The internal data place, partitions as places, add_internal_place (felhom.eu architecture/16 §5-§7, §9; build B)

- internal place: the record /var/lib/felhom-agent/internal-place.json -> mounted at /mnt/belso by fs-UUID like an
  enrolled drive (startup + 20 s tick), kind "internal" in GET /disks; never takes a household drive's /mnt/belso;
  eject/decommission/format refused (dm on the system disk).
- configs/felhom-internal-place: the ruled size rule and the only lvcreate/mkfs of a system-disk volume (installer +
  the new signed op add_internal_place, operator key, no parameters).
- partitions listed per free disk (empty / filesystem / in_use); a data-bearing part's wipe id binds disk id + part
  number + fs-UUID.
- felhom-mkfs-guarded: Felhom's own sibling drive no longer blocks formatting the free part; an unlistable disk refuses.
Tests red-proved (script mutations, Go mutations, the old wrapper measured against the new tests).

Claude-Session: https://claude.ai/code/session_012qRErfCoiTkvDK9N5XHbzb

REUSE.md

@@ -42,6 +42,10 @@
 | `deriveDurableID` | internal/storage/durableid.go | `deriveDurableID(typ, s, backingDevice, uuid) string` | storage-target durable id (DR re-attach key) | Deterministic per type; `uuid:` for usb/local-dir; PBS id includes `#<fingerprint>` |
 | `SystemDisks` / `isSystemBacked` / `RoleForStorage` / `RoleForRawDevice` | internal/storage/role.go | `RoleForRawDevice(device, sysDisks, sysKnown) DeviceRole` | protection-tier classification | Fails safe to `system` (most protected) on any ambiguity; role is AGENT-derived, never caller-supplied |
 | `storage.IdentityResolver` / `Relation` / `MountFor` | internal/storage/identity.go | `HostPath(path) PlaceIdentity`, `Device(dev) PlaceIdentity`, `Relation(a, b) (different, proven, reason)` | physical-disk identity of a storage place (felhom.eu `16-storage-physical-identity.md` §3, v0.157.0) | Reads /sys + /run/udev/data + /proc/mounts only (no block I/O). Judge a drive ONLY on its own mount (`localapi.ownMountIdentity`) — never the containing fs, or an absent drive reads as the root disk. A shared disk key is "same, proven" even when unknown. Pinned by identity_test.go (fixture trees) + samedisk_test.go |
+| `localapi.Server.EnsureInternalPlace` / `InternalPlaceRecord` | internal/localapi/internalplace.go | `EnsureInternalPlace(ctx)` (startup + 20 s tick); `ReadInternalPlace` / `WriteInternalPlace` | the one-disk box's internal data place (felhom.eu `16` §5, v0.158.0): mounts it at /mnt/belso by fs-UUID like an enrolled drive, records it `enrolled`; the controller binds + registers it | Never takes /mnt/belso from a household drive (a foreign mount, or a unit naming another UUID, waits). Never formats/ejects (dm on the system disk → role system). The ONLY maker is the root helper `configs/felhom-internal-place` (installer + signed `add_internal_place`). Pinned by internalplace_test.go |
+| `configs/felhom-internal-place` | configs/ (bundle → /usr/local/sbin) | `plan\|create <planned GiB>` | the ruled size rule (reserve max(16, 10 %) ≤ 48 GiB; ≥ 20 GiB or nothing) + the only lvcreate/mkfs of a system-disk volume | Formats only a felhom-belso with NO signature; refuses a foreign one; never resizes/removes. Sudoers: `^(plan\|create) 0$` only. Pinned by configs/test_felhom_internal_place.py |
+| `storage.candidatePartitions` / `CandidatePartition` | internal/storage/partitions.go | `CandidateDisk.Partitions` | partitions as places (`16` §6): empty / filesystem / in_use per part of a free disk | A part with children or a member type is never listed; a raw /mnt mount counts as Felhom's only when corroborated (felhomOwnedMounts). Pinned by partitions_test.go |
+| partition wipe id `byid:<…-partN>+fsuuid:<uuid>` | internal/storage/durable_device.go | `DeviceDurableID` / `ResolveDurableDevice` | a data-bearing PART binds disk id + part number + filesystem (`16` §6) | Both halves must resolve to the SAME device or the wipe refuses. Whole disks keep the plain id. Pinned by partition_durable_test.go |
 | `ValidateUUID/MountPath/BlockDevice/FSType/SMARTDevice/LVMName`, `UnitNameForMount` | internal/storage/validate.go | `Validate*(v) error` | EVERY arg that reaches a root shell-out | The security boundary; strict whitelists (no by-* symlinks, no dm, no traversal); `systemdEscapePath` computed in-process |
 | `ValidateNetworkMountSpec` | internal/storage/netmount.go | `ValidateNetworkMountSpec(spec) error` | NAS mount input boundary | Same discipline as validate.go; SMB requires a creds ref; mountpoint confined under `NetworkMountRoot` |
 

cmd/felhom-agent/main.go

@@ -959,10 +959,7 @@ func runDaemon(cfg config.Config, logger *slog.Logger, logRing *applog.Ring) int
 	// state. Gates the watchdog's self-heal re-mount to ENROLLED drives, and the local API records
 	// enroll/eject into it. Open failure → ungated legacy remount (logged) so the daemon still runs.
 	var intentReader storage.IntentReader
-	intentStateDir := "/var/lib/felhom-agent"
-	if cfg.Authz.NonceStorePath != "" {
-		intentStateDir = filepath.Dir(cfg.Authz.NonceStorePath) // share the agent's durable state dir
-	}
+	intentStateDir := agentStateDir(cfg)
 	intentStore, ierr := storage.OpenIntentStore(filepath.Join(intentStateDir, "drive-intents.json"))
 	if ierr != nil {
 		logger.Warn("storage: intent store unavailable — self-heal runs UNGATED (legacy remount-any)", "err", ierr)
@@ -1168,7 +1165,11 @@ func runDaemon(cfg config.Config, logger *slog.Logger, logRing *applog.Ring) int
 			}
 			logger.Warn("osupdate: capability probe after the config bundle", "ok", ok, "total", total, "degraded", strings.Join(names, ","))
 		}}
-	jobsRunner := signedjobs.NewRunner(client, gate, signedjobs.ExecutorChain{wipeExec, decommExec, updateExec, dockerExec, pveExec, kernelExec, bundleExec}, cfg.Hub.HostID, logger)
+	// v0.158.0 (felhom.eu `16` §9): the internal data place on an old box — the root helper, then the mount (late-bound
+	// to the local API server built below).
+	internalPlaceExec := signedjobs.NewInternalPlaceExecutor(suRunner,
+		localapi.InternalPlaceFileIn(intentStateDir), logger)
+	jobsRunner := signedjobs.NewRunner(client, gate, signedjobs.ExecutorChain{wipeExec, decommExec, updateExec, dockerExec, pveExec, kernelExec, bundleExec, internalPlaceExec}, cfg.Hub.HostID, logger)
 	loop.SetEnvelopeObserver(hub.MultiObserver(desiredSyncer, jobsRunner))
 
 	// Controller-driven escrow ceremony (v0.88.0): static config facts + the LATE-BOUND DR gate —
@@ -1201,6 +1202,7 @@ func runDaemon(cfg config.Config, logger *slog.Logger, logRing *applog.Ring) int
 	}
 	localSrv := buildLocalAPIServer(cfg, px, backupStore, heavyOps, observer, driveKnown, hostOps, gate, collector, client, intentRec, guestBindStore, formatJobStore, logRing, escrowCeremonyCfg, logger, &localTokens)
 	if localSrv != nil {
+		internalPlaceExec.SetEnsure(localSrv.EnsureInternalPlace)
 		// R-998 (doc 14): POST /host/poweroff — guest shutdown, then host power-off; guards in hostpoweroff.go.
 		pwMode := proxmox.RunnerMode(cfg.Privileged.Mode)
 		if pwMode == "" {
@@ -1419,6 +1421,9 @@ func runDaemon(cfg config.Config, logger *slog.Logger, logRing *applog.Ring) int
 		// filesystem UUID and re-mounts (idempotent `enable --now`) so a letter reshuffle is a no-op.
 		// Type-asserted (the concrete op exposes it; the interface stays lean).
 		mountReasserter := hostOps // concrete *storage.SudoHostOps — exposes ReassertEnrolledMounts
+		// v0.158.0 (felhom.eu `16` §5): the internal data place is mounted like an enrolled drive — first, so the
+		// re-assert below sees its unit.
+		localSrv.EnsureInternalPlace(ctx)
 		if mountReasserter != nil {
 			mountReasserter.ReassertEnrolledMounts(ctx)
 		}
@@ -1456,6 +1461,7 @@ func runDaemon(cfg config.Config, logger *slog.Logger, logRing *applog.Ring) int
 				case <-t.C:
 					// Re-assert mounts first (handles a USB that enumerated late after a host reboot, or a
 					// unit re-disabled at runtime), then re-assert the guest binds against the now-live mounts.
+					localSrv.EnsureInternalPlace(ctx) // `16` §5: a record written since the last tick (the signed job)
 					if mountReasserter != nil {
 						mountReasserter.ReassertEnrolledMounts(ctx)
 					}
@@ -2023,10 +2029,12 @@ func buildLocalAPIServer(cfg config.Config, px *proxmox.Client, store *backup.St
 		// F2-b: recover a guest left with a stale vzdump lock by a reboot-during-backup. Reads + start
 		// go through the API client; the `pct unlock` is the one fenced root-CLI op (no API equivalent).
 		// A1 (v0.62.0): the scan is restricted to felhom-pool members (ownership proven, not assumed).
-		StaleLock:  localapi.NewStaleLockController(px, &proxmox.ExecRunner{Mode: gaMode, SudoPath: cfg.Privileged.SudoPath}, reconcile.DefaultPool, logger),
-		Intent:     intent,     // slice 10 P3: record enroll/eject intent for self-heal
-		GuestBinds: guestBinds, // F9: per-guest bind record for the startup re-assert
-		FormatJobs: formatJobs, // F20-BUG3: detached-format job record + restart recovery
+		StaleLock: localapi.NewStaleLockController(px, &proxmox.ExecRunner{Mode: gaMode, SudoPath: cfg.Privileged.SudoPath}, reconcile.DefaultPool, logger),
+		Intent:    intent, // slice 10 P3: record enroll/eject intent for self-heal
+		// v0.158.0 (felhom.eu `16` §5): the internal data place record, beside the intent store.
+		InternalPlaceFile: localapi.InternalPlaceFileIn(agentStateDir(cfg)),
+		GuestBinds:        guestBinds, // F9: per-guest bind record for the startup re-assert
+		FormatJobs:        formatJobs, // F20-BUG3: detached-format job record + restart recovery
 
 		// Host metrics (slice 9): the shared collector serves GET /host/metrics — a fresh host +
 		// per-storage view to the customer's monitoring page (reuses the slice-4 collector).
@@ -3905,3 +3913,12 @@ func (f *factsReporter) SystemFacts(ctx context.Context) (int, json.RawMessage,
 	f.facts, f.err = f.leg.Facts(ctx, f.vmid)
 	return f.vmid, f.facts, f.err
 }
+
+// agentStateDir is the agent's durable state dir: beside the nonce store when one is configured, else the default.
+// The intent store, the guest-bind record and the internal place record (v0.158.0) all live here.
+func agentStateDir(cfg config.Config) string {
+	if cfg.Authz.NonceStorePath != "" {
+		return filepath.Dir(cfg.Authz.NonceStorePath)
+	}
+	return "/var/lib/felhom-agent"
+}

cmd/felhom-opsign/main.go

@@ -43,7 +43,7 @@ func main() {
 
 func run() error {
 	var (
-		op        = flag.String("op", "", "op class to sign, e.g. storage_wipe | guest_destroy | decommission | agent_update | os_docker_step | os_pve_step | os_kernel_step | agent_config_update")
+		op        = flag.String("op", "", "op class to sign, e.g. storage_wipe | guest_destroy | decommission | agent_update | os_docker_step | os_pve_step | os_kernel_step | agent_config_update | add_internal_place")
 		host      = flag.String("host", "", "target host_id (anti-retarget — the op runs ONLY on this host)")
 		guest     = flag.String("guest", "", "target guest_id (\"\" = host-scoped op)")
 		keyID     = flag.String("key-id", "", "key id of the signing key (must match a pinned agent signer)")

configs/felhom-agent.sudoers

@@ -96,6 +96,14 @@ Cmnd_Alias FELHOM_POWEROFF = \
 Cmnd_Alias FELHOM_VZPARTIAL = \
   /usr/local/sbin/felhom-vzdump-partial-clean ^[A-Za-z][A-Za-z0-9_-]{0\,63} [1-9][0-9]{2\,8} vzdump-(lxc|qemu)-[1-9][0-9]{2\,8}-[0-9]{4}_[0-9]{2}_[0-9]{2}-[0-9]{2}_[0-9]{2}_[0-9]{2}\.(tar\.dat|vma\.dat|tmp)$
 
