant diagonal across 8a to 8d and 10 is
+#      deliberate.
 set -euo pipefail
 script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
 . "$script_dir/cache-lib.sh"
@@ -635,5 +646,84 @@ leftovers=$(find "$root" -maxdepth 1 \( -name '.stage-*' -o -name '.reading-*' \
 ok "no staging or reader-marker scratch left behind"
 rm -f "$scratch/bin/cp"
 
+echo
+echo "=== 11: the consumer's marker actually stops the publisher ==="
+# hardlink_clone_into's reader_lock_acquire call is exercised here, not
+# faked. publish-snapshot-selftest.sh's scenario 6 stands a hand-written
+# marker file in for "a consumer whose clone outlasts the grace period" — a
+# deliberate simplification that does not need this consumer's clone code at
+# all, so it cannot tell reader_lock_acquire apart from no marker existing.
+# This scenario forces the two real scripts to race on the same snapshot: a
+# consumer hardlink-cloning it, and a publisher republishing it out from
+# under that clone, exactly as 8a does to force the identity check — but what
+# is pinned here is not the consumer's response to the rotation (8a's
+# property), it is that the PUBLISHER, reading the SAME marker this
+# consumer's clone wrote, is observed to have entered its drain wait. Deleting
+# reader_lock_acquire (issue #10) leaves the marker never written: the
+# publisher's live_reader_count sees zero readers on its first check and
+# proceeds straight to reclaiming the rotated generation, silently — the run
+# still succeeds, and nothing about its own outcome says so, only the absence
+# of a line in the publisher's log.
+INTLK=$(cache_key feat/interlock-consumer)
+INTLK_BASE=$(cache_key release/5)
+TAG_INTLK=jobIntlk
+rm -rf "$root/snapshot-$INTLK_BASE" "$root/target-$INTLK_BASE"
+make_tree "$root/snapshot-$INTLK_BASE" intlk-gen1
+make_tree "$root/target-$INTLK_BASE" intlk-gen2
+intlk_gen1_inode=$(stat -c '%i' "$root/snapshot-$INTLK_BASE")
+
+cat > "$scratch/bin/cp" <<EOF
+#!/usr/bin/env bash
+# Fires once, only on the consumer's own top-level hardlink clone — identified
+# by its destination, the seed's private staging path. Every other cp in the
+# process tree (the unshare copies, and the publisher's own staging clone)
+# falls through to the real one.
+if [ "\${@: -1}" = "$root/.stage-$TAG_INTLK" ] && [ ! -e "$scratch/firedIntlk" ]; then
+  : > "$scratch/firedIntlk"
+  rc=0; "$real_cp" "\$@" || rc=\$?
+  # Concurrently: a real, second publish of the exact snapshot this consumer
+  # is cloning — the republish that, without the marker this consumer's clone
+  # holds, would reclaim the generation out from under it.
+  ( CACHE_READ_GRACE_SECONDS=10 bash "$script_dir/publish-snapshot.sh" "$INTLK_BASE" "$root" pubIntlk \
+      > "$scratch/logPubIntlk" 2>&1
+    echo \$? > "$scratch/rcPubIntlk" ) &
+  # Hand control back only once the swap is on disk, so the identity read
+  # immediately after this cp is guaranteed to resolve to the new generation
+  # — the same technique 8a uses to force the interleaving rather than hope
+  # for it. reader_lock_release does not run until AFTER this script exits,
+  # so the marker stays live for the publisher's whole swap-and-scan.
+  deadline=\$(( \$(date +%s) + 60 ))
+  while [ "\$(stat -c '%i' "$root/snapshot-$INTLK_BASE" 2>/dev/null)" = "$intlk_gen1_inode" ]; do
+    [ "\$(date +%s)" -lt "\$deadline" ] || { echo "stub cp: the publisher never swapped the snapshot" >&2; exit 92; }
+    sleep 0.05
+  done
+  exit \$rc
+fi
+exec "$real_cp" "\$@"
+EOF
+chmod +x "$scratch/bin/cp"
+
+rcIntlk=0
+seed_with_stub "$INTLK" "$INTLK_BASE" "$root" "$TAG_INTLK" > "$scratch/logIntlk" 2>&1 || rcIntlk=$?
+[ -e "$scratch/firedIntlk" ] \
+  || fail "the stubbed cp never fired: the consumer never raced the publisher, so this scenario proves nothing"
+ok "the consumer's clone raced a real, concurrent republish of its own source"
+wait_for_file "$scratch/rcPubIntlk" "the publisher never finished"
+[ "$(cat "$scratch/rcPubIntlk")" = "0" ] || { tail -40 "$scratch/logPubIntlk"; fail "publish-snapshot.sh exited non-zero"; }
+[ "$rcIntlk" = "0" ] || { tail -40 "$scratch/logIntlk"; fail "the seed exited non-zero"; }
+ok "both sides of the race completed"
+
+# The property under test: not that the run succeeded, but that the publisher
+# itself reports having found a live reader and waited on it. This is silent
+# in the consumer's own log and in the run's exit status alike — only the
+# publisher's log carries it.
+grep -q "readers: waiting for 1 in-flight clone(s) of snapshot-${INTLK_BASE}" "$scratch/logPubIntlk" \
+  || { tail -40 "$scratch/logPubIntlk"; fail "the publisher never reported waiting on the consumer's reader marker — the interlock did not observably engage"; }
+ok "the publisher observably waited on the consumer's own reader marker before reclaiming the rotated snapshot generation"
+leftovers=$(find "$root" -maxdepth 1 \( -name '.stage-*' -o -name '.reading-*' -o -name '.publish-*' \) -print)
+[ -z "$leftovers" ] || fail "scratch left behind: ${leftovers}"
+ok "no staging, reader-marker or deferred-generation scratch left behind"
+rm -f "$scratch/bin/cp"
+
 echo
 echo "seed-target-dir-selftest: ${pass_count} assertions passed"