T3871: make boot-time interface naming deterministic and hw-id aware

Multi-vendor PCIe NIC systems could lose or rename Ethernet/wireless
interfaces on boot, because naming was decided from a single per-device
udev event before all hardware had a chance to enumerate.

Replace that with one authoritative pass, run once configuration is
available during router startup: wait for configured hardware, apply
every hw-id binding, and name whatever has none yet by PCIe distance
from the root complex and MAC address - the same result every boot.

A node with its hw-id deleted (NIC replacement) or its whole
configuration removed is treated as an ordinary open slot, filled the
same way - recovering its original hardware whenever the interfaces
that vacated slots this boot also show up as candidates.

Boot now reports any interface still unresolved, and the pass is covered
by a new test suite in vyos-build named: make testifname

Assisted-by: Claude:claude-sonnet-5

7 files changed, 2269 insertions, 105 deletions

diff --git a/src/helpers/vyos-interface-rescan.py b/src/helpers/vyos-interface-rescan.py
index fea9bca1c..0bc3ac7d0 100755
--- a/src/helpers/vyos-interface-rescan.py
+++ b/src/helpers/vyos-interface-rescan.py
@@ -97,7 +97,8 @@ def get_interface_type(intf: str) -> str:
     return intf_type
 
 def get_new_interfaces() -> dict:
-    """ Read any new interface data left in /run/udev/vyos by vyos_net_name
+    """ Read any new interface data left in /run/udev/vyos by
+    vyos-net-name-resolve.py for interfaces without a configured hw-id
     """
     interfaces = {}
 
diff --git a/src/init/vyos-router b/src/init/vyos-router
index 06ec89d72..8e0a671a6 100755
--- a/src/init/vyos-router
+++ b/src/init/vyos-router
@@ -367,6 +367,26 @@ update_interface_config ()
     fi
 }
 
+# warn (but do not fail boot) about configured hw-id interfaces whose
+# hardware was not found by vyos-net-name-resolve.service
+warn_missing_interface_hardware ()
+{
+    local status_file="/run/vyos-net-name-resolve.json"
+    [ -f "${status_file}" ] || return 0
+
+    jq -r '.missing // {} | to_entries[] | "\(.value) \(.key)"' "${status_file}" \
+        2>/dev/null | while read -r intf hwid; do
+        [ -n "${intf}" ] || continue
+        log_failure_msg "hw-id ${hwid} configured as '${intf}' was not found during boot - check cabling, hardware and driver/firmware"
+    done
+
+    jq -r '.pending_unresolved // [] | .[]' "${status_file}" 2>/dev/null | \
+        while read -r intf; do
+        [ -n "${intf}" ] || continue
+        log_failure_msg "interface '${intf}' still has no hw-id configured after this boot's naming pass - bind it manually, e.g. 'set interfaces ethernet ${intf} hw-id <mac>', or remove the node if it is no longer needed"
+    done
+}
+
 cleanup_post_commit_hooks () {
     # Remove links from the post-commit hooks directory.
     # note that this approach only supports hooks that are "configured",
@@ -610,6 +630,12 @@ start ()
 
     disabled migrate || migrate_bootfile || overall_status=1
 
+    # config.boot is only guaranteed to exist/be current from this point on
+    # (tmpfs mount + encrypted config unlock + syntax migration have all
+    # already happened above) - hw-id based interface naming must be
+    # resolved against it before anything below applies interface config.
+    systemctl start vyos-net-name-resolve.service || overall_status=1
+
     restore_if_missing_preconfig_script
 
