agent v0.34.0: intermediary mount model — shared parent + host-side attach/detach + reconcile

Replaces the per-drive 'pct set -mpN' bind with ONE permanent parent bind
/mnt/felhom-drives plus host-side felhom-data swaps underneath it (propagates
into the running guest live, no pct, no reboot; C1-immune; confined; fail-closed
when absent). EnsureSharedParent installs a boot unit ordered Before=pve-guests.
ReassertGuestBinds is now a pure host-side reconcile. /disks reports GuestPath +
BoundUnderParent for the controller repoint+gate. Non-hollow tests + companions.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -3,6 +3,33 @@
 All notable changes to **felhom-agent** are recorded here. Update on every code
 change that gets pushed.
 
+## v0.34.0 — intermediary mount model: shared-parent + host-side attach/detach + reconcile (2026-06-15)
+
+The drive hot-swap re-architecture (SPIKE-intermediary-mount). Replaces the per-drive `pct set -mpN`
+bind (which needed a guest reboot to activate and bricked the guest when a drive was absent at boot)
+with a SINGLE permanent parent bind `/mnt/felhom-drives` plus host-side swaps underneath it.
+
+- `internal/localapi/intermediary.go` — `GuestBinder.EnsureSharedParent` (mkdir + self-bind +
+  `--make-shared` + installs/enables a `felhom-shared-parent.service` ordered **Before=pve-guests** so
+  the guest's parent bind inherits the shared peer group as `slave`); `AttachDrive` (`mount --bind
+  /mnt/<name>/felhom-data /mnt/felhom-drives/<name>` — propagates into the RUNNING guest live, no pct,
+  no reboot; confined to felhom-data; the stable dir stays host-root-owned = fail-closed); `DetachDrive`
+  (`umount`, leaving the bare fail-closed dir); `StablePathForRaw`/`DriveNameFromRaw`; `isHostMountpoint`.
+- `ReassertGuestBinds` is now a pure HOST-SIDE reconcile: for each enrolled+present drive ensure its
+  felhom-data is bound under the parent (no guest-config read, no slot, no reboot) — fixes F9 and
+  drive-reconnect for free. Runs at startup (ensures the shared parent first).
+- `handleDiskGuestAttach` uses `AttachDrive` (returns the stable `guest_path`); eject + decommission
+  call `DetachDrive`. Legacy `AttachBind`/`DetachBind` retained for the transition (decommission still
+  `--delete`s any lingering legacy mp).
+- `/disks` reporting adds `GuestPath` (the stable `/mnt/felhom-drives/<name>` the controller repoints
+  HDD_PATH to) and `BoundUnderParent` (live-in-guest signal for the controller's drive-absent gate).
+- Provision adds the one permanent parent bind (`-mp8 /mnt/felhom-drives,mp=/mnt/felhom-drives`).
+
+Tests (non-hollow + companions): `TestGuestAttach_BindsUnderParent` (uses AttachDrive not legacy pct),
+`TestReassertGuestBinds_RestoresMissingBind` (host-side reconcile, legacy AttachBind never called),
+`TestStablePathForRaw_DriveName`, `TestDisks_GuestPathAndBoundUnderParent`. Sudoers: new
+`FELHOM_INTERMEDIARY` alias (mount/umount under /mnt/felhom-drives, the unit install, the parent bind).
+
 ## v0.33.0 — C1 net: pre-start self-heal hook + decommission mp-delete (2026-06-15)
 
 The transitional defense for the C1 brick (B3 critical bug) ahead of the intermediary-mount

cmd/felhom-agent/main.go

@@ -44,7 +44,7 @@ import (
 
 // version is the agent version. Overridable at build time with
 // -ldflags "-X main.version=<v>"; defaults to the in-repo CHANGELOG version.
-var version = "0.33.0"
+var version = "0.34.0"
 
 // runGuestHook is the PVE pre-start hook body (`felhom-agent guest-hook <vmid> <phase>`). On the
 // pre-start phase it creates placeholder dirs for any absent bind-mount source so the guest always boots

configs/felhom-agent.sudoers

@@ -71,4 +71,23 @@ Cmnd_Alias FELHOM_GUESTHOOK = \
   /usr/sbin/pct set [0-9]* --hookscript local\:snippets/felhom-guest-hook.sh, \
   /usr/sbin/pct set [0-9]* --delete mp[0-9]*
 
-felhom-agent ALL=(root) NOPASSWD: FELHOM_MOUNT, FELHOM_DISK, FELHOM_PROVISION, FELHOM_FORMAT, FELHOM_DNSMASQ, FELHOM_GUESTHOOK
+# Intermediary mount model (the drive hot-swap re-architecture). The agent keeps a SHARED host parent
+# /mnt/felhom-drives (self-bind + make-shared + a boot-persistence systemd unit) and binds/unbinds each
+# drive's felhom-data namespace UNDERNEATH it so the change propagates into the running guest live (no
+# pct, no reboot). The agent fine-validates the drive name + confines paths before any exec; the trailing
+# `*` (matching the comma-laden mp spec) mirrors the existing FELHOM_PROVISION pattern.
+Cmnd_Alias FELHOM_INTERMEDIARY = \
+  /usr/bin/mkdir -p /mnt/felhom-drives, \
+  /usr/bin/mkdir -p /mnt/felhom-drives/*, \
+  /usr/bin/mkdir -p /mnt/*/felhom-data, \
+  /usr/bin/chown 100000\:100000 /mnt/*/felhom-data, \
+  /usr/bin/mount --bind /mnt/felhom-drives /mnt/felhom-drives, \
+  /usr/bin/mount --make-shared /mnt/felhom-drives, \
+  /usr/bin/mount --bind /mnt/*/felhom-data /mnt/felhom-drives/*, \
+  /usr/bin/umount /mnt/felhom-drives/*, \
+  /usr/bin/install -m 0755 -- /tmp/felhom-shared-parent.sh /usr/local/sbin/felhom-shared-parent.sh, \
+  /usr/bin/install -m 0644 -- /tmp/felhom-shared-parent.service /etc/systemd/system/felhom-shared-parent.service, \
+  /usr/bin/systemctl enable felhom-shared-parent.service, \
+  /usr/sbin/pct set [0-9]* -mp8 /mnt/felhom-drives*
+
+felhom-agent ALL=(root) NOPASSWD: FELHOM_MOUNT, FELHOM_DISK, FELHOM_PROVISION, FELHOM_FORMAT, FELHOM_DNSMASQ, FELHOM_GUESTHOOK, FELHOM_INTERMEDIARY

internal/localapi/decommission_test.go

@@ -169,8 +169,8 @@ func TestReassertGuestBinds_SkipsDecommissioned(t *testing.T) {
 		8200: {"mp0": "local-lvm:8,mp=/var/lib/docker"}, // bind missing → would re-add if not gated
 	})
 	srvD.ReassertGuestBinds(context.Background())
-	if gaD.count() != 0 {
-		t.Fatalf("decommissioned drive was re-bound (%d AttachBind) — intent gate missing", gaD.count())
+	if gaD.attachDriveCount() != 0 {
+		t.Fatalf("decommissioned drive was re-bound (%d AttachDrive) — intent gate missing", gaD.attachDriveCount())
 	}
 
