diff --git a/.gitignore b/.gitignore
index 1aab090..04abae2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,6 +20,13 @@ fleetd.out
 fleetd/fleetd.out
 logs/
 
+# fleetd #635 follow-up — scripts/config-edit.sh's backup directory. No leading slash, so this is
+# ignored at every depth: the real one lives under fleetd/ (also named in fleetd/.gitignore, next
+# to the config it backs up), and scripts/test-config-edit.sh's own throwaway fixtures build one
+# under the repo root while the suite runs. --config can point anywhere, so the directory name is
+# ignored everywhere rather than only where the live daemon happens to use it.
+.config-backups/
+
 # fleetd #480: the lead rollover handover file. `leadRollover.handoverPath` points here, and the
 # outgoing lead rewrites it on every rollover. It is a snapshot of one moment's live state —
 # unpushed branches, running builds, open questions — so it is stale the moment it is written and
diff --git a/fleetd/.gitignore b/fleetd/.gitignore
index 5b6d1fa..5a25259 100644
--- a/fleetd/.gitignore
+++ b/fleetd/.gitignore
@@ -7,6 +7,13 @@ dependency-reduced-pom.xml
 fleetd.yaml
 bridged.yaml
 
+# fleetd #635 follow-up — scripts/config-edit.sh's backups of fleetd.yaml. A backup of a file
+# that must never be committed inherits that requirement. The directory is the real protection
+# (it keeps working even if the backup naming changes); the glob is a backstop for a stray
+# backup written the old way, directly beside fleetd.yaml, or by an older copy of the script.
+.config-backups/
+fleetd.yaml.bak.*
+
 # CB-505 audit trail + daemon stdout/stderr — runtime records, never source
 logs/
 
diff --git a/scripts/config-edit.sh b/scripts/config-edit.sh
new file mode 100755
index 0000000..7d47d63
--- /dev/null
+++ b/scripts/config-edit.sh
@@ -0,0 +1,726 @@
+#!/usr/bin/env bash
+#
+# The one auditable way to edit the live fleetd.yaml.
+#
+# fleetd ticket #635 — why this exists at all: fleetd.yaml is gitignored and holds the live
+# fleet's settings. A bad raw edit reaches a daemon that is already serving, so a direct `Edit`
+# on it is refused by policy. This script is the allow-listed alternative, and it is not just
+# convenience — it is the thing a raw file write can never give you: a backup, a parse check
+# BEFORE the file is installed, and the daemon's own reload verdict read back afterwards. An
+# edit to a live config is not finished when the bytes are written. It is finished when the
+# daemon has said what it did with them.
+#
+# What the daemon says, and how this script finds it — measured against `ConfigRef.java` on
+# fleetd commit 158a2a8, 2026-10-01:
+#
+#   1. `ConfigRef` re-reads fleetd.yaml only when the WATCHER sees the mtime move (every 10s by
+#      default — read the real interval out of the daemon's own startup line, "config watch: ...
+#      re-read when it changes (every Ns)"). So a verdict never appears before the next tick.
+#   2. `ConfigRef.Outcome.summary()` logs exactly one of five strings (ConfigRef.java:371-391):
+#        config reload refused — <error message>
+#        config reload refused — these keys cannot change under a running daemon: <keys>. ...
+#        config reloaded
+#        config reloaded; these changes need a restart to take effect: <keys>
+#        config reloaded; partially live — <key: detail | ...>
+#      A parse/validation failure logs a DIFFERENT line instead, before any summary ever runs
+#      (ConfigRef.java:425): "config reload from <path> refused, keeping the running config:
+#      <message>". This script recognises both shapes of refusal.
+#   3. The em dash in those strings is a real multi-byte character — match the stable prefix
+#      "config reload refused" (or "...refused, keeping the running config" for the parse-failure
+#      shape), never the dash itself.
+#   4. A cold-key change (bind/herdrSocket/memberHerdrSocket/broker/auth) throws away the WHOLE
+#      reload — the running config keeps every old value, not only the cold one.
+#   5. A deferred/split change IS applied (current.set(fresh) runs) — "needs a restart" is a
+#      SUCCESS with a follow-up, never a failure.
