From 0ea81e0e96c8d2b2008d1351f6f2f7e79af8e96b Mon Sep 17 00:00:00 2001
From: jochens <jschoubben@gmail.com>
Date: Thu, 12 Nov 2026 22:57:56 +0100
Subject: [PATCH] Design 42 zfs-owns-zfs: answer the open question in the
 node-engine, name issue 1979

The lead answered that a resource following a set value and one line
per list entry are built in the node-engine in this milestone, so the
module's files, units and handlers are placed only once their value is
set, as ADR 0679 holds. The cron-to-calendar fix leaves the milestone
and stays an ordering edge the scheduled run waits on.
---
 00-META/glossary.md                           |   2 +-
 .../01-to-be/42-milestones/zfs-owns-zfs.md    | 181 ++++++++++--------
 .../42-the-machines-modules-in-order.md       |   4 +-
 3 files changed, 100 insertions(+), 87 deletions(-)

diff --git a/00-META/glossary.md b/00-META/glossary.md
index 2d091ee6..d431c9e1 100644
--- a/00-META/glossary.md
+++ b/00-META/glossary.md
@@ -1023,7 +1023,7 @@ becomes a message). **Decided by** ADR 0227, 0231, 0240, 0252, 0283, 0564, 0668.
 - **ZFS snapshot** — a read-only point in time of one ZFS dataset on a machine, kept inside that dataset's pool, so
   it guards against a mistake and never against the pool's loss; taken by a person with `zfs_snapshot`, or by the zfs
   module's scheduled run, which names its own `mesh-<kind>-<time>`, marks them and removes only those past their keep
-  count (ADR 0679 §7; design 42 zfs-owns-zfs §17, §18). Never bare, beside a ledger's snapshot and the stream snapshot
+  count (ADR 0679 §7; design 42 zfs-owns-zfs §19, §20). Never bare, beside a ledger's snapshot and the stream snapshot
   (see [Homonyms](#homonyms)); not a backup or a restore point, which are kept elsewhere.
   *Not:* ~~pool snapshot~~, ~~dataset snapshot~~
 - **disk readings** — the size of each data item a node's modules declare, measured by its `measure` and kept
diff --git a/03-DESIGN/01-to-be/42-milestones/zfs-owns-zfs.md b/03-DESIGN/01-to-be/42-milestones/zfs-owns-zfs.md
index 35d70ca3..c246b27f 100644
--- a/03-DESIGN/01-to-be/42-milestones/zfs-owns-zfs.md
+++ b/03-DESIGN/01-to-be/42-milestones/zfs-owns-zfs.md
@@ -26,61 +26,79 @@ ZFS snapshots; each is changed only once its config value is set (ADR 0679). The
 main file's, [*The zfs module*](../42-the-machines-modules-in-order.md#the-zfs-module). This part holds every line
 the milestone builds, cited as "design 42 zfs-owns-zfs §n".
 
-**Where.** Three repositories, one delivery group with one check: `mesh-host` (the node-engine: §1, §2),
-mesh-catalog's checks (§3) and mesh-catalog's `modules/zfs` (§4 to §25). **Ordering edge:** the zfs module's new
-version needs the node-engine of §1 and §2 on its machine (a node-engine capability edge the delivery plan derives,
-§4); §3 has no edge, it gates the catalog's own check.
-
-**Open before develop.** Lines §9, §10 and §11 carry an open design question (Q1 at the end of this part); their
-subtasks wait for its answer. Nothing else in this part waits on it.
+**Where.** Built under issue 1979. Three repositories, one delivery group with one check: `mesh-host` (the
+node-engine: §2, §3, §4, its three subtasks of issue 1979), mesh-catalog's checks (§5) and mesh-catalog's
+`modules/zfs` (§6 to §27). **Ordering edges:** the zfs module's new version needs the node-engine of §2, §3 and §4
+on its machine (a node-engine capability edge the delivery plan derives, §6), and its scheduled run needs the
+node-engine's cron-to-calendar fix of §1, built outside this milestone; §5 has no edge, it gates the catalog's own
+check.
 