 	// companion: enrolled → DOES rebind (same present drive + missing bind).
@@ -183,8 +183,11 @@ func TestReassertGuestBinds_SkipsDecommissioned(t *testing.T) {
 		8200: {"mp0": "local-lvm:8,mp=/var/lib/docker"},
 	})
 	srvE.ReassertGuestBinds(context.Background())
-	if gaE.count() != 1 {
-		t.Fatalf("enrolled drive should rebind (got %d AttachBind) — gate too aggressive", gaE.count())
+	if gaE.attachDriveCount() != 1 {
+		t.Fatalf("enrolled drive should rebind (got %d AttachDrive) — gate too aggressive", gaE.attachDriveCount())
+	}
+	if gaE.attachDrives[0] != "/mnt/felhom-usb" {
+		t.Fatalf("reconcile bound the wrong path: %v", gaE.attachDrives)
 	}
 }
 
@@ -208,8 +211,8 @@ func TestReCommission_ReRecords(t *testing.T) {
 		8200: {"mp0": "local-lvm:8,mp=/var/lib/docker"},
 	})
 	srv.ReassertGuestBinds(context.Background())
-	if ga.count() != 1 {
-		t.Fatalf("re-commissioned drive should rebind (got %d)", ga.count())
+	if ga.attachDriveCount() != 1 {
+		t.Fatalf("re-commissioned drive should rebind under the parent (got %d AttachDrive)", ga.attachDriveCount())
 	}
 }
 

internal/localapi/disks.go

@@ -67,9 +67,18 @@ type GuestLister interface {
 // mount (slice 10 P2, Model A) and reboots the guest to activate persisted-but-inactive binds (the
 // host-side live inject is blocked on unprivileged guests). Satisfied by *GuestBinder.
 type GuestAttacher interface {
+	// AttachDrive (intermediary model) binds the drive's felhom-data under the shared parent so it
+	// appears live in the guest at the returned stable path — no pct, no reboot. `where` = raw /mnt/<name>.
+	AttachDrive(ctx context.Context, where string) (guestPath string, err error)
+	// DetachDrive unmounts the drive's felhom-data from the shared parent (live, fail-closed).
+	DetachDrive(ctx context.Context, where string) error
+	// EnsureSharedParent makes the host stable parent shared + installs the boot-persistence unit.
+	EnsureSharedParent(ctx context.Context) error
+	// AttachBind is the LEGACY per-drive `pct set -mpN` bind (pre-intermediary). Retained for the
+	// transition; new attaches use AttachDrive.
 	AttachBind(ctx context.Context, vmid int, mountKey, where string) error
-	// DetachBind removes a mountpoint slot from the guest config (the decommission C1 fix — a removed
-	// bind can't brick the next boot with a missing source). Runs on the running guest (no start lock).
+	// DetachBind removes a LEGACY mountpoint slot from the guest config (the decommission C1 fix — a
+	// removed bind can't brick the next boot with a missing source). Runs on the running guest.
 	DetachBind(ctx context.Context, vmid int, mountKey string) error
 	RebootGuest(ctx context.Context, vmid int) error
 }
@@ -120,8 +129,18 @@ type DiskInfo struct {
 	// GuestAttached reports whether THIS guest (the token's vmid) actually has the drive's felhom-data
 	// namespace bound into its config — i.e. the drive is usable IN the guest, not merely present on the
 	// host. F9: host presence (State=attached) != guest-usable; this is the missing signal that made the
-	// HDD look available when it wasn't bound. Only meaningful for user-data drives.
+	// HDD look available when it wasn't bound. Only meaningful for user-data drives. LEGACY (per-drive
+	// `pct set -mpN` model) — the intermediary model uses BoundUnderParent.
 	GuestAttached bool `json:"guest_attached"`
+	// GuestPath is the drive's STABLE in-guest path in the intermediary-mount model
+	// (/mnt/felhom-drives/<name>). This is what the controller repoints HDD_PATH to and registers as the
+	// storage path. Set for /mnt/<name> drives; "" otherwise. Distinct from MountPath (the RAW host PVE
+	// mount the agent ops on).
+	GuestPath string `json:"guest_path,omitempty"`
+	// BoundUnderParent reports whether the drive's felhom-data is currently bound under the shared parent
+	// at GuestPath (a host mount-table check) — i.e. live + usable in the guest in the intermediary model.
+	// The controller's drive-absent gate + auto-restart key on this (and State).
+	BoundUnderParent bool `json:"bound_under_parent"`
 }
 
