gitdan-actions/scripts/prune-cache-selftest.sh

#!/usr/bin/env bash
# Regression test for prune-cache.sh. Builds a real scratch git repo standing
# in for `origin` and a real scratch directory standing in for the cache root,
# then runs the ACTUAL script against both — not a simulation of its logic.
#
# What each scenario demonstrates, and why the controls matter as much as the
# fixes (a scenario that always passes proves nothing):
#
#   1. DEAD BRANCH PRUNED, not gated on disk pressure — a cache whose branch
#      no longer exists on origin is removed even with plenty of free space.
#      Waiting for pressure to notice means paying for dead caches until then.
#   2. LIVE BRANCH SURVIVES despite being OLDER than the dead one — liveness,
#      not age, is what decides pass 1.
#   3. PROTECTED REFS NEVER EVICTED under forced disk pressure, even when
#      their caches are the oldest on disk and would rank first for LRU.
#   4. LOCKED CACHE PROTECTED even when dead, old, and under pressure — and
#      the pass's closing summary agrees with the decline it just logged,
#      rather than reporting that it found nothing.
#   5. STALE LOCK NOT HONOURED FOREVER — the same cache with a lock older than
#      STALE_LOCK_SECONDS is evicted, so a crashed job cannot pin a directory
#      permanently.
#   6. LIVENESS UNAVAILABLE FAILS SAFE — origin unreachable: a genuinely dead
#      cache is NOT pruned, the log says so plainly, and the pressure fallback
#      still works independently. "Unavailable" degrades to pressure-only, not
#      to no eviction at all.
#   7. TARGET DIRS EVICTED BEFORE SNAPSHOTS — the ordering that differs from
#      the obvious one. A snapshot is hardlinked to the caches cloned from it,
#      so evicting it frees almost nothing while costing every future PR its
#      warm start.
#   8. SELF-CLEAR REPORTS LOUDLY to the job summary, not just a log warning.
#   9. OWN CACHE NEVER EVICTED by a sibling pass.
#  10. SCOPED TO THE CACHE ROOT — a decoy outside it (standing in for another
#      project's volume) is never touched.
#  11. A LIVE READER MARKER PROTECTS A CACHE the same way a lock file does — a
#      directory somebody is hardlink-cloning this instant is not a candidate,
#      however dead and however tight the disk.
#  12. AND SO DOES ONE PUBLISHED INSIDE THE CHECK-TO-UNLINK WINDOW, which is
#      the property a check-then-delete eviction does NOT have. This is the
#      one that fails against the pre-fix script.
#  13. A DEFERRED EVICTION IS RECLAIMED, but not while its reader is live.
#      Nothing else globs a dotted name, so an unswept one is disk lost for
#      good on the volume whose whole problem is disk.
#  14. AND NOT WHILE ANOTHER PASS MAY STILL BE EVICTING IT. An aside with no
#      readers is indistinguishable from one a concurrent pass has just
#      renamed and not yet decided about; reclaiming that one lets `rm -rf`
#      empty a tree its owner may still restore under a live cache name. Its
#      fixture is an OLD directory renamed a moment ago — production's shape,
#      and what lets it tell the two timestamps apart.
#  15. A MERGED-BUT-UNDELETED BRANCH IS DEAD TOO. A branch the forge did not
#      delete at merge stays on `ls-remote` forever, so scenario 1's signal
#      never fires for it — which is how three 40 GB caches sat on a full
#      volume until somebody removed them by hand (gitdan-actions#20). A
#      branch whose tip is an ancestor of a protected branch's tip is pruned
#      like a deleted one; an unmerged branch beside it is not.
#  16. AND "CANNOT TELL" IS STILL NOT DEATH, at both granularities: a branch
#      whose tip is not in this checkout is kept with a warning naming it,
#      and a shallow checkout — where a missing object is the normal case —
#      withholds the whole signal rather than reading it as "nothing merged".
#      The deleted-branch signal keeps working in both.
#  17. THE FREE-SPACE REQUIREMENT IS MEASURED OFF THE SOURCE, not taken as a
#      percentage of the volume: the pass evicts until the clone the seed is
#      about to make fits, and stops there rather than draining the volume.
#      When it cannot get there it FAILS, naming the shortfall and every
#      directory it kept instead — because the seed would otherwise fail
#      seconds later against a staging path that names nothing.
#  18. AND ON THE LAYOUT THAT PRODUCED THE BUG: three equal-sized caches, one
#      of them a merged-but-undeleted branch's, with disk to spare. Exactly
#      that one goes. Equal sizes and no pressure are the point — nothing but
#      the merge state can be what decides.
set -euo pipefail
script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
. "$script_dir/cache-lib.sh"
prune="$script_dir/prune-cache.sh"
# Two scenarios below put a stub of a real tool on PATH for one command.
# Captured once, here, rather than read back at each of those sites: a `$PATH`
# read after the first of them is indistinguishable, to a static check, from
# reading the modification the subshell lost.
outer_path="$PATH"