     run_preconfig_script
@@ -617,6 +643,7 @@ start ()
     run_postupgrade_script
 
     update_interface_config || overall_status=1
+    warn_missing_interface_hardware
 
     disabled system_activate || system_activate || overall_status=1
 
diff --git a/src/system/vyos-net-name-resolve.py b/src/system/vyos-net-name-resolve.py
new file mode 100755
index 000000000..7934e8442
--- /dev/null
+++ b/src/system/vyos-net-name-resolve.py
@@ -0,0 +1,640 @@
+#!/usr/bin/env python3
+#
+# Copyright VyOS maintainers and contributors <maintainers@vyos.io>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# Single authoritative pass that enforces "interfaces/{ethernet,wireless}/
+# */hw-id" from config.boot onto the live system. It runs once, after udev
+# has settled, and decides names from a fully-formed view of the hardware
+# instead of reacting to individual "add" uevents.
+#
+# The old udev-time approach (src/udev/vyos_net_name, invoked straight from
+# a udev rule) decided the final, hw-id based name from a single sysfs
+# snapshot taken at the moment one interface's "add" event was evaluated.
+# On systems with several different NIC vendors/drivers that snapshot is
+# unreliable: the DRIVERS attribute walk-up and the interface's permanent
+# MAC address are not guaranteed to be populated yet, and neither gets a
+# second chance since each uevent is only evaluated once. This script
+# sidesteps that by re-reading live state after hardware has had time to
+# settle, and by verifying/repairing the outcome rather than guessing once.
+
+import json
+import logging
+import logging.handlers
+import re
+import tempfile
+import time
+from pathlib import Path
+from sys import exit
+
+from vyos.configtree import ConfigTree
+from vyos.defaults import directories
+from vyos.migrate import ConfigMigrate
+from vyos.utils.process import rc_cmd
+from vyos.utils.process import run
+
+# Bounded wait for all configured hw-id hardware to appear. NICs needing a
+# longer firmware/link-training window are rare enough that this has not
+# been exposed as a CLI knob yet.
+HARDWARE_WAIT_TIMEOUT = 10
+HARDWARE_WAIT_POLL = 0.25
+
+# Bounded wait for hardware without a configured hw-id to settle before
+# bootstrap-naming it. There is no specific MAC to wait for here, so
+# "N consecutive identical snapshots" stands in for "hardware has stopped
+# registering/renaming interfaces".
+HARDWARE_SETTLE_TIMEOUT = 10
+HARDWARE_SETTLE_STABLE_POLLS = 3
+
+config_path = '/opt/vyatta/etc/config/config.boot'
+vyos_udev_dir = directories['vyos_udev_dir']
+status_file = Path('/run/vyos-net-name-resolve.json')
+
+logger = logging.getLogger()
+
+
+def _load_config_boot() -> ConfigTree:
+    """Parse config.boot into a ConfigTree, migrating stale syntax if
+    needed. Returns None if there is no persisted config yet (livecd/ISO).
+    """
+    if not Path(config_path).is_file():
+        return None
+
+    try:
+        config_file = Path(config_path).read_text()
+    except OSError as e:
+        logger.critical(f'OSError {e}')
+        exit(1)
+
+    try:
+        return ConfigTree(config_file)
+    except Exception:
+        try:
+            logger.debug('updating component version string syntax')
+            # this will update the component version string syntax,
+            # required for updates 1.2 --> 1.3/1.4
+            with tempfile.NamedTemporaryFile() as fp:
+                Path(fp.name).write_text(config_file)
+                config_migrate = ConfigMigrate(fp.name)
+                if config_migrate.syntax_update_needed():
+                    config_migrate.update_syntax()
+                    config_migrate.write_config()
+                config_file = Path(fp.name).read_text()
+
+            return ConfigTree(config_file)
+        except Exception as e:
+            logger.critical(f'ConfigTree error: {e}')
+            exit(1)
+
+
+def get_configfile_interfaces() -> dict:
+    """Read hw-id -> name mapping for ethernet/wireless from config.boot"""
+    interfaces: dict = {}
+
+    config = _load_config_boot()
+    if config is None:
+        return interfaces
+
+    for base in (['interfaces', 'ethernet'], ['interfaces', 'wireless']):
+        if not config.exists(base):
+            continue
+        for intf in config.list_nodes(base):
+            path = base + [intf, 'hw-id']
+            if not config.exists(path):
+                logger.warning(f"no 'hw-id' entry for {intf}")
+                continue
+            hwid = config.return_value(path).lower()
+            if hwid in interfaces:
+                logger.warning(
+                    f'multiple entries for {hwid}: {interfaces[hwid]}, {intf}'
+                )
+                continue
+            interfaces[hwid] = intf
+
+    logger.debug(f'config file entries: {interfaces}')
+    return interfaces
+
+
+def get_pending_hwid_nodes() -> dict:
+    """Interface nodes that exist under interfaces/{ethernet,wireless} in
+    config.boot but have no 'hw-id' leaf - e.g. the documented "NIC
+    replaced" remediation (`delete interfaces ethernet eth1 hw-id`)
+    intentionally leaves the node (and its other settings, like address)
+    in place, expecting the SAME node to receive a fresh hw-id. These
+    names have no known MAC yet - that is the point - so they cannot be
+    folded into get_configfile_interfaces()'s MAC-keyed dict; they are
+    surfaced here, grouped by type, so main() can try to match them to
+    this boot's unconfigured hardware (see match_pending_nodes()).
+    """
+    pending = {'ethernet': set(), 'wireless': set()}
+
+    config = _load_config_boot()
+    if config is None:
+        return pending
+
+    for intf_type, base in (('ethernet', ['interfaces', 'ethernet']),
+                             ('wireless', ['interfaces', 'wireless'])):
+        if not config.exists(base):
+            continue
+        for intf in config.list_nodes(base):
+            if not config.exists(base + [intf, 'hw-id']):
+                pending[intf_type].add(intf)
+
+    return pending
+
+
+def get_permanent_mac(ifname: str, sys_class_net: str = '/sys/class/net') -> str:
+    """Best-effort permanent hardware address of an interface.
+
+    Falls back to the interface's current address if the driver does not
+    support reporting a permanent address separately (ethtool -P).
+
+    sys_class_net is overridable for testing against a fake sysfs tree.
+    """
+    code, out = rc_cmd(f'ethtool -P {ifname}')
+    if code == 0:
+        m = re.search(r'([0-9a-fA-F]{2}(:[0-9a-fA-F]{2}){5})', out)
+        if m and m.group(1) != '00:00:00:00:00:00':
+            return m.group(1).lower()
+
+    try:
+        return Path(f'{sys_class_net}/{ifname}/address').read_text().strip().lower()
+    except OSError:
+        return ''
+
+
+def discover_physical_interfaces(sys_class_net: str = '/sys/class/net') -> dict:
+    """Return {kernel_name: mac} for every interface backed by a real bus
+    device - excludes lo, bridges, bonds, VLANs, veth, tunnels, etc.
+
+    sys_class_net is overridable for testing against a fake sysfs tree.
+    """
+    interfaces = {}
+    net_dir = Path(sys_class_net)
+    if not net_dir.is_dir():
+        return interfaces
+
+    for entry in net_dir.iterdir():
+        if not (entry / 'device').exists():
+            continue
+        mac = get_permanent_mac(entry.name, sys_class_net)
+        if mac:
+            interfaces[entry.name] = mac
+
+    return interfaces
+
+
+def wait_for_hardware(configured_macs: set, timeout: float = HARDWARE_WAIT_TIMEOUT,
+                       poll: float = HARDWARE_WAIT_POLL) -> tuple:
+    """Poll until every configured hw-id has shown up, or until timeout"""
+    deadline = time.monotonic() + timeout
+    current = discover_physical_interfaces()
+    while True:
+        missing = configured_macs - set(current.values())
+        if not missing or time.monotonic() >= deadline:
+            return current, missing
+        time.sleep(poll)
+        current = discover_physical_interfaces()
+
+
+def wait_for_settle(initial: dict, timeout: float = HARDWARE_SETTLE_TIMEOUT,
+                     poll: float = HARDWARE_WAIT_POLL,
+                     stable_polls: int = HARDWARE_SETTLE_STABLE_POLLS) -> dict:
+    """Poll until discover_physical_interfaces() returns the same snapshot
+    stable_polls times in a row, or until timeout. Used before bootstrap-
+    naming hardware that has no configured hw-id to wait for by MAC.
+    """
+    deadline = time.monotonic() + timeout
+    current = initial
+    stable = 1 if current else 0
+    while stable < stable_polls and time.monotonic() < deadline:
+        time.sleep(poll)
+        seen = discover_physical_interfaces()
+        stable = stable + 1 if seen == current else 1
+        current = seen
+    return current
+
+
+def is_wireless_interface(name: str, sys_class_net: str = '/sys/class/net') -> bool:
+    """Race-free wireless check: existence of the phy80211 symlink, not the
+    interface's current (possibly still cosmetic/pre-bootstrap) name.
+    """
+    return (Path(sys_class_net) / name / 'phy80211').exists()
+
+
+PCI_BDF_RE = re.compile(r'^[0-9a-f]{4}:[0-9a-f]{2}:[0-9a-f]{2}\.[0-9a-f]$')
+
+# No real hop-count can reach this - reserves it as a sort-last sentinel
+# for interfaces whose bus topology can't be determined (USB NICs, or a
+# device symlink that doesn't exist/resolve).
+PCIE_DISTANCE_UNKNOWN = 999
+
+
+def pcie_distance(name: str, sys_class_net: str = '/sys/class/net') -> int:
+    """Approximate PCIe bus distance from the root complex - counts PCI
+    domain:bus:device.function segments (e.g. 0000:00:1f.6) in the fully
+    resolved sysfs path of the interface's 'device' symlink. Non-PCI hops
+    (virtioN, usbN, the net/<ifname> tail, ...) simply don't match and are
+    skipped, so virtio's device->virtioN->real-PCI-parent indirection
+    needs no special-casing. Multi-function siblings at the same slot
+    contribute exactly one matching segment each, so they are not
+    double-counted relative to their shared depth.
+
+    Returns PCIE_DISTANCE_UNKNOWN (sorts after every real hop-count) if
+    the 'device' symlink is missing/unresolvable, or the resolved path
+    has no PCI BDF segment at all (e.g. a USB NIC).
+    """
+    device_link = Path(sys_class_net) / name / 'device'
+    try:
+        resolved = device_link.resolve(strict=True)
+    except (OSError, RuntimeError):
+        return PCIE_DISTANCE_UNKNOWN
+
+    hops = sum(1 for part in resolved.parts if PCI_BDF_RE.match(part))
+    return hops if hops > 0 else PCIE_DISTANCE_UNKNOWN
+
+
+def find_available(names: set, prefix: str) -> str:
+    """Find the lowest free index for a given interface name prefix"""
+    index_list = []
+    for name in names:
+        if not name.startswith(prefix):
+            continue
+        suffix = name[len(prefix):]
+        if suffix.isdigit():
+            index_list.append(int(suffix))
+
+    if not index_list:
+        return f'{prefix}0'
+
+    index_list.sort()
+    # find 'holes' in list, if any
+    missing = sorted(set(range(index_list[0], index_list[-1])) - set(index_list))
+    if missing:
+        return f'{prefix}{missing[0]}'
+
+    return f'{prefix}{index_list[-1] + 1}'
+
+
+def find_next_available(names: set, prefix: str, floor: int = 0) -> str:
+    """Find the lowest free index for a prefix, scanning up from floor.
+
+    Unlike find_available(), this always starts the scan at floor (0 by
+    default) rather than at the lowest index already present in `names` -
+    used for bootstrap naming, where a gap must be backfillable even when
+    it sits below every other index currently in `names` (e.g. `names`
+    contains only 'eth5' and 'eth9', but 'eth0'..'eth4' and 'eth6'..'eth8'
+    are genuinely free). A slot only stays unavailable here because it is
+    explicitly present in `names` - the caller decides what belongs there
+    (configured hw-id targets, pending nodes, ...), not this function.
+    """
+    n = floor
+    while f'{prefix}{n}' in names:
+        n += 1
+    return f'{prefix}{n}'
+
+
+def compute_rename_plan(configured: dict, current: dict, pending: dict = None) -> dict:
+    """Build {from_name: to_name} for every interface that needs to move to
+    its CLI hw-id name. Also relocates any interface that currently squats
+    on a name owned by a different hw-id, so the rightful owner can take it.
+    """
+    plan = {}
+    current_by_mac = {mac: name for name, mac in current.items()}
+    target_owner_mac = {name: mac for mac, name in configured.items()}
+
+    for mac, target in configured.items():
+        source = current_by_mac.get(mac)
+        if source and source != target:
+            plan[source] = target
+
+    unchanged = set(current) - set(plan)
+    # every configured target is reserved, even one whose hw-id hasn't
+    # shown up yet this boot (missing/faulty/slow driver) - a squatter must
+    # never be relocated onto a name that hardware still owns, or it would
+    # just need relocating again the moment that hardware actually appears.
+    # A pending (hw-id-less but still-configured) node name is reserved the
+    # same way: it may be about to be reclaimed by the exact NIC that just
+    # vacated it (see match_pending_nodes()), and even when it isn't, its
+    # other settings (address, description, ...) are still live in
+    # config.boot and must not be handed to an unrelated squatter.
+    reserved = set(configured.values())
+    if pending:
+        reserved |= pending.get('ethernet', set()) | pending.get('wireless', set())
+
+    for name, mac in current.items():
+        if name in plan:
+            continue
+        owner_mac = target_owner_mac.get(name)
+        if owner_mac is not None and owner_mac != mac:
+            prefix = re.sub(r'\d+$', '', name) or name
+            taken = unchanged | set(plan.values()) | set(plan.keys()) | reserved
+            new_name = find_available(taken, prefix)
+            plan[name] = new_name
+            unchanged.discard(name)
+
+    return plan
+
+
+def unmatched_candidates(configured: dict, current: dict, existing_plan: dict) -> list:
+    """Physical interfaces this boot with no configured hw-id - the pool
+    both ordinary bootstrap naming and pending-node reclaim matching draw
+    from. This deliberately INCLUDES squatters compute_rename_plan() is
+    already evicting from a configured target name: excluding them here
+    let their mac skip match_pending_nodes() entirely, so an unconfigured
+    NIC that happened to be squatting on someone else's hw-id slot could
+    silently get a permanent, possibly-ambiguous hw-id via ordinary
+    bootstrap naming instead of being reclaimed or held back like any
+    other unconfigured candidate. Their eviction destination from
+    existing_plan still stands as the fallback - match_pending_nodes()
+    (via main()'s reclaim loop) or compute_bootstrap_plan() only override
+    it, they never leave a squatter un-evicted.
+    """
+    return [(mac, name) for name, mac in current.items()
+            if mac not in configured]
+
+
+def compute_bootstrap_plan(configured: dict, current: dict, existing_plan: dict) -> dict:
+    """Build {from_name: to_name} for physical interfaces that have no
+    configured hw-id at all, assigning them a canonical name within their
+    type group (ethernet/wireless) ordered by PCIe distance from the root
+    complex first and MAC address as a tie-break, instead of leaving them
+    at whatever name the racy udev-time fast path produced. Ordering by
+    topology rather than raw MAC magnitude means an onboard/directly
+    CPU-attached NIC isn't sorted after add-in cards just because its MAC
+    happens to be numerically higher. This is what makes a box's very
+    first boot - before any hw-id exists - just as deterministic as every
+    boot after hw-id is written (PCIe wiring and MAC are both static
+    hardware properties), since the name assigned here gets frozen into
+    config.boot by vyos-interface-rescan.py the same way a real hw-id
+    match would.
+
+    A pending node's name (hw-id deleted, node kept - see
+    get_pending_hwid_nodes()) is treated as just another available slot
+    here, exactly like a numeric gap - not reserved for it specifically.
+    That is what lets a pending node recover its OWN original hardware
+    whenever it and some other now-unclaimed NIC become free in the same
+    boot (e.g. a different interface's config was fully deleted at the
+    same time): PCIe distance and MAC are static per-NIC properties, so
+    the relative sort order among any subset of NICs is identical on
+    every boot. Removing whichever NICs stay configured from that fixed
+    order leaves the rest in the same relative order they always had -
+    which, since a box's very first boot assigns names by this exact
+    sort, is precisely each one's original slot. No pending-node-specific
+    matching logic is needed for this to hold; it falls out of sorting
+    the same way every time. main() attributes a resulting name back to
+    a "reclaim" after the fact by checking it against `pending`'s node
+    names - see there.
+
+    existing_plan is the hw-id based plan already computed by
+    compute_rename_plan(): its RIGHTFUL-OWNER targets (an interface moving
+    to its own configured hw-id name) are reserved so a bootstrap name can
+    never collide with a configured one. A squatter compute_rename_plan()
+    is evicting from a configured target IS still bootstrap candidacy here
+    (see unmatched_candidates()) - its OWN eviction destination is only a
+    provisional fallback that this function is about to recompute for it
+    from scratch, so that value must not also count as "taken" (it would
+    needlessly block a lower slot the unified ascending fill might
+    otherwise give it, or another candidate, once real).
+
+    A numeric slot is only ever off-limits here because a real, currently
+    configured hw-id target still occupies or reserves it. A gap left by
+    fully deleting an interface's config, or a pending node whose hw-id
+    alone was deleted, carry no such reservation and are freely (and
+    identically) backfilled - there is no remaining signal in config.boot
+    to treat those two cases differently, and either way the admin's own
+    action is what freed the slot.
+    """
+    plan = {}
+    candidates = unmatched_candidates(configured, current, existing_plan)
+    if not candidates:
+        return plan
+
+    candidate_names = {name for _, name in candidates}
+    # a plan entry whose source IS one of this function's own candidates
+    # is a squatter's provisional eviction fallback, about to be
+    # recomputed below - only a rightful-owner move's target is a real,
+    # authoritative reservation
+    rightful_movers = {src: target for src, target in existing_plan.items()
+                        if src not in candidate_names}
+    # a rightful mover's CURRENT (source) name looks occupied right now,
+    # but safe_bulk_rename()'s two-phase scratch-name staging vacates it
+    # before any target name is actually claimed - so it must not count
+    # as taken here either, or a candidate that belongs there (e.g. a
+    # pending node whose name happens to be some other configured mac's
+    # racy cosmetic position this boot) gets pushed to a fresh slot
+    # instead for no reason.
+    taken = (set(current) - candidate_names - set(rightful_movers)) \
+        | set(rightful_movers.values())
+
+    for mac, name in sorted(candidates, key=lambda c: (pcie_distance(c[1]), c[0])):
+        prefix = 'wlan' if is_wireless_interface(name) else 'eth'
+        new_name = find_next_available(taken, prefix)
+        taken.add(new_name)
+        if new_name != name:
+            plan[name] = new_name
+
+    return plan
+
+
+def get_ifindex(name: str) -> str:
+    try:
+        return Path(f'/sys/class/net/{name}/ifindex').read_text().strip()
+    except OSError:
+        return name
+
+
+def rename_interface(old: str, new: str) -> bool:
+    run(f'ip link set dev {old} down')
+    code = run(f'ip link set dev {old} name {new}')
+    if code != 0:
+        logger.error(f"failed to rename '{old}' -> '{new}' (exit {code})")
+        return False
+    logger.info(f"renamed '{old}' -> '{new}'")
+    return True
+
+
+def safe_bulk_rename(plan: dict) -> dict:
+    """Two-phase rename: stage every interface via a unique scratch name
+    (derived from its ifindex, which is always unique) before assigning
+    final names. This makes the whole batch collision-proof regardless of
+    permutations/cycles between current and target names - a straight
+    from->to rename can fail if the target name is still held by another
+    interface earlier/later in the same plan.
+    """
+    if not plan:
+        return {}
+
+    applied = {}
+    scratch = {}
+    for old, target in plan.items():
+        tmp = f'vyeth{get_ifindex(old)}'
+        if rename_interface(old, tmp):
+            scratch[tmp] = (old, target)
+            applied[old] = target
+
+    for tmp, (old, target) in scratch.items():
+        if rename_interface(tmp, target):
+            run(f'ip link set dev {target} up')
+        else:
+            # still sitting under the scratch name, not the target - don't
+            # report it as renamed, and don't leave it down indefinitely
+            del applied[old]
+            run(f'ip link set dev {tmp} up')
+
+    return applied
+
+
+def sync_rescan_hints(current_state: dict, configured: dict,
+                       stale_names: set = frozenset()) -> None:
+    """Leave a hint under vyos_udev_dir for every interface that has no
+    hw-id configured yet, so vyos-interface-rescan.py can auto-populate
+    config.boot. Remove stale/no-longer-hw-id-needed hints.
+    """
+    try:
+        Path(vyos_udev_dir).mkdir(parents=True, exist_ok=True)
+    except OSError as e:
+        logger.critical(f'error creating rescan hint directory: {e}')
+        return
+
+    for name, mac in current_state.items():
+        hint = Path(vyos_udev_dir) / name
+        if mac in configured:
+            hint.unlink(missing_ok=True)
+        else:
+            try:
+                hint.write_text(mac)
+            except OSError as e:
+                logger.error(f'could not write rescan hint for {name}: {e}')
+
+    for old_name in stale_names:
+        if old_name not in current_state:
+            (Path(vyos_udev_dir) / old_name).unlink(missing_ok=True)
+
+
+def write_status(configured: dict, found: dict, missing: set, plan: dict,
+                  pending: dict = None, reclaimed: dict = None,
+                  candidates: list = None) -> None:
+    """candidates is the full unmatched_candidates() list evaluated this
+    boot (before reclaim/bootstrap assignment) - surfaced here so a
+    pending node left unresolved for lack of hardware is self-diagnosable
+    from this one file: 'pending_unresolved' names what needed a match,
+    'unconfigured_candidates' names every physical interface that was in
+    the running for one, without needing a separate `ip -br link show` or
+    `show configuration commands` to reconstruct the same picture by hand.
+    """
+    pending = pending or {}
+    reclaimed = reclaimed or {}
+    candidates = candidates or []
+    all_pending = pending.get('ethernet', set()) | pending.get('wireless', set())
+    status = {
+        'configured': configured,
+        'found': sorted(found.values()),
+        'missing': {mac: configured[mac] for mac in sorted(missing)},
+        'renamed': plan,
+        'pending_unresolved': sorted(all_pending - set(reclaimed.values())),
+        'reclaimed': reclaimed,
+        'unconfigured_candidates': {name: mac for mac, name in candidates},
+    }
+    try:
+        status_file.write_text(json.dumps(status, indent=2))
+    except OSError as e:
+        logger.error(f'could not write status file: {e}')
+
+
+def main():
+    configured = get_configfile_interfaces()
+    pending = get_pending_hwid_nodes()
+
+    if configured:
+        current, missing = wait_for_hardware(set(configured))
+        for mac in sorted(missing):
+            logger.warning(
+                f"hw-id '{mac}' configured as '{configured[mac]}' was not found "
+                f'within {HARDWARE_WAIT_TIMEOUT}s - hardware may be missing, '
+                'still initializing, or its driver failed to load'
+            )
+        plan = compute_rename_plan(configured, current, pending)
+    else:
+        logger.info('no hw-id configured yet')
+        current, missing, plan = discover_physical_interfaces(), set(), {}
+
+    all_pending = pending.get('ethernet', set()) | pending.get('wireless', set())
+
+    candidates = []
+    if all_pending or any(mac not in configured for mac in current.values()):
+        # bootstrap-name whatever has no hw-id match, deterministically by
+        # PCIe distance and MAC, instead of leaving it at its racy cosmetic
+        # udev-time name - this is what vyos-interface-rescan.py will
+        # freeze into config.boot. A NIC that just lost its hw-id (the
+        # documented "delete hw-id to force regeneration" remediation)
+        # competes for this same ascending fill exactly like a numeric
+        # gap does - see compute_bootstrap_plan() for why that recovers
+        # its own original hardware rather than an arbitrary one.
+        #
+        # The `all_pending` half of this condition matters even when
+        # `current` (from wait_for_hardware() above, bounded only on
+        # already-CONFIGURED macs) shows nothing unconfigured yet: on a
+        # system with several different NIC vendors/drivers, the exact
+        # hardware a pending node needs can simply not have finished
+        # probing at this snapshot. Without this, wait_for_settle() below
+        # would never even run, giving that slower hardware zero extra
+        # time to appear before this boot gives up on the pending node.
+        current = wait_for_settle(current)
+        candidates = unmatched_candidates(configured, current, plan)
+        plan.update(compute_bootstrap_plan(configured, current, plan))
+
+    # attribute any candidate that landed on a pending node's name back to
+    # that node - so its rescan hint lands there and vyos-interface-
+    # rescan.py can write the real hw-id into the node's existing settings
+    # (address, description, ...) - and warn about any pending node still
+    # without a hw-id after this pass (a candidate may have existed and
+    # landed on a lower-numbered unrelated slot instead - this is not
+    # necessarily a hardware shortage).
+    reclaimed = {}
+    for mac, name in candidates:
+        final_name = plan.get(name, name)
+        if final_name in all_pending:
+            reclaimed[mac] = final_name
+            logger.info(
+                f"reclaiming pending node '{final_name}' for hw-id '{mac}' "
+                'this boot'
+            )
+    for name in sorted(all_pending - set(reclaimed.values())):
+        logger.warning(
+            f"pending node '{name}' still has no hw-id after this boot's "
+            'naming pass'
+        )
+
+    applied = safe_bulk_rename(plan)
+
+    final_current = discover_physical_interfaces()
+    # configured is passed unmutated (not merged with `reclaimed`): the
+    # reclaimed mac still has no real hw-id in config.boot yet, so it must
+    # still get a rescan hint under its (now reclaimed) name, letting
+    # vyos-interface-rescan.py write the hw-id into the existing node.
+    sync_rescan_hints(final_current, configured, set(applied.keys()))
+    write_status(configured, current, missing, applied,
+                 pending=pending, reclaimed=reclaimed, candidates=candidates)
+
+
+if __name__ == '__main__':
+    syslog_handler = logging.handlers.SysLogHandler(address='/dev/log')
+    formatter = logging.Formatter(f'{Path(__file__).name}: %(message)s')
+    syslog_handler.setFormatter(formatter)
+
+    logger.addHandler(syslog_handler)
+    logger.setLevel(logging.DEBUG)
+
+    main()
diff --git a/src/systemd/vyos-net-name-resolve.service b/src/systemd/vyos-net-name-resolve.service
new file mode 100644
index 000000000..ec7c45636
--- /dev/null
+++ b/src/systemd/vyos-net-name-resolve.service
@@ -0,0 +1,17 @@
+[Unit]
+Description=VyOS deterministic hw-id based interface naming
+Documentation=man:vyos-net-name-resolve.py(8)
+
+# Started explicitly by vyos-router (like frr.service/vyos-netlinkd.service)
+# once /opt/vyatta/etc/config is mounted and config.boot exists - which, for
+# an encrypted config volume, only happens after vyos-router has unlocked
+# and mounted it. It cannot be ordered independently before vyos-router:
+# there is no config.boot to read before that point.
+DefaultDependencies=no
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/libexec/vyos/system/vyos-net-name-resolve.py
+TimeoutStartSec=90
+StandardOutput=journal+console
diff --git a/src/tests/helper.py b/src/tests/helper.py
index 2c4421d0a..5a74525b7 100644
--- a/src/tests/helper.py
+++ b/src/tests/helper.py
@@ -14,9 +14,20 @@
 