+#
+# Four outcomes, and they stay four (see the exit code table below). The one most likely to be
+# gotten wrong is "cannot tell" (exit 5): the daemon may be down, or the watcher may be stalled,
+# and folding that into either "refused" or "applied" is worse than never checking at all,
+# because a caller then acts on a verdict nobody actually read. So exit 5 never restores — a
+# visible, recoverable edit beats an invisible revert of a GOOD edit.
+#
+# Usage:
+#   scripts/config-edit.sh --check
+#   scripts/config-edit.sh --set <yq-path>=<value> [--set ...]
+#   scripts/config-edit.sh --from <candidate.yaml>
+#   scripts/config-edit.sh --dry-run --set <yq-path>=<value>
+#   scripts/config-edit.sh --restore
+#
+# `--set .a.b=` (an empty value — a forgotten typo) is REFUSED, not accepted as "clear the
+# field": a null value falls back to its default rather than erroring, which is silent, not
+# safe. To clear a key on purpose, write a literal null: `--set .a.b=null`. Every other value
+# is always written as a YAML string (via yq's strenv(), never spliced into the expression), so
+# there is currently no --set spelling for the literal three-character STRING "null" itself — use
+# --from for that rare case.
+#
+# Overrides (so this is drivable with no daemon — see scripts/test-config-edit.sh):
+#   --config <path>        default: fleetd/fleetd.yaml
+#   --log <path>           default: fleetd/fleetd.out
+#   --wait-seconds <n>     default: 4x the watch interval this script reads out of --log (10 -> 40)
+#
+# Exit codes (the --check/--restore/usage-error paths are reported separately, see below):
+#   0  applied; verdict read; clean
+#   3  applied; verdict read; needs a restart (deferred or split keys named)
+#   4  REFUSED by the daemon; backup restored (and the restore's own verdict reported if seen)
+#   5  CANNOT TELL — no verdict line inside the wait window. Nothing is restored.
+#
+# Never prints a secret. fleetd.yaml keeps credentials out by indirection (broker.uriEnv,
+# gitTokenEnv) but this script does not rely on that staying true: every diff it prints is piped
+# through `redact`, which (a) blanks the userinfo of any `scheme://user:pass@host` and (b) masks
+# the whole value on any line whose key looks like a credential. See `redact` below.
+
+set -euo pipefail
+
+REPO="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+SELF="$REPO/scripts/config-edit.sh"
+
+CONFIG="$REPO/fleetd/fleetd.yaml"
+LOG="$REPO/fleetd/fleetd.out"
+WAIT_SECONDS_OVERRIDE=""
+FALLBACK_PORT=8765
+
+MODE=""
+DRY_RUN=0
+SETS=()
+FROM_FILE=""
+
+# fleetd #635 follow-up — a signal (or any early exit while a candidate is still uninstalled) must
+# not leave a `.config-edit.XXXXXX` file sitting beside the live config forever. CAND is global
+# (never a function-local) on purpose: this ONE trap, set once, covers every path that ever
+# creates a candidate — run_edit and dry_run_diff both assign it, and clear it back to "" once the
+# file is consumed (installed, or explicitly removed), so a later, unrelated exit never retries a
+# path that already served its purpose.
+CAND=""
+cleanup_candidate() { [ -n "$CAND" ] && rm -f "$CAND" 2>/dev/null; return 0; }
+trap cleanup_candidate EXIT INT TERM
+
+say()  { printf '\n\033[1m== %s\033[0m\n' "$*"; }
+ok()   { printf '   ok    %s\n' "$*"; }
+warn() { printf '   WARN  %s\n' "$*"; }
+die()  { printf '\n   FAIL  %s\n\n' "$*" >&2; exit 1; }
+
+set_mode() {
+  local new="$1"
+  if [ -n "$MODE" ] && [ "$MODE" != "$new" ]; then
+    die "cannot combine --$MODE and --$new in one invocation"
+  fi
+  MODE="$new"
+}
+
+while [ $# -gt 0 ]; do
+  case "$1" in
+    --check)   set_mode check; shift ;;
+    --restore) set_mode restore; shift ;;
+    --set)
+      [ $# -ge 2 ] || die "--set requires <yq-path>=<value>"
+      set_mode set
+      SETS+=("$2")
+      shift 2 ;;
+    --from)
+      [ $# -ge 2 ] || die "--from requires a candidate file path"
+      set_mode from
+      FROM_FILE="$2"
+      shift 2 ;;
+    --dry-run) DRY_RUN=1; shift ;;
+    --config)
+      [ $# -ge 2 ] || die "--config requires a path"
+      CONFIG="$2"; shift 2 ;;
+    --log)
+      [ $# -ge 2 ] || die "--log requires a path"
+      LOG="$2"; shift 2 ;;
+    --wait-seconds)
+      [ $# -ge 2 ] || die "--wait-seconds requires a number of seconds"
+      WAIT_SECONDS_OVERRIDE="$2"; shift 2 ;;
+    -h|--help) sed -n '3,70p' "$SELF"; exit 0 ;;
+    *) echo "unknown option: $1 (try --help)" >&2; exit 2 ;;
+  esac
+done
+
+[ -n "$MODE" ] || die "no action given — use --check, --set, --from, or --restore (see --help)"
+
+# ------------------------------------------------------------------------------------- redaction
+#
+# Two independent passes, applied to every diff this script ever prints:
+#   1. `scheme://user:pass@host` -> `scheme://<redacted>@host`, globally (the `g` flag matters —
+#      a line can carry more than one URI).
