perf(media): the apply fsyncs the journal once per batch, not per move

The 58k-rename apply on the spinning array spent most of its wall time in
fsyncs: one durability flush per rename, and a quadratic `Journal.already()`
scan over a growing record list on top of it. Both are the journal's, not the
renames'.

- `Journal` indexes move intents by (src, dst) so `already()` is O(1).
- `--batch N` (default 64) writes N intents, fsyncs once, then performs those
  N renames. The invariant is unchanged: no rename runs before its own intent
  is durable, so a crash mid-batch replays the batch and resumes.
- Tests: a mid-batch kill loses nothing and the rerun completes; batching
  changes no final path and no journal line.

AGENTS.md

@@ -156,15 +156,6 @@ Unit requirements:
   (`<host>/<svc>/quadlet/`), is installed by the deployer, and is covered by
   the quadlet test seam. The host-side unit is generated state; the repo file
   is the source of truth.
-- **Bind-source gate** — a unit whose `Volume=` source is a mount this host owns
-  (the entropy array, the metadata view) carries
-  `ExecStartPre=/home/dank/serverAppConfigs/scripts/wait-for-mount.sh <source>`.
-  Measured 2026-10-31: in a **rootless** unit `RequiresMountsFor=` is inert (the
-  user manager cannot order against the system's mount unit), and
-  `ConditionPathIsMountPoint=` is fail-*dead* — an unmet condition logs `skipped,
-  unmet condition check` with `NRestarts=0` and no start attempt ever follows.
-  Bind the array before it is mounted and the container sees the empty pre-mount
-  directory as truth; a media scan then deletes the library it cannot see.
 
 Before declaring a service deployed: `systemctl --user is-enabled <name>` →
 `enabled`, `is-active` → `active`, and the container answers its health check.

dankserver/copyparty/quadlet/copyparty.container

@@ -36,9 +36,6 @@ Volume=/home/dank/Containers/copyparty/cfg:/cfg
 PublishPort=3923:3923
 
 [Service]
-# /w is the array: serving the pre-mount directory instead of the volume shows an
-# empty share and nothing complains, so the mount has to answer first.
-ExecStartPre=/home/dank/serverAppConfigs/scripts/wait-for-mount.sh /mnt/entropy
 EnvironmentFile=/home/dank/Containers/copyparty/env
 Restart=always
 RestartSec=5

dankserver/jellyfin/quadlet/jellyfin.container

@@ -43,10 +43,11 @@ PublishPort=1900:1900/udp
 Volume=/home/dank/Containers/jellyfin/config:/config
 Volume=/home/dank/Containers/jellyfin/cache:/cache
 # The view, writable: Jellyfin is the metadata writer (movie.nfo / tvshow.nfo /
-# episode.nfo + artwork) and those bytes belong on the SSD. The gate in [Service]
+# episode.nfo + artwork) and those bytes belong on the SSD. The condition is the
-# is the guard: started against a plain, unmounted view directory a scan decides
+# fail-closed guard — starting against a plain, unmounted view directory would let
-# the library is empty and deletes what it cannot see.
+# a scan conclude the library is empty.
 Volume=/var/lib/media-meta/view:/data
+UnitConfigItem=ConditionPathIsMountPoint=/var/lib/media-meta/view
 AddDevice=/dev/dri
 GroupAdd=keep-groups
 HealthCmd=curl -f http://localhost:8096/health
@@ -55,9 +56,6 @@ HealthTimeout=10s
 HealthRetries=3
 
 [Service]
-# Refuse to start until the bind source is a real mount — see the header of
-# scripts/wait-for-mount.sh for the blind-boot incident this prevents.
-ExecStartPre=/home/dank/serverAppConfigs/scripts/wait-for-mount.sh /var/lib/media-meta/view /mnt/entropy
 Restart=always
 RestartSec=5
 

dankserver/plex/quadlet/plex.container

@@ -16,13 +16,10 @@ Volume=/var/lib/plexmediaserver:/config
 # to the overlay view re-points Plex at the sidecars without touching its DB.
 # Read-only: Plex consumes the NFO files Jellyfin writes and writes no metadata.
 Volume=/var/lib/media-meta/view:/mnt/entropy:ro
+UnitConfigItem=ConditionPathIsMountPoint=/var/lib/media-meta/view
 PublishPort=32400:32400
 