scratch=$(mktemp -d)
trap 'rm -rf "$scratch"' EXIT
pass_count=0
fail() { echo "ASSERTION FAILED: $*" >&2; [ -n "${1:-}" ] && [ -f "$scratch/log" ] && { echo "--- log ---" >&2; cat "$scratch/log" >&2; }; exit 1; }
ok() { pass_count=$((pass_count + 1)); echo "PASS: $*"; }
assert_gone() { [ -e "$1" ] && fail "expected gone: $1 ($2)"; ok "$2"; }
assert_kept() { [ -e "$1" ] || fail "expected kept: $1 ($2)"; ok "$2"; }
assert_log() { grep -q -- "$1" "$scratch/log" || fail "expected in log: $1 ($2)"; ok "$2"; }

echo "=== building a scratch origin with real branches ==="
origin="$scratch/origin.git"; git init -q --bare "$origin"
work="$scratch/work"; git init -q "$work"
(
  cd "$work"
  git -c user.email=t@t -c user.name=t -c commit.gpgsign=false commit -q --allow-empty -m init
  git branch -M main
  git checkout -q -b dev; git -c user.email=t@t -c user.name=t -c commit.gpgsign=false commit -q --allow-empty -m dev
  git checkout -q -b feat/live; git -c user.email=t@t -c user.name=t -c commit.gpgsign=false commit -q --allow-empty -m live
  git remote add origin "$origin"
  git push -q origin main dev feat/live
)
cd "$work"

MAIN=$(cache_key main); DEV=$(cache_key dev); LIVE=$(cache_key feat/live)
DEAD=$(cache_key feat/dead); OWN=$(cache_key feat/own)

root="$scratch/cache"
mk() { mkdir -p "$root/$1"; head -c 4096 /dev/zero > "$root/$1/blob"; touch -d "$2" "$root/$1/.cache-last-used"; }
reset_cache() {
  rm -rf "$root"; mkdir -p "$root"
  mk "target-$MAIN"  '2020-01-01'
  mk "snapshot-$MAIN" '2020-01-01'
  mk "target-$DEV"   '2020-01-01'
  mk "snapshot-$DEV" '2020-01-01'
  mk "target-$LIVE"  '2020-01-02'   # older than the dead one, deliberately
  mk "target-$DEAD"  '2030-01-01'   # newest on disk, but its branch is gone
  mk "snapshot-$DEAD" '2030-01-01'
  mk "target-$OWN"   '2025-01-01'
}
# run_prune <df-override> [settle-seconds]
#
# The settle window is only set when a scenario asks for it, so every other
# scenario — scenario 14 above all — runs against the script's own default
# rather than against a value this file chose.
run_prune() {
  local free="${1:-}"
  if [ -n "${2:-}" ]; then export EVICTION_ASIDE_SETTLE_SECONDS="$2"; else unset EVICTION_ASIDE_SETTLE_SECONDS; fi
  CACHE_DF_OVERRIDE="$free" GITHUB_STEP_SUMMARY="$scratch/summary" \
    bash "$prune" "$root" "$root/target-$OWN" "dev main" 10 > "$scratch/log" 2>&1 \
    || { cat "$scratch/log"; fail "prune-cache.sh exited non-zero"; }
}