 // handleDisks lists the host's drives + data-bearing flags (read-only/benign).
@@ -153,6 +172,14 @@ func (s *Server) handleDisks(w http.ResponseWriter, r *http.Request, vmid int) {
 			UsedFraction:  t.UsedFraction,
 			GuestAttached: t.MountPath != "" && boundPaths[t.MountPath],
 		}
+		// Intermediary model: the stable in-guest path + whether felhom-data is bound under the parent.
+		// Only user-data /mnt/<name> drives have a guest path (system/backup mounts never cross in).
+		if di.Role == string(storage.RoleUserData) {
+			if gp := StablePathForRaw(t.MountPath); gp != "" {
+				di.GuestPath = gp
+				di.BoundUnderParent = s.boundUnderParent(gp)
+			}
+		}
 		// Inspect the backing device for the UI's data-bearing hint (the authoritative check
 		// is re-run at format time on the actual device).
 		if t.BackingDevice != "" {
@@ -245,6 +272,13 @@ func (s *Server) handleDiskEject(w http.ResponseWriter, r *http.Request, vmid in
 	// self-heal watchdog leaves it alone — an OFFICIAL eject is the only thing that sets this (P3); an
 	// out-of-band unmount records nothing and is healed.
 	s.recordIntent(r.Context(), req.Where, "ejected")
+	// Intermediary model: unmount the felhom-data bind from under the shared parent FIRST (live, fail-
+	// closed in the guest), so nothing references the raw mount before we unmount it.
+	if s.guestAttach != nil {
+		if err := s.guestAttach.DetachDrive(r.Context(), req.Where); err != nil {
+			s.logger.Warn("local-api: eject guest-detach (intermediary) failed", "vmid", vmid, "where", req.Where, "err", err)
+		}
+	}
 	if err := s.disks.Unmount(r.Context(), req.Where); err != nil {
 		s.logger.Error("local-api: disk eject", "vmid", vmid, "where", req.Where, "err", err)
 		writeErr(w, http.StatusBadRequest, "eject failed: "+err.Error())
@@ -301,9 +335,14 @@ func (s *Server) handleDiskDecommission(w http.ResponseWriter, r *http.Request,
 	// `mpN` in the config → pre-start mount failure → all apps down. Runs on the running guest (config
 	// edit, no start lock → no deadlock). Best-effort: a missing slot is already clean.
 	if s.guestAttach != nil {
+		// Intermediary model: unmount the felhom-data bind from under the shared parent (live, no reboot).
+		if err := s.guestAttach.DetachDrive(r.Context(), req.Where); err != nil {
+			s.logger.Warn("local-api: guest-detach (intermediary) failed", "vmid", vmid, "where", req.Where, "err", err)
+		}
+		// Legacy per-drive model: delete any lingering `mpN` slot (no-op post-migration; C1 fix otherwise).
 		if slot := s.guestSlotForPath(r.Context(), vmid, req.Where); slot != "" {
 			if err := s.guestAttach.DetachBind(r.Context(), vmid, slot); err != nil {
-				s.logger.Warn("local-api: guest-detach failed — mp left in config (reboot may brick until reconciled)",
+				s.logger.Warn("local-api: guest-detach (legacy mp) failed — mp left in config",
 					"vmid", vmid, "slot", slot, "where", req.Where, "err", err)
 			}
 		}
@@ -344,41 +383,24 @@ func (s *Server) handleDiskGuestAttach(w http.ResponseWriter, r *http.Request, v
 		writeErr(w, http.StatusBadRequest, "where must be an absolute /mnt/<name> path (no traversal)")
 		return
 	}
-	// Read the guest config for idempotency + free-slot selection.
-	cfg, err := s.guests.GuestConfig(r.Context(), vmid)
+	// Intermediary model: ensure the host shared parent, then bind the drive's felhom-data UNDER it. It
+	// propagates into the running guest LIVE — no pct, no slot, no reboot. AttachDrive is idempotent (a
+	// no-op when the stable path is already a mountpoint), so this is the re-enroll path too.
+	if err := s.guestAttach.EnsureSharedParent(r.Context()); err != nil {
+		s.logger.Warn("local-api: guest-attach — shared parent ensure failed (continuing)", "vmid", vmid, "err", err)
+	}
+	stable, err := s.guestAttach.AttachDrive(r.Context(), where)
 	if err != nil {
-		s.logger.Error("local-api: guest-attach guest config", "vmid", vmid, "err", err)
-		writeErr(w, http.StatusBadGateway, "could not read guest config")
-		return
-	}
-	mounts := cfg.MountPoints()
-	// Idempotency: already bound at `where`? (a bind's mp= equals the guest path). Still (re)record the
-	// ENROLLED intent — a drive bound at a prior boot must be known to self-heal even if never
-	// re-attached this process lifetime.
-	for key, spec := range mounts {
-		if _, mp, _ := parseMount(spec); mp == where {
-			s.recordIntent(r.Context(), where, "enrolled")
-			s.recordGuestBind(r.Context(), vmid, where)
-			s.logger.Info("local-api: guest-attach idempotent (already bound)", "vmid", vmid, "where", where, "slot", key)
-			writeOK(w, map[string]any{"vmid": vmid, "attached": where, "slot": key, "already": true})
-			return
-		}
-	}
-	slot, ok := freeMountSlot(mounts)
-	if !ok {
-		writeErr(w, http.StatusConflict, "no free mountpoint slot on the guest")
-		return
-	}
-	if err := s.guestAttach.AttachBind(r.Context(), vmid, slot, where); err != nil {
-		s.logger.Error("local-api: guest-attach", "vmid", vmid, "where", where, "slot", slot, "err", err)
+		s.logger.Error("local-api: guest-attach (intermediary)", "vmid", vmid, "where", where, "err", err)
 		writeErr(w, http.StatusBadGateway, "guest-attach failed: "+err.Error())
 		return
 	}
-	// Record the drive as ENROLLED so the self-heal watchdog will reconcile it (P3), and persist the
-	// per-guest bind so the startup re-assert can restore it after a re-provision (F9).
+	// Record the drive as ENROLLED so the self-heal reconcile keeps it bound (P3), and persist the
+	// per-guest bind so the startup reconcile restores it after a re-provision (F9 — now host-side only).
 	s.recordIntent(r.Context(), where, "enrolled")
 	s.recordGuestBind(r.Context(), vmid, where)
-	writeOK(w, map[string]any{"vmid": vmid, "attached": where, "slot": slot})
+	s.logger.Info("local-api: guest-attach bound under shared parent", "vmid", vmid, "where", where, "guest_path", stable)
+	writeOK(w, map[string]any{"vmid": vmid, "attached": where, "guest_path": stable})
 }
 
 type guestRebootRequest struct {
@@ -663,6 +685,15 @@ func (s *Server) handleDiskFormat(w http.ResponseWriter, r *http.Request, vmid i
 		"device is system/backup-protected — format requires an operator signature ("+dec.Reason+")")
 }
 
+// boundUnderParent reports whether a drive's felhom-data is currently bound at its stable guest path
+// (intermediary model). Injectable via s.boundCheck for tests; defaults to the host mount-table read.
+func (s *Server) boundUnderParent(stablePath string) bool {
+	if s.boundCheck != nil {
+		return s.boundCheck(stablePath)
+	}
+	return isHostMountpoint(stablePath)
+}
+
 // guestBoundPaths returns the set of guest mountpoint paths (the `mp=` of each entry in the guest's
 // config) — i.e. the host drives actually BOUND into the guest. F9: this is the guest-attached signal
 // (`GuestAttached`) that distinguishes a guest-usable drive from one merely present on the host. A bind
@@ -725,16 +756,22 @@ func (s *Server) recordGuestBind(ctx context.Context, vmid int, where string) {
 	s.logger.Info("local-api: guest-bind recorded for startup re-assert", "vmid", vmid, "where", where, "durable_id", id)
 }
 