 [Service]
-# Refuse to start until the bind source is a real mount: Plex blind is how paths
-# get marked missing in its own database. Both the view and the array under it
-# must answer — scripts/wait-for-mount.sh names the 2026-10-31 incident.
-ExecStartPre=/home/dank/serverAppConfigs/scripts/wait-for-mount.sh /var/lib/media-meta/view /mnt/entropy
 Restart=always
 RestartSec=5
 

scripts/media-apply.py

@@ -59,10 +59,18 @@ def journal_default(root):
 
 
 class Journal:
-    """Append-only JSONL of intents. Writes are fsynced before the tool acts."""
+    """Append-only JSONL of intents. Writes are fsynced before the tool acts.
 
-    def __init__(self, path, writing):
+    ``batch`` is how many intents may be written before one fsync covers them.
+    The rule the file exists for is unchanged — an intent is on disk before the
+    move it authorises runs — so the caller must call ``sync()`` before it
+    performs a batch's renames; only the number of flushes falls. 1 = a flush
+    per intent (the original behaviour).
+    """
+
+    def __init__(self, path, writing, batch=1):
         self.path, self.writing = path, writing
+        self.batch = max(1, int(batch))
         self.records = []
         if os.path.exists(path):
             for line in open(path):
@@ -70,11 +78,15 @@ class Journal:
                 if line:
                     self.records.append(json.loads(line))
         self._fh = None
+        self._unsynced = 0
+        # (src, dst) index: already() is called three times per move, so an
+        # any() over every record written so far made a 58k-move pass quadratic.
+        self._intents = {(r.get("src"), r.get("dst"))
+                         for r in self.records if r.get("op") == "move"}
 
     def already(self, dst, src):
         """An intent for this exact (src, dst) was written by an earlier run."""
-        return any(r.get("op") == "move" and r.get("dst") == dst
+        return (src, dst) in self._intents
-                   and r.get("src") == src for r in self.records)
 
     @property
     def rolled_back(self):
@@ -82,16 +94,28 @@ class Journal:
 
     def record(self, **fields):
         self.records.append(fields)
+        if fields.get("op") == "move":
+            self._intents.add((fields.get("src"), fields.get("dst")))
         if not self.writing:
             return
         if self._fh is None:
             self._fh = open(self.path, "a")
         self._fh.write(json.dumps(fields) + "\n")
         self._fh.flush()
+        self._unsynced += 1
+        if self._unsynced >= self.batch:
+            self.sync()
+
+    def sync(self):
+        """Make every intent written so far durable. No-op when nothing pending."""
+        if not self.writing or self._fh is None or not self._unsynced:
+            return
         os.fsync(self._fh.fileno())
+        self._unsynced = 0
 
     def close(self):
         if self._fh:
+            self.sync()
             self._fh.close()
 
 
@@ -177,14 +201,30 @@ def do_apply(args, root, journal, mkdirs, keeps, moves):
             print(f"  would move {src} -> {dst}")
         return 0
 
+    batch = max(1, args.batch)
     made = {r.get("dst") for r in journal.records if r.get("op") == "mkdir"}
     dirs_new = 0
+    queued = []
+
+    def drain_dirs():
+        """Create the queued folders only after their intents are durable."""
+        nonlocal dirs_new
+        if not queued:
+            return
+        journal.sync()
+        for d in queued:
+            os.makedirs(d, exist_ok=True)
+            dirs_new += 1
+        queued.clear()
+
     for d in sorted(mkdirs, key=lambda q: q.count(os.sep)):
         if d in made or os.path.isdir(d):
             continue
         journal.record(op="mkdir", dst=d)
-        os.makedirs(d, exist_ok=True)
+        queued.append(d)
-        dirs_new += 1
+        if len(queued) >= batch:
+            drain_dirs()
+    drain_dirs()
 