+# Internal data place („Belső tárhely", felhom.eu architecture/16 §5, §7; agent v0.158.0). ONE root helper
+# (configs/felhom-internal-place, from the config bundle) creates <vg>/felhom-belso in the local-lvm thin pool by the
+# ruled size rule and formats ONLY that volume, ONLY when it carries no signature. The agent calls it from the signed
+# `add_internal_place` job (an old box), always with 0 GiB planned: its guest's volumes already exist. `plan` changes
+# nothing. The installer runs the helper as root itself (a new box).
+Cmnd_Alias FELHOM_INTERNALPLACE = \
+  /usr/local/sbin/felhom-internal-place ^(plan|create) 0$
+
 # Intermediary mount model (the drive hot-swap re-architecture). The agent keeps a SHARED host parent
 # /mnt/felhom-drives (self-bind + make-shared) and binds/unbinds each drive's felhom-data namespace UNDERNEATH it so the
 # change propagates into the running guest live. The boot-persistence script + unit are FIXED files from the config
@@ -328,4 +336,4 @@ Cmnd_Alias FELHOM_GUESTNET = \
   /usr/sbin/pct ^exec [0-9]+ -- pgrep -x dhclient$, \
   /usr/sbin/pct ^exec [0-9]+ -- dhclient -pf /run/dhclient\.eth0\.pid -lf /var/lib/dhcp/dhclient\.eth0\.leases eth0$
 
-felhom-agent ALL=(root) NOPASSWD: FELHOM_MOUNT, FELHOM_DISK, FELHOM_PROVISION, FELHOM_FORMAT, FELHOM_DNSMASQ, FELHOM_GUESTHOOK, FELHOM_INTERMEDIARY, FELHOM_CONTROLLERSWAP, FELHOM_STALELOCK, FELHOM_FSTRIM, FELHOM_NETMOUNT, FELHOM_WG, FELHOM_SELFUPDATE, FELHOM_SSHD, FELHOM_OOB, FELHOM_PBSDR, FELHOM_BACKUPTARGET, FELHOM_SELFHEAL, FELHOM_ESCROW, FELHOM_GUESTNET, FELHOM_SCRATCH_TEARDOWN, FELHOM_OSAPPLY, FELHOM_POWEROFF, FELHOM_VZPARTIAL
+felhom-agent ALL=(root) NOPASSWD: FELHOM_MOUNT, FELHOM_DISK, FELHOM_PROVISION, FELHOM_FORMAT, FELHOM_DNSMASQ, FELHOM_GUESTHOOK, FELHOM_INTERMEDIARY, FELHOM_CONTROLLERSWAP, FELHOM_STALELOCK, FELHOM_FSTRIM, FELHOM_NETMOUNT, FELHOM_WG, FELHOM_SELFUPDATE, FELHOM_SSHD, FELHOM_OOB, FELHOM_PBSDR, FELHOM_BACKUPTARGET, FELHOM_SELFHEAL, FELHOM_ESCROW, FELHOM_GUESTNET, FELHOM_SCRATCH_TEARDOWN, FELHOM_OSAPPLY, FELHOM_POWEROFF, FELHOM_VZPARTIAL, FELHOM_INTERNALPLACE

configs/felhom-internal-place

@@ -0,0 +1,103 @@
+#!/bin/bash
+# felhom-internal-place — make the one-disk box's internal data place („Belső tárhely"), felhom.eu
+# architecture/16-storage-physical-identity.md §5, §7 (sizes ruled by the operator 2026-10-16). Installed as
+# /usr/local/sbin/felhom-internal-place (config bundle). Called by felhom-host-install.sh (a new box) and by the agent's
+# signed `add_internal_place` job (an old box) — ONE implementation of the size rule and of the only mkfs it does.
+#
+#   felhom-internal-place plan   <planned GiB>   → prints the numbers, changes nothing
+#   felhom-internal-place create <planned GiB>   → makes the place (or finds it), prints the result
+#
+# <planned GiB> is thin space still to be promised to the guest (rootfs + data volume) that does not exist yet:
+# the installer passes 32 + the data volume; an old box passes 0 (its guest's volumes are already counted).
+#
+# The rule (16 §7, ruled): reserve = max(16 GiB, 10 % of the pool), at most 48 GiB; internal = pool − reserve −
+# every thin volume already promised in the pool − <planned>, made only when ≥ 20 GiB. So nothing in the pool is ever
+# promised beyond pool − reserve: a pool at 100 % stops every volume on the box.
+#
+# It trusts nothing it is told. Every rule is checked here, as root, and any doubt REFUSES (exit 1):
+#   - the pool is the `lvmthin: local-lvm` section of /etc/pve/storage.cfg (its vgname/thinpool), nothing else;
+#   - the only volume it creates, formats or reads is <vg>/felhom-belso;
+#   - it formats ONLY a felhom-belso that carries no signature at all (blkid -p finds nothing) — the one it just made,
+#     or one a crash left between lvcreate and mkfs; any other content REFUSES; it never resizes or removes anything.
+# Output, one line: „created uuid=<fs-uuid> gib=<n>", „formatted uuid=… gib=…" (a crash left it empty), „existing uuid=<fs-uuid> gib=<n>", „skipped <why>" (exit 0),
+# or „plan pool=… reserve=… promised=… planned=… internal=…". Pinned by configs/test_felhom_internal_place.py.
+set -u
+STORAGE_CFG=${FELHOM_STORAGE_CFG:-/etc/pve/storage.cfg}
+LV_NAME=felhom-belso
+LABEL=felhom-belso
+MIN_GIB=20
+
+die() { echo "felhom-internal-place: REFUSED: $*" >&2; exit 1; }
+
+pool_of_local_lvm() { # prints "<vg> <thinpool>" of the lvmthin storage local-lvm, or nothing
+	awk '
+		/^[a-z]+:[ \t]/ { split($0, h, /:[ \t]+/); type = h[1]; id = h[2]; sub(/[ \t]+$/, "", id); in_s = (type == "lvmthin" && id == "local-lvm"); next }
+		in_s && /^[ \t]+vgname[ \t]/ { vg = $2 }
+		in_s && /^[ \t]+thinpool[ \t]/ { tp = $2 }
+		END { if (vg != "" && tp != "") print vg, tp }
+	' "$STORAGE_CFG"
+}
+
+gib_floor() { echo $(( $1 / 1073741824 )); }
+
+[[ $# -eq 2 ]] || die "usage: felhom-internal-place plan|create <planned GiB>"
+MODE=$1; PLANNED=$2
+[[ "$MODE" == plan || "$MODE" == create ]] || die "mode must be plan or create"
+[[ "$PLANNED" =~ ^(0|[1-9][0-9]{0,5})$ ]] || die "planned GiB must be a whole number"
+
+read -r VG POOL < <(pool_of_local_lvm) || true
+[[ -n "${VG:-}" && -n "${POOL:-}" ]] || die "no lvmthin storage local-lvm in $STORAGE_CFG"
+[[ "$VG" =~ ^[A-Za-z0-9_.+-]+$ && "$POOL" =~ ^[A-Za-z0-9_.+-]+$ ]] || die "unexpected vg/pool name"
+
+pool_b=$(lvs --noheadings --nosuffix --units b -o lv_size "$VG/$POOL" 2>/dev/null | tr -d ' ')
+[[ "$pool_b" =~ ^[0-9]+$ ]] || die "cannot read the size of $VG/$POOL"
+pool_gib=$(gib_floor "$pool_b")
+
+# Every thin volume promised in the pool (its virtual size) — except the place itself and vzdump's short-lived
+# snapshots (snap_*_vzdump), which exist only during a whole-box copy and are what the reserve is for.
+promised_b=0; have_lv=false
+while read -r name pl size; do
+	[[ -n "${name:-}" ]] || continue
+	[[ "$pl" == "$POOL" ]] || continue
+	if [[ "$name" == "$LV_NAME" ]]; then have_lv=true; continue; fi
+	[[ "$name" =~ ^snap_.*_vzdump$ ]] && continue
+	[[ "$size" =~ ^[0-9]+$ ]] || die "cannot read the size of $VG/$name"
+	promised_b=$(( promised_b + size ))
+done < <(lvs --noheadings --nosuffix --units b -o lv_name,pool_lv,lv_size "$VG" 2>/dev/null)
+promised_gib=$(( (promised_b + 1073741823) / 1073741824 ))   # rounded UP: never promise a partial GiB twice
+
+reserve=$(( pool_gib / 10 )); (( reserve < 16 )) && reserve=16; (( reserve > 48 )) && reserve=48
+internal=$(( pool_gib - reserve - promised_gib - PLANNED ))
+
+if [[ "$MODE" == plan ]]; then
+	echo "plan pool=$pool_gib reserve=$reserve promised=$promised_gib planned=$PLANNED internal=$internal exists=$have_lv"
+	exit 0
+fi
+
+DEV=/dev/$VG/$LV_NAME
+is_block() { [[ "$(stat -L -c %F "$1" 2>/dev/null)" == "block special file" ]]; }
+fs_uuid() { blkid -p -s UUID -o value "$DEV" 2>/dev/null; }
+fs_type() { blkid -p -s TYPE -o value "$DEV" 2>/dev/null; }
+fs_label() { blkid -p -s LABEL -o value "$DEV" 2>/dev/null; }
+lv_gib() { gib_floor "$(lvs --noheadings --nosuffix --units b -o lv_size "$VG/$LV_NAME" 2>/dev/null | tr -d ' ')"; }
+
+if $have_lv; then
+	is_block "$DEV" || die "$DEV is not an active block device"
+	t=$(fs_type)
+	if [[ -n "$t" ]]; then
+		[[ "$t" == ext4 && "$(fs_label)" == "$LABEL" ]] || die "$DEV holds something that is not Felhom's ($t) — left alone"
+		echo "existing uuid=$(fs_uuid) gib=$(lv_gib)"; exit 0
+	fi
+	# A felhom-belso with NO signature: a crash between lvcreate and mkfs. Nothing can be on it — format it.
+	[[ -z "$(blkid -p -o value "$DEV" 2>/dev/null)" ]] || die "$DEV carries a signature blkid cannot name — left alone"
+else
+	(( internal >= MIN_GIB )) || { echo "skipped only $internal GiB free for it (pool $pool_gib, reserve $reserve, promised $promised_gib, planned $PLANNED; needs $MIN_GIB)"; exit 0; }
+	lvcreate -q -y -V "${internal}G" -T "$VG/$POOL" -n "$LV_NAME" >/dev/null || die "lvcreate failed"
+	is_block "$DEV" || die "$DEV did not appear after lvcreate"
+	[[ -z "$(blkid -p -o value "$DEV" 2>/dev/null)" ]] || die "the new $DEV already carries a signature — left alone"
+	made=created
+fi
+mkfs.ext4 -q -L "$LABEL" "$DEV" >/dev/null || die "mkfs.ext4 failed on $DEV"
+u=$(fs_uuid)
+[[ "$u" =~ ^[0-9a-fA-F-]{36}$ ]] || die "no filesystem UUID after mkfs on $DEV"
+echo "${made:-formatted} uuid=$u gib=$(lv_gib)"

configs/felhom-mkfs-guarded.sh

@@ -58,14 +58,34 @@ fi
 
 # 3) mounted OUTSIDE Felhom's own drive area = a live foreign filesystem → catastrophic. Mounts under
 #    /mnt/felhom-drives are our own drives (the agent detaches before a re-init) → allowed.
-while read -r mp; do
-  [[ -z "$mp" ]] && continue
-  case "$mp" in
-    /mnt/felhom-drives|/mnt/felhom-drives/*) : ;;
-    *) die "device (or a partition) is mounted at $mp ($dev)" ;;
-  esac
-done < <(lsblk -nro MOUNTPOINT "$whole" 2>/dev/null || true)
-
+#    Agent v0.158.0 (felhom.eu architecture/16 §6, partitions as places): a SIBLING partition that is Felhom's own
+#    enrolled drive is mounted TWICE — raw at /mnt/<name> and under /mnt/felhom-drives (R-220). That raw mount is
+#    allowed only when the same device is ALSO mounted under /mnt/felhom-drives, a state only Felhom's enrolment
+#    produces. The TARGET itself mounted anywhere outside /mnt/felhom-drives, or any mount elsewhere (/srv, /media,
+#    /mnt/a/b), still REFUSES. Read from the kernel's mount table, every node of the disk (partitions and children).
+PROC_MOUNTS=/proc/mounts
+node_mounts() { awk -v d="$1" '$1 == d { print $2 }' "$PROC_MOUNTS"; }
+disk_nodes="$(lsblk -nrpo NAME "$whole" 2>/dev/null || true)"
+[[ -n "$disk_nodes" ]] || die "cannot list the nodes of $whole — refusing"
+while read -r node; do
+  [[ -z "$node" ]] && continue
+  own=false
+  while read -r mp; do
+    case "$mp" in /mnt/felhom-drives/*) own=true ;; esac
+  done < <(node_mounts "$node")
+  while read -r mp; do
+    [[ -z "$mp" ]] && continue
+    case "$mp" in
+      /mnt/felhom-drives|/mnt/felhom-drives/*) : ;;
+      *)
+        if [[ "$node" != "$dev" && "$own" == true && "$mp" =~ ^/mnt/[A-Za-z0-9_][A-Za-z0-9_.-]*$ ]]; then
+          : # a sibling that is Felhom's own enrolled drive (raw mount + managed mount)
+        else
+          die "device (or a partition) is mounted at $mp ($node)"
+        fi ;;
+    esac
+  done < <(node_mounts "$node")
+done <<< "$disk_nodes"
 # 4) read-only device (audit D1): a device the kernel marks RO is never a formattable data disk.
 wbase="${whole#/dev/}"
 rof="/sys/block/$wbase/ro"

configs/felhom-os-apply

@@ -191,6 +191,8 @@ BUNDLE_FILES = [
     ("/usr/local/sbin/felhom-backup-target-apply", "felhom-backup-target-apply", 0o755, "bash", "replace"),
     # R-1006 (agent v0.156.0): the only delete of backup files — a dead half-written vzdump, re-checked as root.
     ("/usr/local/sbin/felhom-vzdump-partial-clean", "felhom-vzdump-partial-clean", 0o755, "bash", "replace"),
+    # felhom.eu architecture/16 §5 (agent v0.158.0): the internal data place — the only lvcreate/mkfs of a system-disk volume.
+    ("/usr/local/sbin/felhom-internal-place", "felhom-internal-place", 0o755, "bash", "replace"),
     ("/usr/local/sbin/felhom-os-apply", "felhom-os-apply", 0o755, "python", "replace"),
     ("/usr/local/sbin/felhom-crash-guard", "felhom-crash-guard", 0o755, "python", "replace"),
     # R-861 (agent v0.146.0): the content checker for every agent-staged file a root program reads, and the two FIXED