 import sys
 import importlib.util
+from importlib.machinery import SourceFileLoader
 
 def prepare_module(file_path='', module_name=''):
+    """Load file_path as module_name, returning the loaded module.
+
+    file_path may be an extensionless script (e.g. udev helpers under
+    src/udev/) - spec_from_file_location() cannot infer a loader for those
+    from the suffix alone, so fall back to an explicit SourceFileLoader.
+    """
     spec = importlib.util.spec_from_file_location(module_name, file_path)
+    if spec is None:
+        loader = SourceFileLoader(module_name, file_path)
+        spec = importlib.util.spec_from_loader(module_name, loader)
     module = importlib.util.module_from_spec(spec)
     spec.loader.exec_module(module)
     sys.modules[module_name] = module
+    return module
diff --git a/src/tests/test_net_name_resolve.py b/src/tests/test_net_name_resolve.py
new file mode 100644
index 000000000..cc401ddb3
--- /dev/null
+++ b/src/tests/test_net_name_resolve.py
@@ -0,0 +1,1534 @@
+# Copyright VyOS maintainers and contributors <maintainers@vyos.io>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# Coverage for T3871 (boot race on hw-id based interface naming): the
+# MAC-driven, collision-safe rename plan that replaces the old per-uevent
+# udev decision, the find_available() crash it used to hit, the
+# ethtool/sysfs permanent-MAC fallback, and the config.boot-availability
+# ordering corner case (vyos-net-name-resolve must run from inside
+# vyos-router, after the config directory is mounted/decrypted, not as an
+# independently-scheduled early-boot unit).
+
+import json
+import os
+import shutil
+import tempfile
+import unittest
+from unittest import mock
+
+from helper import prepare_module
+
+_here = os.path.dirname(__file__)
+
+resolver = prepare_module(
+    os.path.join(_here, '../system/vyos-net-name-resolve.py'),
+    'vyos_net_name_resolve')
+vyos_net_name = prepare_module(
+    os.path.join(_here, '../udev/vyos_net_name'),
+    'vyos_net_name')
+
+
+class TestGetPendingHwidNodes(unittest.TestCase):
+    """A node that exists under interfaces/{ethernet,wireless} but has no
+    hw-id (e.g. after `delete interfaces ethernet eth1 hw-id`, the
+    documented "NIC replaced" remediation) must be surfaced separately
+    from the MAC-keyed configured dict, since it has no MAC to key by yet
+    - this is what lets main() try to reclaim it for the exact NIC that
+    vacated it, instead of silently orphaning its other settings.
+    """
+
+    def setUp(self):
+        self.tmp = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.tmp, ignore_errors=True)
+        self.config_path = os.path.join(self.tmp, 'config.boot')
+        self._orig_config_path = resolver.config_path
+        resolver.config_path = self.config_path
+        self.addCleanup(setattr, resolver, 'config_path', self._orig_config_path)
+
+    def _write_config(self, text):
+        with open(self.config_path, 'w') as f:
+            f.write(text)
+
+    def test_node_with_hwid_not_pending(self):
+        self._write_config(
+            'interfaces {\n'
+            '    ethernet eth0 {\n'
+            '        hw-id 00:11:22:33:44:55\n'
+            '    }\n'
+            '}\n'
+        )
+        self.assertEqual(resolver.get_pending_hwid_nodes(),
+                          {'ethernet': set(), 'wireless': set()})
+
+    def test_node_without_hwid_is_pending(self):
+        self._write_config(
+            'interfaces {\n'
+            '    ethernet eth1 {\n'
+            '        address 10.99.1.1/24\n'
+            '    }\n'
+            '}\n'
+        )
+        self.assertEqual(resolver.get_pending_hwid_nodes(),
+                          {'ethernet': {'eth1'}, 'wireless': set()})
+
+    def test_mixed_ethernet_and_wireless(self):
+        self._write_config(
+            'interfaces {\n'
+            '    ethernet eth0 {\n'
+            '        hw-id 00:11:22:33:44:55\n'
+            '    }\n'
+            '    ethernet eth1 {\n'
+            '        address 10.99.1.1/24\n'
+            '    }\n'
+            '    wireless wlan0 {\n'
+            '        ssid example\n'
+            '    }\n'
+            '}\n'
+        )
+        self.assertEqual(resolver.get_pending_hwid_nodes(),
+                          {'ethernet': {'eth1'}, 'wireless': {'wlan0'}})
+
+    def test_no_interfaces_section(self):
+        self._write_config('system {\n    host-name vyos\n}\n')
+        self.assertEqual(resolver.get_pending_hwid_nodes(),
+                          {'ethernet': set(), 'wireless': set()})
+
+    def test_no_config_boot_at_all(self):
+        # livecd/ISO case - config_path doesn't exist
+        self.assertEqual(resolver.get_pending_hwid_nodes(),
+                          {'ethernet': set(), 'wireless': set()})
+
+
+class TestFindAvailableCrashFix(unittest.TestCase):
+    """find_available() used to raise IndexError on an empty candidate set
+    (index_list[0]) and ValueError on a name with no trailing digit
+    (int('')) - both are realistic inputs on a box's first boot, or when a
+    biosdevname/predefined name has no numeric suffix.
+    """
+
+    def test_resolver_empty_set(self):
+        self.assertEqual(resolver.find_available(set(), 'eth'), 'eth0')
+
+    def test_resolver_no_prefix_match(self):
+        self.assertEqual(resolver.find_available({'wlan3'}, 'eth'), 'eth0')
+
+    def test_resolver_contiguous(self):
+        names = {'eth0', 'eth1', 'eth2'}
+        self.assertEqual(resolver.find_available(names, 'eth'), 'eth3')
+
+    def test_resolver_fills_hole(self):
+        self.assertEqual(resolver.find_available({'eth2', 'eth5'}, 'eth'), 'eth3')
+
+    def test_resolver_no_hole_appends(self):
+        self.assertEqual(resolver.find_available({'eth2', 'eth3'}, 'eth'), 'eth4')
+
+    def test_vyos_net_name_empty_dict(self):
+        self.assertEqual(vyos_net_name.find_available({}, 'eth'), 'eth0')
+
+    def test_vyos_net_name_no_digit_suffix(self):
+        self.assertEqual(
+            vyos_net_name.find_available({'m': 'wlan3'}, 'eth'), 'eth0')
+
+    def test_vyos_net_name_contiguous(self):
+        intfs = {'a': 'eth0', 'b': 'eth1'}
+        self.assertEqual(vyos_net_name.find_available(intfs, 'eth'), 'eth2')
+
+    def test_vyos_net_name_is_available(self):
+        self.assertTrue(vyos_net_name.is_available({'a': 'eth0'}, 'eth1'))
+        self.assertFalse(vyos_net_name.is_available({'a': 'eth0'}, 'eth0'))
+
+    def test_vyos_net_name_mod_ifname(self):
+        self.assertEqual(vyos_net_name.mod_ifname('e5'), 'eth3')
+        self.assertEqual(vyos_net_name.mod_ifname('e2'), 'eth0')
+        self.assertEqual(vyos_net_name.mod_ifname('e1'), 'eth1')
+        self.assertEqual(vyos_net_name.mod_ifname('wlan0'), 'wlan0')
+
+
+class TestUnmatchedCandidates(unittest.TestCase):
+    """Field report: an unconfigured NIC that happens to be squatting on a
+    DIFFERENT interface's configured hw-id slot this boot (e.g. due to
+    probe-order scrambling) was excluded here just because
+    compute_rename_plan() already scheduled it for eviction. That skipped
+    it past match_pending_nodes() entirely, so a squatter that was really
+    the exact NIC a pending node should reclaim - or one that made a
+    reclaim genuinely ambiguous - fell through to ordinary bootstrap
+    naming and got a permanent hw-id with no ambiguity check at all.
+    Squatters must stay in this pool; only their eviction destination
+    (still computed by compute_rename_plan()) is a fallback, not a reason
+    to hide them from reclaim/ambiguity handling.
+    """
+
+    def test_squatter_is_still_a_candidate(self):
+        configured = {'m0': 'eth1'}
+        current = {'eth1': 'squatter-mac', 'eth9': 'm0'}
+        existing_plan = {'eth1': 'eth3', 'eth9': 'eth1'}
+        candidates = resolver.unmatched_candidates(configured, current, existing_plan)
+        self.assertEqual(candidates, [('squatter-mac', 'eth1')])
+
+    def test_rightful_owner_still_excluded(self):
+        configured = {'m0': 'eth0'}
+        current = {'eth0': 'm0'}
+        candidates = resolver.unmatched_candidates(configured, current, {})
+        self.assertEqual(candidates, [])
+
+
+class TestComputeRenamePlan(unittest.TestCase):
+    """The authoritative rename plan is what fixes the multi-vendor NIC
+    boot race: it is driven purely by MAC address, independent of
+    ifindex/probe order, and must never produce a colliding assignment.
+    """
+
+    def test_noop_when_already_correct(self):
+        configured = {'m0': 'eth0', 'm1': 'eth1'}
+        current = {'eth0': 'm0', 'eth1': 'm1'}
+        self.assertEqual(resolver.compute_rename_plan(configured, current), {})
+
+    def test_rename_independent_of_probe_order(self):
+        # m0/m1 landed on unrelated names this boot (e.g. a different
+        # vendor driver won the probe race) - the plan must still point
+        # them at their configured targets regardless.
+        configured = {'m0': 'eth0', 'm1': 'eth1'}
+        current = {'eth5': 'm0', 'eth3': 'm1'}
+        plan = resolver.compute_rename_plan(configured, current)
+        self.assertEqual(plan, {'eth5': 'eth0', 'eth3': 'eth1'})
+
+    def test_full_swap_cycle(self):
+        # eth0 and eth1 need to trade names - a naive from->to rename
+        # would collide; the two-phase scratch-name staging must not.
+        configured = {'m0': 'eth1', 'm1': 'eth0'}
+        current = {'eth0': 'm0', 'eth1': 'm1'}
+        plan = resolver.compute_rename_plan(configured, current)
+        self.assertEqual(plan, {'eth0': 'eth1', 'eth1': 'eth0'})
+
+    def test_squatter_relocated(self):
+        # an unconfigured interface currently sits on a name a configured
+        # hw-id needs - it must be moved out of the way, not left there.
+        configured = {'m0': 'eth0'}
+        current = {'eth0': 'unconfigured-mac', 'eth5': 'm0'}
+        plan = resolver.compute_rename_plan(configured, current)
+        self.assertEqual(plan['eth5'], 'eth0')
+        self.assertNotEqual(plan['eth0'], 'eth0')
+        self.assertTrue(plan['eth0'].startswith('eth'))
+
+    def test_squatter_never_relocated_onto_a_missing_hwid_target(self):
+        # macMissing's hardware hasn't shown up this boot (removed/faulty/
+        # slow driver), so its reserved target 'eth1' never appears in
+        # `current` and the main hw-id loop skips it entirely (source is
+        # None) - the squatter being relocated off of 'eth0' must still not
+        # be handed 'eth1', or it would need relocating again the moment
+        # that hardware actually appears.
+        configured = {'macA': 'eth0', 'macMissing': 'eth1'}
+        current = {'eth0': 'squatterMac', 'eth2': 'macA'}
+        plan = resolver.compute_rename_plan(configured, current)
+        self.assertEqual(plan.get('eth2'), 'eth0')
+        self.assertNotEqual(plan.get('eth0'), 'eth1')
+
+    def test_squatter_never_relocated_onto_a_pending_hwid_less_node(self):
+        # 'eth1' has no hw-id at all (e.g. `delete interfaces ethernet
+        # eth1 hw-id`, the documented remediation for a replaced NIC) but
+        # its config node - and settings like address - still exist. A
+        # squatter being relocated off of 'eth0' must not be handed 'eth1'
+        # either, or it would permanently steal the exact slot the
+        # original NIC needs to reclaim.
+        configured = {'macA': 'eth0'}
+        pending = {'ethernet': {'eth1'}, 'wireless': set()}
+        current = {'eth0': 'squatterMac', 'eth2': 'macA'}
+        plan = resolver.compute_rename_plan(configured, current, pending)
+        self.assertEqual(plan.get('eth2'), 'eth0')
+        self.assertNotEqual(plan.get('eth0'), 'eth1')
+
+    def test_missing_hardware_no_crash_no_entry(self):
+        # hw-id configured but the NIC never showed up (missing/faulty) -
+        # must be skipped, not crash or incorrectly assign another interface.
+        configured = {'m0': 'eth0', 'missing-mac': 'eth9'}
+        current = {'eth5': 'm0'}
+        plan = resolver.compute_rename_plan(configured, current)
+        self.assertEqual(plan, {'eth5': 'eth0'})
+
+    def test_rename_introducing_a_gap(self):
+        # user edits the CLI so m2's node is renamed eth2 -> eth10 while
+        # keeping the same hw-id, leaving eth5..eth9 unused.
+        configured = {
+            'm0': 'eth0', 'm1': 'eth1', 'm2': 'eth10',
+            'm3': 'eth3', 'm4': 'eth4',
+        }
+        current = {
+            'eth0': 'm0', 'eth1': 'm1', 'eth2': 'm2',
+            'eth3': 'm3', 'eth4': 'm4',
+        }
+        plan = resolver.compute_rename_plan(configured, current)
+        self.assertEqual(plan, {'eth2': 'eth10'})
+
+    def test_rename_introducing_a_gap_with_scrambled_fastpath(self):
+        # same as above, but this boot's cosmetic udev fast-path lands m2
+        # on an unrelated name and coincidentally puts a different NIC on
+        # the now-meaningless old 'eth2'.
+        configured = {
+            'm0': 'eth0', 'm1': 'eth1', 'm2': 'eth10',
+            'm3': 'eth3', 'm4': 'eth4',
+        }
+        current = {
+            'eth0': 'm0', 'eth1': 'm1', 'eth7': 'm2',
+            'eth2': 'm3', 'eth4': 'm4',
+        }
+        plan = resolver.compute_rename_plan(configured, current)
+        self.assertEqual(plan.get('eth7'), 'eth10')
+        self.assertEqual(plan.get('eth2'), 'eth3')
+        self.assertNotIn('eth2', configured.values())
+
+
+class TestWaitForSettle(unittest.TestCase):
+    """There is no specific MAC to wait for when bootstrap-naming hardware
+    without a configured hw-id, so settling is detected as N consecutive
+    identical discover_physical_interfaces() snapshots instead.
+    """
+
+    def test_returns_after_n_consecutive_stable_polls(self):
+        snapshots = [
+            {'eth0': 'm0'},           # still changing
+            {'eth0': 'm0', 'eth1': 'm1'},  # still changing
+            {'eth0': 'm0', 'eth1': 'm1'},  # 1st stable repeat
+            {'eth0': 'm0', 'eth1': 'm1'},  # 2nd stable repeat -> settled
+        ]
+        with mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=snapshots):
+            result = resolver.wait_for_settle(
+                {}, timeout=5, poll=0, stable_polls=3)
+        self.assertEqual(result, {'eth0': 'm0', 'eth1': 'm1'})
+
+    def test_bounded_by_timeout_when_never_stable(self):
+        counter = iter(range(1000))
+
+        def ever_changing(*_a, **_kw):
+            return {'eth0': f'm{next(counter)}'}
+
+        clock = iter([0, 0.1, 20, 20])
+        with mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=ever_changing), \
+             mock.patch('time.monotonic', side_effect=lambda: next(clock)):
+            result = resolver.wait_for_settle(
+                {}, timeout=10, poll=0, stable_polls=3)
+        # must return SOMETHING (the last snapshot seen), not hang or crash
+        self.assertIn('eth0', result)
+
+    def test_stable_polls_of_one_returns_on_initial_snapshot(self):
+        with mock.patch.object(resolver, 'discover_physical_interfaces') as m:
+            result = resolver.wait_for_settle(
+                {'eth0': 'm0'}, timeout=5, poll=0, stable_polls=1)
+        m.assert_not_called()
+        self.assertEqual(result, {'eth0': 'm0'})
+
+
+class TestIsWirelessInterface(unittest.TestCase):
+    """Wireless detection must be race-free - it has to be correct even
+    when the interface's current name is a leftover from the cosmetic
+    udev-time fast path and doesn't look like a wlan name at all.
+    """
+
+    def setUp(self):
+        self.tmp = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.tmp, ignore_errors=True)
+        # phy80211 is always a symlink to a real sysfs node in practice -
+        # exists() follows symlinks, so the test target must actually exist
+        self.phy_target = os.path.join(self.tmp, 'phy0')
+        os.mkdir(self.phy_target)
+
+    def test_phy80211_present_is_wireless(self):