+#   2. Any line whose key looks like TOKEN|SECRET|PASSWORD|PASSWD|PASSPHRASE|CREDENTIAL|URI|_KEY,
+#      matched case-insensitively against the key text (uriEnv, gitTokenEnv, ... are camelCase,
+#      not SCREAMING_CASE) has its whole value blanked, diff marker and indentation kept so the
+#      shape of the change is still visible. Deliberately conservative: a false-positive
+#      redaction on an unrelated line costs nothing, an unredacted secret is a security defect
+#      (acceptance criterion 7).
+#
+# fleetd #635 follow-up (ticket comment 17670, defect 7) — a masked key line is not the whole
+# story: a YAML block scalar (`|`, `|-`, `>`, `>-`, ...) puts the VALUE on the lines that follow
+# the key, each indented deeper than it. The key-name match above only ever sees the key line
+# itself, so those continuation lines used to flow straight through unredacted while the key line
+# right above them printed a reassuring "<redacted>" — an incomplete redactor that looks complete
+# is worse than one that visibly does nothing, because it stops a reviewer from looking further.
+# The fix is structural, not another name to match: once a key line is masked, every following
+# line indented STRICTLY DEEPER than that key is masked too, by indentation alone, until the
+# indentation returns to the key's own level or shallower. This needs no knowledge of the key's
+# name and so protects a block scalar under any masked key, present or future.
+#
+# `redact` is always fed `diff -u` output, and every line of a unified diff starts with exactly
+# one of ' ', '+', '-' (the three body markers; '@'/'-'/'+' for the three header-line kinds too).
+# That one leading character is NOT part of the YAML indentation, and must be stripped before
+# indentation is measured or a key is matched — otherwise a changed ('+' or '-') line reads one
+# column shallower than it really is, and either wrongly escapes a continuation mask or wrongly
+# ends one early. Tabs are out of scope: YAML forbids them for indentation, and this is a bounded
+# fix, not a YAML parser.
+redact() {
+  local line prefix content indent lead key
+  local masked=0 masked_indent=0 saved_nocasematch=0
+  shopt -q nocasematch && saved_nocasematch=1
+  shopt -s nocasematch
+  sed -E 's#://[^@]*@#://<redacted>@#g' | while IFS= read -r line || [ -n "$line" ]; do
+    case "$line" in
+      [\ +-]*) prefix="${line:0:1}"; content="${line:1}" ;;
+      *)       prefix="";            content="$line" ;;
+    esac
+
+    indent=0
+    while [ "${content:$indent:1}" = " " ]; do indent=$((indent + 1)); done
+
+    if [ "$masked" = 1 ] && [ "$indent" -gt "$masked_indent" ]; then
+      printf '%s%*s<redacted>\n' "$prefix" "$indent" ""
+      continue
+    fi
+    masked=0
+
+    if [[ "$content" =~ ^([[:space:]]*)([A-Za-z0-9_.-]+:) ]]; then
+      lead="${BASH_REMATCH[1]}"
+      key="${BASH_REMATCH[2]}"
+      if [[ "$key" =~ (TOKEN|SECRET|PASSWORD|PASSWD|PASSPHRASE|CREDENTIAL|URI|_KEY) ]]; then
+        printf '%s%s%s <redacted>\n' "$prefix" "$lead" "$key"
+        masked=1
+        masked_indent="$indent"
+        continue
+      fi
+    fi
+    printf '%s\n' "$line"
+  done
+  [ "$saved_nocasematch" = 1 ] || shopt -u nocasematch
+}
+
+# ------------------------------------------------------------------------------------- the probe
+#
+# Probe the SOCKET, never `pgrep`/`ps -f` — both print argv, and argv holds `NAME=value`, making
+# either a credential channel. The port comes from the config's own `bind.port`; 8765 is only a
+# fallback when that key is absent or the file does not parse yet.