echo
echo "=== 1/2: dead pruned unconditionally; older-but-live survives ==="
reset_cache
run_prune "1000000 900000"   # 90% free: no pressure at all
assert_gone "$root/target-$DEAD" "dead branch's target dir pruned with no disk pressure"
assert_gone "$root/snapshot-$DEAD" "dead branch's snapshot pruned too"
assert_kept "$root/target-$LIVE" "live branch survives despite an older marker than the dead one"
assert_log "no matching branch on origin" "eviction reason reported"

echo
echo "=== 3: protected refs never evicted under forced pressure ==="
reset_cache
run_prune "1000000 1000"     # 0.1% free
assert_kept "$root/target-$DEV" "dev's target dir survives disk pressure"
assert_kept "$root/snapshot-$DEV" "dev's snapshot survives disk pressure"
assert_kept "$root/target-$MAIN" "main's target dir survives disk pressure"
assert_kept "$root/snapshot-$MAIN" "main's snapshot survives disk pressure"

echo
echo "=== 9: own cache never evicted by a sibling pass ==="
assert_kept "$root/target-$OWN" "this run's own cache survives"

echo
echo "=== 7: target dirs evicted before snapshots ==="
reset_cache
# Only the live branch is evictable; give it both a target dir and a snapshot
# with identical markers so ordering, not age, decides.
mk "snapshot-$LIVE" '2020-01-02'
# The df override is a fixed reading, so the pressure loop drains everything
# evictable — which is what makes the ORDER the observable property here, not
# what survives. Assert the eviction order directly from the log.
run_prune "1000000 1000"
order=$(grep -o "evicted \(target\|snapshot\)-$LIVE" "$scratch/log" | sed "s/evicted //")
[ "$(printf '%s\n' "$order" | head -1)" = "target-$LIVE" ] \
  || fail "expected target-$LIVE to be evicted before snapshot-$LIVE, got: $order"
ok "target dirs are evicted before snapshots"

echo
echo "=== 4: a fresh lock protects a dead, old, under-pressure cache ==="
reset_cache
date +%s > "$root/target-$DEAD/.ci-lock-ci-1"
run_prune "1000000 1000"
assert_kept "$root/target-$DEAD" "locked cache survives both passes"
assert_log "held open by" "lock reported in the log"
# With the locked one the only dead cache left, the pass has declined every
# dead cache it found — at which point "no dead-branch caches found" is a
# false summary of the decline logged two lines above it.
rm -rf "$root/snapshot-$DEAD"
run_prune "1000000 900000"
assert_kept "$root/target-$DEAD" "still not evicted when it is the only dead cache"
assert_log "none pruned this pass" "a pass that declined every dead cache reports that"
if grep -q "no dead-branch caches found" "$scratch/log"; then
  fail "the closing summary contradicts the decline logged above it"
fi
ok "the summary does not claim it found nothing"

echo
echo "=== 5: a stale lock is not honoured forever ==="
reset_cache
echo 0 > "$root/target-$DEAD/.ci-lock-ci-1"
touch -d '2000-01-01' "$root/target-$DEAD/.ci-lock-ci-1"
run_prune "1000000 900000"
assert_gone "$root/target-$DEAD" "cache with an abandoned lock is evicted"
assert_log "treating as abandoned" "abandoned lock reported in the log"

echo
echo "=== 6: liveness unavailable fails safe, pressure fallback still works ==="
reset_cache
(
  cd "$work" && git remote set-url origin "$scratch/nonexistent.git"
)
run_prune "1000000 900000"   # no pressure
assert_kept "$root/target-$DEAD" "dead cache NOT pruned when liveness is unavailable"
assert_log "treating as UNAVAILABLE" "unavailability reported plainly, not folded into 'no branches'"
run_prune "1000000 1000"     # now with pressure
if [ -e "$root/target-$DEAD" ] && [ -e "$root/target-$LIVE" ]; then
  fail "pressure fallback did nothing when liveness was unavailable"
fi
ok "pressure fallback still evicts when liveness is unavailable"
(cd "$work" && git remote set-url origin "$origin")