+        path = os.path.join(self.tmp, 'wlan0')
+        os.mkdir(path)
+        os.symlink(self.phy_target, os.path.join(path, 'phy80211'))
+        self.assertTrue(resolver.is_wireless_interface('wlan0', self.tmp))
+
+    def test_no_phy80211_is_not_wireless(self):
+        os.mkdir(os.path.join(self.tmp, 'eth0'))
+        self.assertFalse(resolver.is_wireless_interface('eth0', self.tmp))
+
+    def test_detection_independent_of_misleading_name(self):
+        # named like a leftover cosmetic ethernet guess, but it's a real
+        # wifi card - must still be classified wireless
+        path = os.path.join(self.tmp, 'eth7')
+        os.mkdir(path)
+        os.symlink(self.phy_target, os.path.join(path, 'phy80211'))
+        self.assertTrue(resolver.is_wireless_interface('eth7', self.tmp))
+
+
+class TestPcieDistance(unittest.TestCase):
+    """PCIe hop-depth is what lets bootstrap naming reflect physical slot
+    position instead of raw MAC magnitude - a NIC wired straight to the
+    root complex must not sort after an add-in card just because its MAC
+    happens to be numerically higher.
+    """
+
+    def setUp(self):
+        self.tmp = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.tmp, ignore_errors=True)
+        # fake /sys/devices tree, separate from the fake /sys/class/net
+        # entries, so symlink targets can point at realistic PCI-bus-shaped
+        # paths the way a real /sys/class/net/<if>/device symlink does
+        self.devices_root = os.path.join(self.tmp, 'devices')
+        os.makedirs(self.devices_root)
+
+    def _make_iface_pointing_at(self, name, *path_segments):
+        """Create <tmp>/<name>/device as a symlink to a fake sysfs device
+        node at devices_root/<path_segments...>.
+        """
+        target = os.path.join(self.devices_root, *path_segments)
+        os.makedirs(target, exist_ok=True)
+        iface_path = os.path.join(self.tmp, name)
+        os.mkdir(iface_path)
+        os.symlink(target, os.path.join(iface_path, 'device'))
+
+    def test_shallow_device_one_pci_segment(self):
+        # e.g. a NIC directly under the root complex: pci0000:00/0000:00:1f.6
+        self._make_iface_pointing_at('eth0', 'pci0000:00', '0000:00:1f.6')
+        self.assertEqual(resolver.pcie_distance('eth0', self.tmp), 1)
+
+    def test_deep_device_behind_bridges(self):
+        # e.g. an add-in card behind two cascaded PCIe bridges
+        self._make_iface_pointing_at(
+            'eth1', 'pci0000:00', '0000:00:1c.0',
+            '0000:01:00.0', '0000:02:04.0')
+        self.assertEqual(resolver.pcie_distance('eth1', self.tmp), 3)
+
+    def test_virtio_indirection_not_miscounted(self):
+        # verified-real virtio_net layout: device -> virtioN node, whose
+        # OWN parent is the true PCI BDF - the virtioN segment itself must
+        # be skipped, not counted as a hop.
+        self._make_iface_pointing_at(
+            'eth2', 'pci0000:00', '0000:00:12.0', 'virtio2', 'net')
+        self.assertEqual(resolver.pcie_distance('eth2', self.tmp), 1)
+
+    def test_missing_device_symlink_returns_sentinel(self):
+        os.mkdir(os.path.join(self.tmp, 'eth3'))  # no 'device' entry at all
+        self.assertEqual(resolver.pcie_distance('eth3', self.tmp),
+                          resolver.PCIE_DISTANCE_UNKNOWN)
+
+    def test_broken_device_symlink_returns_sentinel(self):
+        iface_path = os.path.join(self.tmp, 'eth4')
+        os.mkdir(iface_path)
+        os.symlink(os.path.join(self.devices_root, 'does-not-exist'),
+                    os.path.join(iface_path, 'device'))
+        self.assertEqual(resolver.pcie_distance('eth4', self.tmp),
+                          resolver.PCIE_DISTANCE_UNKNOWN)
+
+    def test_no_pci_segment_at_all_returns_sentinel(self):
+        # simulated USB NIC: resolved path has no PCI BDF component
+        self._make_iface_pointing_at('eth5', 'usb1', '1-1', '1-1:1.0')
+        self.assertEqual(resolver.pcie_distance('eth5', self.tmp),
+                          resolver.PCIE_DISTANCE_UNKNOWN)
+
+
+class TestComputeBootstrapPlan(unittest.TestCase):
+    """Bootstrap naming is what makes a box's very first boot (before any
+    hw-id exists) deterministic, the same way hw-id makes every boot after
+    that deterministic - it must depend only on PCIe topology and MAC
+    rank, never on whatever name the racy cosmetic fast-path happened to
+    assign. pcie_distance is held constant by default in these tests, so
+    they exercise pure MAC-rank ordering (see TestPcieDistance for the
+    topology-ordering cases specifically).
+    """
+
+    def setUp(self):
+        patcher = mock.patch.object(resolver, 'is_wireless_interface',
+                                     return_value=False)
+        self.is_wireless = patcher.start()
+        self.addCleanup(patcher.stop)
+
+        distance_patcher = mock.patch.object(resolver, 'pcie_distance',
+                                              return_value=0)
+        self.pcie_distance = distance_patcher.start()
+        self.addCleanup(distance_patcher.stop)
+
+    def test_sorted_by_mac_independent_of_current_names(self):
+        # names are in the OPPOSITE order of their MACs
+        current = {'eth5': 'bb', 'eth2': 'aa'}
+        plan = resolver.compute_bootstrap_plan({}, current, {})
+        self.assertEqual(plan, {'eth2': 'eth0', 'eth5': 'eth1'})
+
+    def test_noop_when_already_in_canonical_rank_order(self):
+        current = {'eth0': 'aa', 'eth1': 'bb'}
+        plan = resolver.compute_bootstrap_plan({}, current, {})
+        self.assertEqual(plan, {})
+
+    def test_configured_targets_are_never_overwritten(self):
+        configured = {'m0': 'eth0'}
+        current = {'eth0': 'm0', 'eth9': 'm2', 'eth8': 'm1'}
+        plan = resolver.compute_bootstrap_plan(configured, current, {})
+        self.assertNotIn('eth0', plan.values())
+        self.assertEqual(plan.get('eth8'), 'eth1')
+        self.assertEqual(plan.get('eth9'), 'eth2')
+
+    def test_new_interface_backfills_a_gap_with_no_pending_node(self):
+        # eth1 is a gap between two hw-id'd interfaces, but nothing in
+        # config.boot reserves it (no hw-id, no pending node either - the
+        # interface was fully deleted at some point, or never existed) -
+        # a new, unrelated NIC discovered this boot is free to take it,
+        # the same as it would on a system with no config for it at all.
+        configured = {'m0': 'eth0', 'm2': 'eth2'}
+        current = {'eth0': 'm0', 'eth2': 'm2', 'eth9': 'new-mac'}
+        plan = resolver.compute_bootstrap_plan(configured, current, {})
+        self.assertEqual(plan, {'eth9': 'eth1'})
+
+    def test_multiple_new_interfaces_backfill_gaps_in_order(self):
+        configured = {'m0': 'eth0', 'm2': 'eth2'}
+        current = {
+            'eth0': 'm0', 'eth2': 'm2',
+            'ethB': 'bb', 'ethA': 'aa',
+        }
+        plan = resolver.compute_bootstrap_plan(configured, current, {})
+        # lower mac 'aa' takes the gap at eth1 first, 'bb' continues to
+        # the next free slot, eth3 - not "skip past the gap to eth3/eth4"
+        self.assertEqual(plan, {'ethA': 'eth1', 'ethB': 'eth3'})
+
+    def test_ethernet_and_wireless_numbered_independently(self):
+        self.is_wireless.side_effect = lambda name: name == 'radio0'
+        current = {'ifaceB': 'bb', 'radio0': 'aa'}
+        plan = resolver.compute_bootstrap_plan({}, current, {})
+        self.assertEqual(plan.get('radio0'), 'wlan0')
+        self.assertEqual(plan.get('ifaceB'), 'eth0')
+
+    def test_squatter_already_in_existing_plan_excluded(self):
+        # 'eth0' is a squatter the hw-id plan already decided to move away
+        # (existing_plan key) - it IS still bootstrap candidacy (see
+        # unmatched_candidates()), but must never be handed a second,
+        # conflicting assignment on top of its existing_plan eviction.
+        existing_plan = {'eth0': 'eth3'}
+        current = {'eth0': 'unconfigured-mac', 'eth7': 'm0'}
+        plan = resolver.compute_bootstrap_plan({'m0': 'eth1'}, current,
+                                                existing_plan)
+        self.assertNotIn('eth0', plan)
+
+    def test_bootstrap_targets_never_collide_with_existing_plan_values(self):
+        # existing_plan says an interface currently named 'oldname' is
+        # moving to 'eth0' - nothing else in `current` is named 'eth0' or
+        # 'eth*' at all, so if that target isn't reserved, find_available()
+        # would freely hand 'eth0' to the bootstrap candidate too.
+        existing_plan = {'oldname': 'eth0'}
+        current = {'oldname': 'm0', 'newnic': 'unconfigured-mac'}
+        plan = resolver.compute_bootstrap_plan({'m0': 'eth0'}, current,
+                                                existing_plan)
+        self.assertNotEqual(plan.get('newnic'), 'eth0')
+
+    def test_smaller_pcie_distance_wins_over_higher_mac(self):
+        # 'bb' has the numerically higher MAC but sits closer to the root
+        # complex - it must be named first despite losing on MAC alone.
+        current = {'eth5': 'bb', 'eth2': 'aa'}
+        self.pcie_distance.side_effect = lambda name: {'eth5': 0, 'eth2': 3}[name]
+        plan = resolver.compute_bootstrap_plan({}, current, {})
+        self.assertEqual(plan, {'eth5': 'eth0', 'eth2': 'eth1'})
+
+    def test_same_pcie_distance_falls_back_to_mac_order(self):
+        current = {'eth5': 'bb', 'eth2': 'aa'}
+        self.pcie_distance.side_effect = lambda name: 2  # tie for both
+        plan = resolver.compute_bootstrap_plan({}, current, {})
+        self.assertEqual(plan, {'eth2': 'eth0', 'eth5': 'eth1'})
+
+    def test_unknown_pcie_distance_sorts_last(self):
+        # 'aa' has the numerically lowest MAC but an undeterminable bus
+        # position (e.g. a USB NIC) - it must not jump the queue.
+        current = {'eth9': 'cc', 'eth5': 'bb', 'ethX': 'aa'}
+        self.pcie_distance.side_effect = lambda name: {
+            'eth9': 1, 'eth5': 2, 'ethX': resolver.PCIE_DISTANCE_UNKNOWN,
+        }[name]
+        plan = resolver.compute_bootstrap_plan({}, current, {})
+        self.assertEqual(plan, {'eth9': 'eth0', 'eth5': 'eth1', 'ethX': 'eth2'})
+
+    def test_pcie_distance_ordering_independent_of_ethernet_wireless_split(self):
+        # distance-based ordering applies within each type group separately,
+        # same as MAC does today - a wlan candidate's distance must not
+        # affect eth numbering or vice versa.
+        self.is_wireless.side_effect = lambda name: name == 'radio0'
+        current = {'ifaceB': 'bb', 'radio0': 'aa'}
+        self.pcie_distance.side_effect = lambda name: {
+            'ifaceB': 5, 'radio0': 0,
+        }[name]
+        plan = resolver.compute_bootstrap_plan({}, current, {})
+        self.assertEqual(plan.get('radio0'), 'wlan0')
+        self.assertEqual(plan.get('ifaceB'), 'eth0')
+
+
+class TestComputeBootstrapPlanPendingSlots(unittest.TestCase):
+    """A pending node's name (see get_pending_hwid_nodes()) carries no
+    special reservation in compute_bootstrap_plan() at all - it is just
+    another name with nothing configured for it, exactly like a numeric
+    gap. main() is what attributes a candidate landing on such a name
+    back to a "reclaim" afterward, by cross-checking it against
+    get_pending_hwid_nodes() - not this function's job (see main()).
+    """
+
+    def setUp(self):
+        patcher = mock.patch.object(resolver, 'is_wireless_interface',
+                                     return_value=False)
+        self.is_wireless = patcher.start()
+        self.addCleanup(patcher.stop)
+
+        distance_patcher = mock.patch.object(resolver, 'pcie_distance',
+                                              return_value=0)
+        self.pcie_distance = distance_patcher.start()
+        self.addCleanup(distance_patcher.stop)
+
+    def test_open_name_filled_like_an_ordinary_gap(self):
+        # 'eth1' has nothing configured for it - whether that is because
+        # its whole node was deleted or just its hw-id makes no
+        # difference here, it is simply the lowest open name.
+        configured = {'m0': 'eth0'}
+        current = {'eth0': 'm0', 'eth9': 'new-mac'}
+        plan = resolver.compute_bootstrap_plan(configured, current, {})
+        self.assertEqual(plan.get('eth9'), 'eth1')
+
+    def test_ascending_fill_has_no_preference_between_open_names(self):
+        # two open names (eth1, eth4 - the reason either is open makes no
+        # difference) and two candidates - the lower-sorted candidate
+        # takes the lower-numbered open name, unconditionally.
+        configured = {'m0': 'eth0', 'm2': 'eth2', 'm3': 'eth3'}
+        current = {'eth0': 'm0', 'eth2': 'm2', 'eth3': 'm3',
+                   'eth9': 'bb', 'eth8': 'aa'}
+        plan = resolver.compute_bootstrap_plan(configured, current, {})
+        self.assertEqual(plan.get('eth8'), 'eth1')
+        self.assertEqual(plan.get('eth9'), 'eth4')
+
+    def test_closed_subset_recovers_original_slot_assignment(self):
+        # the vyos-build check-qemu-install --ifnametest shape, at the
+        # function level: two NICs' original slots opened up in the same
+        # boot (one via full node deletion, one via hw-id-only deletion).
+        # PCIe distance and MAC are static per-NIC properties, so the two
+        # freed candidates' relative sort order is identical to their
+        # original first-boot assignment order - re-running the same
+        # ascending sort over just the two open names recovers each one's
+        # own original slot, with no pending-specific logic involved.
+        configured = {
+            '00:00:5e:00:53:00': 'eth0', '00:00:5e:00:53:01': 'eth1',
+            '00:00:5e:00:53:03': 'eth3', '00:00:5e:00:53:05': 'eth5',
+            '00:00:5e:00:53:06': 'eth6', '00:00:5e:00:53:07': 'eth7',
+        }
+        current = {name: mac for mac, name in configured.items()}
+        current.update({'eth9': '00:00:5e:00:53:02',
+                        'eth8': '00:00:5e:00:53:04'})
+        plan = resolver.compute_bootstrap_plan(configured, current, {})
+        self.assertEqual(plan.get('eth9'), 'eth2')
+        self.assertEqual(plan.get('eth8'), 'eth4')
+
+    def test_open_names_currently_squatted_by_a_rightful_mover_are_not_taken(self):
+        # real boot reproduction (via the resolver's own status file,
+        # captured mid-failure): the cosmetic fast-path this boot had
+        # every configured mac sitting on some OTHER configured mac's
+        # target name (a full rotation), including the two open names
+        # (eth1 - pending, eth6 - fully deleted) both currently squatted
+        # by macs that are about to move elsewhere via a rightful-owner
+        # move. existing_plan's SOURCE names looked "taken" at the exact
+        # moment this function ran, but safe_bulk_rename()'s two-phase
+        # staging vacates every source before any target is claimed - so
+        # they must not count as taken, or the two real candidates get
+        # needlessly pushed to fresh eth8/eth9-style slots instead of
+        # their own open names.
+        configured = {
+            '00:00:5e:00:53:00': 'eth0', '00:00:5e:00:53:02': 'eth2',
+            '00:00:5e:00:53:03': 'eth3', '00:00:5e:00:53:04': 'eth4',
+            '00:00:5e:00:53:05': 'eth5', '00:00:5e:00:53:07': 'eth7',
+        }
+        current = {
+            'eth4': '00:00:5e:00:53:00', 'eth6': '00:00:5e:00:53:02',
+            'eth7': '00:00:5e:00:53:03', 'eth2': '00:00:5e:00:53:04',
+            'eth3': '00:00:5e:00:53:05', 'eth1': '00:00:5e:00:53:07',
+            'eth0': '00:00:5e:00:53:06',  # unconfigured - squats on eth0
+            'eth5': '00:00:5e:00:53:01',  # unconfigured - squats on eth5
+        }
+        existing_plan = resolver.compute_rename_plan(configured, current,
+                                                      {'ethernet': {'eth1'},
