fix(gc-hosts): filter discovered guests against flake to exclude non-NixOS hosts

pve1 runs non-NixOS guests (FreeIPA domain-controller, Proxmox Data Manager, etc.)
alongside NixOS ones. Validate each discovered hostname against the set of
hostnames defined in nixosConfigurations before adding it to the gc list.

Brings back the flake eval but uses it correctly: extract all hostname values
(not target-name keys) to build a filter set, then only include pve1 guests
whose name matches a flake-managed NixOS host.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/gc-hosts.sh

@@ -0,0 +1,237 @@
+#!/usr/bin/env bash
+# gc-hosts.sh — Run nix-collect-garbage -d on all live NixOS hosts.
+#
+# The host list is rebuilt on every run:
+#   1. This workstation (nixos) — always first
+#   2. pve1 — always second (non-NixOS Proxmox node with Nix installed)
+#   3. Every NixOS guest currently running on pve1 (discovered via pct/qm list)
+#
+# nix-cache is excluded: gc-ing the shared binary cache evicts store paths
+# that other hosts depend on for substitution.
+#
+# NixOS hosts: tries "sudo -n nix-collect-garbage -d" first (works when
+# wheelNeedsPassword = false, e.g. the HA cluster).  Falls back to user-level
+# "nix-collect-garbage -d" if sudo needs a password — still collects
+# unreferenced store paths and old nixos-user profile generations, but leaves
+# old system generations in place.
+# pve1: runs "bash -l -c nix-collect-garbage -d" as the login user so
+# /etc/profile is sourced and the Nix daemon's PATH is set up automatically.
+#
+# Usage (from repo root):
+#   bash scripts/gc-hosts.sh [--dry-run]
+
+set -euo pipefail
+cd "$(dirname "$0")/.."
+source scripts/env.sh 2>/dev/null || true
+source scripts/lib/nix-eval.sh 2>/dev/null || true
+
+# ── config ────────────────────────────────────────────────────────────────────
+
+: "${MAX_JOBS:=8}"
+: "${NIXOS_USER:=nixos}"
+: "${PVE1_SSH_USER:=${PROXMOX_SSH_USER:-wayne}}"
+
+# GC connections use BatchMode — no interactive prompts, just succeed or fail.
+SSH_OPTS=(-o StrictHostKeyChecking=no -o BatchMode=yes -o ConnectTimeout=10)
+# Discovery connections do NOT use BatchMode so that sudo can prompt if needed
+# (pct/qm list require root access on Proxmox).
+SSH_QUERY_OPTS=(-o StrictHostKeyChecking=no -o ConnectTimeout=10)
+
+DRY_RUN=0
+for arg in "$@"; do
+  case "$arg" in
+    --dry-run) DRY_RUN=1 ;;
+    *) echo "Unknown option: $arg" >&2; exit 1 ;;
+  esac
+done
+
+# ── build the host list ───────────────────────────────────────────────────────
+
+# ORDERED_HOSTS: names in display/execution order.
+# HOST_TARGET[name]: SSH target string (user@host).
+# HOST_TYPE[name]: "nixos" (try sudo gc, fallback user) | "nix" (login-shell gc).
+declare -a  ORDERED_HOSTS=()
+declare -A  HOST_TARGET=()
+declare -A  HOST_TYPE=()
+declare -A  _SEEN_HOSTNAMES=()   # dedup tracker
+
+_add_host() {
+  local name="$1" target="$2" type="$3"
+  if [[ -n "${_SEEN_HOSTNAMES[$name]+_}" ]]; then return; fi
+  _SEEN_HOSTNAMES[$name]=1
+  ORDERED_HOSTS+=("$name")
+  HOST_TARGET[$name]="$target"
+  HOST_TYPE[$name]="$type"
+}
+
+# 1. Workstation (hard-wired first)
+_add_host "nixos" "${NIXOS_USER}@nixos" "nixos"
+
+# 2. pve1 (hard-wired second; non-NixOS, no system generations)
+_add_host "pve1" "${PVE1_SSH_USER}@${PVE1_HOST}" "nix"
+
+# 3. Dynamically discover running NixOS guests on pve1
+#
+# create-proxmox-resource.sh names every guest after its NixOS hostname:
+#   pct create ... --hostname <nixos-hostname>  (LXC)
+#   qm  create ... --name    <nixos-hostname>   (VM)
+# So pct/qm list output already contains the NixOS hostname directly.