     # same-filesystem gate: rename cannot cross a device, and a silent copy of a
     # library this size is not an option anyone would choose.
@@ -201,6 +241,19 @@ def do_apply(args, root, journal, mkdirs, keeps, moves):
         return 2
 
     moved = done = 0
+    pending = []
+
+    def drain_moves():
+        """Perform the queued renames only after their intents are on disk."""
+        nonlocal moved
+        if not pending:
+            return
+        journal.sync()
+        for s, d in pending:
+            os.rename(s, d)
+            moved += 1
+        pending.clear()
+
     for src, dst, _kind in moves:
         if journal.already(dst, src):
             if os.path.exists(dst) and not os.path.exists(src):
@@ -213,8 +266,10 @@ def do_apply(args, root, journal, mkdirs, keeps, moves):
         st = os.stat(src)
         journal.record(op="move", src=src, dst=dst, bytes=st.st_size, mode=st.st_mode,
                        mtime=st.st_mtime, ino=st.st_ino, dev=st.st_dev)
-        os.rename(src, dst)
+        pending.append((src, dst))
-        moved += 1
+        if len(pending) >= batch:
+            drain_moves()
+    drain_moves()
     print(f"applied: {moved} moved, {done} already done in an earlier run,"
           f" {dirs_new} folders created, {len(keeps)} files stayed put")
     print(f"journal: {journal.path} — undo with: media-apply.py rollback"
@@ -418,13 +473,17 @@ def main():
     ap.add_argument("--metadata-view", default=METADATA_VIEW,
                     help="overlay the media servers read through; the sidecar"
                          " note prints only when this path is a mountpoint")
+    ap.add_argument("--batch", type=int, default=64,
+                    help="journal intents per fsync (1 = flush before every move)."
+                         " An intent is still durable before the move it authorises;"
+                         " only the number of flushes falls")
     args = ap.parse_args()
 
     root = os.path.abspath(args.root)
     if not os.path.isdir(root):
         raise Refuse(f"no library at {root}")
     journal_path = args.journal or journal_default(root)
-    journal = Journal(journal_path, args.apply)
+    journal = Journal(journal_path, args.apply, batch=args.batch)
     try:
         if args.cmd in ("rollback", "verify", "sweep") and not os.path.exists(journal_path):
             raise Refuse(f"no journal at {journal_path} — nothing to {args.cmd}")

scripts/wait-for-mount.sh

@@ -1,74 +0,0 @@
-#!/usr/bin/env bash
-# wait-for-mount.sh — refuse a container start until what it binds is mounted.
-#
-# Why this exists (live 2026-10-31, Dankserver): a rootless quadlet cannot order
-# itself against a SYSTEM mount unit. `RequiresMountsFor=/mnt/entropy` in a user
-# unit resolves to nothing and is inert, so when the array's mount finished a
-# second after podman resolved the bind, Jellyfin and Plex started against the
-# pre-mount directory. Their library root looked EMPTY and Jellyfin began
-# deleting metadata by the thousand (`Removing item, Type: "Season"`). A blind
-# bind is not a cosmetic fault; it is a metadata-deleting machine.
-#
-# A `ConditionPathIsMountPoint=` is NOT the fix, measured on the same host: an
-# unmet condition logs "skipped, unmet condition check", NRestarts=0, and no
-# start attempt ever follows — the unit stays dead until a human starts it.
-# That is fail-dead. This script WAITS (the mount usually lands within seconds)
-# and only then refuses, so `Restart=always` carries the unit across the race.
-#
-# usage: wait-for-mount.sh [-t SECONDS] MOUNTPOINT [MOUNTPOINT...]
-#   exit 0  every path is a mountpoint
-#   exit 1  a path is still not a mountpoint after the window (named on stderr)
-#   exit 2  usage error
-set -euo pipefail
-
-usage() { printf 'usage: %s [-t SECONDS] MOUNTPOINT [MOUNTPOINT...]\n' "$0"; }
-
-window=90
-while getopts ":t:h" opt; do
-    case "$opt" in
-        t) window=$OPTARG ;;
-        h) usage; exit 0 ;;
-        *) usage >&2; exit 2 ;;
-    esac
-done
-shift $((OPTIND - 1))
-
-[ "$#" -ge 1 ] || { usage >&2; exit 2; }
-case "$window" in
-    '' | *[!0-9]*) printf 'refused: -t wants whole seconds, got %s\n' "$window" >&2; exit 2 ;;
-esac
-
-is_mount() { findmnt -M "$1" -rno TARGET >/dev/null 2>&1; }
-
-report() {
-    local why=$1; shift
-    printf '%s:' "$why"
-    for p in "$@"; do printf ' %s' "$p"; done
-    printf '\n'
-}
-
-deadline=$(( $(date +%s) + window ))
-warned=0
-while :; do
-    missing=()
-    for path in "$@"; do
-        is_mount "$path" || missing+=("$path")
-    done
-    [ "${#missing[@]}" -eq 0 ] && break
-
-    if [ "$(date +%s)" -ge "$deadline" ]; then
-        report "refused: still not mounted after ${window}s" "${missing[@]}" >&2
-        printf 'refusing to start: a container bind-mounted here would see the empty\n' >&2
-        printf 'directory underneath and conclude the library is empty — which is how a\n' >&2
-        printf 'scan begins deleting metadata it cannot find.\n' >&2
-        exit 1
-    fi
-    if [ "$warned" -eq 0 ]; then
-        report "waiting for mount(s) this unit depends on" "${missing[@]}"
-        warned=1
-    fi
-    sleep 1
-done
-
-[ "$warned" -eq 0 ] || printf 'mounted; proceeding.\n'
-exit 0