+                                                       'wireless': set()})
+        plan = resolver.compute_bootstrap_plan(configured, current,
+                                                existing_plan)
+        self.assertEqual(plan.get('eth5'), 'eth1')
+        self.assertEqual(plan.get('eth0'), 'eth6')
+
+
+class TestSafeBulkRename(unittest.TestCase):
+    """The two-phase rename must accurately report what actually happened -
+    a phase-2 (scratch -> final target) failure must not be reported as a
+    successful rename, and must not leave the interface down indefinitely
+    under a name nothing else knows about.
+    """
+
+    def setUp(self):
+        patcher = mock.patch.object(resolver, 'get_ifindex',
+                                     side_effect=lambda name: name)
+        patcher.start()
+        self.addCleanup(patcher.stop)
+
+    def test_all_renames_succeed(self):
+        with mock.patch.object(resolver, 'run', return_value=0):
+            applied = resolver.safe_bulk_rename({'eth5': 'eth0'})
+        self.assertEqual(applied, {'eth5': 'eth0'})
+
+    def test_phase_two_failure_is_not_reported_as_applied(self):
+        # 'ip link set dev vyetheth5 name eth0' fails (exit 1); everything
+        # else (down, the phase-1 rename to scratch) succeeds
+        def fake_run(command, *_a, **_kw):
+            return 1 if command == 'ip link set dev vyetheth5 name eth0' else 0
+
+        with mock.patch.object(resolver, 'run', side_effect=fake_run):
+            applied = resolver.safe_bulk_rename({'eth5': 'eth0'})
+
+        self.assertNotIn('eth5', applied)
+        self.assertNotEqual(applied.get('eth5'), 'eth0')
+
+    def test_phase_two_failure_brings_scratch_name_back_up(self):
+        calls = []
+
+        def fake_run(command, *_a, **_kw):
+            calls.append(command)
+            return 1 if command == 'ip link set dev vyetheth5 name eth0' else 0
+
+        with mock.patch.object(resolver, 'run', side_effect=fake_run):
+            resolver.safe_bulk_rename({'eth5': 'eth0'})
+
+        self.assertIn('ip link set dev vyetheth5 up', calls)
+        self.assertNotIn('ip link set dev eth0 up', calls)
+
+    def test_one_failure_does_not_affect_other_renames_in_the_batch(self):
+        def fake_run(command, *_a, **_kw):
+            return 1 if command == 'ip link set dev vyetheth5 name eth0' else 0
+
+        with mock.patch.object(resolver, 'run', side_effect=fake_run):
+            applied = resolver.safe_bulk_rename({'eth5': 'eth0', 'eth9': 'eth1'})
+
+        self.assertNotIn('eth5', applied)
+        self.assertEqual(applied.get('eth9'), 'eth1')
+
+
+class TestGetPermanentMac(unittest.TestCase):
+    """Part of the original race is reading a MAC before the driver has
+    programmed the permanent address. Verify the ethtool-first,
+    sysfs-fallback behaviour, including drivers that report an all-zero
+    'unsupported' permanent address instead of failing outright.
+    """
+
+    def test_ethtool_permanent_address(self):
+        with mock.patch.object(
+                resolver, 'rc_cmd',
+                return_value=(0, 'Permanent address: aa:bb:cc:dd:ee:ff\n')):
+            self.assertEqual(resolver.get_permanent_mac('eth0'),
+                              'aa:bb:cc:dd:ee:ff')
+
+    def test_ethtool_zero_address_falls_back_to_sysfs(self):
+        with mock.patch.object(
+                resolver, 'rc_cmd',
+                return_value=(0, 'Permanent address: 00:00:00:00:00:00\n')), \
+             mock.patch('pathlib.Path.read_text',
+                        return_value='11:22:33:44:55:66\n'):
+            self.assertEqual(resolver.get_permanent_mac('eth0'),
+                              '11:22:33:44:55:66')
+
+    def test_ethtool_unsupported_falls_back_to_sysfs(self):
+        with mock.patch.object(
+                resolver, 'rc_cmd',
+                return_value=(1, 'Operation not supported')), \
+             mock.patch('pathlib.Path.read_text',
+                        return_value='11:22:33:44:55:66\n'):
+            self.assertEqual(resolver.get_permanent_mac('eth0'),
+                              '11:22:33:44:55:66')
+
+    def test_no_mac_available_returns_empty(self):
+        with mock.patch.object(resolver, 'rc_cmd', return_value=(1, '')), \
+             mock.patch('pathlib.Path.read_text', side_effect=OSError):
+            self.assertEqual(resolver.get_permanent_mac('eth0'), '')
+
+
+class TestDiscoverPhysicalInterfaces(unittest.TestCase):
+    """Only interfaces with a real bus 'device' link are candidates -
+    bridges/bonds/VLANs/veth must be excluded regardless of name, since
+    this replaces the racy udev DRIVERS=="?*" check with a stable,
+    post-settle sysfs read.
+    """
+
+    def setUp(self):
+        self.tmp = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.tmp, ignore_errors=True)
+
+        def make_iface(name, mac=None, has_device=True):
+            path = os.path.join(self.tmp, name)
+            os.mkdir(path)
+            if has_device:
+                os.mkdir(os.path.join(path, 'device'))
+            if mac:
+                with open(os.path.join(path, 'address'), 'w') as f:
+                    f.write(mac + '\n')
+
+        make_iface('eth0', mac='aa:aa:aa:aa:aa:00')
+        make_iface('eth1', mac='aa:aa:aa:aa:aa:01')
+        make_iface('br0', mac='aa:aa:aa:aa:aa:99', has_device=False)
+        make_iface('lo', has_device=False)
+
+    def test_only_physical_interfaces_with_mac(self):
+        with mock.patch.object(resolver, 'rc_cmd', return_value=(1, '')):
+            found = resolver.discover_physical_interfaces(self.tmp)
+        self.assertEqual(found, {
+            'eth0': 'aa:aa:aa:aa:aa:00',
+            'eth1': 'aa:aa:aa:aa:aa:01',
+        })
+        self.assertNotIn('br0', found)
+        self.assertNotIn('lo', found)
+
+
+class TestSyncRescanHints(unittest.TestCase):
+    """New/unconfigured hardware must still be surfaced to
+    vyos-interface-rescan.py, already-configured interfaces must not, and
+    hints left under a pre-rename name must not linger once the resolver
+    has moved that interface to its hw-id target.
+    """
+
+    def setUp(self):
+        self.tmp = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.tmp, ignore_errors=True)
+        self._orig_dir = resolver.vyos_udev_dir
+        resolver.vyos_udev_dir = self.tmp
+        self.addCleanup(setattr, resolver, 'vyos_udev_dir', self._orig_dir)
+
+    def test_writes_hint_for_unconfigured_interface(self):
+        resolver.sync_rescan_hints({'eth5': 'new-mac'}, configured={})
+        hint = os.path.join(self.tmp, 'eth5')
+        self.assertTrue(os.path.isfile(hint))
+        with open(hint) as f:
+            self.assertEqual(f.read(), 'new-mac')
+
+    def test_no_hint_for_configured_interface(self):
+        resolver.sync_rescan_hints({'eth0': 'm0'}, configured={'m0': 'eth0'})
+        self.assertFalse(os.path.exists(os.path.join(self.tmp, 'eth0')))
+
+    def test_stale_hint_removed_after_rename(self):
+        # udev's cosmetic fast-path wrote a hint under the pre-rename name;
+        # the resolver then moved that interface to its hw-id target.
+        stale = os.path.join(self.tmp, 'eth7')
+        with open(stale, 'w') as f:
+            f.write('m2')
+        resolver.sync_rescan_hints({'eth10': 'm2'}, configured={'m2': 'eth10'},
+                                    stale_names={'eth7'})
+        self.assertFalse(os.path.exists(stale))
+
+
+
+class TestMainFirstBootBootstrap(unittest.TestCase):
+    """Direct regression guard for the gap this feature closes: main()
+    used to leave a fully-unconfigured system's interfaces at whatever
+    racy cosmetic name they already had, with no settle wait at all, and
+    freeze that into the rescan hints vyos-interface-rescan.py persists.
+    """
+
+    def setUp(self):
+        self.udev_dir = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.udev_dir, ignore_errors=True)
+        self._orig_udev_dir = resolver.vyos_udev_dir
+        resolver.vyos_udev_dir = self.udev_dir
+        self.addCleanup(setattr, resolver, 'vyos_udev_dir', self._orig_udev_dir)
+
+        status_dir = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, status_dir, ignore_errors=True)
+        self._orig_status_file = resolver.status_file
+        resolver.status_file = resolver.Path(status_dir) / 'status.json'
+        self.addCleanup(setattr, resolver, 'status_file', self._orig_status_file)
+
+    def test_empty_configfile_bootstrap_renames_and_hints_new_names(self):
+        # a tiny fake kernel: name -> mac, mutated by simulated 'ip link'
+        # calls so discover_physical_interfaces() reflects renames for real
+        state = {'eth5': 'bb', 'eth2': 'aa'}  # cosmetic fast-path leftover
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value={}), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value={'ethernet': set(), 'wireless': set()}), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        hints = set(os.listdir(self.udev_dir))
+        # renamed into MAC-rank order: lower mac 'aa' -> eth0, higher 'bb' -> eth1
+        self.assertEqual(hints, {'eth0', 'eth1'})
+        with open(os.path.join(self.udev_dir, 'eth0')) as f:
+            self.assertEqual(f.read(), 'aa')
+        with open(os.path.join(self.udev_dir, 'eth1')) as f:
+            self.assertEqual(f.read(), 'bb')
+
+    def test_pending_node_still_settles_when_its_hardware_is_slow_to_appear(self):
+        # field report: a pending node ended up permanently bound to a
+        # fresh eth8/eth9-style name despite its own hardware genuinely
+        # being present - because that hardware (a slower driver, exactly
+        # the multi-vendor-NIC race this whole feature addresses) simply
+        # had not shown up in the FIRST, unsettled discover_physical_
+        # interfaces() snapshot wait_for_hardware() returns as soon as all
+        # already-CONFIGURED macs are found. Since that snapshot showed
+        # nothing unconfigured yet, main()'s gate into wait_for_settle()
+        # never even ran, giving the slow hardware zero extra time to
+        # appear before the boot gave up. A pending node in play must
+        # force wait_for_settle() to run regardless of what the early
+        # snapshot shows, so slower hardware still gets its chance.
+        configured = {'m0': 'eth0'}
+        pending = {'ethernet': {'eth1'}, 'wireless': set()}
+
+        calls = {'n': 0}
+
+        def fake_discover(*_a, **_kw):
+            calls['n'] += 1
+            if calls['n'] <= 2:
+                return {'eth0': 'm0'}  # m1's hardware not visible yet
+            return {'eth0': 'm0', 'eth9': 'm1'}  # now it has appeared
+
+        state = {'eth0': 'm0', 'eth9': 'm1'}
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        self.assertEqual(state.get('eth1'), 'm1')
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['reclaimed'], {'m1': 'eth1'})
+        self.assertEqual(status['pending_unresolved'], [])
+
+    def test_reported_reproduction_end_to_end(self):
+        # exact reported scenario: eth0/eth2 keep their hw-id, eth1's hw-id
+        # was deleted (the documented "NIC replaced" remediation) but its
+        # node - and an address setting - stay in config.boot. The same
+        # physical NIC (mac 'm1') must come back as 'eth1', not bootstrap
+        # past the floor to 'eth3', and must still get a rescan hint under
+        # 'eth1' so vyos-interface-rescan.py can refill its hw-id.
+        configured = {'m0': 'eth0', 'm2': 'eth2'}
+        pending = {'ethernet': {'eth1'}, 'wireless': set()}
+        # cosmetic fast-path already placed everything at its final
+        # hw-id'd name except the replaced NIC, which landed on a racy name
+        state = {'eth0': 'm0', 'eth2': 'm2', 'eth9': 'm1'}
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        # the NIC is back at 'eth1', not bootstrapped past the floor to 'eth3'
+        self.assertEqual(state.get('eth1'), 'm1')
+        self.assertNotIn('eth3', state)
+
+        # still gets a rescan hint under its reclaimed name, so
+        # vyos-interface-rescan.py can write the real hw-id into the
+        # existing 'eth1' node (preserving its other settings, e.g. address)
+        hints = set(os.listdir(self.udev_dir))
+        self.assertEqual(hints, {'eth1'})
+        with open(os.path.join(self.udev_dir, 'eth1')) as f:
+            self.assertEqual(f.read(), 'm1')
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['reclaimed'], {'m1': 'eth1'})
+        self.assertEqual(status['pending_unresolved'], [])
+
+    def test_fully_deleted_interfaces_backfill_their_gaps_end_to_end(self):
+        # reported scenario: eth3, eth6 and eth7 were fully deleted (not
+        # just their hw-id - the whole node, so get_pending_hwid_nodes()
+        # has nothing for them either) while eth0,1,2,4,5,8,9 stay
+        # configured. The three now-unconfigured NICs must backfill the
+        # gaps at 3/6/7 in MAC order, not bootstrap past the highest
+        # configured index (9) to 10/11/12.
+        configured = {
+            'm0': 'eth0', 'm1': 'eth1', 'm2': 'eth2', 'm4': 'eth4',
+            'm5': 'eth5', 'm8': 'eth8', 'm9': 'eth9',
+        }
+        pending = {'ethernet': set(), 'wireless': set()}
+        state = {name: mac for mac, name in configured.items()}
+        # realistic macs, deliberately NOT alphabetically matching their
+        # old slot, so the test can't pass by coincidence
+        state.update({'ethX': 'ff:ff:ff:ff:ff:07',
+                       'ethY': 'aa:aa:aa:aa:aa:03',
+                       'ethZ': 'cc:cc:cc:cc:cc:06'})
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        # the three gaps got backfilled in ascending MAC order, not pushed
+        # past the highest configured index to eth10/eth11/eth12
+        self.assertEqual(state.get('eth3'), 'aa:aa:aa:aa:aa:03')
+        self.assertEqual(state.get('eth6'), 'cc:cc:cc:cc:cc:06')
+        self.assertEqual(state.get('eth7'), 'ff:ff:ff:ff:ff:07')
+        self.assertNotIn('eth10', state)
+        self.assertNotIn('eth11', state)
+        self.assertNotIn('eth12', state)
+
+    def test_stray_leftover_interface_still_fills_both_open_names(self):
+        # field report: deleting only eth7's hw-id and rebooting produced
+        # "could not be safely auto-matched" instead of a clean reclaim,
+        # because a stray interface left over from an earlier, unrelated
+        # boot (e.g. a scratch vyethN name stuck after a failed rename)
+        # was also present, making this a 1 pending/2 candidate case. Both
+        # names now reliably get a real hw-id either way - the lower-
+        # sorted candidate takes the lower-numbered open name (the
+        # ordinary gap at eth3), the higher-sorted one takes the pending
+        # node - nothing is left unresolved, and there is no way to know
+        # (or need to know) which candidate was "really" eth7's own past
+        # hardware once its hw-id is gone.
+        configured = {
+            'm0': 'eth0', 'm1': 'eth1', 'm2': 'eth2', 'm4': 'eth4',
+            'm5': 'eth5', 'm6': 'eth6',
+        }
+        pending = {'ethernet': {'eth7'}, 'wireless': set()}
+        state = {name: mac for mac, name in configured.items()}
+        state.update({'eth9': 'aa:bb:cc:dd:ee:07',      # lower-sorted candidate
+                      'vyeth13': 'ff:ff:ff:ff:ff:99'})  # higher-sorted candidate
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        # the lower-sorted candidate fills the ordinary gap (eth3), the
+        # higher-sorted one fills the pending node (eth7) - both real,
+        # both deterministic, nothing left unresolved
+        self.assertEqual(state.get('eth3'), 'aa:bb:cc:dd:ee:07')
+        self.assertEqual(state.get('eth7'), 'ff:ff:ff:ff:ff:99')
+
+        hints = set(os.listdir(self.udev_dir))
+        self.assertEqual(hints, {'eth3', 'eth7'})
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['pending_unresolved'], [])