+resolve_port() {
+  local file="$1" port
+  if [ -f "$file" ] && command -v yq >/dev/null 2>&1; then
+    port="$(yq eval '.bind.port' "$file" 2>/dev/null || true)"
+  else
+    port=""
+  fi
+  case "$port" in
+    ''|null) echo "$FALLBACK_PORT" ;;
+    *) echo "$port" ;;
+  esac
+}
+
+daemon_listening() {
+  local port="$1"
+  if command -v nc >/dev/null 2>&1; then
+    nc -z -w1 127.0.0.1 "$port" 2>/dev/null
+  else
+    ( exec 3<>"/dev/tcp/127.0.0.1/$port" ) 2>/dev/null
+  fi
+}
+
+# --------------------------------------------------------------------------------- the log marker
+#
+# Take the log's line count BEFORE touching anything. Every later read of "what did the daemon
+# say" starts strictly after this mark, so a refusal from hours ago can never be mistaken for
+# this edit's verdict. Same approach as scripts/redeploy-fleetd.sh's RESTART_MARK.
+log_mark() {
+  local file="$1"
+  if [ -f "$file" ]; then
+    wc -l < "$file" 2>/dev/null || echo 0
+  else
+    echo 0
+  fi
+}
+
+read_verdict_after_marker() {
+  local file="$1" mark="$2"
+  [ -f "$file" ] || return 0
+  tail -n "+$((mark + 1))" "$file" 2>/dev/null || true
+}
+
+# Classifies one log LINE. Echoes one of: refused | clean | needs-restart | none. Always
+# succeeds (every branch ends in `echo`), so it is safe to call from inside `$( )`.
+classify_verdict_line() {
+  local line="$1"
+  case "$line" in
+    *'config reload refused'*) echo refused ;;
+    *'config reload from '*'refused, keeping the running config'*) echo refused ;;
+    *'config reloaded'*)
+      case "$line" in
+        *'need a restart'*|*'partially live'*) echo needs-restart ;;
+        *) echo clean ;;
+      esac ;;
+    *) echo none ;;
+  esac
+  return 0
+}
+
+scan_region_for_verdict() {
+  local region="$1" line kind
+  [ -n "$region" ] || return 1
+  while IFS= read -r line || [ -n "$line" ]; do
+    kind="$(classify_verdict_line "$line")"
+    if [ "$kind" != "none" ]; then
+      VERDICT_KIND="$kind"
+      VERDICT_LINE="$line"
+      return 0
+    fi
+  done <<< "$region"
+  return 1
+}
+
+# Sets VERDICT_KIND/VERDICT_LINE and returns 0 on the first verdict line found after $mark;
+# returns 1 (VERDICT_KIND=none) if none appeared inside $wait_s seconds. Checks once before each
+# sleep AND once more after the last sleep, the same boundary idiom
+# scripts/redeploy-fleetd.sh's wait_for_daemon_exit/wait_for_new_pid already use.
+wait_for_verdict() {
+  local log="$1" mark="$2" wait_s="$3" _i region
+  VERDICT_KIND="none"
+  VERDICT_LINE=""
+  for _i in $(seq "$wait_s"); do
+    region="$(read_verdict_after_marker "$log" "$mark")"
+    scan_region_for_verdict "$region" && return 0
+    sleep 1
+  done
+  region="$(read_verdict_after_marker "$log" "$mark")"
+  scan_region_for_verdict "$region" && return 0
+  return 1
+}
+
+last_verdict_line() {
+  local file="$1" line out=""
+  [ -f "$file" ] || return 0
+  while IFS= read -r line || [ -n "$line" ]; do
+    if [ "$(classify_verdict_line "$line")" != "none" ]; then
+      out="$line"
+    fi
+  done < "$file"
+  printf '%s' "$out"
+}
+
+default_wait_seconds() {
+  local log="$1" interval=""
+  if [ -f "$log" ]; then
+    interval="$(grep -F 'config watch:' "$log" 2>/dev/null | tail -1 \
+      | sed -E 's/.*\(every ([0-9]+)s\).*/\1/' || true)"
+  fi
+  case "$interval" in
+    ''|*[!0-9]*) interval=10 ;;
+  esac
+  echo $((interval * 4))
+}
+
+# ----------------------------------------------------------------------------------- the backup
+#
+# Timestamped, never pruned — "keep backups" per the ticket. A pid suffix avoids a same-second
+# collision between two invocations.