echo
echo "=== 8: self-clear reports to the job summary ==="
reset_cache
rm -rf "$root/target-$DEAD" "$root/snapshot-$DEAD" "$root/target-$LIVE"
: > "$scratch/summary"
run_prune "1000000 1000"     # nothing evictable left but the run's own cache
assert_log "clearing own" "self-clear reported in the log"
grep -q 'self-clear' "$scratch/summary" || fail "self-clear missing from the job summary"
ok "self-clear reported to the job summary, not only the log"
[ -d "$root/target-$OWN" ] || fail "self-clear left the own directory missing"
[ -z "$(ls -A "$root/target-$OWN")" ] || fail "self-clear did not actually empty the directory"
ok "own cache wiped and recreated empty"

echo
echo "=== 10: scoped to the cache root ==="
reset_cache
decoy="$scratch/other-project"; mkdir -p "$decoy/target-$DEAD"; touch "$decoy/target-$DEAD/blob"
run_prune "1000000 1000"
assert_kept "$decoy/target-$DEAD" "a cache outside the cache root is never touched"

echo
echo "=== 11: a live reader marker protects a cache, like a lock file does ==="
reset_cache
date +%s > "$root/.reading-target-$DEAD-job1"
run_prune "1000000 1000"
assert_kept "$root/target-$DEAD" "a cache being hardlink-cloned right now survives both passes"
assert_log "currently cloning it" "the reader is named in the log, not silently honoured"
rm -f "$root/.reading-target-$DEAD-job1"

echo
echo "=== 12: a reader marker published INSIDE the check-to-unlink window ==="
reset_cache
# A consumer publishes its marker whenever it starts a clone, which can be at
# any instant — including after the pass has checked for markers and before it
# unlinks. That window is real time, not a theoretical interleaving: `du -sk`
# on a multi-GB cache runs for seconds, and the pass runs one on every
# candidate. It is reproduced deterministically here by making that very `du`
# publish the marker, which places it strictly after the check and strictly
# before the unlink — exactly where a check-then-delete eviction cannot see
# it. The candidate must still be standing afterwards, with its contents
# intact and nothing left renamed aside.
mkdir -p "$scratch/bin"
real_du=$(command -v du)
cat > "$scratch/bin/du" <<EOF
#!/usr/bin/env bash
for arg; do
  case "\$arg" in */target-$DEAD) date +%s > "$root/.reading-target-$DEAD-racer" ;; esac
done
exec "$real_du" "\$@"
EOF
chmod +x "$scratch/bin/du"
( PATH="$scratch/bin:$outer_path"; run_prune "1000000 900000" )
[ -e "$root/.reading-target-$DEAD-racer" ] || fail "the racing marker was never published — scenario 12 proves nothing"
assert_kept "$root/target-$DEAD" "a cache claimed inside the eviction window is not unlinked"
assert_kept "$root/target-$DEAD/blob" "the reprieved cache still has its contents"
assert_log "restored, not evicted" "the reprieve is reported, not silent"
[ -z "$(ls -d "$root"/.evicting-* 2>/dev/null)" ] || fail "an aside directory was left behind after the reprieve"
ok "nothing left renamed aside once the eviction is declined"
rm -f "$root/.reading-target-$DEAD-racer"