+        self.assertEqual(status['reclaimed'], {'ff:ff:ff:ff:ff:99': 'eth7'})
+
+    def test_second_pending_node_fills_lowest_numbered_first_when_hardware_is_short(self):
+        # two pending nodes (eth1 and eth7), but only one candidate showed
+        # up this boot - a hardware shortage, not ambiguity. The lower-
+        # numbered node fills; the higher-numbered one stays genuinely
+        # unresolved and reported, since there simply isn't enough
+        # hardware to satisfy both.
+        configured = {'m0': 'eth0'}
+        pending = {'ethernet': {'eth1', 'eth7'}, 'wireless': set()}
+        state = {'eth0': 'm0', 'eth9': 'aa:bb:cc:dd:ee:07'}
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        self.assertEqual(state.get('eth1'), 'aa:bb:cc:dd:ee:07')
+        self.assertNotIn('eth7', state)
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['pending_unresolved'], ['eth7'])
+        self.assertEqual(status['reclaimed'], {'aa:bb:cc:dd:ee:07': 'eth1'})
+
+    def test_two_candidates_for_one_pending_node_fill_deterministically(self):
+        # field report: deleting eth2's hw-id (leaving its node in place)
+        # produced "0 unconfigured candidates" on a later boot, because an
+        # EARLIER boot with 2 candidates present had left the pending node
+        # unresolved and its rightful hardware un-hinted, orphaning it.
+        # Per the deterministic-fill policy, one pending node with two
+        # candidates now reliably resolves: with only 'eth0' configured,
+        # 'eth1' is also a genuinely open name here, so the lower-sorted
+        # candidate fills it first and the higher-sorted one fills the
+        # pending node ('eth2') - nothing is left unresolved or un-hinted
+        # either way.
+        configured = {'m0': 'eth0'}
+        pending = {'ethernet': {'eth2'}, 'wireless': set()}
+        state = {
+            'eth0': 'm0',
+            'racyA': 'aa:bb:cc:dd:ee:02',  # lower-sorted candidate
+            'racyB': 'ff:ff:ff:ff:ff:99',  # higher-sorted candidate
+        }
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        # the lower-sorted candidate (racyA) fills the lower open name
+        # (eth1); the higher-sorted one (racyB) reclaims the pending node
+        self.assertEqual(state.get('eth1'), 'aa:bb:cc:dd:ee:02')
+        self.assertEqual(state.get('eth2'), 'ff:ff:ff:ff:ff:99')
+
+        hints = set(os.listdir(self.udev_dir))
+        self.assertEqual(hints, {'eth1', 'eth2'})
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['pending_unresolved'], [])
+        self.assertEqual(status['reclaimed'], {'ff:ff:ff:ff:ff:99': 'eth2'})
+
+    def test_two_pending_nodes_two_candidates_both_fill_deterministically(self):
+        # two NICs' hw-id were deleted before the same reboot (eth0 and
+        # eth2, nodes left in place), and both came back racily named.
+        # Sorted pending names (eth0 < eth2) pair with sorted candidates
+        # (by MAC here, since pcie_distance ties) - both fill in one boot,
+        # with no unresolved node left behind.
+        configured = {
+            'm1': 'eth1', 'm3': 'eth3', 'm4': 'eth4',
+            'm5': 'eth5', 'm6': 'eth6', 'm7': 'eth7',
+        }
+        pending = {'ethernet': {'eth0', 'eth2'}, 'wireless': set()}
+        state = {name: mac for mac, name in configured.items()}
+        state.update({
+            'racyA': 'aa:bb:cc:dd:ee:00',
+            'racyB': 'aa:bb:cc:dd:ee:02',
+        })
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        self.assertEqual(state.get('eth0'), 'aa:bb:cc:dd:ee:00')
+        self.assertEqual(state.get('eth2'), 'aa:bb:cc:dd:ee:02')
+
+        hints = set(os.listdir(self.udev_dir))
+        self.assertEqual(hints, {'eth0', 'eth2'})
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['pending_unresolved'], [])
+        self.assertEqual(status['reclaimed'], {
+            'aa:bb:cc:dd:ee:00': 'eth0',
+            'aa:bb:cc:dd:ee:02': 'eth2',
+        })
+
+    def test_squatting_pending_candidate_still_reclaims_correctly(self):
+        # field report: deleting eth7's hw-id (node left in place) produced
+        # a "0 unconfigured candidates" boot even though eth7's real
+        # hardware was present, and it later turned up permanently bound
+        # to a fresh eth8/eth9-style name. Root cause: eth7's hardware
+        # (mac07) happened to be squatting on eth2's configured hw-id slot
+        # this boot (probe-order scrambling) - compute_rename_plan()
+        # already scheduled it for eviction, which used to make
+        # unmatched_candidates() skip it entirely, so it never reached the
+        # ascending fill and fell through to a stale, unrelated fallback
+        # destination instead. A squatting candidate must still reclaim
+        # its pending node exactly like a non-squatting one would, when it
+        # is the only open name and the only candidate this boot.
+        configured = {
+            'm0': 'eth0', 'm1': 'eth1', 'm2': 'eth2', 'm3': 'eth3',
+            'm4': 'eth4', 'm5': 'eth5', 'm6': 'eth6',
+        }
+        pending = {'ethernet': {'eth7'}, 'wireless': set()}
+        state = {name: mac for mac, name in configured.items()}
+        state.update({
+            'eth2': 'aa:bb:cc:dd:ee:07',  # eth7's hardware squats on eth2
+            'eth9': 'm2',                 # m2's rightful NIC, racy this boot
+        })
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        # m2 still lands on its own configured slot, and the squatter
+        # reclaims 'eth7' - not some unrelated fresh bootstrap slot
+        self.assertEqual(state.get('eth2'), 'm2')
+        self.assertEqual(state.get('eth7'), 'aa:bb:cc:dd:ee:07')
+        self.assertNotIn('eth8', state)
+        self.assertNotIn('eth9', state)
+
+        hints = set(os.listdir(self.udev_dir))
+        self.assertEqual(hints, {'eth7'})
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['reclaimed'], {'aa:bb:cc:dd:ee:07': 'eth7'})
+        self.assertEqual(status['pending_unresolved'], [])
+
+    def test_squatting_candidate_and_extra_candidate_fill_ascending(self):
+        # same squatter-eviction shape as the test above, but with a
+        # second, unrelated candidate also present this boot, and exactly
+        # two open names (one ordinary gap, one pending node) for the two
+        # candidates - a closed system. The lower-sorted candidate (the
+        # squatter, evicted off of a configured slot) takes the lower-
+        # numbered open name (the gap); the higher-sorted one takes the
+        # higher-numbered one (the pending node) - both get a real,
+        # deterministic hw-id, one of them attributed as a reclaim.
+        configured = {
+            'm0': 'eth0', 'm1': 'eth1', 'm2': 'eth2',
+            'm3': 'eth3', 'm4': 'eth4', 'm5': 'eth5',
+        }
+        pending = {'ethernet': {'eth7'}, 'wireless': set()}
+        state = {name: mac for mac, name in configured.items()}
+        state.update({
+            'eth3': 'aa:bb:cc:dd:ee:07',   # squats on m3's configured slot
+            'eth9': 'm3',                  # m3's rightful NIC, racy this boot
+            'racyC': 'ff:ff:ff:ff:ff:99',  # unrelated leftover candidate
+        })
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        # m3 still lands on its own configured slot; the squatter takes
+        # the lower-numbered open gap, the stray takes the pending node
+        self.assertEqual(state.get('eth3'), 'm3')
+        self.assertEqual(state.get('eth6'), 'aa:bb:cc:dd:ee:07')
+        self.assertEqual(state.get('eth7'), 'ff:ff:ff:ff:ff:99')
+
+        hints = set(os.listdir(self.udev_dir))
+        self.assertEqual(hints, {'eth6', 'eth7'})
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['pending_unresolved'], [])
+        self.assertEqual(status['reclaimed'], {'ff:ff:ff:ff:ff:99': 'eth7'})
+
+    def test_gap_backfill_and_pending_reclaim_coexist_in_the_same_boot(self):
+        # the exact vyos-build check-qemu-install --ifnametest shape: one
+        # interface's whole config node is fully deleted (a free numeric
+        # gap) while a DIFFERENT interface's hw-id alone is deleted (a
+        # pending node) in the very same reboot
+        # (del_idx, hwid_idx = random.sample(range(8), 2)). Both must
+        # resolve independently in one boot: the pending node (eth2)
+        # reliably gets a real hw-id, and the fully-deleted gap (eth5)
+        # backfills with whatever hardware is left - no manual step
+        # needed for either.
+        configured = {
+            'm0': 'eth0', 'm1': 'eth1', 'm3': 'eth3', 'm4': 'eth4',
+            'm6': 'eth6', 'm8': 'eth8', 'm9': 'eth9',
+        }
+        pending = {'ethernet': {'eth2'}, 'wireless': set()}
+        state = {name: mac for mac, name in configured.items()}
+        state.update({
+            'eth7': 'aa:bb:cc:dd:ee:02',  # eth2's real hardware, racy this boot
+            'eth5': 'ff:ff:ff:ff:ff:05',  # eth5 fully deleted, its own hardware freed
+        })
+
+        def fake_discover(*_a, **_kw):
+            return dict(state)
+
+        def fake_run(command, *_a, **_kw):
+            parts = command.split()
+            if 'name' in parts:
+                old = parts[parts.index('dev') + 1]
+                new = parts[parts.index('name') + 1]
+                if old in state:
+                    state[new] = state.pop(old)
+            return 0
+
+        with mock.patch.object(resolver, 'get_configfile_interfaces',
+                                return_value=configured), \
+             mock.patch.object(resolver, 'get_pending_hwid_nodes',
+                                return_value=pending), \
+             mock.patch.object(resolver, 'discover_physical_interfaces',
+                                side_effect=fake_discover), \
+             mock.patch.object(resolver, 'is_wireless_interface',
+                                return_value=False), \
+             mock.patch.object(resolver, 'pcie_distance', return_value=0), \
+             mock.patch.object(resolver, 'run', side_effect=fake_run), \
+             mock.patch('time.sleep'):
+            resolver.main()
+
+        self.assertEqual(state.get('eth2'), 'aa:bb:cc:dd:ee:02')
+        self.assertEqual(state.get('eth5'), 'ff:ff:ff:ff:ff:05')
+
+        status = json.loads(resolver.status_file.read_text())
+        self.assertEqual(status['pending_unresolved'], [])
+        self.assertEqual(status['reclaimed'], {'aa:bb:cc:dd:ee:02': 'eth2'})
+
+
+class TestWriteStatus(unittest.TestCase):
+    """A pending node that couldn't be safely auto-matched must be
+    reported so vyos-router can surface a boot-time warning - it must
+    never regress into another silent, buried-syslog-only failure like
+    the one this whole fix closes.
+    """
+
+    def setUp(self):
+        status_dir = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, status_dir, ignore_errors=True)
+        self._orig_status_file = resolver.status_file
+        resolver.status_file = resolver.Path(status_dir) / 'status.json'
+        self.addCleanup(setattr, resolver, 'status_file', self._orig_status_file)
+
+    def _read_status(self):
+        return json.loads(resolver.status_file.read_text())
+
+    def test_pending_unresolved_reported_when_no_match(self):
+        pending = {'ethernet': {'eth1', 'eth4'}, 'wireless': set()}
+        resolver.write_status({}, {}, set(), {}, pending=pending, reclaimed={})
+        status = self._read_status()
+        self.assertEqual(status['pending_unresolved'], ['eth1', 'eth4'])
+
+    def test_reclaimed_not_reported_as_unresolved(self):
+        pending = {'ethernet': {'eth1'}, 'wireless': set()}
+        reclaimed = {'m1': 'eth1'}
+        resolver.write_status({}, {}, set(), {}, pending=pending,
+                               reclaimed=reclaimed)
+        status = self._read_status()
+        self.assertEqual(status['pending_unresolved'], [])
+        self.assertEqual(status['reclaimed'], {'m1': 'eth1'})
+
+    def test_no_pending_no_crash(self):
+        resolver.write_status({}, {}, set(), {})
+        status = self._read_status()
+        self.assertEqual(status['pending_unresolved'], [])
+        self.assertEqual(status['reclaimed'], {})
+
+    def test_unconfigured_candidates_reported_for_diagnosis(self):
+        # the full unmatched_candidates() list from main(), so an
+        # ambiguous reclaim (zero or multiple candidates for a pending
+        # node) is diagnosable from this one file alone - which physical
+        # interfaces were actually competing - without needing a separate
+        # `ip -br link show` or `show configuration commands` to
+        # reconstruct the same picture by hand.
+        pending = {'ethernet': {'eth7'}, 'wireless': set()}
+        candidates = [('aa:bb:cc:dd:ee:07', 'eth9'), ('aa:bb:cc:dd:ee:99', 'vyeth13')]
+        resolver.write_status({}, {}, set(), {}, pending=pending,
+                               reclaimed={}, candidates=candidates)
+        status = self._read_status()
+        self.assertEqual(status['pending_unresolved'], ['eth7'])
+        self.assertEqual(status['unconfigured_candidates'], {
+            'eth9': 'aa:bb:cc:dd:ee:07',
+            'vyeth13': 'aa:bb:cc:dd:ee:99',
+        })
+
+    def test_unconfigured_candidates_defaults_empty(self):
+        resolver.write_status({}, {}, set(), {})
+        status = self._read_status()
+        self.assertEqual(status['unconfigured_candidates'], {})
+
+
+class TestBootOrdering(unittest.TestCase):
+    """Regression guard for the config.boot availability corner case:
+    /opt/vyatta/etc/config/config.boot does not exist until vyos-router
+    mounts (and, for an encrypted config volume, decrypts) the config
+    directory itself. vyos-net-name-resolve must be started explicitly
+    from inside vyos-router after that point, and must not be
+    reintroduced as an independently-scheduled unit ordered before
+    vyos-router/network-pre.target/cloud-init.
+    """
+
+    def setUp(self):
+        path = os.path.join(_here, '../init/vyos-router')
+        with open(path) as f:
+            self.lines = f.readlines()
+
+    def _first_index(self, needle):
+        for i, line in enumerate(self.lines):
+            if needle in line:
+                return i
+        self.fail(f"'{needle}' not found in src/init/vyos-router")
+
+    def test_resolver_runs_after_migrate_and_before_config_apply(self):
+        # search for call SITES, not the function definitions further up
+        migrate = self._first_index('migrate_bootfile || overall_status=1')
+        resolve = self._first_index(
+            'systemctl start vyos-net-name-resolve.service')
+        update_iface = self._first_index('update_interface_config || overall_status=1')
+        load_boot = self._first_index('disabled configure || load_bootfile')
+
+        self.assertLess(migrate, resolve,
+            'resolver must run after config.boot is migrated/current')
+        self.assertLess(resolve, update_iface,
+            'resolver must run before new-hardware rescan consumes its hints')
+        self.assertLess(resolve, load_boot,
+            'resolver must run before the CLI config is applied')
+
+    def test_service_unit_not_independently_ordered_before_vyos_router(self):
+        path = os.path.join(_here, '../systemd/vyos-net-name-resolve.service')
+        with open(path) as f:
+            unit = f.read()
+        self.assertNotIn('Before=vyos-router.service', unit)
+        self.assertNotIn('Before=network-pre.target', unit)
+        self.assertNotIn('WantedBy=', unit)
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/src/udev/vyos_net_name b/src/udev/vyos_net_name
index f5c3b9f1b..388cc78be 100755
--- a/src/udev/vyos_net_name
+++ b/src/udev/vyos_net_name
@@ -19,20 +19,28 @@ import re
 import time
 import logging
 import logging.handlers
-import tempfile
 from pathlib import Path
 from sys import argv
 