 ## The prerequisites
 
-1. **The node-engine writes a valid calendar for a cron step.** The node-engine's `calendarFor` (the schedule of a
-   `process` resource turned into a timer's `OnCalendar`) writes a field `*/N` as `0/N` for the minute and the hour
-   and as `1/N` for the day of the month and the month; the day of the week is unchanged. Today `*/15 * * * *` becomes
-   `*-*-* *:*/15:00`, which the service manager refuses, so the zfs module's scrub timer fails (ADR 0679 §14).
-   Checked by a table test of `calendarFor` over `*/15 * * * *` (`*-*-* *:0/15:00`), `0 */6 * * *`
-   (`*-*-* 0/6:00:00`), `0 0 */2 * *` (`*-*-1/2 00:00:00`) and the existing cases unchanged.
+1. **The scheduled run waits on the node-engine's valid calendar for a cron step** (ADR 0679 §14). The node-engine
+   writes a schedule's field `*/N` as `0/N` for the minute and the hour and as `1/N` for the day of the month and the
+   month; today `*/15 * * * *` becomes `*-*-* *:*/15:00`, which the service manager refuses, so the zfs module's scrub
+   timer fails. That fix is not built in this milestone: the operator gave it to another session, which tracks it in
+   an issue of its own. It is an ordering edge: the module's new version, whose scheduled run (§19) keeps its
+   `*/15 * * * *` schedule, is delivered to the home server only once a node-engine with that fix runs there.
+   Checked by the delivery plan naming the edge, and by `<node>/node-service-manager.status` of the module's timer
+   showing it active (acceptance test 3).
 2. **The node-engine's apply of a module stops at its first failed resource.** When one resource of a module fails,
    the node-engine applies none of that module's later resources in the declared order; the report names the
    failed resource with its error and each one left unapplied, and the module's phase is `failed`. Resources already
    applied stay as applied. Other modules on the node go on as today. Today the apply goes on, and stopped the
    distribution's scrub timer after the module's own timer failed (ADR 0679 §14). Checked by a unit test: a module of
    three resources whose second fails leaves the third untouched and reports it as left.
-3. **The catalog refuses a second writer of one file.** mesh-catalog's checks refuse a catalog in which two
+3. **The node-engine declares a resource only while a config value holds** (lead's answer, 2026-11-12, to this
+   part's design question: build it in the node-engine, design-it-as-it-should-be; ADR 0679 §3, §8). A resource of
+   any type may carry the manifest field `if-config`: a list of conditions, each `<key>` (the module's config value is
+   set and is neither `false`, `off`, `none` nor an empty list) or `<key>=<value>` (the value equals it; for a list
+   value, the list holds that entry). The resource is declared while any condition holds, and not at all while none
+   does. A resource that leaves the declaration this way is removed as any resource that leaves it: a file written
+   over gets its original back (ADR 0118), a unit gets its found state back (ADR 0269). The controller's catalog check
+   refuses an `if-config` key the module does not declare under `config`. Checked by the node-engine's table test (a
+   value unset, `off`, set; a list with and without the entry; a value going from set to unset removes the resource
+   and puts the original back) and the catalog check's own test.
+4. **A template writes one line per entry** (lead's answer, 2026-11-12, as §3; ADR 0679 §4). A template file may
+   hold `${config-lines:<key>:<prefix>}`: for a list value one line per entry, `<prefix><entry>`, in the list's order;
+   for a set scalar value one line `<prefix><value>`; nothing for an unset value or an empty list. With a fourth part,
+   `${config-lines:<key>:<prefix>:mib-bytes}`, a number given in MiB is written in bytes. The prefix is literal text
+   with no `}`, `$` or newline, refused by the catalog check; an entry holding a newline is refused before the file is
+   written, and the file is left as it was. Checked by the node-engine's table test (a list of two, an empty list, an
+   unset and a set scalar, `mib-bytes`, a newline in an entry) and the catalog check's own test.
+5. **The catalog refuses a second writer of one file.** mesh-catalog's checks refuse a catalog in which two
    modules' manifests declare a `file` resource at one path, naming both modules and the path (ADR 0679 §14; ADR 0051
    §9, rival ownership). A file only read is not a writer. Checked by the check's own test over two manifests that
    declare one path (refused) and two that declare different paths (passed); it runs in the catalog's check on
    every pull request.
-4. **The order on the machine.** The zfs module's new version declares its own timer resource (the scheduled run of
-   §17) before the resources that stop the distribution's scrub timers, so by §2 those are stopped only once the
-   module's own timer is active (ADR 0679 §14). The delivery plan places the node-engine of §1 and §2 on the home
-   server before the module (the capability edge above). Checked by the module's manifest test, which pins the
+6. **The order on the machine.** The zfs module's new version declares its own timer resource (the scheduled run of
+   §19) before the resources that stop the distribution's scrub timers, so by §2 those are stopped only once the
+   module's own timer is active (ADR 0679 §14). The delivery plan places the node-engine of §2, §3 and §4 on the home server before the
+   module (the capability edge above), and §1's edge holds the module until the calendar fix runs there. Checked by the module's manifest test, which pins the
    resource order, and by acceptance test 3 of the main file.
 