configs/test_felhom_internal_place.py

@@ -0,0 +1,217 @@
+#!/usr/bin/env python3
+"""Tests for configs/felhom-internal-place (felhom.eu architecture/16 §5, §7 — sizes ruled 2026-10-16).
+
+The helper is run for real under bash; `lvs`, `lvcreate`, `blkid`, `mkfs.ext4` and `stat` are PATH stubs that read and
+write one JSON state file, so nothing on this machine is touched. Every refusal has a positive control: the same setup
+without the one condition goes through — so a test cannot pass because the helper refuses everything.
+Run: python3 configs/test_felhom_internal_place.py   (also run by the Go suite, internal/internalplace)
+"""
+import json, os, pathlib, stat, subprocess, tempfile, unittest
+
+HELPER = pathlib.Path(__file__).resolve().parent / "felhom-internal-place"
+GIB = 1 << 30
+
+STUB_LVS = r'''#!/usr/bin/env python3
+import json, os, sys
+st = json.load(open(os.environ["IP_STATE"]))
+args = [a for a in sys.argv[1:] if not a.startswith("-") and a not in ("b",)]
+fields = sys.argv[sys.argv.index("-o") + 1].split(",")
+target = args[-1]
+for lv in st["lvs"]:
+    full = st["vg"] + "/" + lv["name"]
+    if target == st["vg"] or target == full:
+        row = {"lv_name": lv["name"], "pool_lv": lv.get("pool", ""), "lv_size": str(lv["size"])}
+        print("  " + " ".join(row[f] for f in fields))
+'''
+STUB_LVCREATE = r'''#!/usr/bin/env python3
+import json, os, sys
+p = os.environ["IP_STATE"]; st = json.load(open(p))
+a = sys.argv[1:]
+size = int(a[a.index("-V") + 1].rstrip("G")) * (1 << 30)
+vg, pool = a[a.index("-T") + 1].split("/")
+st["lvs"].append({"name": a[a.index("-n") + 1], "pool": pool, "size": size, "active": True})
+st.setdefault("calls", []).append("lvcreate " + " ".join(a))
+if st.get("dirty_new"): st["fs"]["felhom-belso"] = {"TYPE": "", "RAW": "junk"}
+json.dump(st, open(p, "w"))
+'''
+STUB_BLKID = r'''#!/usr/bin/env python3
+import json, os, sys
+st = json.load(open(os.environ["IP_STATE"]))
+fs = st["fs"].get(os.path.basename(sys.argv[-1]), {})
+if "-s" in sys.argv:
+    v = fs.get(sys.argv[sys.argv.index("-s") + 1], "")
+    if v: print(v)
+else:
+    vals = [fs.get(k, "") for k in ("TYPE", "LABEL", "UUID", "RAW") if fs.get(k)]
+    if vals: print("\n".join(vals))
+'''
+STUB_MKFS = r'''#!/usr/bin/env python3
+import json, os, sys
+p = os.environ["IP_STATE"]; st = json.load(open(p))
+dev = os.path.basename(sys.argv[-1])
+st["fs"][dev] = {"TYPE": "ext4", "LABEL": sys.argv[sys.argv.index("-L") + 1], "UUID": "0b6e4c5a-1d2e-4f3a-9b8c-7d6e5f4a3b2c"}
+st.setdefault("calls", []).append("mkfs.ext4 " + " ".join(sys.argv[1:]))
+json.dump(st, open(p, "w"))
+'''
+STUB_STAT = r'''#!/usr/bin/env python3
+import json, os, sys
+st = json.load(open(os.environ["IP_STATE"]))
+name = os.path.basename(sys.argv[-1])
+if any(lv["name"] == name and lv.get("active", True) for lv in st["lvs"]): print("block special file")
+else: sys.exit(1)
+'''
+
+CFG = "dir: local\n\tpath /var/lib/vz\n\tcontent iso,backup\n\nlvmthin: local-lvm\n\tthinpool data\n\tvgname pve\n\tcontent rootdir,images\n"
+
+
+class Box:
+    def __init__(self, pool_gib, lvs=(), fs=None, cfg=CFG, **extra):
+        self.t = tempfile.TemporaryDirectory()
+        r = pathlib.Path(self.t.name)
+        self.bin = r / "bin"; self.bin.mkdir()
+        for name, body in (("lvs", STUB_LVS), ("lvcreate", STUB_LVCREATE), ("blkid", STUB_BLKID),
+                           ("mkfs.ext4", STUB_MKFS), ("stat", STUB_STAT)):
+            f = self.bin / name; f.write_text(body); f.chmod(0o755)
+        self.cfg = r / "storage.cfg"; self.cfg.write_text(cfg)
+        self.state = r / "state.json"
+        st = {"vg": "pve", "lvs": [{"name": "data", "pool": "", "size": pool_gib * GIB}] + [dict(l) for l in lvs],
+              "fs": fs or {}}
+        st.update(extra)
+        self.state.write_text(json.dumps(st))
+
+    def run(self, *args):
+        env = {"PATH": f"{self.bin}:/usr/bin:/bin", "IP_STATE": str(self.state), "FELHOM_STORAGE_CFG": str(self.cfg)}
+        p = subprocess.run(["bash", str(HELPER), *args], env=env, capture_output=True, text=True)
+        return p.returncode, p.stdout.strip(), p.stderr.strip()
+
+    def st(self):
+        return json.loads(self.state.read_text())
+
+    def calls(self):
+        return self.st().get("calls", [])
+
+    def close(self):
+        self.t.cleanup()
+
+
+def thin(name, gib, pool="data"):
+    return {"name": name, "pool": pool, "size": gib * GIB}
+
+
+class Sizes(unittest.TestCase):
+    """The operator's table (SPACE-CHECK §4, ruled 2026-10-16), as the helper computes it on a fresh box."""
+
+    def plan(self, pool, planned, lvs=()):
+        b = Box(pool, lvs)
+        try:
+            rc, out, err = b.run("plan", str(planned))
+            self.assertEqual(rc, 0, err)
+            self.assertEqual(b.calls(), [], "plan must change nothing")
+            return dict(kv.split("=") for kv in out.split()[1:])
+        finally:
+            b.close()
+
+    def test_the_ruled_table(self):
+        # disk → pool (GiB), data volume (planned = 32 + mp0), expected internal
+        for pool, mp0, reserve, internal in ((140, 50, 16, 42), (349, 100, 34, 183), (800, 130, 48, 590), (1720, 130, 48, 1510)):
+            got = self.plan(pool, 32 + mp0)
+            self.assertEqual((int(got["reserve"]), int(got["internal"])), (reserve, internal), (pool, got))
+
+    def test_promised_volumes_count_but_vzdump_snapshots_and_other_pools_do_not(self):
+        got = self.plan(349, 0, [thin("vm-9201-disk-0", 32), thin("vm-9201-disk-1", 250),
+                                 thin("snap_vm-9201-disk-1_vzdump", 250), thin("vm-500-disk-0", 40, pool="other")])
+        self.assertEqual((int(got["promised"]), int(got["internal"])), (282, 33), got)
+
+
+class Create(unittest.TestCase):
+    def test_a_fresh_box_gets_the_place(self):
+        b = Box(349)
+        try:
+            rc, out, err = b.run("create", "132")
+            self.assertEqual(rc, 0, err)
+            self.assertRegex(out, r"^created uuid=[0-9a-f-]{36} gib=183$")
+            self.assertEqual(len([c for c in b.calls() if c.startswith("lvcreate")]), 1)
+            self.assertIn("-V 183G -T pve/data -n felhom-belso", b.calls()[0])
+            self.assertIn("-L felhom-belso", b.calls()[1])
+        finally:
+            b.close()
+
+    def test_too_little_space_makes_nothing(self):
+        b = Box(53)   # demo-hp's 128 GB disk
+        try:
+            rc, out, err = b.run("create", str(32 + 50))
+            self.assertEqual(rc, 0, err)
+            self.assertTrue(out.startswith("skipped "), out)
+            self.assertEqual(b.calls(), [])
+        finally:
+            b.close()
+
+    def test_an_existing_place_is_found_never_formatted(self):
+        fs = {"felhom-belso": {"TYPE": "ext4", "LABEL": "felhom-belso", "UUID": "11111111-2222-3333-4444-555555555555"}}
+        b = Box(349, [thin("felhom-belso", 183)], fs)
+        try:
+            rc, out, err = b.run("create", "0")
+            self.assertEqual(rc, 0, err)
+            self.assertEqual(out, "existing uuid=11111111-2222-3333-4444-555555555555 gib=183")
+            self.assertEqual(b.calls(), [], "an existing place must never be created or formatted again")
+        finally:
+            b.close()
+
+    def test_a_foreign_filesystem_on_the_name_is_refused(self):
+        # positive control: test_an_existing_place_is_found_never_formatted (same LV, Felhom's label) goes through
+        for fs in ({"TYPE": "xfs", "LABEL": "felhom-belso", "UUID": "x"}, {"TYPE": "ext4", "LABEL": "films", "UUID": "y"}):
+            b = Box(349, [thin("felhom-belso", 183)], {"felhom-belso": fs})
+            try:
+                rc, out, err = b.run("create", "0")
+                self.assertEqual(rc, 1, (fs, out))
+                self.assertIn("REFUSED", err)
+                self.assertEqual(b.calls(), [], fs)
+            finally:
+                b.close()
+
+    def test_a_crash_between_lvcreate_and_mkfs_is_finished(self):
+        b = Box(349, [thin("felhom-belso", 183)], {})
+        try:
+            rc, out, err = b.run("create", "0")
+            self.assertEqual(rc, 0, err)
+            self.assertRegex(out, r"^formatted uuid=")
+            self.assertEqual([c.split()[0] for c in b.calls()], ["mkfs.ext4"])
+        finally:
+            b.close()
+
+    def test_an_unnamed_signature_is_refused(self):
+        b = Box(349, [thin("felhom-belso", 183)], {"felhom-belso": {"RAW": "something"}})
+        try:
+            rc, out, err = b.run("create", "0")
+            self.assertEqual(rc, 1, out)
+            self.assertEqual(b.calls(), [])
+        finally:
+            b.close()
+
+    def test_a_new_volume_that_is_not_empty_is_not_formatted(self):
+        b = Box(349, dirty_new=True)
+        try:
+            rc, out, err = b.run("create", "132")
+            self.assertEqual(rc, 1, out)
+            self.assertNotIn("mkfs", " ".join(b.calls()))
+        finally:
+            b.close()
+
+    def test_bad_arguments_and_no_local_lvm_are_refused(self):
+        b = Box(349, cfg="dir: local\n\tpath /var/lib/vz\n")
+        try:
+            self.assertEqual(b.run("create", "0")[0], 1)
+            self.assertEqual(b.calls(), [])
+        finally:
+            b.close()
+        b = Box(349)
+        try:
+            for args in (("create", "-1"), ("create", "1x"), ("wipe", "0"), ("create",)):
+                self.assertEqual(b.run(*args)[0], 1, args)
+            self.assertEqual(b.calls(), [])
+        finally:
+            b.close()
+
+
+if __name__ == "__main__":
+    unittest.main()