serverAppConfigs-docs/Dankserver/Media Metadata View.md

@@ -46,11 +46,10 @@ view really is a mountpoint.
 | Installer | `scripts/media-view.sh` — `plan` / `install` / `verify` / `status` / `reap` |
 | Written by | Jellyfin only (Plex binds read-only); nothing else in the fleet touches it |
 
-Both consumers gate their start on the view with
+Both consumers guard the view with
-`ExecStartPre=/home/dank/serverAppConfigs/scripts/wait-for-mount.sh` (it waits
+`UnitConfigItem=ConditionPathIsMountPoint=/var/lib/media-meta/view`, and
-for the mount, then refuses), and `scripts/deploy.sh dankserver --service
+`scripts/deploy.sh dankserver --service jellyfin|plex` calls `media-view.sh
-jellyfin|plex` calls `media-view.sh install` + `verify` before it restarts
+install` + `verify` before it restarts either container.
-either container.
 
 | Consumer | Bind | Mode | Why that path |
 |---|---|---|---|
@@ -81,20 +80,11 @@ the defaults are the host values above.
   refuse via `lsblk -dno ROTA` if the upper base lives on the array: an overlay
   whose upper is the spinners is the original problem with extra steps, and it
   silently turns every metadata write back into a seek.
-- **A container that binds the array must refuse to start until the mount
+- **Never mount the view over an unmounted lower.** `RequiresMountsFor=/mnt/entropy`
-  answers.** Live 2026-10-31: the array's mount and the media containers raced at
+  plus the container `ConditionPathIsMountPoint` guards: an empty `lowerdir`
-  boot, podman resolved the bind against the pre-mount directory, and both
+  presents an *empty library* as truth, and a media scan would then clear the
-  servers came up blind — Jellyfin read an empty library and began
+  database of everything. systemd does not create a mount point, so `install`
-  `Removing item, Type: "Season"` by the thousand. Two dependencies people reach
+  creates `view` itself; without it the mount simply fails.
-  for do not work here, both measured on that host: `RequiresMountsFor=` in a
-  **rootless** unit is inert (the user manager cannot order against the system's
-  `mnt-entropy.mount`), and `ConditionPathIsMountPoint=` is fail-*dead* — an
-  unmet condition logs `skipped, unmet condition check` with `NRestarts=0` and no
-  start attempt ever follows, so the unit waits for a human. The working guard is
-  `scripts/wait-for-mount.sh` as `ExecStartPre`: it waits out the race, refuses by
-  name after its window, and `Restart=always` carries the unit from there.
-  systemd does not create a mount point, so `install` creates `view` itself;
-  without it the mount simply fails.
 - **Never delete through the view.** A delete writes an overlayfs whiteout
   (`.wh.<name>`) in the upper layer, which hides the array's copy without
   removing it — the file reappears the moment the view is unmounted, and the
@@ -117,8 +107,7 @@ the defaults are the host values above.
 