 ## What the module owns
 
-5. **The packages.** The manifest declares `zfs-utils` and `zfs-dkms` present (ADR 0679 §1; ADR 0303 §2: the
+7. **The packages.** The manifest declares `zfs-utils` and `zfs-dkms` present (ADR 0679 §1; ADR 0303 §2: the
    node-engine installs a missing one, upgrades none, removes none). `zfs-utils-debug` is not declared and is left as
    found. Fate: the README's "It installs nothing" goes; it says the two packages and why the debug package is not
    the module's. Read by `pacman_packages` as declared by `zfs`. Checked by the manifest test.
-6. **One pool, renamed `pool`.** The config value `scrub-pool` becomes `pool` (ADR 0679 §1): type string, trusted,
+8. **One pool, renamed `pool`.** The config value `scrub-pool` becomes `pool` (ADR 0679 §1): type string, trusted,
    required, same description but for the rename. It is moved by mesh-config's rename window (mesh-config answers both
    names meanwhile; its seat verb `renames` says the window), and every template and the module's code read `pool`.
    One pool per assignment; the manifest has no per-pool form and none is added. The module reads, never writes,
    `/etc/zfs/zpool.cache` and `/etc/zfs/zfs-list.cache`. Checked by the manifest test (no `scrub-pool` left) and the
    rename's live read in `zfs_config`.
-7. **What is not its own.** `sharenfs` and `sharesmb` are on no list of §13; a setting naming them is refused
-   (§8), and `zfs_config` never reports either as drift (ADR 0679 §2). The pool's files are the operator's (ADR
-   0051). Checked by §24's refused-forms test.
+9. **What is not its own.** `sharenfs` and `sharesmb` are on no list of §15; a setting naming them is refused
+   (§10), and `zfs_config` never reports either as drift (ADR 0679 §2). The pool's files are the operator's (ADR
+   0051). Checked by §26's refused-forms test.
 
 ## The config values and their forms
 
-8. **Every new value is "not managed" until set, and has a fixed form** (ADR 0679 §3, §4). Each value below has no
+10. **Every new value is "not managed" until set, and has a fixed form** (ADR 0679 §3, §4). Each value below has no
    default in the manifest; absent means not managed: the module writes nothing, converges nothing and reports no
    drift for it. A value of another form is refused by the module's own parse, before any file is written or command
-   run, emitting `config.refused` (§18). Trusted values (every list and object below, and `hostid`) are set on the
+   run, emitting `config.refused` (§22). Trusted values (every list and object below, and `hostid`) are set on the
    operator's Approve (ADR 0348 §4, §8). The module never reads a value from the machine into config.
    - `arc-max`, `arc-min` (number): whole MiB, `arc-min` ≤ `arc-max`, `arc-max` at least 64 and below the machine's
      memory read from `/proc/meminfo`. ZFS's read cache in memory (the ARC) is bounded by them.
@@ -101,48 +119,53 @@ subtasks wait for its answer. Nothing else in this part waits on it.
    - `pool-properties` (object, trusted): `autotrim`, `autoexpand`, `autoreplace` (`on`, `off`, `default`) and
      `failmode` (`wait`, `continue`, `panic`, `default`).
    - `dataset-properties` (object, trusted): a dataset of the pool (the pool's name or one beginning `<pool>/`) to
-     properties of §13's list with their forms.
+     properties of §15's list with their forms.
    - `snapshots` (object, trusted): `datasets` (list of datasets of the pool; absent means every filesystem of the
      pool), and keep counts `hourly` (0 to 48), `daily` (0 to 62), `weekly` (0 to 104), `monthly` (0 to 120); absent
      or all zero means none.
-   - `hostid` (string, trusted): `generate`, written once (§12).
-   Checked by §24's refused-forms tests, one table per value.
+   - `hostid` (string, trusted): `generate`, written once (§14).
+   Checked by §26's refused-forms tests, one table per value.
 