-from vyos.configtree import ConfigTree
 from vyos.defaults import directories
 from vyos.utils.process import cmdl
 from vyos.utils.boot import boot_configuration_complete
 from vyos.utils.locking import Lock
-from vyos.migrate import ConfigMigrate
 
 # Define variables
 vyos_udev_dir = directories['vyos_udev_dir']
-config_path = '/opt/vyatta/etc/config/config.boot'
+
+# NOTE: this script only picks a provisional name for a physical interface
+# as it is discovered by udev - it is a best-effort placeholder and does
+# NOT look at 'hw-id' in config.boot. The authoritative, hw-id based name
+# (if one is configured) is applied afterwards, once, by
+# vyos-net-name-resolve.py (src/system/vyos-net-name-resolve.py), which
+# runs after all hardware has settled. Deciding hw-id names here, from a
+# single per-uevent sysfs snapshot, is what caused interface names to be
+# unreliable on systems with multiple NIC vendors/drivers: the DRIVERS
+# attribute and the interface's permanent MAC address are not guaranteed
+# to be populated yet at the moment a single "add" uevent is evaluated,
+# and there is no second chance to re-evaluate it.
 
 
 def is_available(intfs: dict, intf_name: str) -> bool:
@@ -44,16 +52,24 @@ def is_available(intfs: dict, intf_name: str) -> bool:
 