+#
+# fleetd #635 follow-up — lands under a DEDICATED, gitignored directory beside the config
+# (<dir>/.config-backups/), never beside the config file itself. The whole reason fleetd.yaml is
+# gitignored is that it must never be committed, and a backup of it inherits that requirement — a
+# bare `fleetd.yaml.bak.*` next to a tracked directory is one `git add -A`/`git add .` away from
+# committing the live config. A directory beats a glob on its own: the glob only protects today's
+# naming, a location keeps working even if the naming changes later. (See .gitignore for the glob
+# kept anyway, as a backstop for a stray backup written the old way.)
+BACKUP_DIRNAME=".config-backups"
+
+backup_dir_for() {
+  local src="$1"
+  printf '%s/%s' "$(dirname "$src")" "$BACKUP_DIRNAME"
+}
+
+backup_config() {
+  local src="$1" ts backup dir base
+  dir="$(backup_dir_for "$src")"
+  mkdir -p "$dir" \
+    || die "could not create the backup directory $dir — refusing to edit without a backup. The live config at $src was NOT touched."
+  ts="$(date -u +%Y%m%dT%H%M%S)Z"
+  base="$(basename "$src")"
+  backup="${dir}/${base}.bak.${ts}.$$"
+  cp "$src" "$backup" \
+    || die "could not create a backup at $backup — refusing to edit without one. The live config at $src was NOT touched."
+  printf '%s' "$backup"
+}
+
+newest_backup() {
+  local cfg="$1" dir base
+  dir="$(backup_dir_for "$cfg")"
+  base="$(basename "$cfg")"
+  ls -t "${dir}/${base}".bak.* 2>/dev/null | head -1 || true
+}
+
+# ------------------------------------------------------------------------------------ the file mode
+#
+# fleetd #635 follow-up — `mv` from a mktemp candidate carries mktemp's 0600 onto the live path
+# forever (measured: 644 -> 600 after one --set), and a restore does not undo it either, because
+# `cp` onto an EXISTING file keeps the DESTINATION's mode, not the source's. Capture the live
+# file's mode before anything touches it, and reapply it to whatever lands on that path
+# afterwards — the candidate before install, and the config again after a restore — so an edit
+# changes the file's CONTENT only, never its permissions. BSD `stat -f '%Lp'` first (matches this
+# project's dev machine), GNU `stat -c '%a'` as the fallback. Prints nothing when the file does
+# not exist yet, so apply_mode then does nothing and a first-ever edit falls back to the normal
+# umask default rather than inventing a number.
+file_mode() {
+  local file="$1"
+  [ -f "$file" ] || return 0
+  stat -f '%Lp' "$file" 2>/dev/null || stat -c '%a' "$file" 2>/dev/null || true
+}
+
+apply_mode() {
+  local file="$1" mode="$2"
+  [ -n "$mode" ] || return 0
+  chmod "$mode" "$file" 2>/dev/null || true
+}
+
+# --------------------------------------------------------------------------- candidate builders
+#
+# Never edit the live file in place. Each builder fills $1 (a temp file already sitting in the
+# SAME directory as the live config, so the later `mv` install is a rename, not a cross-device
+# copy — see run_edit).
+# fleetd #635 follow-up — a forgotten value (`--set .a.b=`, a plausible typo) must never be
+# accepted as "clear the field". `*=*` alone cannot tell "--set .a.b=" from "--set .a.b=7" apart
+# — both contain an `=` — so the guard has to look at the VALUE, not the shape of the argument.
+# An empty value refuses outright: nothing is installed, and the message names the likely cause
+# AND the two ways to actually mean it (clear on purpose, or an intentional empty string via
+# --from). Measured against the real daemon loader: a quoted empty string reads back as a null
+# field (`quoted empty -> OK int=null`), and a null numeric field FALLS BACK TO ITS DEFAULT rather
+# than erroring — so this is not a cosmetic nit, it is the one shape of edit that widens capacity
+# silently instead of failing loudly, which is exactly what this script exists to catch.