 ## Files, units and the event daemon
 
-9. **The node-engine places the module's files** (ADR 0679 §1, §4, §8). `/etc/modprobe.d/zfs.conf` holds one
-   `options zfs` line per set value: `zfs_arc_max` and `zfs_arc_min` in bytes from `arc-max` and `arc-min`, then each
-   `module-options` entry; with nothing set it holds only its header comment, which sets nothing. `/etc/zfs/zed.d/zed.rc`
-   holds the package's own lines with `ZED_SCRUB_AFTER_RESILVER=1` when `resilver_finish-start-scrub` is among the
-   handlers, and no `ZED_NOTIFY_*` or mail line. `/etc/default/zfs` holds the package's own content; no value of ADR
-   0679 changes it, so it is the module's only to have one writer. Every line is generated from parsed values, never
-   from free text, and a test refuses a newline, a quote, `$`, a backtick and a semicolon in every field (§24). A file
-   the node-engine writes over keeps its original, put back when the module leaves (ADR 0118, §22). **Open: Q1** (how a
-   file is written only when its value is set, and how one line per list entry is rendered).
-10. **The units.** The node-engine declares `zfs-import-cache.service`, `zfs-mount.service`, `zfs.target` and
+11. **The node-engine places the module's files** (ADR 0679 §1, §4, §8), by §3 and §4.
+   `/etc/modprobe.d/zfs.conf` carries `if-config: [arc-max, arc-min, module-options]` and holds, by §4, a header
+   comment, then `options zfs zfs_arc_max=` and `options zfs zfs_arc_min=` with `arc-max` and `arc-min` in bytes
+   (`mib-bytes`), then `options zfs ` with each `module-options` entry; with none of the three set the file is not
+   placed. The module's own `zed.rc` is placed in its folder (§13), not over the package's: it holds the package's
+   variables but every `ZED_NOTIFY_*` and mail line, and `ZED_SCRUB_AFTER_RESILVER=1`, which only the handler
+   `resilver_finish-start-scrub` reads, so it acts only where that handler is placed. The package's
+   `/etc/zfs/zed.d/zed.rc` and `/etc/default/zfs` are left as the package wrote them: no value of ADR 0679 changes
+   either, so writing them would only rewrite what ADR 0679 §3 leaves alone; `zfs_config` shows both as the
+   package's, and a `.pacnew` beside either as a warning. Every line is from a parsed value, never from free text, and
+   a test refuses a newline, a quote, `$`, a backtick and a semicolon in every field (§26). Checked by the manifest
+   test and §26.
+12. **The units.** The node-engine declares `zfs-import-cache.service`, `zfs-mount.service`, `zfs.target` and
     `zfs-import.target` running and enabled at boot, as they are on the home server today, so declaring them changes
     nothing; `zfs-import-scan.service`, `zfs-share.service` and `zfs-volume-wait.service` are declared with no state
-    (ADR 0117), owned and left as found; `zfs-zed.service` is running and enabled when `zed` is `on`, stopped and
-    disabled when `off`, and left as found when not managed; the distribution's `zfs-trim-weekly@<pool>.timer` and
-    `zfs-trim-monthly@<pool>.timer` are stopped and disabled once `trim-schedule` is set (the module's run trims,
-    §17), and the distribution's scrub timers stopped and disabled after the module's own (§4). Read by
-    `<node>/node-service-manager.status`. **Open: Q1** (a unit state that follows a value only once it is set).
-11. **ZED's handlers without links** (ADR 0679 §11). With `zed` on, the module places each handler of `zed-handlers`
-    as a file in its own folder `/etc/zfs/mesh-zed.d` (a copy of the package's script by its content, mode 0755,
-    root's) and a drop-in for `zfs-zed.service` whose `ExecStart` adds `-d /etc/zfs/mesh-zed.d`; `zed.rc` is read
-    from there too, as a copy of §9's. The package's links in `/etc/zfs/zed.d` stay as the package left them and are
-    not read while the drop-in holds. The mesh creates no symlinks. The node-engine restarts `zfs-zed.service` on a
-    change of the drop-in, a handler or `zed.rc`. Checked by the manifest test (no link resource) and a live
-    `<node>/node-files.list` of the folder. **Open: Q1** (placed only when `zed` is on).
-12. **The machine's ZFS id.** `/etc/hostid` is written only when `hostid` is `generate` and the file is absent, by the apply
-    of §15 with `zgenhostid`; never rewritten. Before the Approve, the value's description and `zfs_config` say that
+    (ADR 0117), owned and left as found. `zfs-zed.service` is declared twice by §3: running and enabled with
+    `if-config: [zed=on]`, stopped and disabled with `if-config: [zed=off]`, and so not declared, and left as found,
+    while `zed` is not managed. The distribution's `zfs-trim-weekly@<pool>.timer` and `zfs-trim-monthly@<pool>.timer`
+    are stopped and disabled with `if-config: [trim-schedule]` (the module's run trims, §19). The distribution's scrub
+    timers are stopped and disabled after the module's own (§6). Read by `<node>/node-service-manager.status`.
+    Checked by the manifest test (each unit, its state and its condition).
+13. **ZED's handlers without links** (ADR 0679 §11). The module's folder `/etc/zfs/mesh-zed.d` (root's, 0755), its
+    `zed.rc` (§11) and a drop-in for `zfs-zed.service` whose `ExecStart` adds `-d /etc/zfs/mesh-zed.d` carry
+    `if-config: [zed=on]`. Each handler is a file of its own in that folder, a copy of the package's script by its
+    content kept in the module's files archive, mode 0755, with `if-config: [zed-handlers=<its name>]`, so only the
+    handlers set are placed. The package's links in `/etc/zfs/zed.d` stay as the package left them and are not read
+    while the drop-in holds. The mesh creates no symlinks. The node-engine restarts `zfs-zed.service` on a change of
+    the drop-in, a handler or `zed.rc` (`restart-on`). Checked by the manifest test (no link resource, each handler's
+    condition) and a live `<node>/node-files.list` of the folder.
+14. **The machine's ZFS id.** `/etc/hostid` is written only when `hostid` is `generate` and the file is absent, by the apply
+    of §17 with `zgenhostid`; never rewritten. Before the Approve, the value's description and `zfs_config` say that
     the pool must then be imported once by hand after the next reboot to check it imports under the new id; the
     module never reboots. Emits `config.applied` with target `file`. Checked by a unit test (absent file: one
     `zgenhostid`; present file: none).
 