echo
echo "=== 13: a deferred eviction is reclaimed, but not under a live reader ==="
reset_cache
aside="$root/.evicting-target-$DEAD-9999"
mkdir -p "$aside"; head -c 4096 /dev/zero > "$aside/blob"
date +%s > "$root/.reading-target-$DEAD-job1"
# The settle window (scenario 14) gates this sweep first and would decide both
# runs on its own. A directory's ctime is what that window reads and cannot be
# backdated the way `touch -d` backdates an mtime, so the window is moved out
# of the way rather than the directory aged into it.
run_prune "1000000 900000" 0
assert_kept "$aside" "a deferred eviction is not reclaimed while a job is still reading it"
assert_log "deferring its reclamation again" "the continued deferral is reported"
rm -f "$root/.reading-target-$DEAD-job1"
run_prune "1000000 900000" 0
assert_gone "$aside" "a deferred eviction is reclaimed once its reader is gone"
assert_log "reclaiming deferred eviction" "the reclamation is reported"

echo
echo "=== 14: an aside another pass may still be evicting is left alone ==="
reset_cache
aside="$root/.evicting-target-$DEAD-9999"
# Built the way the pass builds one — an old cache directory renamed a moment
# ago — because the two ages that describe it disagree, and which of them the
# window reads is the whole mechanism. `mkdir`-ing the aside directly would
# give it a fresh mtime as well as a fresh ctime, and a fixture whose two
# clocks agree cannot tell %Z from %Y: the settle window would read the wrong
# one, never fire for any real aside, and this scenario would not notice.
victim="$root/target-$DEAD-victim"
mkdir -p "$victim"; head -c 4096 /dev/zero > "$victim/blob"
touch -d '2020-01-01' "$victim"      # an old cache, which is every cache
mv -T "$victim" "$aside"             # set aside a moment ago
# Deliberately no reader marker: the reader gate would pass this straight
# through, which is the whole point. An aside with no readers is exactly what
# a pass that has just renamed one aside and not yet decided about it looks
# like, and `rm -rf` traverses fd-relative — so reclaiming it out from under
# that pass lets it republish a half-emptied tree under a live cache name.
run_prune "1000000 900000"
assert_kept "$aside" "an aside younger than the settle window is not reclaimed"
assert_kept "$aside/blob" "and is left intact, not part-way emptied"
assert_log "may still be evicting it" "the deferral gives its actual reason"

echo
echo "=== 15: a merged-but-undeleted branch is dead too ==="
# A branch the forge did not delete at merge, which `ls-remote` then reports
# forever. Built the way that happens: a branch merged into dev with a merge
# commit, still pushed, beside one branched at the same point and NOT merged.
git="git -c user.email=t@t -c user.name=t -c commit.gpgsign=false"
(
  cd "$work"
  git checkout -q dev
  git checkout -q -b feat/merged
  $git commit -q --allow-empty -m merged
  git checkout -q dev
  $git merge -q --no-ff feat/merged -m "merge feat/merged"
  git checkout -q -b feat/unmerged
  $git commit -q --allow-empty -m unmerged
  git checkout -q dev
  git push -q origin dev feat/merged feat/unmerged
)
MERGED=$(cache_key feat/merged); UNMERGED=$(cache_key feat/unmerged)
reset_cache
mk "target-$MERGED"   '2030-01-01'
mk "snapshot-$MERGED" '2030-01-01'
mk "target-$UNMERGED" '2020-01-01'   # older, deliberately: merge state decides, not age
run_prune "1000000 900000"           # 90% free: no pressure at all
assert_log "merged-branch detection anchored on" "the pass says what it anchored ancestry on"
assert_gone "$root/target-$MERGED" "a merged branch's cache is pruned though its branch is still on origin"
assert_gone "$root/snapshot-$MERGED" "and so is its snapshot"
assert_kept "$root/target-$UNMERGED" "an unmerged branch's cache survives, though it is the older of the two"
assert_log "merged into dev" "the eviction names the branch it was merged into"