-// ReassertGuestBinds re-adds, on agent startup (the host's bring-up/reconcile trigger), any enrolled
-// user-data drive bind a guest is MISSING from its config (F9 — a re-provision drops the mp, and nothing
-// previously restored it). For each recorded (vmid, durable-id): only when the durable-id STILL resolves
-// to a present, mounted drive AND the guest lacks the bind, it re-runs AttachBind. "On durable-id match"
-// — a swapped or absent drive is never auto-bound. The re-added bind is config state; it activates on the
-// guest's next reboot (logged), exactly like the enroll flow. Safe to call repeatedly (idempotent).
+// ReassertGuestBinds is the intermediary-model startup reconcile: for every ENROLLED + PRESENT enrolled
+// drive, it ensures the drive's felhom-data is bound under the shared parent (host-side, via AttachDrive)
+// so it's live in the guest. This is PURE host-side mount work — NO pct, NO guest-config read, NO reboot
+// — and it fixes F9 (a re-provision drops nothing host-side) AND drive-returned reconnection for free.
+// It first ensures the host shared parent exists (so a fresh boot has it before any bind). "On durable-id
+// match" + intent-gated: a swapped, ejected, or decommissioned drive is never auto-bound. AttachDrive is
+// idempotent (a no-op when already bound), so this is safe to call repeatedly. Runs at agent startup and
+// on a drive-returned event.
 func (s *Server) ReassertGuestBinds(ctx context.Context) {
-	if s.guestBinds == nil || s.guestAttach == nil || s.guests == nil {
+	if s.guestBinds == nil || s.guestAttach == nil {
 		return
 	}
+	// Make sure the host stable parent is shared + boot-persistent before we bind anything under it.
+	if err := s.guestAttach.EnsureSharedParent(ctx); err != nil {
+		s.logger.Warn("reconcile: shared parent ensure failed — binds may not propagate live", "err", err)
+	}
 	// durable-id -> current host mount path (present drives only), from the agent's own storage view.
 	mountByDurable := map[string]string{}
 	if targets, err := s.storage.Observe(ctx); err == nil {
@@ -744,52 +781,30 @@ func (s *Server) ReassertGuestBinds(ctx context.Context) {
 			}
 		}
 	} else {
-		s.logger.Warn("F9 re-assert: storage view unavailable — skipping", "err", err)
+		s.logger.Warn("reconcile: storage view unavailable — skipping", "err", err)
 		return
 	}
 	for vmid, ids := range s.guestBinds.Guests() {
-		cfg, err := s.guests.GuestConfig(ctx, vmid)
-		if err != nil {
-			s.logger.Warn("F9 re-assert: skip guest (config read failed)", "vmid", vmid, "err", err)
-			continue
-		}
-		mounts := cfg.MountPoints()
-		boundPaths := map[string]bool{}
-		for _, spec := range mounts {
-			if _, mp, _ := parseMount(spec); mp != "" {
-				boundPaths[mp] = true
-			}
-		}
 		for _, id := range ids {
-			// Intent-aware (B2, the load-bearing correctness fix): NEVER re-bind a drive that is not
-			// currently `enrolled` — an ejected or decommissioned drive must not auto-rebind into the
-			// guest on agent restart, even if it is still host-mounted. Covers both the self-serve and
-			// the operator-signed decommission paths (both land on IntentDecommissioned). A nil intent
-			// store falls back to legacy bind-all (ungated), matching the watchdog's nil-intent rule.
+			// Intent-aware (B2, load-bearing): NEVER bind a drive that is not currently `enrolled` — an
+			// ejected or decommissioned drive must not auto-rebind, even if still host-mounted. A nil
+			// intent store falls back to bind-all (ungated), matching the watchdog's nil-intent rule.
 			if s.intent != nil && s.intent.Get(id) != storage.IntentEnrolled {
-				s.logger.Warn("F9 re-assert: skipping non-enrolled drive (intent-gated)", "vmid", vmid, "durable_id", id, "intent", string(s.intent.Get(id)))
+				s.logger.Warn("reconcile: skipping non-enrolled drive (intent-gated)", "vmid", vmid, "durable_id", id, "intent", string(s.intent.Get(id)))
 				continue
 			}
 			where, present := mountByDurable[id]
 			if !present {
-				s.logger.Warn("F9 re-assert: enrolled drive not present (durable-id absent) — skipping", "vmid", vmid, "durable_id", id)
+				s.logger.Warn("reconcile: enrolled drive not present (durable-id absent) — skipping", "vmid", vmid, "durable_id", id)
 				continue
 			}
-			if boundPaths[where] {
-				continue // already bound — nothing to re-assert
-			}
-			slot, ok := freeMountSlot(mounts)
-			if !ok {
-				s.logger.Warn("F9 re-assert: no free mountpoint slot on guest", "vmid", vmid, "where", where)
+			stable, err := s.guestAttach.AttachDrive(ctx, where)
+			if err != nil {
+				s.logger.Error("reconcile: AttachDrive failed", "vmid", vmid, "where", where, "err", err)
 				continue
 			}
-			if err := s.guestAttach.AttachBind(ctx, vmid, slot, where); err != nil {
-				s.logger.Error("F9 re-assert: AttachBind failed", "vmid", vmid, "where", where, "slot", slot, "err", err)
-				continue
-			}
-			mounts[slot] = where // reserve the slot so a second enrolled drive takes the next one
-			s.logger.Warn("F9 re-assert: re-attached enrolled drive into guest config (reboot to activate)",
-				"vmid", vmid, "where", where, "slot", slot, "durable_id", id)
+			s.logger.Info("reconcile: enrolled drive bound under shared parent (live, no reboot)",
+				"vmid", vmid, "where", where, "guest_path", stable, "durable_id", id)
 		}
 	}
 }

internal/localapi/disks_test.go

@@ -3,6 +3,7 @@ package localapi
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
 	"log/slog"
 	"net/http"
@@ -394,6 +395,10 @@ type fakeGuestAttacher struct {
 		vmid int
 		slot string
 	}
+	attachDrives    []string // where passed to AttachDrive (intermediary model)
+	detachDrives    []string // where passed to DetachDrive
+	ensureParentN   int      // EnsureSharedParent call count
+	attachDriveFail bool     // when set, AttachDrive returns an error
 }
 
 func (f *fakeGuestAttacher) AttachBind(_ context.Context, vmid int, mountKey, where string) error {
@@ -407,6 +412,35 @@ func (f *fakeGuestAttacher) AttachBind(_ context.Context, vmid int, mountKey, wh
 }
 func (f *fakeGuestAttacher) count() int { f.mu.Lock(); defer f.mu.Unlock(); return len(f.calls) }
 