 ## The pool
 
-13. **Pool and dataset properties** (ADR 0679 §5). For each set pool property the apply runs
+15. **Pool and dataset properties** (ADR 0679 §5). For each set pool property the apply runs
     `zpool set <property>=<value> <pool>`, and for `default` `zpool set <property>=<ZFS's default> <pool>`. For each
     set dataset property it runs `zfs set <property>=<value> <dataset>`, and for `default`
     `zfs inherit <property> <dataset>`, so its source stays default. The dataset list is `compression` (`off`, `lz4`,
@@ -150,8 +173,8 @@ subtasks wait for its answer. Nothing else in this part waits on it.
     (a power of two from `512` to `16M`, with `K` or `M`), `primarycache` and `secondarycache` (`all`, `metadata`,
     `none`), `sync` (`standard`, `always`, `disabled`), `logbias` (`latency`, `throughput`), `quota` and
     `reservation` (`none` or digits with `K`, `M`, `G` or `T`). A property already at its value runs nothing. Each
-    change is read back with `zpool get -Hp` or `zfs get -Hp` and emitted (§18). Checked by §24's convergence tests.
-14. **Cache and log devices** (ADR 0679 §5). From `zpool status -P -L <pool>` the apply knows each device's kernel
+    change is read back with `zpool get -Hp` or `zfs get -Hp` and emitted (§22). Checked by §26's convergence tests.
+16. **Cache and log devices** (ADR 0679 §5). From `zpool status -P -L <pool>` the apply knows each device's kernel
     path, and from the link under `/dev/disk/by-id` each declared name's kernel path. Then, in this order:
     - an entry of the pool whose kernel path is a declared device's, but named by its kernel name, is removed
       (`zpool remove <pool> <entry>`) and added again by its stable name;
@@ -163,28 +186,28 @@ subtasks wait for its answer. Nothing else in this part waits on it.
     - a log device not declared, or one to rename, is removed only while the pool is ONLINE with no read, write or
       checksum errors and no scrub or resilver runs; otherwise it is a wait, `config.waiting` {key, waits-on, since}.
     A declared device that is not present is a wait. Each change is read back from `zpool status -P` and emitted.
-    Checked by §24's convergence tests and acceptance test 2.
-15. **Who applies, and when** (ADR 0679 §8). A `process` resource `zfs-config-apply`, `run: ./zfs-tools apply`, as
+    Checked by §26's convergence tests and acceptance test 2.
+17. **Who applies, and when** (ADR 0679 §8). A `process` resource `zfs-config-apply`, `run: ./zfs-tools apply`, as
     root, oneshot, ordered after `zfs-import.target` and enabled at boot; restarted by the node-engine on a change of
     the module's config file (`restart-on`), which is how a set value reaches it from mesh-config (ADR 0348 §5, §6);
-    started by hand through `zfs_config_apply` (§21). It holds an exclusive lock on `/run/zfs-tools/apply.lock`; a
+    started by hand through `zfs_config_apply` (§23). It holds an exclusive lock on `/run/zfs-tools/apply.lock`; a
     second start waits for it. It runs nothing while a scrub or resilver runs on the pool or before the pool is
     imported: it emits `config.waiting` and the next start applies. It never runs on a timer. While the bus or the
     control-node is down it applies the values its config file last held. It writes `arc-max` and `arc-min` live to
-    `/sys/module/zfs/parameters/zfs_arc_max` and `zfs_arc_min` as well as to §9's file and reads them back; each