+# We validate against the flake to filter out non-NixOS guests on pve1
+# (e.g. FreeIPA, Proxmox Backup Server) that share the same Proxmox node.
+echo "Discovering running guests on ${PVE1_HOST}..."
+
+# Eval the flake once to get the set of hostnames that are actually NixOS.
+# Values are NixOS hostnames (e.g. "docker"); keys are flake targets ("lxc-docker").
+nixos_hostnames=""
+nixos_hostnames="$(
+  nix eval --json "${NIX_EVAL_FLAGS[@]}" .#nixosConfigurations \
+    --apply 'cfgs: builtins.attrValues (builtins.mapAttrs (_: cfg: cfg.config.networking.hostName) cfgs)' \
+    2>/dev/null | jq -r '.[]' | sort -u
+)" || { echo "  warning: flake eval failed — non-NixOS guests will not be filtered" >&2; }
+
+# SSH_QUERY_OPTS (no BatchMode) so sudo can prompt if needed for pct/qm.
+if ssh "${SSH_QUERY_OPTS[@]}" "${PVE1_SSH_USER}@${PVE1_HOST}" "true" 2>/dev/null; then
+  running_guests="$(
+    ssh "${SSH_QUERY_OPTS[@]}" "${PVE1_SSH_USER}@${PVE1_HOST}" bash -s <<'DISCOVER'
+sudo pct list 2>/dev/null | awk 'NR>1 && $2=="running" { print $NF }'
+sudo qm  list 2>/dev/null | awk 'NR>1 && $3=="running" { print $2  }'
+DISCOVER
+  )" || running_guests=""
+
+  while IFS= read -r hostname; do
+    [[ -z "$hostname" ]] && continue
+    # Exclude nix-cache.
+    case "$hostname" in *nix-cache*) continue ;; esac
+    # Skip if not a flake-managed NixOS host (filters non-NixOS pve1 guests).
+    if [[ -n "$nixos_hostnames" ]] && ! grep -qxF "$hostname" <<< "$nixos_hostnames"; then
+      continue
+    fi
+    # Skip if already in the list (e.g. a proxmox-gui guest whose hostname is nixos).
+    if [[ -n "${_SEEN_HOSTNAMES[$hostname]+_}" ]]; then continue; fi
+
+    echo "  + $hostname"
+    _add_host "$hostname" "${NIXOS_USER}@${hostname}" "nixos"
+  done <<< "$(echo "$running_guests" | sort -u)"
+else
+  echo "  warning: ${PVE1_HOST} unreachable — skipping dynamic host discovery" >&2
+fi
+
+echo ""
+echo "Hosts: ${ORDERED_HOSTS[*]}"
+echo ""
+
+# ── dry-run ───────────────────────────────────────────────────────────────────
+
+if [[ "$DRY_RUN" -eq 1 ]]; then
+  echo "[dry-run] commands that would run:"
+  for host in "${ORDERED_HOSTS[@]}"; do
+    target="${HOST_TARGET[$host]}"
+    type="${HOST_TYPE[$host]}"
+    if [[ "$type" == "nixos" ]]; then
+      echo "  ssh ${SSH_OPTS[*]} $target 'sudo -n nix-collect-garbage -d'"
+      echo "  # fallback: ssh ... $target 'nix-collect-garbage -d'"
+    else
+      echo "  ssh ${SSH_OPTS[*]} $target 'bash -l -c nix-collect-garbage -d'"
+    fi
+  done
+  exit 0
+fi
+
+# ── gc worker ─────────────────────────────────────────────────────────────────
+
+gc_one() {
+  local host="$1" target="${HOST_TARGET[$1]}" type="${HOST_TYPE[$1]}" logfile="$2"
+
+  if ! ssh "${SSH_OPTS[@]}" "$target" "true" 2>>"$logfile"; then
+    echo "unreachable"; return
+  fi
+
+  if [[ "$type" == "nixos" ]]; then
+    if ssh "${SSH_OPTS[@]}" "$target" "sudo -n nix-collect-garbage -d" \
+        >>"$logfile" 2>>"$logfile"; then
+      echo "ok(sudo)"; return
+    fi
+    echo "[sudo needs password — falling back to user-level gc]" >>"$logfile"
+    if ssh "${SSH_OPTS[@]}" "$target" "nix-collect-garbage -d" \
+        >>"$logfile" 2>>"$logfile"; then
+      echo "ok(user)"; return
+    fi
+  else
+    # Non-NixOS node: use a login shell so /etc/profile is sourced and the
+    # Nix daemon's bin dir is on PATH (set up by /etc/profile.d/nix-daemon.sh
+    # which the Nix installer adds to /etc/profile).
+    if ssh "${SSH_OPTS[@]}" "$target" "bash -l -c 'nix-collect-garbage -d'" \
+        >>"$logfile" 2>>"$logfile"; then
+      echo "ok"; return
+    fi
+  fi
+
+  echo "failed:$?"
+}
+
+# ── parallel execution ────────────────────────────────────────────────────────
+
+echo "Running gc on ${#ORDERED_HOSTS[@]} hosts (up to ${MAX_JOBS} parallel)..."
+echo ""
+
+TMPDIR_GC="$(mktemp -d)"
+trap 'rm -rf "$TMPDIR_GC"' EXIT
+
+declare -A LOGS=()
+job_count=0
+
+for host in "${ORDERED_HOSTS[@]}"; do
+  logfile="${TMPDIR_GC}/${host}.log"
+  resultfile="${TMPDIR_GC}/${host}.result"
+  LOGS[$host]="$logfile"
+  : > "$logfile"
+
+  ( result="$(gc_one "$host" "$logfile")"; echo "$result" > "$resultfile" ) &
+
+  (( job_count++ )) || true
+  if [[ "$job_count" -ge "$MAX_JOBS" ]]; then
+    wait -n 2>/dev/null || wait
+    (( job_count-- )) || true
+  fi
+done
+
+wait
+
+# ── summary ───────────────────────────────────────────────────────────────────
+
+echo "Results:"
+echo "──────────────────────────────"
+
+ok_hosts=()
+warn_hosts=()
+fail_hosts=()
+
+for host in "${ORDERED_HOSTS[@]}"; do
+  result="$(cat "${TMPDIR_GC}/${host}.result" 2>/dev/null || echo "failed:missing")"
+  case "$result" in
+    ok|"ok(sudo)"|"ok(user)")
+      printf "  %-22s  %s\n" "$host" "$result"
+      ok_hosts+=("$host") ;;
+    unreachable)
+      printf "  %-22s  UNREACHABLE\n" "$host"
+      warn_hosts+=("$host") ;;
+    *)
+      printf "  %-22s  FAILED (%s)\n" "$host" "$result"
+      fail_hosts+=("$host") ;;
+  esac
+done
+
+echo ""
+echo "  ${#ok_hosts[@]} succeeded, ${#warn_hosts[@]} unreachable, ${#fail_hosts[@]} failed"
+
+for host in "${warn_hosts[@]+"${warn_hosts[@]}"}" "${fail_hosts[@]+"${fail_hosts[@]}"}"; do
+  logfile="${LOGS[$host]}"
+  if [[ -s "$logfile" ]]; then
+    echo ""
+    echo "── $host ──"
+    cat "$logfile"
+  fi
+done
+
+echo ""
+[[ "${#fail_hosts[@]}" -eq 0 ]]