echo
echo "=== 16: 'cannot tell' is not death, per branch and per checkout ==="
# A branch whose tip this checkout has never seen. Pushed from a second clone,
# so `ls-remote` reports a SHA that `$work` holds no object for — which is
# what "cannot determine" actually looks like, rather than a stubbed failure.
other="$scratch/other"; git clone -q "$origin" "$other"
(
  cd "$other"
  git checkout -q -b feat/elsewhere origin/dev
  git -c user.email=t@t -c user.name=t -c commit.gpgsign=false commit -q --allow-empty -m elsewhere
  git push -q origin feat/elsewhere
)
ELSEWHERE=$(cache_key feat/elsewhere)
reset_cache
mk "target-$ELSEWHERE" '2030-01-01'
mk "target-$MERGED"    '2030-01-01'
run_prune "1000000 900000"
assert_kept "$root/target-$ELSEWHERE" "a branch whose tip is not in this checkout is kept, not classified dead"
assert_log "cannot tell merged from live" "and the undecidable branch is named, not silently skipped"
assert_gone "$root/target-$MERGED" "while a branch it CAN decide is still pruned in the same pass"

# A shallow checkout, where a missing object is the ordinary case rather than
# a signal — so the whole merged half is withheld. The deleted-branch half is
# unaffected, which is what keeps this a narrowing rather than an outage.
shallow="$scratch/shallow"; git clone -q --depth 1 -b dev "file://$origin" "$shallow"
[ "$(git -C "$shallow" rev-parse --is-shallow-repository)" = true ] \
  || fail "the fixture clone is not shallow — scenario 16's second half proves nothing"
reset_cache
mk "target-$MERGED" '2030-01-01'
(
  cd "$shallow"
  CACHE_DF_OVERRIDE="1000000 900000" GITHUB_STEP_SUMMARY="$scratch/summary" \
    bash "$prune" "$root" "$root/target-$OWN" "dev main" 10
) > "$scratch/log" 2>&1 || { cat "$scratch/log"; fail "prune-cache.sh exited non-zero in a shallow checkout"; }
assert_log "checkout is shallow" "a shallow checkout withholds the merged signal and says why"
assert_kept "$root/target-$MERGED" "and keeps a merged branch's cache rather than guessing"
assert_gone "$root/target-$DEAD" "while the deleted-branch signal still fires"

echo
echo "=== 17: the free-space requirement is measured off the clone's source ==="
# A `df` that answers from the cache root's actual size, because the property
# under test is that the pass STOPS once the requirement is met — which a
# fixed CACHE_DF_OVERRIDE cannot express, since evicting never changes it.
mkdir -p "$scratch/bin17"
real_du=$(command -v du)
build_seed_fixture() {
  rm -rf "$root"; mkdir -p "$root"
  # The source the seed is about to clone. 8 MB of dep-info, which
  # unshare_mutable_paths has to real-copy, beside 16 MB of .rlib that it
  # leaves hardlinked — so a requirement derived from the SIZE of the source
  # would be three times the one derived from its mutable set.
  mkdir -p "$root/snapshot-$DEV/debug/.fingerprint/unit" "$root/snapshot-$DEV/debug/deps"
  head -c $((8 * 1024 * 1024)) /dev/zero > "$root/snapshot-$DEV/debug/.fingerprint/unit/dep-lib"
  head -c $((16 * 1024 * 1024)) /dev/zero > "$root/snapshot-$DEV/debug/deps/libx.rlib"
  touch -d '2020-01-01' "$root/snapshot-$DEV/.cache-last-used"
  # Three live, unmerged branches' caches of 4 MB each, oldest first.
  local i=0
  for b in a b c; do
    i=$((i + 1))
    mkdir -p "$root/target-$(cache_key "feat/$b")"
    head -c $((4 * 1024 * 1024)) /dev/zero > "$root/target-$(cache_key "feat/$b")/blob"
    touch -d "202${i}-01-01" "$root/target-$(cache_key "feat/$b")/.cache-last-used"
  done
  # A volume with 2 MB to spare: under the requirement, over nothing else.
  cap=$(( $($real_du -sk "$root" | awk '{print $1}') + 2048 ))
  cat > "$scratch/bin17/df" <<DFEOF
#!/usr/bin/env bash
used=\$($real_du -sk "$root" | awk '{print \$1}')
echo "Filesystem 1024-blocks Used Available Capacity Mounted-on"
echo "fake $cap \$used \$(( $cap - used )) 50% $root"
DFEOF
  chmod +x "$scratch/bin17/df"
}
(
  cd "$work"
  for b in a b c; do
    git checkout -q dev
    git checkout -q -b "feat/$b"
    git -c user.email=t@t -c user.name=t -c commit.gpgsign=false commit -q --allow-empty -m "$b"
  done
  git checkout -q dev
  git push -q origin feat/a feat/b feat/c
)
# run_seeded_prune <own-ref> <base-ref> — the form cargo-cache/action.yml uses:
# the same pass, told what the seed step it now runs ahead of will clone. The
# headroom knobs are pinned so the arithmetic is the fixture's, not the
# defaults' (whose 2 GiB floor would dwarf any fixture on a test host).
seeded_rc=0
run_seeded_prune() {
  seeded_rc=0
  PATH="$scratch/bin17:$outer_path" \
    CACHE_CLONE_HEADROOM_PERCENT=100 CACHE_CLONE_HEADROOM_FLOOR_KB=1024 \
    GITHUB_STEP_SUMMARY="$scratch/summary" \
    bash "$prune" "$root" "$root/target-$(cache_key "$1")" "dev main" 0 \
      "$(cache_key "$1")" "$(cache_key "$2")" "" \
    > "$scratch/log" 2>&1 || seeded_rc=$?
}