+    `/sys/module/zfs/parameters/zfs_arc_max` and `zfs_arc_min` as well as to §11's file and reads them back; each
     `module-options` entry whose live value differs is a warning naming it, "takes effect at the next module load",
     never success and never unhealthy.
-16. **Never converged, always asked** (ADR 0679 §6). No setting adds, replaces, attaches, detaches or removes a data
+18. **Never converged, always asked** (ADR 0679 §6). No setting adds, replaces, attaches, detaches or removes a data
     device, a spare, a special or a dedup device; none upgrades the pool, destroys a dataset, rolls back, renames or
     clears. The call-site test (`TestTheBundleRunsOnlyReadingVerbsSnapshotAndScrub`, renamed for what it now holds)
     allows `zpool add` only with `cache` or `log`, `zpool remove` only of a cache or log entry, `zpool set`, `zfs set`
-    and `zfs inherit` only for the lists of §8 and §13, `zfs destroy` only as §17 builds it, `zpool trim` only from
+    and `zfs inherit` only for the lists of §10 and §15, `zfs destroy` only as §20 builds it, `zpool trim` only from
     the scheduled run, and refuses `upgrade`, `replace`, `attach`, `detach`, `clear`, `rollback`, `rename`, `-f`, `-r`,
     `-R` and `-d` everywhere.
 
 ## ZFS snapshots on a schedule
 
-17. **The scheduled run** (ADR 0679 §7). The existing `process` resource `zfs-mesh-scrub` (`./zfs-tools scrub-run`,
+19. **The scheduled run** (ADR 0679 §7). The existing `process` resource `zfs-mesh-scrub` (`./zfs-tools scrub-run`,
     every 15 minutes) becomes `zfs-mesh-run` (`./zfs-tools run`), root as today, and does three things each time, in
     order: the scrub when due (as today), a trim when `trim-schedule` is due (`zpool trim <pool>`, by `trim-day` and
     `trim-time` as the scrub reads its own), and the ZFS snapshots when `snapshots` is set. Reason: one schedule
@@ -194,19 +217,19 @@ subtasks wait for its answer. Nothing else in this part waits on it.
     per dataset, never recursive, and sets on each `zfs set mesh:schedule=<kind>`. No ZFS snapshot is taken while the
     pool's capacity (`zpool list -Hp -o capacity`) is above 80 %: a warning says so, and `snapshot.skipped`
     {pool, capacity} is emitted.
-18. **Removed only by their own record.** After taking, per dataset and kind, the run removes the oldest past its keep
-    count, only when it carries `mesh:schedule=<kind>`, is in the ledger `snapshots` (§20), has no hold
+20. **Removed only by their own record.** After taking, per dataset and kind, the run removes the oldest past its keep
+    count, only when it carries `mesh:schedule=<kind>`, is in the ledger `snapshots` (§22), has no hold
     (`zfs holds`) and no clone (`clones` empty): `zfs destroy -- <dataset>@<snapshot>`, never `-r`, `-R` or `-d`. A
     ZFS snapshot taken by hand is never removed. Each removal emits `snapshot.removed` {snapshot, kind, space freed}
     and records the ledger's `removed` operation.
-19. **A person's ZFS snapshot stays apart.** `zfs_snapshot` refuses a name beginning `mesh-`, and emits
+21. **A person's ZFS snapshot stays apart.** `zfs_snapshot` refuses a name beginning `mesh-`, and emits
     `snapshot.taken` with `by: person`; the run emits it with `by: schedule`. A waiter on a person's ZFS snapshot waits on
     `snapshot.taken` with that snapshot's name, which no scheduled one carries. Fate: the README's "No tool of the
-    mesh destroys a snapshot" becomes §18's rule.
+    mesh destroys a snapshot" becomes §20's rule.
 