+func (f *fakeGuestAttacher) AttachDrive(_ context.Context, where string) (string, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if f.attachDriveFail {
+		return "", fmt.Errorf("fake attach-drive failure")
+	}
+	f.attachDrives = append(f.attachDrives, where)
+	return StablePathForRaw(where), nil
+}
+func (f *fakeGuestAttacher) attachDriveCount() int {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return len(f.attachDrives)
+}
+
+func (f *fakeGuestAttacher) DetachDrive(_ context.Context, where string) error {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.detachDrives = append(f.detachDrives, where)
+	return nil
+}
+
+func (f *fakeGuestAttacher) EnsureSharedParent(_ context.Context) error {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.ensureParentN++
+	return nil
+}
+
 func (f *fakeGuestAttacher) DetachBind(_ context.Context, vmid int, mountKey string) error {
 	f.mu.Lock()
 	defer f.mu.Unlock()
@@ -444,8 +478,12 @@ func newAttachServer(t *testing.T, ga GuestAttacher, mounts map[int]map[string]s
 	return srv.Handler()
 }
 
-// A first attach picks the lowest free slot (mp0; mp9 bootstrap is taken) and calls the binder.
-func TestGuestAttach_PicksFreeSlotAndBinds(t *testing.T) {
+// Intermediary model: a guest-attach binds the drive's felhom-data under the shared parent (host-side)
+// and returns its STABLE guest path — no pct slot. EnsureSharedParent runs first.
+//
+// COMPANION GUARD: the legacy `pct set -mpN` AttachBind must NOT be used in the intermediary model — a
+// pre-fix impl that still called AttachBind would trip ga.count()!=0 here.
+func TestGuestAttach_BindsUnderParent(t *testing.T) {
 	ga := &fakeGuestAttacher{}
 	h := newAttachServer(t, ga, map[int]map[string]string{
 		8200: {"mp9": "/var/lib/.../bootstrap,mp=/etc/felhom-bootstrap,ro=1"},
@@ -454,26 +492,27 @@ func TestGuestAttach_PicksFreeSlotAndBinds(t *testing.T) {
 	if w.Code != http.StatusOK {
 		t.Fatalf("attach: got %d want 200 (%s)", w.Code, w.Body.String())
 	}
-	if ga.count() != 1 || ga.calls[0].slot != "mp0" || ga.calls[0].where != "/mnt/felhom-usb" || ga.calls[0].vmid != 8200 {
-		t.Fatalf("AttachBind not called with mp0/where/vmid: %+v", ga.calls)
+	if ga.attachDriveCount() != 1 || ga.attachDrives[0] != "/mnt/felhom-usb" {
+		t.Fatalf("AttachDrive not called with /mnt/felhom-usb: %+v", ga.attachDrives)
+	}
+	if ga.ensureParentN < 1 {
+		t.Fatalf("EnsureSharedParent must run before binding the drive")
+	}
+	if !strings.Contains(w.Body.String(), `"guest_path":"/mnt/felhom-drives/felhom-usb"`) {
+		t.Fatalf("response missing the stable guest_path: %s", w.Body.String())
+	}
+	if ga.count() != 0 {
+		t.Fatalf("legacy pct AttachBind called (%d) — intermediary model must use host-side AttachDrive", ga.count())
 	}
 }
 
-// An already-bound drive is idempotent: returns the existing slot, binder NOT called again.
-func TestGuestAttach_Idempotent(t *testing.T) {
-	ga := &fakeGuestAttacher{}
-	h := newAttachServer(t, ga, map[int]map[string]string{
-		8200: {"mp0": "/mnt/felhom-usb/felhom-data,mp=/mnt/felhom-usb"},
-	})
+// An AttachDrive failure surfaces as 502 (no silent success).
+func TestGuestAttach_AttachDriveFailure(t *testing.T) {
+	ga := &fakeGuestAttacher{attachDriveFail: true}
+	h := newAttachServer(t, ga, map[int]map[string]string{8200: {}})
 	w := do(t, h, "POST", "/disks/guest-attach", "A", `{"where":"/mnt/felhom-usb"}`)
-	if w.Code != http.StatusOK {
-		t.Fatalf("idempotent attach: got %d want 200 (%s)", w.Code, w.Body.String())
-	}
-	if !strings.Contains(w.Body.String(), `"already":true`) {
-		t.Fatalf("expected already:true: %s", w.Body.String())
-	}
-	if ga.count() != 0 {
-		t.Fatalf("AttachBind must NOT be called for an already-bound drive: %+v", ga.calls)
+	if w.Code != http.StatusBadGateway {
+		t.Fatalf("attach failure: got %d want 502 (%s)", w.Code, w.Body.String())
 	}
 }
 

internal/localapi/guestbinds_reassert_test.go

@@ -43,28 +43,30 @@ func usbPresent() fakeStorage {
 	}}
 }
 
-// TestReassertGuestBinds_RestoresMissingBind is the F9 core proof (the operator's "fire the real
-// trigger" requirement): an enrolled drive that is present on the host but MISSING from the guest config
-// (the post-re-provision gap) is auto-re-attached on the startup re-assert — with NO manual guest-attach
-// call. Fails on the pre-fix code (no re-assert existed).
+// TestReassertGuestBinds_RestoresMissingBind is the F9/reconnect core proof: an enrolled, host-present
+// drive is auto-bound under the shared parent on the startup reconcile — host-side (AttachDrive), with NO
+// pct and NO manual guest-attach call.
+//
+// COMPANION GUARD: the legacy `pct set -mpN` AttachBind must NOT be used — a pre-intermediary impl that
+// still re-added a config mp would trip ga.count()!=0.
 func TestReassertGuestBinds_RestoresMissingBind(t *testing.T) {
 	gb := tempBindStore(t)
 	if err := gb.Record(8200, "uuid:usb-1"); err != nil { // enrolled at a prior boot
 		t.Fatal(err)
 	}
 	ga := &fakeGuestAttacher{}
-	// guest 8200 has docker-data only — the felhom-usb bind was dropped by the re-provision.
-	srv := reassertServer(t, ga, usbPresent(), map[int]map[string]string{
-		8200: {"mp0": "local-lvm:8,mp=/var/lib/docker"},
-	}, gb)
+	srv := reassertServer(t, ga, usbPresent(), nil, gb)
 
 	srv.ReassertGuestBinds(context.Background())
 
-	if ga.count() != 1 {
-		t.Fatalf("AttachBind called %d times, want 1 (auto-re-assert on startup)", ga.count())
+	if ga.attachDriveCount() != 1 || ga.attachDrives[0] != "/mnt/felhom-usb" {
+		t.Fatalf("AttachDrive = %v, want one call for /mnt/felhom-usb (host-side reconcile)", ga.attachDrives)
 	}
-	if ga.calls[0].vmid != 8200 || ga.calls[0].where != "/mnt/felhom-usb" {
-		t.Fatalf("re-asserted bind = %+v, want vmid 8200 where /mnt/felhom-usb", ga.calls[0])
+	if ga.count() != 0 {
+		t.Fatalf("legacy pct AttachBind called (%d) — reconcile must be host-side only", ga.count())
+	}
+	if ga.ensureParentN < 1 {
+		t.Fatalf("EnsureSharedParent must run before binding drives under the parent")
 	}
 }
 