build_seed_fixture
run_seeded_prune feat/own dev
[ "$seeded_rc" = 0 ] || { cat "$scratch/log"; fail "prune-cache.sh exited ${seeded_rc} with the requirement satisfiable"; }
assert_log "measured from its mutable set" "the requirement says where it came from"
assert_gone "$root/target-$(cache_key feat/a)" "the oldest cache is evicted to make room for the clone"
assert_gone "$root/target-$(cache_key feat/b)" "and the next oldest, because one was not enough"
assert_kept "$root/target-$(cache_key feat/c)" "and the pass STOPS there rather than draining the volume"
assert_kept "$root/snapshot-$DEV" "the source the seed is about to clone is never a candidate"

# Nothing eligible: every sibling is held open by a running job. The pass
# cannot reach the requirement, and the seed that follows would fail against a
# staging path naming none of this.
build_seed_fixture
for b in a b c; do date +%s > "$root/target-$(cache_key "feat/$b")/.ci-lock-ci-1"; done
run_seeded_prune feat/own dev
[ "$seeded_rc" = 1 ] || { cat "$scratch/log"; fail "expected exit 1 when the clone cannot fit, got ${seeded_rc}" ; }
ok "a clone that cannot be made to fit fails the pass rather than the seed"
assert_log "short by" "the failure names the shortfall"
assert_log "held open by a running job" "and what was kept instead of it, with the reason"
assert_kept "$root/target-$(cache_key feat/a)" "a locked cache is still not evicted, however tight the disk"

echo
echo "=== 18: the layout that produced the bug ==="
# zemyna's volume on 2026-09-07: the base branch's snapshot and target dir,
# plus one target dir for a branch merged the day before and never deleted.
# Equal sizes and 90% free, so neither age nor pressure nor size can be what
# decides — only the merge state.
rm -rf "$root"; mkdir -p "$root"
mk "snapshot-$DEV"  '2026-09-01'
mk "target-$DEV"    '2026-09-01'
mk "target-$MERGED" '2026-09-06'
run_prune "1000000 900000"
assert_kept "$root/snapshot-$DEV" "the base snapshot stays"
assert_kept "$root/target-$DEV" "and the base target dir stays"
assert_gone "$root/target-$MERGED" "and the merged-but-undeleted branch's cache is the one reclaimed"
[ "$(grep -c 'pruned dead-branch cache' "$scratch/log")" = 1 ] \
  || { cat "$scratch/log"; fail "expected exactly one eviction on the zemyna layout"; }
ok "exactly one directory is evicted, and it is that one"

echo
echo "prune-cache-selftest: ${pass_count} assertions passed"