 ## What it says, keeps and shows
 
-20. **Events and kept data** (ADR 0679 §9; ADR 0363 §1; ADR 0595). The module declares a stream of its own, local
+22. **Events and kept data** (ADR 0679 §9; ADR 0363 §1; ADR 0595). The module declares a stream of its own, local
     name `zfs`, kept 30 days, carrying `config.applied` {target (`pool`, `dataset`, `file` or `unit`), key, before,
     after, read-back}, `config.refused` {key, value, reason}, `config.waiting` {key, waits-on, since},
     `snapshot.taken` {snapshot, by}, `snapshot.removed`, `snapshot.skipped`, and today's `scrub.requested`; today's
@@ -215,15 +238,15 @@ subtasks wait for its answer. Nothing else in this part waits on it.
     managed (after its last `config.applied`); a ledger `snapshots`, one instance per ZFS snapshot the run took,
     operations `taken` and `removed`, kept by the ledger's template. The apply process and the run declare the bus
     account (`bus`) that writes them; the tools read them.
-21. **Tools** (ADR 0679 §12). `zfs_config`: every owned value with its setting, what runs on the machine, its state
+23. **Tools** (ADR 0679 §12). `zfs_config`: every owned value with its setting, what runs on the machine, its state
     (`not managed`, `as set`, `waiting` with on what and since, `refused` with why, `takes effect at the next module
-    load`), and a `.pacnew` beside an owned file as a warning. `zfs_config_apply`: starts §15's unit through
+    load`), and a `.pacnew` beside an owned file as a warning. `zfs_config_apply`: starts §17's unit through
     `<node>/node-service-manager.start`, with `why`, and answers from the state `applied` afterwards.
     `zfs_snapshots_schedule`: the schedule, its next run, what it would remove next and the ledger.
     `zfs_snapshots_run_now` and `zfs_snapshots_prune_now`: a run's snapshot or removal step by hand, with `why`.
     `zfs_snapshots_pause` and `zfs_snapshots_resume`: a key `paused` in the state `applied`, read by the run, said in
     the health while it holds. The existing read tools stay. Each is in `replaces` where it replaces a command.
-22. **Health** (ADR 0679 §10). `zfs_health` is unhealthy for a `refused` or a failed command in the state `applied`,
+24. **Health** (ADR 0679 §10). `zfs_health` is unhealthy for a `refused` or a failed command in the state `applied`,
     naming the key and why; warnings: a wait (naming on what and since when), the last scheduled ZFS snapshot older
     than its cadence, a failed run, `autoreplace` on or a spare in the pool while `zed` is not `on`, the pool above
     80 % with snapshots set, a parameter awaiting a module load. Pool faults reach the operator once, never from a ZED
@@ -231,7 +254,7 @@ subtasks wait for its answer. Nothing else in this part waits on it.
     bucket `findings` for a pool or device that leaves ONLINE, saying each as an event, and removing it when the state
     is ONLINE again; the condition keeper raises and clears the condition from it (ADR 0564 §2; design 47 G §383). Its
     process declares the bus account that writes them; today it writes the journal only.
-23. **When the module leaves** (ADR 0679 §13; ADR 0303 §2; ADR 0269). The packages stay. The import, mount and target
+25. **When the module leaves** (ADR 0679 §13; ADR 0303 §2; ADR 0269). The packages stay. The import, mount and target
     units stay enabled and running. `/etc/default/zfs` and `zed.rc` get back their found content (ADR 0118);
     `zfs.conf`, the folder `/etc/zfs/mesh-zed.d` and the drop-in are removed, and before leaving `zfs_config` says that
     the next module load uses ZFS's defaults. The distribution's scrub timer is given back as found (ADR 0269). Pool
@@ -239,23 +262,13 @@ subtasks wait for its answer. Nothing else in this part waits on it.
 