configs/test_felhom_mkfs_guarded.py

@@ -0,0 +1,140 @@
+#!/usr/bin/env python3
+"""Tests for configs/felhom-mkfs-guarded.sh — the ONLY mkfs path the agent's sudoers permits.
+
+First tests of this wrapper (agent v0.158.0), written with its change for partitions as places (felhom.eu
+architecture/16 §6): a SIBLING partition that is Felhom's own enrolled drive (mounted raw at /mnt/<name> AND under
+/mnt/felhom-drives) no longer blocks formatting the empty partition next to it; every other mount still refuses.
+
+HOW IT RUNS ANYWHERE: the wrapper is copied with five literal host paths replaced (each replacement is asserted, so a
+drifted wrapper fails here instead of silently testing nothing): /proc/mounts → a fake mount table, the block-device
+test → true (no real /dev nodes here), the pvs candidates → a stub, /sys/block → a fake tree, the mkfs binaries → a
+recorder. `lsblk` is a PATH stub answering the three calls the wrapper makes from one JSON disk description.
+Every refusal has a positive control (the same disk without the one condition is formatted).
+Run: python3 configs/test_felhom_mkfs_guarded.py   (also run by the Go suite, internal/storage)
+"""
+import json, os, pathlib, subprocess, tempfile, unittest
+
+WRAPPER = pathlib.Path(__file__).resolve().parent / "felhom-mkfs-guarded.sh"
+
+STUB_LSBLK = r'''#!/usr/bin/env python3
+import json, os, sys
+st = json.load(open(os.environ["MG_STATE"]))
+a = sys.argv[1:]; dev = a[-1]
+nodes = st["nodes"]   # [{"name": "/dev/sdb", "pk": "", "fstype": ""}, ...]
+if a[0] == "-ndo" and a[1] == "PKNAME":
+    for n in nodes:
+        if n["name"] == dev and n.get("pk"): print(n["pk"])
+elif a[0] == "-nrpo" and a[1] == "NAME":
+    if not st.get("lsblk_empty"):
+        for n in nodes: print(n["name"])
+elif a[0] == "-nro" and a[1] == "FSTYPE":
+    for n in nodes: print(n.get("fstype", ""))
+elif a[0] == "-nro" and a[1] == "MOUNTPOINT":   # the pre-v0.158.0 wrapper's call: one mountpoint per node, like lsblk
+    mt = [l.split()[:2] for l in open(os.environ["MG_MOUNTS"]) if l.strip()]
+    for n in nodes:
+        mps = [m for d, m in mt if d == n["name"]]
+        print(mps[0] if mps else "")
+'''
+STUB_MKFS = '#!/bin/sh\necho "$0 $*" >> "$MG_CALLS"\n'
+STUB_PVS = '#!/bin/sh\nprintf "%s\\n" $MG_PVS\n'
+
+
+class Disk:
+    def __init__(self, nodes, mounts, ro="0", pvs="", lsblk_empty=False):
+        self.t = tempfile.TemporaryDirectory()
+        r = pathlib.Path(self.t.name)
+        self.bin = r / "bin"; self.bin.mkdir()
+        (self.bin / "lsblk").write_text(STUB_LSBLK); (self.bin / "lsblk").chmod(0o755)
+        for n in ("mkfs.ext4", "mkfs.xfs"):
+            (self.bin / n).write_text(STUB_MKFS); (self.bin / n).chmod(0o755)
+        (self.bin / "pvs").write_text(STUB_PVS); (self.bin / "pvs").chmod(0o755)
+        self.state = r / "state.json"
+        self.state.write_text(json.dumps({"nodes": nodes, "lsblk_empty": lsblk_empty}))
+        self.mounts = r / "mounts"
+        self.mounts.write_text("".join(f"{d} {m} ext4 rw 0 0\n" for d, m in mounts))
+        self.sys = r / "sys"
+        for n in nodes:
+            if not n.get("pk"):
+                d = self.sys / os.path.basename(n["name"]); d.mkdir(parents=True); (d / "ro").write_text(ro + "\n")
+        self.calls = r / "calls"
+        self.pvs = pvs
+        src = WRAPPER.read_text()
+        subs = [
+            ("/proc/mounts", str(self.mounts)),
+            ('[[ -b "$dev" ]]', "true"),
+            ("for c in /usr/sbin/pvs /sbin/pvs; do", f"for c in {self.bin}/pvs; do"),
+            ('rof="/sys/block/', f'rof="{self.sys}/'),
+            ("exec /usr/sbin/mkfs.ext4", f"exec {self.bin}/mkfs.ext4"),
+            ("exec /usr/sbin/mkfs.xfs ", f"exec {self.bin}/mkfs.xfs "),
+        ]
+        for a, b in subs:
+            assert a in src, f"the wrapper no longer contains {a!r} — update this test's substitutions"
+            src = src.replace(a, b)
+        self.copy = r / "mkfs-guarded"; self.copy.write_text(src)
+
+    def run(self, dev, fstype="ext4"):
+        env = {"PATH": f"{self.bin}:/usr/bin:/bin", "MG_STATE": str(self.state), "MG_CALLS": str(self.calls),
+               "MG_MOUNTS": str(self.mounts),
+               "MG_PVS": self.pvs}
+        p = subprocess.run(["bash", str(self.copy), dev, fstype], env=env, capture_output=True, text=True)
+        made = self.calls.read_text().split("\n")[0] if self.calls.exists() else ""
+        return p.returncode, p.stderr.strip(), made
+
+    def close(self):
+        self.t.cleanup()
+
+
+def disk_sdb(sdb1_fstype="ext4", sdb2_fstype=""):
+    return [{"name": "/dev/sdb", "pk": "", "fstype": ""},
+            {"name": "/dev/sdb1", "pk": "sdb", "fstype": sdb1_fstype},
+            {"name": "/dev/sdb2", "pk": "sdb", "fstype": sdb2_fstype}]
+
+
+ROOT = ("/dev/sda2", "/")
+OWN_SDB1 = [("/dev/sdb1", "/mnt/hdd_1"), ("/dev/sdb1", "/mnt/felhom-drives/hdd_1")]
+
+
+class Partitions(unittest.TestCase):
+    def check(self, mounts, dev="/dev/sdb2", nodes=None, want_ok=True, **kw):
+        d = Disk(nodes or disk_sdb(), [ROOT] + mounts, **kw)
+        try:
+            rc, err, made = d.run(dev)
+            if want_ok:
+                self.assertEqual(rc, 0, err)
+                self.assertTrue(made.endswith(f"mkfs.ext4 -F {dev}"), made)
+            else:
+                self.assertEqual(rc, 1, (mounts, made))
+                self.assertIn("REFUSED", err)
+                self.assertEqual(made, "", "a refused format must not run mkfs")
+            return err
+        finally:
+            d.close()
+
+    def test_the_empty_part_next_to_felhoms_own_drive_is_formatted(self):
+        self.check(OWN_SDB1)
+
+    def test_a_sibling_mounted_raw_only_is_refused(self):
+        self.check([("/dev/sdb1", "/mnt/hdd_1")], want_ok=False)
+
+    def test_a_sibling_mounted_elsewhere_is_refused_even_with_a_managed_mount(self):
+        for elsewhere in ("/srv/data", "/media/usb", "/mnt/a/b", "/home/x"):
+            self.check([("/dev/sdb1", elsewhere), ("/dev/sdb1", "/mnt/felhom-drives/hdd_1")], want_ok=False)
+
+    def test_the_target_itself_mounted_raw_is_refused(self):
+        self.check([("/dev/sdb2", "/mnt/films"), ("/dev/sdb2", "/mnt/felhom-drives/films")], want_ok=False)
+
+    def test_the_target_mounted_only_under_felhom_drives_is_formatted(self):
+        self.check([("/dev/sdb2", "/mnt/felhom-drives/films")])
+
+    def test_an_unlistable_disk_is_refused(self):
+        self.check([], want_ok=False, lsblk_empty=True)
+
+    def test_the_catastrophic_cases_still_refuse(self):
+        self.check([("/dev/sdb1", "/")], want_ok=False)                     # system disk
+        self.check(OWN_SDB1, nodes=disk_sdb(sdb1_fstype="LVM2_member"), want_ok=False)  # a member signature
+        self.check(OWN_SDB1, pvs="/dev/sdb1", want_ok=False)                # an LVM PV (pvs)
+        self.check(OWN_SDB1, ro="1", want_ok=False)                         # read-only
+
+
+if __name__ == "__main__":
+    unittest.main()

internal/capability/manifest.go

@@ -118,6 +118,8 @@ var manifest = []Capability{
 	{"guest-shutdown", "household power-off: guest shutdown (R-998)", "/usr/sbin/pct", []string{"shutdown", "9201", "--timeout", "120"}, false, ""},
 	{"host-poweroff", "household power-off: host power-off (R-998)", "/usr/bin/systemctl", []string{"poweroff"}, false, ""},
 	{"vzdump-partial-clean", "dead half-written vzdump removal (R-1006)", "/usr/local/sbin/felhom-vzdump-partial-clean", []string{"local", "9201", "vzdump-lxc-9201-2026_10_14-04_42_18.tar.dat"}, false, ""},
+	{"internal-place-plan", "internal data place: the size plan (16 §7)", "/usr/local/sbin/felhom-internal-place", []string{"plan", "0"}, false, ""},
+	{"internal-place-create", "internal data place: create on an old box (signed add_internal_place)", "/usr/local/sbin/felhom-internal-place", []string{"create", "0"}, false, ""},
 
 	// ---- LAN split-horizon resolver (dnsmasq) ----
 	{"dnsmasq-install", "dnsmasq package install", "/usr/bin/apt-get", []string{"install", "-y", "-q", "dnsmasq"}, false, ""},

internal/capability/r861_injection_test.go

@@ -72,6 +72,11 @@ var r861Injections = []string{
 	"/usr/local/sbin/felhom-vzdump-partial-clean local;id 9201 vzdump-lxc-9201-2026_10_14-04_42_18.tar.dat",
 	"/usr/local/sbin/felhom-vzdump-partial-clean local 9201",
 	"/usr/local/sbin/felhom-vzdump-partial-clean --help",
+	"/usr/local/sbin/felhom-internal-place create 132",
+	"/usr/local/sbin/felhom-internal-place create 0 extra",
+	"/usr/local/sbin/felhom-internal-place create 0;id",
+	"/usr/local/sbin/felhom-internal-place wipe 0",
+	"/usr/local/sbin/felhom-internal-place create",
 }
 
 func TestSudoersRefusesTheR861Injections(t *testing.T) {

internal/localapi/internalplace.go

@@ -0,0 +1,207 @@
+package localapi
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+	"regexp"
+	"sync"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/storage"
+)
+
+// The internal data place („Belső tárhely", agent v0.158.0) — felhom.eu architecture/16-storage-physical-identity.md
+// §5, §7. On a one-disk box the root helper configs/felhom-internal-place makes a second thin volume in local-lvm
+// (<vg>/felhom-belso, ext4, label felhom-belso). The installer (a new box) or the signed add_internal_place job (an old
+// box) then writes InternalPlaceRecord to the agent's state dir. From then on the agent treats the volume exactly like
+// an enrolled drive: a Felhom mount unit by fs-UUID at /mnt/belso (EnsureMount), the `enrolled` intent, and — when the
+// controller asks with its own token (POST /disks/guest-attach) — the bind at /mnt/felhom-drives/belso. So it is a
+// HOST mount under the guest's mp8 parent: not in the guest config, not in vzdump, not in PBS (`16` §5).
+//
+// What it is NOT: a drive the household can format, wipe, eject or decommission. Its device is a device-mapper volume
+// on the system disk, so the role gate (roleForMountPath → system) and the format path (ValidateBlockDevice refuses
+// dm) refuse all four — pinned by internalplace_test.go. Its identity is the system disk's (build A), so a Tier-2 copy
+// between it and sys_drive is never a second copy.
+const (
+	InternalPlaceName  = "belso"
+	InternalPlaceWhere = "/mnt/belso"
+	// InternalPlaceFile is the record's name inside the agent's state dir.
+	InternalPlaceFile = "internal-place.json"
+)
+
+var reFSUUID = regexp.MustCompile(`^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$`)
+
+// InternalPlaceRecord is the state file the maker writes once the volume exists and is formatted.
+type InternalPlaceRecord struct {
+	FSUUID string `json:"fs_uuid"`
+	GiB    int    `json:"gib,omitempty"`
+	MadeBy string `json:"made_by,omitempty"` // "installer" | "signed-job"
+	MadeAt string `json:"made_at,omitempty"`
+}
+
+// ReadInternalPlace reads the record; ok=false when there is none (the common case: a box with no internal place).
+func ReadInternalPlace(file string) (InternalPlaceRecord, bool, error) {
+	var rec InternalPlaceRecord
+	b, err := os.ReadFile(file)
+	if errors.Is(err, os.ErrNotExist) {
+		return rec, false, nil
+	}
+	if err != nil {
+		return rec, false, err
+	}
+	if err := json.Unmarshal(b, &rec); err != nil {
+		return rec, false, fmt.Errorf("internal place record %s: %w", file, err)
+	}
+	if !reFSUUID.MatchString(rec.FSUUID) {
+		return rec, false, fmt.Errorf("internal place record %s: fs_uuid %q is not a filesystem UUID", file, rec.FSUUID)
+	}
+	return rec, true, nil
+}
+
+// WriteInternalPlace writes the record atomically (0600).
+func WriteInternalPlace(file string, rec InternalPlaceRecord) error {
+	if !reFSUUID.MatchString(rec.FSUUID) {
+		return fmt.Errorf("internal place: fs_uuid %q is not a filesystem UUID", rec.FSUUID)
+	}
+	b, err := json.MarshalIndent(rec, "", "  ")
+	if err != nil {
+		return err
+	}
+	tmp := file + ".tmp"
+	if err := os.WriteFile(tmp, append(b, '\n'), 0o600); err != nil {
+		return err
+	}
+	return os.Rename(tmp, file)
+}
+
+// internalPlaceState memoises what EnsureInternalPlace last saw, so the 20-second tick logs a state CHANGE once and
+// does no work on the steady state.
+type internalPlaceState struct {
+	mu      sync.Mutex
+	done    string // the fs-UUID that is mounted and recorded enrolled
+	lastWhy string // the last reason it could not be ensured (logged once per change)
+}
+
+// internalPlaceUUID returns the configured internal place's fs-UUID, or "" when this box has none (or the record is
+// unreadable — logged by EnsureInternalPlace).
+func (s *Server) internalPlaceUUID() string {
+	if s.internalPlaceFile == "" {
+		return ""
+	}
+	rec, ok, err := ReadInternalPlace(s.internalPlaceFile)
+	if err != nil || !ok {
+		return ""
+	}
+	return rec.FSUUID
+}
+
+// isInternalPlace reports whether a host path is this box's internal place: its raw mount (/mnt/belso) or its bind
+// under the guests' shared parent (/mnt/felhom-drives/belso — the path POST /disks/same-disk judges).
+func (s *Server) isInternalPlace(hostPath string) bool {
+	p := path.Clean(hostPath)
+	return (p == InternalPlaceWhere || p == StableParentDir+"/"+InternalPlaceName) && s.internalPlaceUUID() != ""
+}
+
+// EnsureInternalPlace mounts the internal place on the host at /mnt/belso by fs-UUID and records it `enrolled`,
+// when this box has one. Idempotent and cheap on the steady state; safe on the 20-second tick. It never formats,
+// never unmounts, and never mounts anything at /mnt/belso that is not the recorded UUID: a household drive that
+// happens to be named „belso" keeps its mount, and the internal place waits (logged once).
+func (s *Server) EnsureInternalPlace(ctx context.Context) {
+	if s.internalPlaceFile == "" {
+		return
+	}
+	rec, ok, err := ReadInternalPlace(s.internalPlaceFile)
+	if err != nil {
+		s.internalPlaceNote("record unreadable: " + err.Error())
+		return
+	}
+	if !ok {
+		return
+	}
+	uuid := rec.FSUUID
+	st := &s.ipState
+	st.mu.Lock()
+	done := st.done == uuid
+	st.mu.Unlock()
+
+	// What is at /mnt/belso now, if anything?
+	mountedUUID, mounted := "", false
+	if mounts, merr := s.hostReader().Mounts(); merr == nil {
+		for _, m := range mounts {
+			if path.Clean(m.MountPoint) == InternalPlaceWhere {
+				mounted = true
+				if u, okU := s.hostReader().ResolveUUID(m.Device); okU {
+					mountedUUID = u
+				}
+			}
+		}
+	}
+	if mounted && mountedUUID != "" && mountedUUID != uuid {
+		s.internalPlaceNote("another filesystem (uuid " + mountedUUID + ") is mounted at " + InternalPlaceWhere + " — the internal place waits")
+		return
+	}
+	// A Felhom unit for /mnt/belso that names another UUID (a household drive called „belso", unplugged): never
+	// overwrite it — that would silently take the drive's name and mount point.
+	if s.driveTargets != nil {
+		if drives, derr := s.driveTargets.Known(ctx); derr == nil {
+			for _, d := range drives {
+				if path.Clean(d.MountPath) == InternalPlaceWhere && d.UUID != "" && d.UUID != uuid {
+					s.internalPlaceNote("a drive unit for " + InternalPlaceWhere + " names another uuid (" + d.UUID + ") — the internal place waits")
+					return
+				}
+			}
+		}
+	}
+	if mounted && mountedUUID == uuid {
+		if !done {
+			s.recordIntent(ctx, InternalPlaceWhere, "enrolled")
+			st.mu.Lock()
+			st.done, st.lastWhy = uuid, ""
+			st.mu.Unlock()
+			s.logger.Info("internal place: mounted and enrolled", "where", InternalPlaceWhere, "fs_uuid", uuid, "gib", rec.GiB)
+		}
+		return
+	}
+	if s.disks == nil {
+		s.internalPlaceNote("disk management is not configured on this host")
+		return
+	}
+	if s.resolveStorageDevice != nil {
+		if _, rerr := s.resolveStorageDevice("uuid:" + uuid); rerr != nil {
+			s.internalPlaceNote("its volume is not present (uuid " + uuid + ")")
+			return
+		}
+	}
+	start := time.Now()
+	if err := s.disks.EnsureMount(ctx, storage.MountSpec{Name: InternalPlaceName, UUID: uuid, Where: InternalPlaceWhere, FSType: "ext4"}); err != nil {
+		s.internalPlaceNote("mount failed: " + err.Error())
+		return
+	}
+	s.recordIntent(ctx, InternalPlaceWhere, "enrolled")
+	st.mu.Lock()
+	st.done, st.lastWhy = uuid, ""
+	st.mu.Unlock()
+	s.logger.Info("internal place: mounted on the host", "where", InternalPlaceWhere, "fs_uuid", uuid, "gib", rec.GiB,
+		"duration_ms", time.Since(start).Milliseconds())
+}
+
+func (s *Server) internalPlaceNote(why string) {
+	st := &s.ipState
+	st.mu.Lock()
+	changed := st.lastWhy != why
+	st.lastWhy, st.done = why, ""
+	st.mu.Unlock()
+	if changed {
+		s.logger.Warn("internal place: not ensured", "why", why)
+	} else {
+		s.logger.Debug("internal place: still not ensured", "why", why)
+	}
+}
+
+// InternalPlaceFileIn is the record's path inside a state dir.
+func InternalPlaceFileIn(stateDir string) string { return filepath.Join(stateDir, InternalPlaceFile) }