@@ -74,28 +76,11 @@ func TestReassertGuestBinds_SkipsAbsentDurable(t *testing.T) {
 	gb := tempBindStore(t)
 	_ = gb.Record(8200, "uuid:usb-1")
 	ga := &fakeGuestAttacher{}
-	srv := reassertServer(t, ga, fakeStorage{}, map[int]map[string]string{ // empty storage view → absent
-		8200: {"mp0": "local-lvm:8,mp=/var/lib/docker"},
-	}, gb)
+	srv := reassertServer(t, ga, fakeStorage{}, nil, gb) // empty storage view → absent
 
 	srv.ReassertGuestBinds(context.Background())
-	if ga.count() != 0 {
-		t.Fatalf("AttachBind called %d times — must NOT auto-bind an absent/swapped drive", ga.count())
-	}
-}
-
-// TestReassertGuestBinds_SkipsAlreadyBound: when the guest already has the bind, the re-assert is a no-op.
-func TestReassertGuestBinds_SkipsAlreadyBound(t *testing.T) {
-	gb := tempBindStore(t)
-	_ = gb.Record(8200, "uuid:usb-1")
-	ga := &fakeGuestAttacher{}
-	srv := reassertServer(t, ga, usbPresent(), map[int]map[string]string{
-		8200: {"mp0": "local-lvm:8,mp=/var/lib/docker", "mp3": "/mnt/felhom-usb/felhom-data,mp=/mnt/felhom-usb"},
-	}, gb)
-
-	srv.ReassertGuestBinds(context.Background())
-	if ga.count() != 0 {
-		t.Fatalf("AttachBind called %d times — already bound, must be a no-op", ga.count())
+	if ga.attachDriveCount() != 0 {
+		t.Fatalf("AttachDrive called %d times — must NOT auto-bind an absent/swapped drive", ga.attachDriveCount())
 	}
 }
 