 | Symptom | Meaning |
 |---|---|
-| `jellyfin.service` / `plex.service` fail with `refused: still not mounted after 90s: …` | The view or the array is not mounted. Do not start them anyway: `scripts/media-view.sh install`, then `verify`. |
+| `jellyfin.service` / `plex.service` show `ConditionPathIsMountPoint=... was not met` and stay inactive | The view is not mounted. Do not start them anyway: `scripts/media-view.sh install`, then `verify`. |
-| Servers answer, library looks empty, Jellyfin logs `Removing item, Type: "Season"` by the thousand | Blind bind — the container started before the mount and bound the pre-mount directory. `podman exec jellyfin ls /data` against `ls /mnt/entropy` is the whole diagnosis; restarting the container re-resolves the bind. |
 | Jellyfin log: `Read-only file system : '/data/Movies/…/movie.nfo'` | The container is binding the raw array, not the view — the quadlet drifted back or the view is gone. `media-view.sh status`. |
 | A folder appears in a media server with artwork/`.nfo` but no video | Ghost metadata from a relayout. `media-view.sh reap`. |
 | `verify` prints `refused: …/view is not a mountpoint` | A plain directory is sitting where the overlay belongs. That is the fail-closed guard working; `install` on the box. |

serverAppConfigs-docs/Dankserver/Media Relayout.md

@@ -81,6 +81,13 @@ An apply also leaves the release folders it emptied standing where they were —
 hundreds of them at the library root — which is what `sweep` removes, dry-run
 first, from the same journal.
 
+`--batch N` (default 64) makes the journal durable per batch instead of per
+move: N intents are written and fsynced, then those N rename. The rule a crash
+relies on — no rename runs before its intent is on disk — is unchanged, so an
+interrupted apply still replays the batch and resumes with nothing lost. Batch 1
+is the old behaviour; the only reason to name it is debugging, because on the
+spinning array it spends most of a large apply's wall time in fsyncs.
+
 After it lands, both servers need a scan or the change is invisible. [[Plex]] and
 [[Jellyfin]] own the exact requests; two laws hold at this step: `204` is
 acceptance and anything else queued nothing — re-issue the identical request