internal/localapi/internalplace_test.go

@@ -0,0 +1,249 @@
+package localapi
+
+import (
+	"context"
+	"errors"
+	"io"
+	"log/slog"
+	"net/http"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"sync"
+	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/hub"
+	"gitea.dooplex.hu/admin/felhom-agent/internal/storage"
+)
+
+// The internal data place (felhom.eu architecture/16 §5, agent v0.158.0): mounted like an enrolled drive, but never
+// at the cost of a household drive, never formatted, ejected or decommissioned, and the same disk as sys_drive.
+
+const ipUUID = "0b6e4c5a-1d2e-4f3a-9b8c-7d6e5f4a3b2c"
+const ipDev = "/dev/mapper/pve-felhom--belso"
+
+// ipHost is a HostReader whose mount table the test changes, and whose by-uuid map it controls.
+type ipHost struct {
+	mu     sync.Mutex
+	mounts []storage.Mount
+	uuids  map[string]string // device → fs-UUID
+}
+
+func (h *ipHost) Mounts() ([]storage.Mount, error) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	return append([]storage.Mount(nil), h.mounts...), nil
+}
+func (h *ipHost) ResolveUUID(dev string) (string, bool) { u, ok := h.uuids[dev]; return u, ok }
+func (h *ipHost) DeviceExists(string) bool              { return true }
+func (h *ipHost) Rotational(string) (bool, bool)        { return false, false }
+func (h *ipHost) Removable(string) (bool, bool)         { return false, false }
+func (h *ipHost) BlockSlaves(string) ([]string, bool)   { return nil, false }
+
+func newIPHost(extra ...storage.Mount) *ipHost {
+	return &ipHost{
+		// root on a whole-disk partition (as sysOnSDA): the system disk resolves, so a USB drive is user-data.
+		mounts: append([]storage.Mount{{Device: "/dev/sda1", MountPoint: "/", FSType: "ext4"}}, extra...),
+		uuids:  map[string]string{ipDev: ipUUID, "/dev/sdb1": "99999999-aaaa-bbbb-cccc-dddddddddddd"},
+	}
+}
+
+type ipRig struct {
+	srv    *Server
+	disks  *fakeDiskOps
+	intent *fakeIntent
+}
+
+func newIPRig(t *testing.T, host *ipHost, known []storage.KnownTarget, record bool) ipRig {
+	t.Helper()
+	dir := t.TempDir()
+	file := filepath.Join(dir, InternalPlaceFile)
+	if record {
+		if err := WriteInternalPlace(file, InternalPlaceRecord{FSUUID: ipUUID, GiB: 183, MadeBy: "installer"}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	d, in := &fakeDiskOps{}, newFakeIntent()
+	srv, err := NewServer(Options{
+		ListenAddr: "127.0.0.1:0", Guests: &fakeGuests{}, Backups: &fakeBackups{}, Store: &fakeStore{},
+		Storage: fakeStorage{}, Tokens: staticTokens{"A": 8200}, Disks: d, DiskGate: &fakeGate{},
+		HostReader: host, Intent: in, DriveTargets: fakeKnownTargets{drives: known},
+		InternalPlaceFile: file, Logger: slog.New(slog.NewTextHandler(io.Discard, nil)),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	srv.baseCtx = context.Background()
+	srv.resolveStorageDevice = func(id string) (string, error) {
+		if id == "uuid:"+ipUUID {
+			return "/dev/dm-7", nil
+		}
+		return "", errors.New("absent")
+	}
+	return ipRig{srv, d, in}
+}
+
+func TestInternalPlace_NoRecord_DoesNothing(t *testing.T) {
+	r := newIPRig(t, newIPHost(), nil, false)
+	r.srv.EnsureInternalPlace(context.Background())
+	if len(r.disks.mountCalls) != 0 {
+		t.Fatalf("no record: no mount may be made, got %+v", r.disks.mountCalls)
+	}
+}
+
+func TestInternalPlace_Record_MountsByUUIDAtMntBelso(t *testing.T) {
+	r := newIPRig(t, newIPHost(), nil, true)
+	r.srv.EnsureInternalPlace(context.Background())
+	if len(r.disks.mountCalls) != 1 {
+		t.Fatalf("want exactly one EnsureMount, got %+v", r.disks.mountCalls)
+	}
+	got := r.disks.mountCalls[0]
+	if got.UUID != ipUUID || got.Where != InternalPlaceWhere || got.FSType != "ext4" || got.Name != InternalPlaceName {
+		t.Fatalf("EnsureMount spec: %+v", got)
+	}
+}
+
+func TestInternalPlace_AlreadyMounted_EnrolledOnceNoRemount(t *testing.T) {
+	host := newIPHost(storage.Mount{Device: ipDev, MountPoint: InternalPlaceWhere, FSType: "ext4"})
+	r := newIPRig(t, host, nil, true)
+	r.srv.EnsureInternalPlace(context.Background())
+	r.srv.EnsureInternalPlace(context.Background())
+	if len(r.disks.mountCalls) != 0 {
+		t.Fatalf("already mounted: no EnsureMount, got %+v", r.disks.mountCalls)
+	}
+	if r.intent.Get("uuid:"+ipUUID) != storage.IntentEnrolled {
+		t.Fatalf("the internal place must be recorded enrolled")
+	}
+}
+
+// A household drive called „belso" keeps its mount point: the internal place never takes it.
+// Positive control: TestInternalPlace_Record_MountsByUUIDAtMntBelso (the same record, /mnt/belso free).
+func TestInternalPlace_NeverTakesAHouseholdDriveNamedBelso(t *testing.T) {
+	mounted := newIPHost(storage.Mount{Device: "/dev/sdb1", MountPoint: InternalPlaceWhere, FSType: "ext4"})
+	r := newIPRig(t, mounted, nil, true)
+	r.srv.EnsureInternalPlace(context.Background())
+	if len(r.disks.mountCalls) != 0 || r.intent.Get("uuid:"+ipUUID) != "" {
+		t.Fatalf("a foreign filesystem at /mnt/belso: nothing may be mounted or recorded, got %+v", r.disks.mountCalls)
+	}
+	unplugged := []storage.KnownTarget{{Name: "belso", UUID: "99999999-aaaa-bbbb-cccc-dddddddddddd", MountPath: InternalPlaceWhere, MountBacked: true}}
+	r2 := newIPRig(t, newIPHost(), unplugged, true)
+	r2.srv.EnsureInternalPlace(context.Background())
+	if len(r2.disks.mountCalls) != 0 {
+		t.Fatalf("an unplugged household drive's unit for /mnt/belso must not be overwritten, got %+v", r2.disks.mountCalls)
+	}
+}
+
+func TestInternalPlace_VolumeAbsent_NoMount(t *testing.T) {
+	r := newIPRig(t, newIPHost(), nil, true)
+	r.srv.resolveStorageDevice = func(string) (string, error) { return "", errors.New("absent") }
+	r.srv.EnsureInternalPlace(context.Background())
+	if len(r.disks.mountCalls) != 0 {
+		t.Fatalf("absent volume: no mount, got %+v", r.disks.mountCalls)
+	}
+}
+
+// The household cannot eject or decommission it: its device is a device-mapper volume on the system disk.
+// Positive control: the same calls for a whole-disk USB drive (/dev/sdb1) are not refused by role.
+func TestInternalPlace_EjectAndDecommissionRefused(t *testing.T) {
+	host := newIPHost(
+		storage.Mount{Device: ipDev, MountPoint: InternalPlaceWhere, FSType: "ext4"},
+		storage.Mount{Device: "/dev/sdb1", MountPoint: "/mnt/hdd_1", FSType: "ext4"},
+	)
+	r := newIPRig(t, host, nil, true)
+	h := r.srv.Handler()
+	for _, route := range []string{"/disks/eject", "/disks/decommission"} {
+		if w := do(t, h, "POST", route, "A", `{"where":"/mnt/belso"}`); w.Code != http.StatusForbidden {
+			t.Fatalf("%s /mnt/belso: want 403, got %d %s", route, w.Code, w.Body.String())
+		}
+	}
+	if w := do(t, h, "POST", "/disks/eject", "A", `{"where":"/mnt/hdd_1"}`); w.Code == http.StatusForbidden {
+		t.Fatalf("positive control: a USB drive's eject must not be refused by role, got %d %s", w.Code, w.Body.String())
+	}
+	for _, u := range r.disks.unmountCalls {
+		if u == InternalPlaceWhere {
+			t.Fatalf("the internal place must never be unmounted, got %+v", r.disks.unmountCalls)
+		}
+	}
+}
+
+// The consequence `16` §5 needs: a copy between the internal place and sys_drive is the SAME disk (build A then never
+// counts it), and the place is reported as kind internal.
+type ipIdentHost struct{ fakeIdentHost }
+
+func (h *ipIdentHost) KernelName(dev string) (string, bool) {
+	if dev == ipDev {
+		return "dm-7", true
+	}
+	return h.fakeIdentHost.KernelName(dev)
+}
+func (h *ipIdentHost) Slaves(n string) []string {
+	if n == "dm-7" {
+		return []string{"dm-3"} // felhom-belso → the thin pool
+	}
+	if n == "dm-3" {
+		return []string{"sda3"} // the pool → the system disk's LVM partition
+	}
+	return nil
+}
+
+func TestInternalPlace_IsTheSystemDiskAndKindInternal(t *testing.T) {
+	ih := &ipIdentHost{fakeIdentHost{
+		virt:   "none",
+		parent: map[string]string{"sda3": "sda"},
+		props:  map[string]map[string]string{"sda": {"ID_BUS": "ata", "ID_MODEL": "SanDisk", "ID_SERIAL_SHORT": "1"}},
+		mounts: []storage.Mount{
+			{Device: "/dev/mapper/pve-root", MountPoint: "/", FSType: "ext4"},
+			{Device: "/dev/mapper/pve-root", MountPoint: "/mnt/felhom-drives", FSType: "ext4"},
+			{Device: ipDev, MountPoint: InternalPlaceWhere, FSType: "ext4"},
+			{Device: ipDev, MountPoint: "/mnt/felhom-drives/belso", FSType: "ext4"},
+		},
+	}}
+	fg := &fakeGuestsCfg{mounts: map[int]map[string]string{8200: {
+		"mp0": "local-lvm:vm-8200-disk-1,mp=/var/lib/felhom,backup=1,size=100G",
+		"mp8": "/mnt/felhom-drives,mp=/mnt/felhom-drives",
+	}}}
+	dir := t.TempDir()
+	file := filepath.Join(dir, InternalPlaceFile)
+	if err := WriteInternalPlace(file, InternalPlaceRecord{FSUUID: ipUUID}); err != nil {
+		t.Fatal(err)
+	}
+	srv, err := NewServer(Options{
+		ListenAddr: "127.0.0.1:0", Guests: fg, Backups: &fakeBackups{}, Store: &fakeStore{},
+		Storage: fakeStorage{targets: []hub.StorageTarget{provenSSD}}, Tokens: staticTokens{"A": 8200},
+		HostReader: fakeHostReader{mounts: ih.mounts}, Identity: &storage.IdentityResolver{Host: ih},
+		InternalPlaceFile: file, Logger: slog.New(slog.NewTextHandler(io.Discard, nil)),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	srv.baseCtx = context.Background()
+	got, code := sameDisk(t, srv.Handler(), "/mnt/felhom-drives/belso/felhom-data/jellyfin", "/mnt/sys_drive")
+	if code != http.StatusOK || got.Different || !got.Proven || got.Reason != "same_disk" {
+		t.Fatalf("internal place vs sys_drive: want same disk, proven; got %d %+v", code, got)
+	}
+	if got.A.Kind != storage.PlaceKindInternal {
+		t.Fatalf("kind: want %q, got %q", storage.PlaceKindInternal, got.A.Kind)
+	}
+}
+
+func TestInternalPlaceRecord_RefusesANonUUID(t *testing.T) {
+	file := filepath.Join(t.TempDir(), InternalPlaceFile)
+	if err := WriteInternalPlace(file, InternalPlaceRecord{FSUUID: "../../etc"}); err == nil {
+		t.Fatal("a non-UUID must not be written")
+	}
+}
+
+// The root helper's own tests (configs/test_felhom_internal_place.py — the ruled size table, never formatting what
+// holds anything) run with the Go suite.
+func TestInternalPlaceHelperPythonSuite(t *testing.T) {
+	py, err := exec.LookPath("python3")
+	if err != nil {
+		t.Skip("python3 not found")
+	}
+	_, file, _, _ := runtime.Caller(0)
+	script := filepath.Join(filepath.Dir(file), "..", "..", "configs", "test_felhom_internal_place.py")
+	out, err := exec.Command(py, script).CombinedOutput()
+	if err != nil {
+		t.Fatalf("helper suite failed: %v\n%s", err, out)
+	}
+}