 ## How it is checked
 
-24. **Unit tests**, table-driven, one test per area, within the module's 500: no settings gives no `zpool` or `zfs`
+26. **Unit tests**, table-driven, one test per area, within the module's 500: no settings gives no `zpool` or `zfs`
     command that writes; each convergence plan from parsed `zpool status` and `zfs get` output (an add, a kernel name
     to its stable name, a removal, a log removal refused while not healthy, a wait during a scrub); every refused form
     (a newline, quote, `$`, backtick or semicolon in each field; a parameter not on the list; a property not on the
-    lists; a `sharenfs` setting; `-f`; a device with a signature or another pool's label); the call-site test of §16;
+    lists; a `sharenfs` setting; `-f`; a device with a signature or another pool's label); the call-site test of §18;
     pruning never removes a `mesh-` ZFS snapshot without the property or not in the ledger, nor one with a hold or
     clone; `zfs_snapshot` refuses a `mesh-` name; a parameter awaiting a module load is a warning; each change emits
     its event with before and after; a scheduled `snapshot.taken` does not match a person's waiter. The module has no
     integration test; the live checks stand for it, said in the pull request.
-25. **Live, on the home server**: the main file's acceptance tests 1 to 3, in that order.
-
-## Open design questions
-
-- **Q1. A resource that follows a value only once it is set.** ADR 0679 §3 says an unset value writes nothing, §4
-  that the options file and `zed.rc` are generated line by line from the values, and §8 that the node-engine places
-  them. The manifest has no resource declared only when a config value is set (only `if-capability`), and a template
-  fills `${config:<key>}` but makes no line per list entry. §9 to §11 cannot be built as written until this is
-  answered. Recommendation: build both in the node-engine in this milestone, as a fourth prerequisite: a resource
-  field `if-config: <key>` (the resource is declared only while that value is set) and a template form that renders
-  one line per entry of a list value; the record then holds as written.
+27. **Live, on the home server**: the main file's acceptance tests 1 to 3, in that order.
diff --git a/03-DESIGN/01-to-be/42-the-machines-modules-in-order.md b/03-DESIGN/01-to-be/42-the-machines-modules-in-order.md
index 75171245..2d7b7187 100644
--- a/03-DESIGN/01-to-be/42-the-machines-modules-in-order.md
+++ b/03-DESIGN/01-to-be/42-the-machines-modules-in-order.md
@@ -212,13 +212,13 @@ flowchart LR
    drives' kernel names, both stay ONLINE (`zfs_pool_layout`).
 3. The module's own scrub timer is active before the distribution's scrub timer is stopped, read from
    `<node>/node-service-manager.status` of both.
-4. The unit tests of the milestone part's line 24 pass, within the module's budget of 500 unit tests.
+4. The unit tests of the milestone part's line 26 pass, within the module's budget of 500 unit tests.
 
 ## Milestones
 
 | milestone | what it builds | part | state |
 |---|---|---|---|
-| zfs-owns-zfs | the zfs module's ownership of ZFS (ADR 0679), with its three prerequisites in the node-engine and the catalog | [42-milestones/zfs-owns-zfs.md](42-milestones/zfs-owns-zfs.md) | designed |
+| zfs-owns-zfs | the zfs module's ownership of ZFS (ADR 0679), with its prerequisites in the node-engine and the catalog, under issue 1979 | [42-milestones/zfs-owns-zfs.md](42-milestones/zfs-owns-zfs.md) | designed |
 
 The modules of the tables above were built before designs were cut into milestone parts; their remaining lines move
 into a part of their own at their next amendment (playbook 02, *The shape of a design*).