tests/array_mount_gate.bats

@@ -1,96 +0,0 @@
-#!/usr/bin/env bash
-# Seam: a container that binds the entropy array must refuse to start until the
-# thing it binds is actually mounted.
-#
-# Live 2026-10-31, Dankserver: the array's systemd mount STARTED eight seconds
-# before the media containers were created, but a rootless quadlet cannot order
-# itself against a SYSTEM mount unit — `RequiresMountsFor=/mnt/entropy` resolves
-# to nothing in the user manager and is simply inert. So podman resolved the bind
-# against the pre-mount directory (which held one stale subdirectory) and both
-# Jellyfin and Plex came up blind: their library root looked empty, Jellyfin
-# logged thousands of `Removing item, Type: "Season"`, and the array sat at 80 %
-# util doing nothing useful until the host went down. A blind bind is not a
-# cosmetic fault — it is a metadata-deleting machine.
-#
-# The measured fix is `ExecStartPre=<repo>/scripts/wait-for-mount.sh <source>`:
-# it WAITS for the mount and then refuses, so `Restart=always` carries the unit
-# across a slow mount. A `ConditionPathIsMountPoint=` was measured on the same
-# host and is the wrong tool: an unmet condition logs `skipped, unmet condition
-# check` with NRestarts=0 and never a start attempt — the unit stays dead until
-# a human starts it. That is fail-dead, not fail-closed.
-#
-# Tests assert only observable behavior of the gate (exit status and the name it
-# refuses by) and the structural law over the quadlets; never the internals.
-
-load helpers
-
-GATE="$REPO_ROOT/scripts/wait-for-mount.sh"
-
-@test "the gate accepts a path that really is a mountpoint" {
-    run "$GATE" -t 2 /proc
-    [ "$status" -eq 0 ] || { printf '%s\n' "$output" >&2; return 1; }
-}
-
-@test "a plain directory is refused, and refused BY NAME" {
-    dir="$BATS_TEST_TMPDIR/not-a-mount"
-    mkdir "$dir"
-    run "$GATE" -t 1 "$dir"
-    [ "$status" -ne 0 ] || { printf 'accepted a plain directory\n' >&2; return 1; }
-    [[ "$output" == *"$dir"* ]] || { printf 'refusal did not name the path: %s\n' "$output" >&2; return 1; }
-}
-
-@test "a path that does not exist is refused by name" {
-    run "$GATE" -t 1 "$BATS_TEST_TMPDIR/does/not/exist"
-    [ "$status" -ne 0 ]
-    [[ "$output" == *"$BATS_TEST_TMPDIR/does/not/exist"* ]]
-}
-
-@test "the gate holds the deadline instead of deciding on one look" {
-    # A single check that failed at the wrong instant is the boot race itself:
-    # the mount lands a second later and the unit is dead anyway. So the window
-    # must be spent waiting, and that is observable from outside as elapsed time.
-    dir="$BATS_TEST_TMPDIR/never"
-    mkdir "$dir"
-    start=$SECONDS
-    run "$GATE" -t 4 "$dir"
-    elapsed=$((SECONDS - start))
-    [ "$status" -ne 0 ]
-    [ "$elapsed" -ge 4 ] || { printf 'gave up after %ss, window was 4s\n' "$elapsed" >&2; return 1; }
-}
-
-@test "the gate accepts a mount that arrives during its window" {
-    dir="$BATS_TEST_TMPDIR/later"
-    mkdir "$dir"
-    if ! mount --bind /proc "$dir" 2>/dev/null; then
-        skip "creating a mount needs privileges this box does not grant"
-    fi
-    run "$GATE" -t 4 "$dir"
-    umount "$dir" 2>/dev/null || sudo -n umount "$dir" 2>/dev/null || true
-    [ "$status" -eq 0 ] || { printf 'gate did not wait for a mount that arrived: %s\n' "$output" >&2; return 1; }
-}
-
-@test "no unit without the gate binds the array or the metadata view" {
-    bad=""
-    while IFS= read -r unit; do
-        sources=$(sed -n 's/^Volume=\([^:]*\):.*/\1/p' "$unit" \
-            | grep -E '^(/mnt/entropy|/var/lib/media-meta/view)$' | sort -u)
-        [ -n "$sources" ] || continue
-        for src in $sources; do
-            grep -q "ExecStartPre=.*wait-for-mount.sh.* $src\b" "$unit" \
-                || bad="$bad$unit binds $src with no start gate"$'\n'
-        done
-    done < <(find "$REPO_ROOT"/dankserver "$REPO_ROOT"/dankclaw "$REPO_ROOT"/frankbook-pro \
-                 -path '*/quadlet/*.container' -not -path '*.AGENTTRASH*')
-    [ -z "$bad" ] || { printf 'blind binds:\n%s' "$bad" >&2; return 1; }
-}
-
-@test "no gated unit keeps the fail-dead ConditionPathIsMountPoint" {
-    bad=""
-    while IFS= read -r unit; do
-        grep -q "wait-for-mount.sh" "$unit" || continue
-        grep -q "ConditionPathIsMountPoint" "$unit" \
-            && bad="$bad$unit: a gate and an unmet-condition skip cannot coexist"$'\n'
-    done < <(find "$REPO_ROOT"/dankserver "$REPO_ROOT"/dankclaw "$REPO_ROOT"/frankbook-pro \
-                 -path '*/quadlet/*.container' -not -path '*.AGENTTRASH*')
-    [ -z "$bad" ] || { printf 'fail-dead conditions:\n%s' "$bad" >&2; return 1; }
-}