 def find_available(intfs: dict, prefix: str) -> str:
     """Find lowest indexed interface name that is not assigned"""
-    index_list = [
-        int(x.replace(prefix, '')) for x in list(intfs.values()) if prefix in x
-    ]
+    index_list = []
+    for x in intfs.values():
+        if not x.startswith(prefix):
+            continue
+        suffix = x[len(prefix):]
+        if suffix.isdigit():
+            index_list.append(int(suffix))
+
+    if not index_list:
+        return f'{prefix}0'
+
     index_list.sort()
     # find 'holes' in list, if any
     missing = sorted(set(range(index_list[0], index_list[-1])) - set(index_list))
     if missing:
         return f'{prefix}{missing[0]}'
 
-    return f'{prefix}{len(index_list)}'
+    return f'{prefix}{index_list[-1] + 1}'
 
 
 def mod_ifname(ifname: str) -> str:
@@ -89,7 +105,10 @@ def get_biosdevname(ifname: str) -> str:
     try:
         biosname = cmdl(['/sbin/biosdevname', '--policy', 'all_ethN', '-i', ifname])
     except Exception as e:
-        logger.error(f'biosdevname error: {e}')
+        # expected/harmless on most virtualized and some bare-metal
+        # systems - see the XXX above; the caller already falls back to
+        # mod_ifname()'s guess, so this isn't worth more than a debug note
+        logger.debug(f'biosdevname unavailable for {ifname}: {e}')
         biosname = ''
 
     return intf if biosname == '' else biosname
@@ -117,81 +136,6 @@ def leave_rescan_hint(intf_name: str, hwid: str):
         logger.critical(f'OSError {e}')
 
 
-def get_configfile_interfaces() -> dict:
-    """Read existing interfaces from config file"""
-    interfaces: dict = {}
-
-    if not os.path.isfile(config_path):
-        # If the case, then we are running off of livecd; return empty
-        return interfaces
-
-    try:
-        with open(config_path) as f:
-            config_file = f.read()
-    except OSError as e:
-        logger.critical(f'OSError {e}')
-        exit(1)
-
-    try:
-        config = ConfigTree(config_file)
-    except Exception:
-        try:
-            logger.debug('updating component version string syntax')
-            # this will update the component version string syntax,
-            # required for updates 1.2 --> 1.3/1.4
-            with tempfile.NamedTemporaryFile() as fp:
-                with open(fp.name, 'w') as fd:
-                    fd.write(config_file)
-                config_migrate = ConfigMigrate(fp.name)
-                if config_migrate.syntax_update_needed():
-                    config_migrate.update_syntax()
-                    config_migrate.write_config()
-                with open(fp.name) as fd:
-                    config_file = fd.read()
-
-            config = ConfigTree(config_file)
-
-        except Exception as e:
-            logger.critical(f'ConfigTree error: {e}')
-            exit(1)
-
-    base = ['interfaces', 'ethernet']
-    if config.exists(base):
-        eth_intfs = config.list_nodes(base)
-        for intf in eth_intfs:
-            path = base + [intf, 'hw-id']
-            if not config.exists(path):
-                logger.warning(f"no 'hw-id' entry for {intf}")
-                continue
-            hwid = config.return_value(path)
-            if hwid in list(interfaces):
-                logger.warning(
-                    f'multiple entries for {hwid}: {interfaces[hwid]}, {intf}'
-                )
-                continue
-            interfaces[hwid] = intf
-
-    base = ['interfaces', 'wireless']
-    if config.exists(base):
-        wlan_intfs = config.list_nodes(base)
-        for intf in wlan_intfs:
-            path = base + [intf, 'hw-id']
-            if not config.exists(path):
-                logger.warning(f"no 'hw-id' entry for {intf}")
-                continue
-            hwid = config.return_value(path)
-            if hwid in list(interfaces):
-                logger.warning(
-                    f'multiple entries for {hwid}: {interfaces[hwid]}, {intf}'
-                )
-                continue
-            interfaces[hwid] = intf
-
-    logger.debug(f'config file entries: {interfaces}')
-
-    return interfaces
-
-
 def add_assigned_interfaces(intfs: dict):
     """Add interfaces found by previous invocation of udev rule"""
     if not os.path.isdir(vyos_udev_dir):
@@ -209,30 +153,25 @@ def add_assigned_interfaces(intfs: dict):
 
 
 def on_boot_event(intf_name: str, hwid: str, predefined: str = '') -> str:
-    """Called on boot by vyos-router: 'coldplug' in vyatta_net_name"""
-    logger.info(f'lookup {intf_name}, {hwid}')
-    interfaces = get_configfile_interfaces()
-    logger.debug(f'config file interfaces are {interfaces}')
-
-    if hwid in list(interfaces):
-        logger.info(f"use mapping from config file: '{hwid}' -> '{interfaces[hwid]}'")
-        return interfaces[hwid]
+    """Called on boot by vyos-router: 'coldplug' in vyatta_net_name
 
+    Picks a provisional name only - see the module docstring. hw-id from
+    config.boot is deliberately NOT consulted here.
+    """
+    interfaces: dict = {}
     add_assigned_interfaces(interfaces)
-    logger.debug(f'adding assigned interfaces: {interfaces}')
+    logger.debug(f'{intf_name} ({hwid}): already assigned this boot: {interfaces}')
 
     if predefined:
         newname = predefined
-        logger.info(f"predefined interface name for '{intf_name}' is '{newname}'")
     else:
         newname = get_biosdevname(intf_name)
-        logger.info(f"biosdevname returned '{newname}' for '{intf_name}'")
 
     if not is_available(interfaces, newname):
         prefix = re.sub(r'\d+$', '', newname)
         newname = find_available(interfaces, prefix)
 
-    logger.info(f"new name for '{intf_name}' is '{newname}'")
+    logger.info(f"{intf_name} ({hwid}) -> '{newname}'")
 
     leave_rescan_hint(newname, hwid)
 
@@ -252,9 +191,9 @@ if __name__ == '__main__':
 
     logger = logging.getLogger()
     logger.addHandler(syslog_handler)
-    logger.setLevel(logging.DEBUG)
+    logger.setLevel(logging.INFO)
 
-    logger.debug(f'Started with arguments: {argv}')
+    logger.debug(f'started with arguments: {argv}')
 
     if len(argv) > 3:
         predef_name = argv[3]
@@ -266,11 +205,6 @@ if __name__ == '__main__':
     lock.acquire(60)
 
     if not boot_configuration_complete():
-        res = on_boot_event(argv[1], argv[2], predefined=predef_name)
-        logger.debug(f'on boot, returned name is {res}')
-        print(res)
-    else:
-        logger.debug('boot configuration complete')
+        print(on_boot_event(argv[1], argv[2], predefined=predef_name))
 
     lock.release()
-    logger.debug('Finished')