internal/localapi/samedisk.go

@@ -135,6 +135,8 @@ func (s *Server) ownMountIdentity(hostPath string) (storage.PlaceIdentity, strin
 	}
 	kind := storage.PlaceKindDisk
 	switch {
+	case s.isInternalPlace(hostPath): // v0.158.0 `16` §5: the one-disk box's data place, on the system disk
+		kind = storage.PlaceKindInternal
 	case id.Reason == storage.ReasonNetwork:
 		kind = storage.PlaceKindNetwork
 	case strings.HasPrefix(m.Device, "/dev/") && !strings.HasPrefix(m.Device, "/dev/mapper/") && isPartitionPath(m.Device):

internal/localapi/server.go

@@ -208,6 +208,9 @@ type Options struct {
 	// Intent records drive enroll/eject intent for the self-heal watchdog (slice 10 P3). OPTIONAL —
 	// when nil, no intent is recorded (self-heal runs ungated).
 	Intent IntentRecorder
+	// InternalPlaceFile (v0.158.0, felhom.eu `16` §5) is the path of the internal data place record
+	// (InternalPlaceRecord). OPTIONAL — "" means this host has no internal place and EnsureInternalPlace is a no-op.
+	InternalPlaceFile string
 	// GuestBinds persists which user-data drives (by durable-id) are enrolled into each guest, so the
 	// startup re-assert (ReassertGuestBinds) can restore a bind that a re-provision dropped (F9).
 	// OPTIONAL — when nil, guest binds are not recorded and the startup re-assert is a no-op.
@@ -316,12 +319,14 @@ type Server struct {
 	// identity blob from the hub, unseal it with the customer's recovery code, return ONLY the
 	// offsite repository password. OPTIONAL — nil (no hub client configured) makes
 	// POST /escrow/recover-offsite-password answer 503 rather than pretending.
-	escrowRecovery EscrowRecoverer
-	intent         IntentRecorder                      // slice 10 P3 (optional)
-	guestBinds     *GuestBindStore                     // F9 startup bind re-assert record (optional)
-	formatJobs     *FormatJobStore                     // F20-BUG3 detached-format job record (optional)
-	staleLock      StaleLockController                 // F2-b startup stale-lock recovery (optional)
-	partialSweep   func(ctx context.Context, vmid int) // R-1006 start-up sweep of dead vzdump leftovers (optional)
+	escrowRecovery    EscrowRecoverer
+	intent            IntentRecorder                      // slice 10 P3 (optional)
+	internalPlaceFile string                              // v0.158.0 `16` §5 (optional)
+	ipState           internalPlaceState                  // EnsureInternalPlace's memo
+	guestBinds        *GuestBindStore                     // F9 startup bind re-assert record (optional)
+	formatJobs        *FormatJobStore                     // F20-BUG3 detached-format job record (optional)
+	staleLock         StaleLockController                 // F2-b startup stale-lock recovery (optional)
+	partialSweep      func(ctx context.Context, vmid int) // R-1006 start-up sweep of dead vzdump leftovers (optional)
 	// guestPower (F-REBOOT) is per-guest start-attempt state for the guest-power watchdog.
 	// Guarded by guestPowerMu in guestpower.go; in-memory on purpose (see guestPowerState).
 	guestPower map[int]guestPowerState
@@ -455,43 +460,44 @@ func NewServer(o Options) (*Server, error) {
 		cadence = defaultBackupCadence
 	}
 	s := &Server{
-		addr:            o.ListenAddr,
-		cert:            o.Cert,
-		guests:          o.Guests,
-		backups:         o.Backups,
-		store:           o.Store,
-		storage:         o.Storage,
-		driveTargets:    o.DriveTargets,
-		smart:           o.Smart,
-		tokens:          o.Tokens,
-		cadence:         cadence,
-		logger:          o.Logger,
-		now:             func() time.Time { return time.Now().UTC() },
-		disks:           o.Disks,
-		diskGate:        o.DiskGate,
-		guestList:       o.Guests2,
-		guestAttach:     o.GuestAttach,
-		mem:             o.Memory,
-		netStorage:      o.NetStorage,
-		privileged:      o.Privileged,
-		configPath:      o.ConfigPath,
-		stateDir:        o.StateDir,
-		netMountRoot:    storage.NetworkMountRoot,
-		smbCredsDir:     o.SmbCredsDir,
-		escrowStagePath: o.EscrowStagePath,
-		escrowRecovery:  o.EscrowRecovery,
-		intent:          o.Intent,
-		guestBinds:      o.GuestBinds,
-		formatJobs:      o.FormatJobs,
-		staleLock:       o.StaleLock,
-		host:            o.HostReader,
-		ident:           o.Identity,
-		hostMetrics:     o.HostMetrics,
-		hostID:          o.HostID,
-		agentVersion:    o.AgentVersion,
-		logRing:         o.LogRing,
-		jobs:            map[backupJobKey]*backupJob{},
-		swapInFlight:    map[int]bool{},
+		addr:              o.ListenAddr,
+		cert:              o.Cert,
+		guests:            o.Guests,
+		backups:           o.Backups,
+		store:             o.Store,
+		storage:           o.Storage,
+		driveTargets:      o.DriveTargets,
+		smart:             o.Smart,
+		tokens:            o.Tokens,
+		cadence:           cadence,
+		logger:            o.Logger,
+		now:               func() time.Time { return time.Now().UTC() },
+		disks:             o.Disks,
+		diskGate:          o.DiskGate,
+		guestList:         o.Guests2,
+		guestAttach:       o.GuestAttach,
+		mem:               o.Memory,
+		netStorage:        o.NetStorage,
+		privileged:        o.Privileged,
+		configPath:        o.ConfigPath,
+		stateDir:          o.StateDir,
+		netMountRoot:      storage.NetworkMountRoot,
+		smbCredsDir:       o.SmbCredsDir,
+		escrowStagePath:   o.EscrowStagePath,
+		escrowRecovery:    o.EscrowRecovery,
+		intent:            o.Intent,
+		internalPlaceFile: o.InternalPlaceFile,
+		guestBinds:        o.GuestBinds,
+		formatJobs:        o.FormatJobs,
+		staleLock:         o.StaleLock,
+		host:              o.HostReader,
+		ident:             o.Identity,
+		hostMetrics:       o.HostMetrics,
+		hostID:            o.HostID,
+		agentVersion:      o.AgentVersion,
+		logRing:           o.LogRing,
+		jobs:              map[backupJobKey]*backupJob{},
+		swapInFlight:      map[int]bool{},
 	}
 	// R-82 tier resolution. Options.BackupTiers is authoritative when supplied; otherwise ONE tier
 	// is synthesized from Backups + BackupCadence — the pre-R-82 shape, so every existing caller

internal/reconcile/classify.go

@@ -64,6 +64,11 @@ const (
 	// The config bundle (agent v0.143.0, R-840, `11` §5.4.2): the box's ROOT-OWNED files (sudoers, wrappers, units).
 	// Destructive-class (signed, operational key) like agent_update; the root wrapper re-verifies the signature itself.
 	ClassAgentConfigUpdate OpClass = "agent_config_update"
+
+	// The internal data place on an OLD one-disk box (agent v0.158.0, felhom.eu `16` §9): thin space on the system
+	// disk, made by the root helper felhom-internal-place. Destructive-class (signed, operational key): it is an
+	// operator act, never a household button, and no agent-internal provenance may start it.
+	ClassAddInternalPlace OpClass = "add_internal_place"
 )
 
 // Disposition is the classifier verdict.
@@ -132,7 +137,7 @@ func Classify(class OpClass, prov Provenance) Disposition {
 		return Destructive
 	case ClassKeyRotation:
 		return Destructive
-	case ClassAgentUpdate, ClassOSDockerStep, ClassOSPVEStep, ClassOSKernelStep, ClassAgentConfigUpdate:
+	case ClassAgentUpdate, ClassOSDockerStep, ClassOSPVEStep, ClassOSKernelStep, ClassAgentConfigUpdate, ClassAddInternalPlace:
 		// Never benign — no agent-internal provenance can make replacing the agent binary
 		// unsigned-safe (a compromised process must not be able to self-bless an update).
 		return Destructive

internal/signedjobs/internalplace.go

@@ -0,0 +1,91 @@
+package signedjobs
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/localapi"
+	"gitea.dooplex.hu/admin/felhom-agent/internal/proxmox"
+)
+
+// opAddInternalPlace is the op class this executor serves (mirrors reconcile.ClassAddInternalPlace).
+const opAddInternalPlace = "add_internal_place"
+
+// InternalPlaceHelper is the root helper's path (configs/felhom-internal-place, from the config bundle).
+const InternalPlaceHelper = "/usr/local/sbin/felhom-internal-place"
+
+var reHelperResult = regexp.MustCompile(`^(created|existing|formatted) uuid=([0-9a-fA-F-]{36}) gib=([0-9]+)$`)
+
+// InternalPlaceExecutor adds the internal data place to an OLD one-disk box (felhom.eu architecture/16 §9: „one-disk
+// boxes get no internal place by themselves; adding one later is a signed operator job, not a household button").
+// It runs the SAME root helper the installer runs — `felhom-internal-place create 0` (0 GiB planned: the guest's
+// volumes already exist and are counted) — writes the record the agent mounts from, and asks the local API to mount
+// it now. Every safety rule (the ruled size, never format what holds anything) lives in the helper, as root.
+//
+// The op carries no parameters: the size is the rule's, never the signer's. Destructive-class by default (the
+// classifier's fail-safe; ClassAddInternalPlace documents it): it takes thin space on the system disk, so only an
+// operator signature may start it.
+type InternalPlaceExecutor struct {
+	runner     proxmox.Runner
+	recordFile string
+	ensure     func(context.Context) // late-bound: the local API server is built after the jobs runner
+	logger     *slog.Logger
+}
+
+// NewInternalPlaceExecutor wires the executor. ensure may be nil at construction and set later through SetEnsure.
+func NewInternalPlaceExecutor(runner proxmox.Runner, recordFile string, logger *slog.Logger) *InternalPlaceExecutor {
+	if logger == nil {
+		logger = slog.Default()
+	}
+	return &InternalPlaceExecutor{runner: runner, recordFile: recordFile, logger: logger}
+}
+
+// SetEnsure late-binds the mount step (localapi.Server.EnsureInternalPlace).
+func (e *InternalPlaceExecutor) SetEnsure(f func(context.Context)) { e.ensure = f }
+
+// Execute implements signedjobs.Executor for add_internal_place.
+func (e *InternalPlaceExecutor) Execute(ctx context.Context, op string, params json.RawMessage) error {
+	if op != opAddInternalPlace {
+		return ErrNoExecutor
+	}
+	if p := bytes.TrimSpace(params); len(p) > 0 && !bytes.Equal(p, []byte("{}")) && !bytes.Equal(p, []byte("null")) {
+		return fmt.Errorf("add_internal_place: takes no parameters (the size is the ruled rule's), got %s", p)
+	}
+	if e.runner == nil || e.recordFile == "" {
+		return fmt.Errorf("add_internal_place: not wired on this host (no privileged runner or state dir)")
+	}
+	start := time.Now()
+	e.logger.Warn("add_internal_place: executing operator-signed job (the internal data place, `16` §9)")
+	out, stderr, err := e.runner.Run(ctx, InternalPlaceHelper, "create", "0")
+	line := strings.TrimSpace(string(out))
+	if err != nil {
+		return fmt.Errorf("add_internal_place: helper refused: %v: %s", err, strings.TrimSpace(string(stderr)))
+	}
+	if strings.HasPrefix(line, "skipped ") {
+		// Not an error the operator can retry away: the pool has no room by the ruled rule. Fail the job with the
+		// helper's own numbers so the hub shows why.
+		return fmt.Errorf("add_internal_place: %s", line)
+	}
+	m := reHelperResult.FindStringSubmatch(line)
+	if m == nil {
+		return fmt.Errorf("add_internal_place: unexpected helper output %q", line)
+	}
+	gib, _ := strconv.Atoi(m[3])
+	rec := localapi.InternalPlaceRecord{FSUUID: m[2], GiB: gib, MadeBy: "signed-job", MadeAt: time.Now().UTC().Format(time.RFC3339)}
+	if err := localapi.WriteInternalPlace(e.recordFile, rec); err != nil {
+		return fmt.Errorf("add_internal_place: writing the record: %w", err)
+	}
+	if e.ensure != nil {
+		e.ensure(ctx)
+	}
+	e.logger.Warn("add_internal_place: complete", "result", m[1], "fs_uuid", m[2], "gib", gib,
+		"duration_ms", time.Since(start).Milliseconds())
+	return nil
+}