internal/localapi/intermediary.go

@@ -0,0 +1,202 @@
+package localapi
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// Intermediary-mount model (replaces the per-drive `pct set -mpN` bind). A SINGLE permanent parent bind
+// `/mnt/felhom-drives` is set into the guest once (at provision/migration); the host keeps that dir a
+// SHARED mount, and the agent mounts/unmounts each drive's felhom-data namespace UNDERNEATH it host-side
+// (`mount --bind /mnt/<name>/felhom-data /mnt/felhom-drives/<name>`). Mount propagation (host `shared` →
+// guest `slave`) carries the change into the RUNNING guest live — no `pct`, no reboot, and the parent
+// bind source never disappears (so the guest is inherently C1-immune). Confinement holds: only the
+// felhom-data subtree crosses in, never the customer's other top-level dirs. See
+// felhom.eu/documentation/audits/SPIKE-intermediary-mount-2026-06-15.md.
+
+// StableParentDir is the permanent host dir bound once into the guest; drives are swapped underneath it.
+const StableParentDir = "/mnt/felhom-drives"
+
+// sharedParentScript re-establishes the shared parent on every HOST boot. It MUST run before
+// pve-guests.service so the guest's parent bind inherits the shared peer group as `slave` (if the guest
+// starts first, its bind is `private` and drive swaps don't propagate until a guest restart).
+const sharedParentScriptPath = "/usr/local/sbin/felhom-shared-parent.sh"
+const sharedParentScript = `#!/bin/sh
+# felhom stable drive parent: a SHARED bind so the agent can swap backing drives underneath it and the
+# guest sees the change live (no restart). MUST run before pve-guests so the guest's parent bind inherits
+# the shared peer group (slave). Installed + enabled by felhom-agent. Idempotent.
+set -e
+mkdir -p ` + StableParentDir + `
+mountpoint -q ` + StableParentDir + ` || mount --bind ` + StableParentDir + ` ` + StableParentDir + `
+mount --make-shared ` + StableParentDir + `
+`
+
+const sharedParentUnitPath = "/etc/systemd/system/felhom-shared-parent.service"
+const sharedParentUnit = `[Unit]
+Description=Felhom stable drive parent (shared bind for live drive hot-swap)
+DefaultDependencies=no
+After=local-fs.target
+Before=pve-guests.service
+ConditionPathExists=` + sharedParentScriptPath + `
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=` + sharedParentScriptPath + `
+
+[Install]
+WantedBy=multi-user.target
+`
+
+// StablePathForRaw maps a drive's RAW host mount (/mnt/<name>) to its stable in-guest path
+// (/mnt/felhom-drives/<name>). The basename is the drive name — the single source of truth both repos
+// derive the guest path from. Returns "" if `where` is not a /mnt/<name> path.
+func StablePathForRaw(where string) string {
+	name := DriveNameFromRaw(where)
+	if name == "" {
+		return ""
+	}
+	return StableParentDir + "/" + name
+}
+
+// DriveNameFromRaw returns the drive name from a raw /mnt/<name> host mount (the basename), or "" if the
+// path isn't a single-component /mnt/<name>.
+func DriveNameFromRaw(where string) string {
+	if !strings.HasPrefix(where, "/mnt/") {
+		return ""
+	}
+	name := strings.TrimPrefix(where, "/mnt/")
+	if name == "" || strings.ContainsAny(name, "/ \t") {
+		return ""
+	}
+	return name
+}
+
+// EnsureSharedParent makes the host stable parent a SHARED mount and installs+enables the boot-time
+// systemd unit that re-establishes it before pve-guests. Idempotent: it only binds when the dir isn't
+// already a mountpoint (re-binding would stack), and always (re-)marks it shared (a no-op when already
+// shared). Best-effort install of the unit (a host-reboot-persistence concern) — a failed install does
+// not stop the live setup. Called at agent startup and at provision.
+func (b *GuestBinder) EnsureSharedParent(ctx context.Context) error {
+	if err := b.run(ctx, "mkdir", "-p", StableParentDir); err != nil {
+		return fmt.Errorf("shared-parent: mkdir %s: %w", StableParentDir, err)
+	}
+	if !isHostMountpoint(StableParentDir) {
+		if err := b.run(ctx, "mount", "--bind", StableParentDir, StableParentDir); err != nil {
+			return fmt.Errorf("shared-parent: self-bind: %w", err)
+		}
+	}
+	if err := b.run(ctx, "mount", "--make-shared", StableParentDir); err != nil {
+		return fmt.Errorf("shared-parent: make-shared: %w", err)
+	}
+	if err := b.installSharedParentUnit(ctx); err != nil {
+		b.logger.Warn("shared-parent: boot-persistence unit install failed (live setup OK; survives until host reboot)", "err", err)
+	}
+	b.logger.Info("shared-parent: host stable parent is shared", "dir", StableParentDir)
+	return nil
+}
+
+// installSharedParentUnit writes the script + unit (from agent-written temps) and enables the unit so the
+// shared parent is re-established on every host boot before pve-guests. Idempotent.
+func (b *GuestBinder) installSharedParentUnit(ctx context.Context) error {
+	tmpScript := filepath.Join(os.TempDir(), "felhom-shared-parent.sh")
+	if err := os.WriteFile(tmpScript, []byte(sharedParentScript), 0o755); err != nil {
+		return fmt.Errorf("write temp script: %w", err)
+	}
+	defer os.Remove(tmpScript)
+	if err := b.run(ctx, "install", "-m", "0755", "--", tmpScript, sharedParentScriptPath); err != nil {
+		return fmt.Errorf("install script: %w", err)
+	}
+	tmpUnit := filepath.Join(os.TempDir(), "felhom-shared-parent.service")
+	if err := os.WriteFile(tmpUnit, []byte(sharedParentUnit), 0o644); err != nil {
+		return fmt.Errorf("write temp unit: %w", err)
+	}
+	defer os.Remove(tmpUnit)
+	if err := b.run(ctx, "install", "-m", "0644", "--", tmpUnit, sharedParentUnitPath); err != nil {
+		return fmt.Errorf("install unit: %w", err)
+	}
+	if err := b.run(ctx, "systemctl", "daemon-reload"); err != nil {
+		return fmt.Errorf("daemon-reload: %w", err)
+	}
+	if err := b.run(ctx, "systemctl", "enable", "felhom-shared-parent.service"); err != nil {
+		return fmt.Errorf("enable unit: %w", err)
+	}
+	return nil
+}
+
+// AttachDrive binds a drive's felhom-data namespace under the stable parent so it appears live in the
+// guest at the returned stable path (via propagation — no pct, no reboot). `where` is the drive's RAW
+// host PVE mount (/mnt/<name>); only `<where>/felhom-data` crosses into the guest (confinement). The
+// stable per-drive dir is created HOST-ROOT-owned (fail-closed when nothing is mounted under it); the
+// felhom-data namespace is created+chowned to the guest base so the in-guest controller owns it.
+// Idempotent: if the stable path is already a mountpoint, it's a no-op.
+func (b *GuestBinder) AttachDrive(ctx context.Context, where string) (string, error) {
+	stable := StablePathForRaw(where)
+	if stable == "" {
+		return "", fmt.Errorf("guest-attach: %q is not a /mnt/<name> mount", where)
+	}
+	src := where + "/" + felhomDataNS
+	// Ensure the namespace exists + is owned by the guest base (same as the legacy AttachBind).
+	if err := b.run(ctx, "mkdir", "-p", src); err != nil {
+		return "", fmt.Errorf("guest-attach: namespace %s: %w", src, err)
+	}
+	if err := b.run(ctx, "chown", guestMappedRoot, src); err != nil {
+		return "", fmt.Errorf("guest-attach: chown namespace %s: %w", src, err)
+	}
+	// The stable mountpoint dir stays HOST-ROOT-owned (fail-closed) — create it, never chown it.
+	if err := b.run(ctx, "mkdir", "-p", stable); err != nil {
+		return "", fmt.Errorf("guest-attach: stable dir %s: %w", stable, err)
+	}
+	if isHostMountpoint(stable) {
+		b.logger.Info("guest-attach: already bound under parent (idempotent)", "where", where, "stable", stable)
+		return stable, nil
+	}
+	if err := b.run(ctx, "mount", "--bind", src, stable); err != nil {
+		return "", fmt.Errorf("guest-attach: bind %s -> %s: %w", src, stable, err)
+	}
+	b.logger.Info("guest-attach: drive bound under shared parent (live, no reboot)", "where", where, "stable", stable)
+	return stable, nil
+}
+
+// DetachDrive unmounts a drive's felhom-data from the stable parent (propagates OUT of the guest live),
+// leaving the bare HOST-ROOT-owned stable dir → fail-closed (the guest can't write to it even as root,
+// since host uid 0 is unmapped). No pct, no reboot. Idempotent: a non-mountpoint is a no-op.
+func (b *GuestBinder) DetachDrive(ctx context.Context, where string) error {
+	stable := StablePathForRaw(where)
+	if stable == "" {
+		return fmt.Errorf("guest-detach: %q is not a /mnt/<name> mount", where)
+	}
+	if !isHostMountpoint(stable) {
+		return nil // already detached
+	}
+	if err := b.run(ctx, "umount", stable); err != nil {
+		return fmt.Errorf("guest-detach: umount %s: %w", stable, err)
+	}
+	b.logger.Info("guest-detach: drive unmounted from shared parent (live, fail-closed)", "where", where, "stable", stable)
+	return nil
+}
+
+// isHostMountpoint reports whether path is currently a mount target in the host's mount table
+// (/proc/self/mountinfo). Pure read — used for idempotency (skip re-binding) and the BoundUnderParent
+// report. A read error → false (treat as not-mounted; AttachDrive then (re)binds, which is safe).
+func isHostMountpoint(path string) bool {
+	f, err := os.Open("/proc/self/mountinfo")
+	if err != nil {
+		return false
+	}
+	defer f.Close()
+	sc := bufio.NewScanner(f)
+	sc.Buffer(make([]byte, 0, 64*1024), 1024*1024)
+	for sc.Scan() {
+		// mountinfo field 5 (0-indexed 4) is the mount point.
+		fields := strings.Fields(sc.Text())
+		if len(fields) >= 5 && fields[4] == path {
+			return true
+		}
+	}
+	return false
+}