tests/media_overlay.bats

@@ -61,10 +61,7 @@ UNIT="$REPO_ROOT/dankserver/host/systemd/media-meta-view.mount"
 @test "both media servers bind the view and refuse to start without it" {
     for unit in "$JELLY" "$PLEX"; do
         grep -q "^Volume=$MOUNT:" "$unit" || return 1
-        # The refusal is a start GATE, not a Condition: measured on the host, a
+        grep -q "^UnitConfigItem=ConditionPathIsMountPoint=$MOUNT$" "$unit" || return 1
-        # unit whose Condition goes unmet is skipped forever (NRestarts=0, no
-        # start attempt) — fail-dead. The gate waits, then refuses.
-        grep -q "^ExecStartPre=.*wait-for-mount.sh .*$MOUNT" "$unit" || return 1
         # The raw array must no longer be a container source: that bind is what
         # made sidecar sharing impossible (read-only) and metadata slow (seeks).
         ! grep -q '^Volume=/mnt/entropy' "$unit"

tests/media_relayout.bats

@@ -494,6 +494,65 @@ for r in moves:
 PY
 }
 
+# The live pass paid an fsync per move on a spinning array (63 074 of them) and
+# the run took 11 minutes for 58 278 renames. --batch N writes N intents, syncs
+# once, then performs those N moves — the durability rule is unchanged (no move
+# runs before its intent is on disk), only the number of flushes falls.
+@test "a batched apply journals every move and lands the same tree" {
+    plan
+    JOURNAL="$BATS_TEST_TMPDIR/batched.jsonl"
+    run python3 "$APPLY" apply --plan "$OUT" --root "$LIB" --journal "$JOURNAL" \
+        --batch 4 --apply
+    [ "$status" -eq 0 ]
+    local planned journalled
+    planned=$(awk -F'\t' '$1=="move"' "$OUT" | wc -l)
+    journalled=$(grep -c '"op": "move"' "$JOURNAL")
+    [ "$journalled" -eq "$planned" ]
+    run python3 "$APPLY" verify --plan "$OUT" --root "$LIB" --journal "$JOURNAL"
+    [ "$status" -eq 0 ]
+    python3 - "$OUT" <<'PY'
+import os, sys
+moves = [r for r in (l.rstrip("\n").split("\t") for l in open(sys.argv[1]))
+         if r[0] == "move"]
+assert moves, "fixture planned no moves"
+for r in moves:
+    assert os.path.exists(r[2]), f"target missing: {r[2]}"
+    assert not os.path.exists(r[1]), f"source left behind: {r[1]}"
+PY
+}
+
+@test "an apply stopped mid-batch resumes without losing or double-journalling a move" {
+    plan
+    JOURNAL="$BATS_TEST_TMPDIR/interrupted-batch.jsonl"
+    python3 "$APPLY" apply --plan "$OUT" --root "$LIB" --journal "$JOURNAL" \
+        --batch 2 --apply > "$BATS_TEST_TMPDIR/first.log" 2>&1 &
+    local pid=$! i
+    # stop the run the moment a batch of intents is on disk (it may also have
+    # finished already — both outcomes must resume cleanly)
+    for i in $(seq 1 200); do
+        [ -f "$JOURNAL" ] && [ "$(grep -c '"op": "move"' "$JOURNAL" 2>/dev/null || true)" -ge 2 ] && break
+        sleep 0.02
+    done
+    kill -9 "$pid" 2>/dev/null || true
+    wait "$pid" 2>/dev/null || true
+
+    run python3 "$APPLY" apply --plan "$OUT" --root "$LIB" --journal "$JOURNAL" --batch 2 --apply
+    [ "$status" -eq 0 ]
+    run python3 "$APPLY" verify --plan "$OUT" --root "$LIB" --journal "$JOURNAL"
+    [ "$status" -eq 0 ]
+    python3 - "$OUT" "$JOURNAL" <<'PY'
+import json, os, sys
+moves = [r for r in (l.rstrip("\n").split("\t") for l in open(sys.argv[1]))
+         if r[0] == "move"]
+journal = [json.loads(l) for l in open(sys.argv[2])]
+dsts = [j["dst"] for j in journal if j.get("op") == "move"]
+assert len(dsts) == len(set(dsts)), "a destination was journalled twice"
+assert len(dsts) == len(moves), f"journalled {len(dsts)} of {len(moves)} moves"
+for r in moves:
+    assert os.path.exists(r[2]) and not os.path.exists(r[1]), r[2]
+PY
+}
+
 @test "rollback puts every file back where the census found it" {
     plan
     apply_plan