internal/signedjobs/internalplace_test.go

@@ -0,0 +1,94 @@
+package signedjobs
+
+import (
+	"context"
+	"errors"
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/localapi"
+	"gitea.dooplex.hu/admin/felhom-agent/internal/reconcile"
+)
+
+// add_internal_place (felhom.eu architecture/16 §9, agent v0.158.0): the operator's job for an OLD one-disk box.
+
+type ipRunner struct {
+	out, stderr string
+	err         error
+	calls       [][]string
+}
+
+func (r *ipRunner) Run(_ context.Context, name string, args ...string) ([]byte, []byte, error) {
+	r.calls = append(r.calls, append([]string{name}, args...))
+	return []byte(r.out), []byte(r.stderr), r.err
+}
+func (r *ipRunner) RunStdin(ctx context.Context, _ io.Reader, name string, args ...string) ([]byte, []byte, error) {
+	return r.Run(ctx, name, args...)
+}
+
+func ipExec(t *testing.T, r *ipRunner) (*InternalPlaceExecutor, string, *int) {
+	t.Helper()
+	file := filepath.Join(t.TempDir(), localapi.InternalPlaceFile)
+	e := NewInternalPlaceExecutor(r, file, slog.New(slog.NewTextHandler(io.Discard, nil)))
+	n := 0
+	e.SetEnsure(func(context.Context) { n++ })
+	return e, file, &n
+}
+
+func TestAddInternalPlace_RunsTheHelperWritesTheRecordAndMounts(t *testing.T) {
+	r := &ipRunner{out: "created uuid=0b6e4c5a-1d2e-4f3a-9b8c-7d6e5f4a3b2c gib=33\n"}
+	e, file, ensured := ipExec(t, r)
+	if err := e.Execute(context.Background(), "add_internal_place", []byte(`{}`)); err != nil {
+		t.Fatal(err)
+	}
+	if len(r.calls) != 1 || strings.Join(r.calls[0], " ") != InternalPlaceHelper+" create 0" {
+		t.Fatalf("the helper must be called exactly as `create 0`, got %v", r.calls)
+	}
+	rec, ok, err := localapi.ReadInternalPlace(file)
+	if err != nil || !ok || rec.FSUUID != "0b6e4c5a-1d2e-4f3a-9b8c-7d6e5f4a3b2c" || rec.GiB != 33 || rec.MadeBy != "signed-job" {
+		t.Fatalf("record: %+v ok=%v err=%v", rec, ok, err)
+	}
+	if *ensured != 1 {
+		t.Fatalf("the mount must be asked for once, got %d", *ensured)
+	}
+}
+
+func TestAddInternalPlace_NoRoomOrRefusalOrGarbage_WritesNothing(t *testing.T) {
+	for name, r := range map[string]*ipRunner{
+		"skipped": {out: "skipped only 7 GiB free for it (pool 53, reserve 16, promised 102, planned 0; needs 20)"},
+		"refused": {err: errors.New("exit status 1"), stderr: "felhom-internal-place: REFUSED: holds something"},
+		"garbage": {out: "created uuid=../../etc gib=1"},
+	} {
+		e, file, ensured := ipExec(t, r)
+		if err := e.Execute(context.Background(), "add_internal_place", nil); err == nil {
+			t.Fatalf("%s: want an error", name)
+		}
+		if _, statErr := os.Stat(file); !os.IsNotExist(statErr) || *ensured != 0 {
+			t.Fatalf("%s: no record and no mount may follow, stat=%v ensured=%d", name, statErr, *ensured)
+		}
+	}
+}
+
+func TestAddInternalPlace_TakesNoParametersAndIgnoresOtherOps(t *testing.T) {
+	r := &ipRunner{out: "created uuid=0b6e4c5a-1d2e-4f3a-9b8c-7d6e5f4a3b2c gib=33"}
+	e, _, _ := ipExec(t, r)
+	if err := e.Execute(context.Background(), "add_internal_place", []byte(`{"gib":900}`)); err == nil || len(r.calls) != 0 {
+		t.Fatalf("a size from the signer must be refused before the helper runs, err=%v calls=%v", err, r.calls)
+	}
+	if err := e.Execute(context.Background(), "decommission", []byte(`{}`)); !errors.Is(err, ErrNoExecutor) {
+		t.Fatalf("another op: want ErrNoExecutor, got %v", err)
+	}
+}
+
+func TestAddInternalPlace_IsSignatureOnly(t *testing.T) {
+	if got := reconcile.Classify(reconcile.ClassAddInternalPlace, reconcile.Provenance{}); got != reconcile.Destructive {
+		t.Fatalf("add_internal_place must need an operator signature, classified %v", got)
+	}
+	if string(reconcile.ClassAddInternalPlace) != opAddInternalPlace {
+		t.Fatalf("op string drift: %q vs %q", reconcile.ClassAddInternalPlace, opAddInternalPlace)
+	}
+}

internal/storage/candidates.go

@@ -13,14 +13,16 @@ import (
 // (guarded, Impl-1) and/or mounts + binds. Blank disks are "initialize"-only; disks already carrying a
 // mountable FS are ALSO "attach" candidates.
 type CandidateDisk struct {
-	Device      string `json:"device"`       // whole disk, e.g. /dev/sdd
-	SizeBytes   int64  `json:"size_bytes"`   // 0 when unreadable
+	Device      string `json:"device"`     // whole disk, e.g. /dev/sdd
+	SizeBytes   int64  `json:"size_bytes"` // 0 when unreadable
 	Model       string `json:"model,omitempty"`
-	FSType      string `json:"fstype,omitempty"`      // first filesystem found ("" = blank)
-	DataBearing bool   `json:"data_bearing"`          // has any FS / partition (→ wipe-confirm downstream)
-	Mountable   bool   `json:"mountable"`             // carries an ext4/xfs FS the agent can mount as-is
+	FSType      string `json:"fstype,omitempty"`       // first filesystem found ("" = blank)
+	DataBearing bool   `json:"data_bearing"`           // has any FS / partition (→ wipe-confirm downstream)
+	Mountable   bool   `json:"mountable"`              // carries an ext4/xfs FS the agent can mount as-is
 	MountSource string `json:"mount_source,omitempty"` // the node to mount for attach (e.g. /dev/sdd1)
 	DurableID   string `json:"durable_id,omitempty"`   // "uuid:<fs-uuid>" if it has an FS; "" for a blank disk
+	// Partitions (v0.158.0, felhom.eu `16` §6): each partition of this disk as its own place — see partitions.go.
+	Partitions []CandidatePartition `json:"partitions,omitempty"`
 }
 
 // mountableFSTypes are the filesystems the agent can mount as-is (EnsureMount) → an "attach" candidate.
@@ -83,6 +85,8 @@ func (h *SudoHostOps) buildCandidate(dev, name string) CandidateDisk {
 			if len(nodes) > 1 {
 				c.DataBearing = true
 			}
+			c.Partitions = candidatePartitions(lout, name, readSysPartSize, readSysPartNumber, h.host.ResolveUUID,
+				felhomOwnedMounts(dev, nodes, h.mountTable))
 		}
 	}
 	return c

internal/storage/durable_device.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"regexp"
 	"sort"
 	"strings"
 )
@@ -24,8 +25,13 @@ var devDiskRoot = "/dev/disk"
 const (
 	durableByID   = "byid:"
 	durableByUUID = "byuuid:"
+	// partFSUUIDSep joins a partition's by-id link and its fs-UUID in one wipe id (v0.158.0, `16` §6).
+	partFSUUIDSep = "+fsuuid:"
 )
 
+// rePartLink matches a by-id link of a PARTITION (udev appends -part<N> to the disk's link).
+var rePartLink = regexp.MustCompile(`-part[1-9][0-9]{0,2}$`)
+
 // byIDPriority ranks /dev/disk/by-id link prefixes most-stable-first: wwn (hardware world-wide
 // name) > nvme-eui (NVMe EUI) > nvme-/ata-/scsi-/usb- (model+serial). dm-/lvm-/md- names are
 // excluded (they are mapper constructs, not the physical disk we want to bind a wipe to).
@@ -41,6 +47,14 @@ func DeviceDurableID(device string) (string, error) {
 	}
 	// 1. best by-id link pointing at this device.
 	if name := bestByIDLink(target); name != "" {
+		// v0.158.0 (felhom.eu `16` §6): a PARTITION's link already carries the disk id + the part number
+		// (wwn-…-part2). When the part holds a filesystem, its fs-UUID is bound too, so a part that was reformatted —
+		// or another disk's part2 that took the link — derives a different id and the wipe refuses.
+		if rePartLink.MatchString(name) {
+			if uuid := byUUIDFor(target); uuid != "" {
+				return durableByID + name + partFSUUIDSep + uuid, nil
+			}
+		}
 		return durableByID + name, nil
 	}
 	// 2. fallback: a filesystem UUID symlink.
@@ -56,10 +70,29 @@ func ResolveDurableDevice(durableID string) (string, error) {
 	switch {
 	case strings.HasPrefix(durableID, durableByID):
 		name := strings.TrimPrefix(durableID, durableByID)
+		fsUUID := ""
+		if i := strings.Index(name, partFSUUIDSep); i >= 0 {
+			name, fsUUID = name[:i], name[i+len(partFSUUIDSep):]
+			if !rePartLink.MatchString(name) || !safeLinkName(fsUUID) {
+				return "", fmt.Errorf("storage: unsafe durable id %q", durableID)
+			}
+		}
 		if !safeLinkName(name) {
 			return "", fmt.Errorf("storage: unsafe durable id %q", durableID)
 		}
-		return filepath.EvalSymlinks(filepath.Join(devDiskRoot, "by-id", name))
+		dev, err := filepath.EvalSymlinks(filepath.Join(devDiskRoot, "by-id", name))
+		if err != nil || fsUUID == "" {
+			return dev, err
+		}
+		// Both halves must name the SAME device now (`16` §6): the part by its disk id + number, and its filesystem.
+		byFS, ferr := filepath.EvalSymlinks(filepath.Join(devDiskRoot, "by-uuid", fsUUID))
+		if ferr != nil {
+			return "", fmt.Errorf("storage: durable id %q: its filesystem %s no longer resolves: %w", durableID, fsUUID, ferr)
+		}
+		if byFS != dev {
+			return "", fmt.Errorf("storage: durable id %q: the part (%s) and its filesystem (%s) are different devices now", durableID, dev, byFS)
+		}
+		return dev, nil
 	case strings.HasPrefix(durableID, durableByUUID):
 		uuid := strings.TrimPrefix(durableID, durableByUUID)
 		if !safeLinkName(uuid) {

internal/storage/mkfs_guarded_suite_test.go

@@ -0,0 +1,24 @@
+package storage
+
+import (
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+// The root mkfs wrapper's own tests (configs/test_felhom_mkfs_guarded.py, agent v0.158.0 — a sibling partition that
+// is Felhom's own drive no longer blocks formatting the part next to it; every other mount still refuses) run with
+// the Go suite.
+func TestMkfsGuardedPythonSuite(t *testing.T) {
+	py, err := exec.LookPath("python3")
+	if err != nil {
+		t.Skip("python3 not found")
+	}
+	_, file, _, _ := runtime.Caller(0)
+	script := filepath.Join(filepath.Dir(file), "..", "..", "configs", "test_felhom_mkfs_guarded.py")
+	out, err := exec.Command(py, script).CombinedOutput()
+	if err != nil {
+		t.Fatalf("wrapper suite failed: %v\n%s", err, out)
+	}
+}

internal/storage/partition_durable_test.go

@@ -0,0 +1,112 @@
+package storage
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+// The data-bearing partition path binds the disk id + the part number + the fs-UUID (felhom.eu architecture/16 §6,
+// agent v0.158.0). The wipe re-resolve (localapi antiRetargetResolveExpect) formats only when resolve(id) succeeds AND
+// DeviceDurableID(that device) == id — the round trip these tests pin, in the three ways a target can move.
+
+type partFixture struct{ base, root string }
+
+func newPartFixture(t *testing.T) partFixture {
+	t.Helper()
+	if runtime.GOOS == "windows" {
+		t.Skip("symlink fixtures run on Linux")
+	}
+	f := partFixture{base: t.TempDir()}
+	f.root = filepath.Join(f.base, "disk")
+	for _, d := range []string{"sdb", "sdb1", "sdb2", "sdc2"} {
+		if err := os.WriteFile(filepath.Join(f.base, d), []byte("x"), 0o600); err != nil {
+			t.Fatal(err)
+		}
+	}
+	os.MkdirAll(filepath.Join(f.root, "by-id"), 0o755)
+	os.MkdirAll(filepath.Join(f.root, "by-uuid"), 0o755)
+	withDevDiskRoot(t, f.root)
+	return f
+}
+
+func (f partFixture) link(t *testing.T, sub, name, dev string) {
+	t.Helper()
+	p := filepath.Join(f.root, sub, name)
+	os.Remove(p)
+	if err := os.Symlink(filepath.Join(f.base, dev), p); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func (f partFixture) dev(name string) string { return filepath.Join(f.base, name) }
+
+func (f partFixture) standard(t *testing.T) {
+	f.link(t, "by-id", "wwn-0x5000aaaa", "sdb")
+	f.link(t, "by-id", "ata-TOSHIBA_MQ04_65NOP-part1", "sdb1")
+	f.link(t, "by-id", "wwn-0x5000aaaa-part1", "sdb1")
+	f.link(t, "by-id", "wwn-0x5000aaaa-part2", "sdb2")
+	f.link(t, "by-uuid", "1111-films", "sdb2")
+}
+
+func roundTrip(id string) (string, bool) {
+	dev, err := ResolveDurableDevice(id)
+	if err != nil {
+		return "", false
+	}
+	again, err := DeviceDurableID(dev)
+	return dev, err == nil && again == id
+}
+
+func TestPartitionWipeID_BindsDiskPartAndFilesystem(t *testing.T) {
+	f := newPartFixture(t)
+	f.standard(t)
+	id, err := DeviceDurableID(f.dev("sdb2"))
+	if err != nil || id != "byid:wwn-0x5000aaaa-part2+fsuuid:1111-films" {
+		t.Fatalf("a part with a filesystem: want disk id + part + fs-UUID, got %q %v", id, err)
+	}
+	if dev, ok := roundTrip(id); !ok || dev != f.dev("sdb2") {
+		t.Fatalf("the unchanged part must round-trip, got %q %v", dev, ok)
+	}
+	// A blank part (no filesystem) and a whole disk keep the plain by-id binding.
+	if id1, _ := DeviceDurableID(f.dev("sdb1")); id1 != "byid:wwn-0x5000aaaa-part1" {
+		t.Fatalf("a blank part: want the plain part link, got %q", id1)
+	}
+	if idDisk, _ := DeviceDurableID(f.dev("sdb")); idDisk != "byid:wwn-0x5000aaaa" {
+		t.Fatalf("a whole disk keeps today's id, got %q", idDisk)
+	}
+}
+
+func TestPartitionWipeID_ReformattedPartRefuses(t *testing.T) {
+	f := newPartFixture(t)
+	f.standard(t)
+	id, _ := DeviceDurableID(f.dev("sdb2"))
+	os.Remove(filepath.Join(f.root, "by-uuid", "1111-films"))
+	f.link(t, "by-uuid", "2222-other", "sdb2") // someone reformatted the part since the household confirmed
+	if _, ok := roundTrip(id); ok {
+		t.Fatalf("a reformatted part must not round-trip (the wipe would hit a different filesystem)")
+	}
+}
+
+func TestPartitionWipeID_LinkMovedToAnotherDiskRefuses(t *testing.T) {
+	f := newPartFixture(t)
+	f.standard(t)
+	id, _ := DeviceDurableID(f.dev("sdb2"))
+	f.link(t, "by-id", "wwn-0x5000aaaa-part2", "sdc2") // a different node took the part link; the fs is still sdb2
+	if _, err := ResolveDurableDevice(id); err == nil || !strings.Contains(err.Error(), "different devices") {
+		t.Fatalf("the part link and its filesystem on different devices must refuse, got %v", err)
+	}
+}
+
+func TestPartitionWipeID_RefusesAForgedCompound(t *testing.T) {
+	f := newPartFixture(t)
+	f.standard(t)
+	f.link(t, "by-uuid", "3333-whole", "sdb") // a filesystem straight on the whole disk: both halves name sdb
+	for _, id := range []string{"byid:wwn-0x5000aaaa+fsuuid:3333-whole", "byid:wwn-0x5000aaaa-part2+fsuuid:../x"} {
+		if _, err := ResolveDurableDevice(id); err == nil {
+			t.Fatalf("%q must be refused", id)
+		}
+	}
+}

internal/storage/partitions.go

@@ -0,0 +1,104 @@
+package storage
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// Partitions as places (agent v0.158.0) — felhom.eu architecture/16-storage-physical-identity.md §6.
+//
+// A disk that passed the WHOLE-disk unclaimed filter (classifyClaim: not the system disk, no LVM/ZFS/RAID/LUKS/swap
+// member on any node, no foreign mount on any node) also lists its partitions, each with its own state:
+//
+//	empty       no filesystem, no children           → „format this part" (self-serve: the agent's probe says blank)
+//	filesystem  ext4/xfs (mountable) or another fs   → „use this part" when mountable; „format this part" only through
+//	                                                   the customer-confirmed data-bearing path (the agent's own probe)
+//	in_use      already Felhom's own drive           → shown, never offered (it is a registered drive already)
+//
+// A partition with children (LVM, a mapper) is not listed. The design's separate „a filesystem with no files" state is
+// folded into `filesystem` on purpose: telling the two apart needs a root read-only mount, and the data-bearing path's
+// confirmation is the safer default for both (`16` §13). Creating, deleting or resizing a partition: never here (D5).
+// The format binding is the partition's own by-id link (…-partN: the disk id + the partition number) via
+// DeviceDurableID, re-resolved before mkfs (wipe_reresolve.go); the attach key is its fs-UUID.
+type CandidatePartition struct {
+	Device    string `json:"device"` // e.g. /dev/sdb2
+	Number    int    `json:"number,omitempty"`
+	SizeBytes int64  `json:"size_bytes"`
+	FSType    string `json:"fstype,omitempty"`
+	State     string `json:"state"` // empty | filesystem | in_use
+	Mountable bool   `json:"mountable"`
+	DurableID string `json:"durable_id,omitempty"` // uuid:<fs-uuid> — the attach key ("" when empty)
+	MountedAt string `json:"mounted_at,omitempty"` // in_use: Felhom's own mount
+}
+
+const (
+	PartEmpty      = "empty"
+	PartFilesystem = "filesystem"
+	PartInUse      = "in_use"
+)
+
+// candidatePartitions is the pure lister: the whole disk's lsblk tree → its partitions. sizeOf/numberOf read /sys,
+// uuidOf the by-uuid links, owned is the set of mountpoints corroborated as Felhom's own (felhomOwnedMounts).
+func candidatePartitions(lsblkJSON []byte, wholeName string, sizeOf func(string) int64, numberOf func(string) int,
+	uuidOf func(string) (string, bool), owned map[string]bool) []CandidatePartition {
+	var doc struct {
+		BlockDevices []lsblkDev `json:"blockdevices"`
+	}
+	if json.Unmarshal(lsblkJSON, &doc) != nil {
+		return nil
+	}
+	var out []CandidatePartition
+	for _, d := range doc.BlockDevices {
+		if d.Name != wholeName {
+			continue
+		}
+		for _, p := range d.Children {
+			if len(p.Children) > 0 || memberFSTypes[p.FSType] {
+				continue // LVM/mapper on it, or a member: not a place (the disk filter refuses these anyway)
+			}
+			c := CandidatePartition{Device: "/dev/" + p.Name, Number: numberOf(p.Name), SizeBytes: sizeOf(p.Name), FSType: p.FSType}
+			switch {
+			case p.MountPoint != "" && (underFelhomDrives(p.MountPoint) || owned[p.MountPoint]):
+				c.State, c.MountedAt = PartInUse, p.MountPoint
+			case p.MountPoint != "":
+				continue // mounted by something else: never offered (the disk filter refuses the disk anyway)
+			case p.FSType == "":
+				c.State = PartEmpty
+			default:
+				c.State = PartFilesystem
+				c.Mountable = mountableFSTypes[p.FSType]
+				if u, ok := uuidOf(c.Device); ok && u != "" {
+					c.DurableID = "uuid:" + u
+				}
+			}
+			out = append(out, c)
+		}
+	}
+	return out
+}
+
+// readSysPartNumber reads /sys/class/block/<part>/partition (0 when unreadable).
+func readSysPartNumber(name string) int {
+	b, err := os.ReadFile(filepath.Join("/sys/class/block", name, "partition"))
+	if err != nil {
+		return 0
+	}
+	n, _ := strconv.Atoi(strings.TrimSpace(string(b)))
+	return n
+}
+
+// readSysPartSize reads a partition's size in bytes from /sys/class/block/<part>/size (512-byte sectors).
+func readSysPartSize(name string) int64 {
+	b, err := os.ReadFile(filepath.Join("/sys/class/block", name, "size"))
+	if err != nil {
+		return 0
+	}
+	s, err := strconv.ParseInt(strings.TrimSpace(string(b)), 10, 64)
+	if err != nil {
+		return 0
+	}
+	return s * 512
+}

internal/storage/partitions_test.go

@@ -0,0 +1,73 @@
+package storage
+
+import (
+	"strings"
+	"testing"
+)
+
+// Partitions as places (felhom.eu architecture/16 §6, agent v0.158.0): every partition of a free disk with its own
+// state; Felhom's own drive shown but never offered; anything foreign, layered or a member never listed.
+
+const partTree = `{"blockdevices":[
+ {"name":"sdb","fstype":null,"mountpoint":null,"children":[
+   {"name":"sdb1","fstype":"ext4","mountpoint":"/mnt/felhom-drives/hdd_1"},
+   {"name":"sdb2","fstype":null,"mountpoint":null},
+   {"name":"sdb3","fstype":"ntfs","mountpoint":null},
+   {"name":"sdb4","fstype":"xfs","mountpoint":null},
+   {"name":"sdb5","fstype":"ext4","mountpoint":"/mnt/films"},
+   {"name":"sdb6","fstype":"ext4","mountpoint":"/srv/data"},
+   {"name":"sdb7","fstype":"LVM2_member","mountpoint":null,"children":[{"name":"vg-lv","fstype":"ext4","mountpoint":null}]},
+   {"name":"sdb8","fstype":"crypto_LUKS","mountpoint":null}
+ ]},
+ {"name":"sdc","fstype":null,"mountpoint":null,"children":[{"name":"sdc1","fstype":null,"mountpoint":null}]}
+]}`
+
+func listParts(owned map[string]bool) map[string]CandidatePartition {
+	got := candidatePartitions([]byte(partTree), "sdb",
+		func(n string) int64 { return int64(len(n)) << 30 },
+		func(n string) int { return int(n[len(n)-1] - '0') },
+		func(dev string) (string, bool) { return "uuid-of-" + strings.TrimPrefix(dev, "/dev/"), true },
+		owned)
+	m := map[string]CandidatePartition{}
+	for _, p := range got {
+		m[p.Device] = p
+	}
+	return m
+}
+
+func TestPartitions_StatesPerPartition(t *testing.T) {
+	m := listParts(map[string]bool{"/mnt/films": true})
+	want := map[string]string{"/dev/sdb1": PartInUse, "/dev/sdb2": PartEmpty, "/dev/sdb3": PartFilesystem,
+		"/dev/sdb4": PartFilesystem, "/dev/sdb5": PartInUse}
+	if len(m) != len(want) {
+		t.Fatalf("want exactly %d listed partitions, got %+v", len(want), m)
+	}
+	for dev, st := range want {
+		if m[dev].State != st {
+			t.Fatalf("%s: want %s, got %+v", dev, st, m[dev])
+		}
+	}
+	if m["/dev/sdb2"].DurableID != "" || m["/dev/sdb2"].Mountable {
+		t.Fatalf("an empty part has no attach key: %+v", m["/dev/sdb2"])
+	}
+	if !m["/dev/sdb4"].Mountable || m["/dev/sdb4"].DurableID != "uuid:uuid-of-sdb4" || m["/dev/sdb4"].Number != 4 {
+		t.Fatalf("an xfs part is usable by its fs-UUID: %+v", m["/dev/sdb4"])
+	}
+	if m["/dev/sdb3"].Mountable {
+		t.Fatalf("ntfs is a filesystem the agent does not mount as-is: %+v", m["/dev/sdb3"])
+	}
+}
+
+// A raw /mnt/<name> mount counts as Felhom's own ONLY when corroborated (felhomOwnedMounts); else it is foreign and
+// the part is not listed. Positive control: TestPartitions_StatesPerPartition (the same mount, corroborated).
+func TestPartitions_UncorroboratedMountIsNotOffered(t *testing.T) {
+	m := listParts(nil)
+	if _, ok := m["/dev/sdb5"]; ok {
+		t.Fatalf("an uncorroborated /mnt/films mount must not be listed, got %+v", m["/dev/sdb5"])
+	}
+	for _, dev := range []string{"/dev/sdb6", "/dev/sdb7", "/dev/sdb8", "/dev/sdc1"} {
+		if _, ok := m[dev]; ok {
+			t.Fatalf("%s must never be listed (foreign mount, LVM, LUKS, another disk)", dev)
+		}
+	}
+}