internal/localapi/intermediary_test.go

@@ -0,0 +1,82 @@
+package localapi
+
+import (
+	"context"
+	"io"
+	"log/slog"
+	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/hub"
+	"gitea.dooplex.hu/admin/felhom-agent/internal/storage"
+)
+
+func TestStablePathForRaw_DriveName(t *testing.T) {
+	cases := []struct {
+		where, name, stable string
+	}{
+		{"/mnt/felhom-usb", "felhom-usb", "/mnt/felhom-drives/felhom-usb"},
+		{"/mnt/felhom-flash", "felhom-flash", "/mnt/felhom-drives/felhom-flash"},
+		{"/mnt/felhom-drives/x", "", ""}, // nested (slash in remainder) → not a /mnt/<name> raw mount
+		{"/var/lib/vz", "", ""},          // not under /mnt
+		{"/mnt/", "", ""},                // empty name
+	}
+	for _, c := range cases {
+		if got := DriveNameFromRaw(c.where); got != c.name {
+			t.Errorf("DriveNameFromRaw(%q) = %q, want %q", c.where, got, c.name)
+		}
+		if got := StablePathForRaw(c.where); got != c.stable {
+			t.Errorf("StablePathForRaw(%q) = %q, want %q", c.where, got, c.stable)
+		}
+	}
+}
+
+// TestDisks_GuestPathAndBoundUnderParent asserts the intermediary reporting the controller relies on: a
+// user-data drive gets a STABLE guest path (/mnt/felhom-drives/<name>) and BoundUnderParent reflects the
+// host mount check; a SYSTEM mount gets neither (it never crosses into the guest).
+//
+// COMPANION GUARD: a pre-fix impl that left GuestPath empty (no repoint signal) or that reported
+// BoundUnderParent ignoring the real mount state would fail the assertions below.
+func TestDisks_GuestPathAndBoundUnderParent(t *testing.T) {
+	d := &fakeDiskOps{probe: storage.DeviceProbe{Probed: true, HasFilesystem: true, FSType: "ext4"}}
+	sv := fakeStorage{targets: []hub.StorageTarget{
+		{Name: "usb", Type: hub.StorageTypeUSB, BackingDevice: "/dev/sdb1", MountPath: "/mnt/felhom-usb"},
+		{Name: "flash", Type: hub.StorageTypeUSB, BackingDevice: "/dev/sdc1", MountPath: "/mnt/felhom-flash"},
+		{Name: "system", Type: "local", MountPath: "/var/lib/vz"}, // system role → no guest path
+	}}
+	fg := &fakeGuestsCfg{}
+	srv, err := NewServer(Options{
+		ListenAddr: "127.0.0.1:0", Guests: fg, Backups: &fakeBackups{}, Store: &fakeStore{},
+		Storage: sv, Tokens: staticTokens{"A": 8200},
+		Disks: d, DiskGate: &fakeGate{}, HostReader: sysOnSDA(),
+		Logger: slog.New(slog.NewTextHandler(io.Discard, nil)),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	srv.baseCtx = context.Background()
+	// felhom-usb is bound under the parent; felhom-flash is not.
+	srv.boundCheck = func(p string) bool { return p == "/mnt/felhom-drives/felhom-usb" }
+
+	disks := decodeDisks(t, do(t, srv.Handler(), "GET", "/disks", "A", "").Body.Bytes())
+	byMount := map[string]DiskInfo{}
+	for _, di := range disks {
+		byMount[di.MountPath] = di
+	}
+
+	if gp := byMount["/mnt/felhom-usb"].GuestPath; gp != "/mnt/felhom-drives/felhom-usb" {
+		t.Errorf("usb GuestPath = %q, want /mnt/felhom-drives/felhom-usb", gp)
+	}
+	if !byMount["/mnt/felhom-usb"].BoundUnderParent {
+		t.Errorf("usb should report BoundUnderParent=true (bound under the parent)")
+	}
+	if byMount["/mnt/felhom-flash"].BoundUnderParent {
+		t.Errorf("flash should report BoundUnderParent=false (not bound)")
+	}
+	if gp := byMount["/mnt/felhom-flash"].GuestPath; gp != "/mnt/felhom-drives/felhom-flash" {
+		t.Errorf("flash GuestPath = %q, want /mnt/felhom-drives/felhom-flash", gp)
+	}
+	// A SYSTEM mount must never get a guest path (it does not cross into the guest).
+	if gp := byMount["/var/lib/vz"].GuestPath; gp != "" {
+		t.Errorf("system mount GuestPath = %q, want empty (never crosses into the guest)", gp)
+	}
+}

internal/localapi/server.go

@@ -171,6 +171,10 @@ type Server struct {
 	// tests override it. (DiskInfo.DurableID stays the uuid: storage id — that one feeds /disks/assign.)
 	deviceDurableID func(device string) (string, error)
 
+	// boundCheck reports whether a stable guest path has felhom-data bound under it (intermediary model).
+	// Optional — nil defaults to the real host mount-table read (isHostMountpoint); tests inject a fake.
+	boundCheck func(string) bool
+
 	jobsMu sync.Mutex
 	jobs   map[int]*backupJob // per-guest backup job state (slice 8B)
 

internal/provision/backhalf.go

@@ -31,6 +31,13 @@ const (
 	// mappedRoot is the unprivileged-LXC host uid/gid that maps to the guest's root (spike
 	// gotcha 1): files chowned to this appear as root:root 0600 inside the guest.
 	mappedRoot = "100000:100000"
+	// stableParentDir is the permanent host dir bound once into the guest (intermediary mount model);
+	// the agent swaps drive felhom-data namespaces underneath it host-side. Mirrors
+	// localapi.StableParentDir (kept as a literal to avoid a provision→localapi import edge).
+	stableParentDir = "/mnt/felhom-drives"
+	// parentBindSlot is the dedicated mpN for the single permanent parent bind. mp8 — high enough to not
+	// collide with bring-up data mounts (mp0..), below the mp9 bootstrap.
+	parentBindSlot = "mp8"
 )
 
 // BackHalf populates a guest's bootstrap config mount host-side (F3). It mints the per-guest
@@ -155,6 +162,20 @@ func (b *BackHalf) Provision(ctx context.Context, in Input) (Result, error) {
 		b.logger.Warn("provision: pre-start hook registration failed (non-fatal)", "vmid", in.VMID, "err", err)
 	}
 
+	// 7. Intermediary mount model: add the ONE permanent parent bind so enrolled data drives appear in
+	//    the guest LIVE (the agent later binds each drive's felhom-data UNDER /mnt/felhom-drives host-side
+	//    — no per-drive mp, no reboot). The host SHARED state + boot-persistence unit are the agent
+	//    daemon's job (EnsureSharedParent at startup); here we ensure the dir exists (pct validates the
+	//    bind source) and attach the parent bind. Best-effort + non-fatal.
+	if err := b.run(ctx, "mkdir", "-p", stableParentDir); err != nil {
+		b.logger.Warn("provision: stable parent dir create failed (non-fatal)", "vmid", in.VMID, "err", err)
+	} else {
+		parentSpec := fmt.Sprintf("%s,mp=%s", stableParentDir, stableParentDir)
+		if err := b.run(ctx, "pct", "set", strconv.Itoa(in.VMID), "-"+parentBindSlot, parentSpec); err != nil {
+			b.logger.Warn("provision: parent bind attach failed (non-fatal)", "vmid", in.VMID, "slot", parentBindSlot, "err", err)
+		}
+	}
+
 	b.logger.Info("provision: back-half complete",
 		"vmid", in.VMID, "mount", mountKey, "guest_path", guestPath, "endpoint", in.Endpoint)
 	// tok intentionally goes out of scope here — never logged, never returned.