doc: plakar out of the current architecture, kept as reference

backup-strategy.md now leads with the three target legs (local incus
push to sdb, nuc pull over WireGuard, restic to S3 for DBs and
selected trees) and carries the plakar/ks2 story in a closing History
section. restic-backup.md, install.md, local-backup-cron.md and the
ks2 docs describe the predecessor only as 'the first S3
implementation', with one operational note that plakar is still
installed for issue #2338 reproduction.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ks4/restic-backup.md

@@ -1,25 +1,18 @@
 # restic backups on ks4 — the S3 leg
 
-Status: **live since 2026-08-28** — restic replaced plakar as the S3
-backup tool (plakar crons off, its kloset kept for
-[#2338](https://github.com/PlakarKorp/plakar/issues/2338); see §8).
-Architecture: **two tools** — `incus copy` for replication (local sdb,
-nuc after FTTH), **restic** for everything S3. Data leg (`restic-data`)
-runs nightly at 05:00. The instance leg (`restic-incus`, §6) is
-**shelved** (2026-08-28): instances are covered by replication, so
-duplicating their filesystems into S3 buys little. The script and the
-(empty) repo stay in place should that change.
+Status: **live since 2026-08-28.** This is the S3 backup leg of the
+[strategy](../backup-strategy.md): database dumps + selected
+filesystem trees into the `restic-data` bucket, nightly at 05:00.
+Instances themselves are handled by replication (sdb, nuc after FTTH),
+not by this leg — an instance-filesystem leg (`restic-incus`, §6) was
+written and **shelved**; its script and empty repo stay in place
+should that change.
 
-Why: plakar's incremental cost scales with tree size, not churn
-(~800 MiB parent metadata re-read from S3 + hours of CPU per night on
-a 500k-file tree — measured, reported as
-[PlakarKorp/plakar#2338](https://github.com/PlakarKorp/plakar/issues/2338)).
-restic keeps its comparison state in a local cache: a night costs a
-local stat-walk plus the churn — the rsync cost model. Neither restic
-nor rustic has plakar's source-plugin architecture, but none is
-needed: instances are reached via `incus file mount` (FUSE over the
-same per-instance sftp API our plakar integration used) — zero
-patches to maintain (see §6).
+Why restic: its comparison state lives in a **local cache**, so a
+night costs a local stat-walk plus the churn — the rsync cost model,
+with dedup, compression and encryption on top. (The predecessor and
+the measurements that motivated the switch are in
+[plakar-s3-data.md](plakar-s3-data.md) — reference only.)
 
 ## 1. Repositories — two buckets, two drivers (decided 2026-08-25)
 
@@ -28,7 +21,7 @@ patches to maintain (see §6).
 | `restic-data` | SQL dumps + **all** fs sources (8 small + nextcloud + seafile) | `restic-backup.sh` |
 | `restic-incus` | *(shelved — empty repo, see §6)* the `backup`-project replicas, per-file via mount | `restic-incus-backup.sh` |
 
-Mirrors the plakar-era split (data leg / incus leg). Accepted
+Two repos so each can be pruned and checked independently. Accepted
 trade-off: `restic-data` carries the giants' blobs (~3–5 M once
 seafile is in), so **every operation on it loads a ~1.5–2 GiB
 index** — mitigated by running the whole nightly as a *single*
@@ -168,9 +161,9 @@ done
 
 ## 5. Nightly driver — `scripts/restic-backup.sh`
 
-Same shape as the plakar drivers (flock, env, loud logging). Phases:
+Shape: flock, env file, loud logging. Phases:
 
-1. **dumps** — lifted verbatim from `plakar-backup.sh`: incus DB
+1. **dumps** — incus DB
    dumps + auto-discovered MariaDB/PostgreSQL (native and docker)
    dumps into the dump dir (during the parallel week restic dumps
    into its own `/backup/dumps`; carry the archived `geo.sql` over
@@ -227,7 +220,7 @@ byte once a year, ~25 GiB read per week.
 Neither restic nor rustic accepts source plugins, and forking the
 backup tool is the wrong place to carry a patch. Instead, incus
 exposes any instance (including **stopped replicas**) as a FUSE mount
-over the same per-instance sftp API the plakar integration used:
+over the per-instance sftp API:
 
 ```sh
 for inst in $(incus list --project backup -c n -f csv); do
@@ -252,8 +245,7 @@ opt-out via a variable — the no-manifest-drift rule survives the tool
 change. Chained after the 01:00 incus-copy once validated, same
 freshness reasoning as before.
 
-Bonus over plakar: one shared repo dedups the Ubuntu base across all
-16 replicas. Restore granularity: per-file; instance definitions ride
+One shared repo would dedup the Ubuntu base across all replicas. Restore granularity: per-file; instance definitions ride
 the dump tree (`incus/<inst>.yaml` + `incus-global-db.sql`).
 
 ## 7. Restore test (gate)
@@ -267,24 +259,26 @@ diff -r … && rm -rf /backup/restore-test
 
 ## 8. Cutover (done) + what is left
 
-- **Cutover 2026-08-28**: plakar's 04:30 and Sunday crons are off;
-  restic's 05:00 data leg is the S3 backup. The formal parallel-week
+Legacy on the box: plakar is still installed and its `plakar-data`
+bucket still exists, kept only to reproduce
+[#2338](https://github.com/PlakarKorp/plakar/issues/2338) if upstream
+asks; no cron references it. The empty `plakar-incus` bucket can be
+deleted.
+
+- **Cutover 2026-08-28**: the previous S3 leg's crons are off and
+  restic's 05:00 run is the S3 backup. The formal parallel-week
   comparison was cut short — the evidence had already settled it
-  (plakar: ~800 MiB metadata re-read and 3–4 h per night on the
+  (predecessor: ~800 MiB metadata re-read and 3–4 h per night on the
   nextcloud tree, churn-independent; restic: seed at 60–115 MiB/s,
-  local-cache incrementals). plakar's measurements stay in
+  local-cache incrementals). Details in
   [plakar-s3-data.md](plakar-s3-data.md).
 - **Left to do**: restore test on the complete `restic-data`; re-enable
   the interim ks2 push until FTTH; then the ks2 decommission gates
   ([../ks2/plan.md](../ks2/plan.md)). The instance leg (§6) is
   shelved, not pending.
-- **plakar retirement, one exception**: keep plakar installed and
-  keep the `plakar-data` kloset until
-  [#2338](https://github.com/PlakarKorp/plakar/issues/2338) concludes
-  — the issue offers debug runs against that repository. Delete the
-  `plakar-incus` bucket immediately; `plakar-data` a few weeks later.
-  The `integration-incus` repo retires from production; optionally
-  still publish to PlakarKorp/hub as a community contribution.
+- **Old tool**: see the legacy note above; the `integration-incus`
+  repo retires from production (optionally still published to
+  PlakarKorp/hub as a community contribution).
 - **Interim ks2 push** (until the nuc leg seeds after FTTH, expected
   before end of September): re-enable the replica push so instances
   keep an off-site copy meanwhile: