feat: add guarded bootstrap undo

CHANGELOG.md

@@ -13,6 +13,7 @@ on the way to cutting its first release, and this file starts there.
 - `rig platform` prints a stable machine `ID`, derived from `/etc/machine-id`, never the raw value (#95)
 - Platform, drill, docs and labels changes receive dedicated scope labels (#119)
 - CI drills the install lifecycle against a real tree — install from the checkout, converge to an empty diff, uninstall to proven absence (#106)
+- `rig bootstrap --undo` removes only a tailnet join rig can prove it made (#63)
 - `kimi-box` joins the box tenant roles — the Kimi CLI agent guest (#109)
 - The `changelog-armed` guard returns, version-keyed (#112, ceremony#13)
 - The `.ceremony/` doctrine mirror, verified by `docs-sync` on every PR (#112, ceremony#19)

bin/rig

@@ -33,6 +33,10 @@ commands:
       tenant roles); custom and workstation take none. join=login
       (workstation) needs no key: interactive login, node must come up
       untagged. Run as root.
+  bootstrap --undo
+      Leave the tailnet only when /etc/rig/role proves rig performed the
+      join, then remove that marker. Refuses for pre-existing or old unknown
+      joins, and while a GitHub runner is installed. Run as root.
   bootstrap <claude-box|codex-box|grok-box|kimi-box|staging-box> [--user <name>]
       The box TENANT roles: converge a box-minted guest. The '-box' suffix
       names the family (a guest, vs the '-server' machine roles above).

commands/bootstrap-undo.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# rig bootstrap --undo — remove only off-box state rig can prove it created.
+set -euo pipefail
+
+log() { printf 'rig-bootstrap: %s\n' "$*"; }
+die() { printf 'rig-bootstrap: ERROR: %s\n' "$*" >&2; exit 1; }
+
+MARKER="${RIG_ROLE_MARKER:-/etc/rig/role}"
+RUNNER_DIR="${RIG_RUNNER_DIR:-/home/github-runner/actions-runner}"
+
+[ "$(id -u)" -eq 0 ] || die "must run as root"
+[ -e "$MARKER" ] || die "no /etc/rig/role marker — refusing to touch the tailnet"
+
+if [ -e "$RUNNER_DIR/.runner" ]; then
+  die "a GitHub runner is installed — run 'rig runner remove' first so undo does not leave a ghost runner in the repository"
+fi
+
+join_by=""
+while IFS= read -r field; do
+  case "$field" in
+    join-by=*) join_by="${field#join-by=}" ;;
+  esac
+done < <(tr '[:space:]' '\n' < "$MARKER")
+
+case "$join_by" in
+  rig) ;;
+  preexisting)
+    die "the tailnet join predates this bootstrap run (join-by=preexisting), so rig will not remove state it did not create; run 'tailscale logout' by hand if that is intended" ;;
+  "")
+    die "the role marker predates join-by provenance, so rig cannot prove it made this tailnet join and will not remove it; re-run bootstrap to write a current marker, or run 'tailscale logout' by hand" ;;
+  *)
+    die "the role marker has unknown join-by=$join_by, so rig cannot prove it made this tailnet join and will not remove it; run 'tailscale logout' by hand if that is intended" ;;
+esac
+
+# The same back-out/keep law as first-join verification: logout is earned only
+# when the marker proves rig performed the join. Preserve the marker on failure
+# so the operation remains retryable and never reports a half-undone machine.
+if ! tailscale logout; then
+  die "tailscale logout failed; role marker kept so 'rig bootstrap --undo' can be retried"
+fi
+
+rm -f -- "$MARKER"
+log "tailnet join removed; role marker removed"

commands/bootstrap.sh

@@ -32,6 +32,9 @@ usage: rig bootstrap <control-plane-server|workload-server|runner-server|
        rig bootstrap <claude-box|codex-box|grok-box|kimi-box|staging-box> [--user <name>]
                      (the box TENANT roles — see their own --help; they take
                       no --users, see below)
+       rig bootstrap --undo
+                     leave the tailnet only when the role marker proves rig
+                     performed the join, then remove the role marker
 
   --users     the users file this box's operators come from — REQUIRED. It is
               applied as bootstrap's last phase, exactly as `rig users apply
@@ -114,6 +117,10 @@ EOF
 # --- args (validated before the root check, so errors are testable) ---------
 ROLE="${1:-}"
 case "$ROLE" in
+  --undo)
+    shift
+    [ $# -eq 0 ] || die "bootstrap --undo takes no arguments" 2
+    exec "$HERE/bootstrap-undo.sh" ;;
   control-plane-server|workload-server|runner-server|staging-server|dev-server|workstation|custom) shift ;;
   claude-box|codex-box|grok-box|kimi-box|staging-box)
     # The box TENANT roles (#31) are a different family — guests a box mints,
@@ -534,6 +541,7 @@ if ! command -v tailscale >/dev/null 2>&1; then
   log "installing tailscale"
   curl -fsSL https://tailscale.com/install.sh | sh
 fi
+JOIN_BY=preexisting
 if tailscale status >/dev/null 2>&1; then
   log "tailnet already joined; skipping tailscale up (no pre-auth key needed)"
   # ...but skipping `tailscale up` also skipped --hostname, so the TAILNET name
@@ -574,6 +582,7 @@ elif [ "$JOIN" = "login" ]; then
   log "joining tailnet as ${TS_HOSTNAME} (interactive login; follow the URL tailscale prints)"
   tailscale up --hostname="$TS_HOSTNAME"
   verify_user_owned back-out
+  JOIN_BY=rig
 else
   # env override, else prompt; never touches disk. The prompt only fires on a
   # tty: with no terminal, a bare `read` exits non-zero and `set -e` would end
@@ -594,6 +603,7 @@ else
   log "joining tailnet as ${TS_HOSTNAME} (tag comes from the pre-auth key)"
   tailscale up --authkey="$TS_AUTHKEY" --hostname="$TS_HOSTNAME"
   verify_effective_tag back-out
+  JOIN_BY=rig
 fi
 
 # --- role marker --------------------------------------------------------------
@@ -611,11 +621,12 @@ fi
 # those exist in the field by the thousand and nothing will rewrite them.
 MARKER=/etc/rig/role
 MARKER_TMP="$(mktemp)"
-printf 'role=%s root-door=%s host=%s join=%s\n' "$ROLE" "$ROOT_DOOR" "$HOST" "$JOIN" > "$MARKER_TMP"
+printf 'role=%s root-door=%s host=%s join=%s join-by=%s\n' \
+  "$ROLE" "$ROOT_DOOR" "$HOST" "$JOIN" "$JOIN_BY" > "$MARKER_TMP"
 if ! cmp -s "$MARKER_TMP" "$MARKER" 2>/dev/null; then
   mkdir -p /etc/rig
   install -m 0644 "$MARKER_TMP" "$MARKER"
-  log "role marker written: role=$ROLE root-door=$ROOT_DOOR host=$HOST join=$JOIN"
+  log "role marker written: role=$ROLE root-door=$ROOT_DOOR host=$HOST join=$JOIN join-by=$JOIN_BY"
 else
   log "role marker already current"
 fi