+#
+# A deliberate clear needs its own spelling, because `""` and YAML `null` are NOT the same value
+# to the loader (`""` is a valid empty String; `null` means absent, and an Integer field reads
+# either the same way — null — but a String field would keep `""` as a real value). `--set
+# .a.b=null` is that spelling: it writes a literal, unquoted `null` via yq, never the string
+# "null" through strenv(). One consequence worth knowing: there is currently no --set spelling
+# for the three-character STRING "null" itself (it collides with the clear spelling) — use
+# --from for that rare case.
+apply_set_pairs() {
+  local cand="$1" kv path value
+  shift
+  for kv in "$@"; do
+    case "$kv" in
+      *=*) : ;;
+      *) die "--set expects <yq-path>=<value>, got: '$kv'" ;;
+    esac
+    path="${kv%%=*}"
+    path="${path#.}"
+    value="${kv#*=}"
+    if [ -z "$value" ]; then
+      die "--set '$kv' has an EMPTY value — refusing. Nothing was installed. A forgotten value
+          would NULL the field, and a null value falls back to its default rather than erroring —
+          silent, not safe. Did you mean --set .${path}=null to clear it on purpose, or --from a
+          file if you need a genuinely empty string?"
+    fi
+    # fleetd #635 follow-up (ticket comment 17673, defect 8) — these two failure messages used to
+    # echo the full "$kv" (path=value, exactly as the operator typed it), unredacted. The operator
+    # already has the value, so a terminal is not where this leaks — the risk is where the output
+    # goes NEXT: this fleet pastes command output into tickets, PRs and fleet_reply bodies, and a
+    # failure is exactly when someone copies it to ask for help. Print the PATH, which is what's
+    # needed to fix the command, and never the value. $kv is not key:value-shaped YAML, so piping
+    # it through redact would just pass it straight through — a false sense of coverage, the same
+    # mistake as defect 7.
+    if [ "$value" = "null" ]; then
+      yq eval -i ".${path} = null" "$cand" \
+        || die "yq could not clear --set '.${path}=null' — nothing was installed. The live config is unchanged."
+      continue
+    fi
+    CONFIG_EDIT_SET_VALUE="$value" yq eval -i ".${path} = strenv(CONFIG_EDIT_SET_VALUE)" "$cand" \
+      || die "yq could not apply --set '.${path}=<value>' — nothing was installed. The live config is unchanged."
+  done
+}
+
+build_from_set() {
+  local cand="$1"
+  cp "$CONFIG" "$cand"
+  apply_set_pairs "$cand" "${SETS[@]}"
+}
+
+build_from_file() {
+  local cand="$1"
+  [ -f "$FROM_FILE" ] || die "--from file not found: $FROM_FILE"
+  cp "$FROM_FILE" "$cand"
+}
+
+parse_check() {
+  yq eval '.' "$1" >/dev/null 2>&1
+}
+
+install_candidate() {
+  local cand="$1" live="$2"
+  mv -f "$cand" "$live"
+}
+
+# -------------------------------------------------------------------------------- the report path
+#
+# Prints the literal command the operator (or a test) can run to restore the backup by hand — the
+# absolute path to THIS script plus the overrides actually in force, so it works from any cwd.
+restore_command_line() {
+  printf '%q --restore --config %q --log %q --wait-seconds %q' "$SELF" "$CONFIG" "$LOG" "$WAIT_SECONDS"
+}
+
+# State 4 only: restore the pre-edit backup, then wait for a SECOND verdict confirming the
+# restore itself reloaded cleanly. Never claims a restore it did not observe — if the second wait
+# also times out, it says so plainly rather than reporting "restored" as though confirmed.
+restore_and_confirm() {
+  local backup="$1" mark2 orig_mode
+  orig_mode="$(file_mode "$CONFIG")"
+  mark2="$(log_mark "$LOG")"
+  cp "$backup" "$CONFIG" \
+    || die "could not restore $backup onto $CONFIG — the live config is left as the REFUSED edit. Fix this by hand immediately: cp \"$backup\" \"$CONFIG\""
+  apply_mode "$CONFIG" "$orig_mode"
+  ok "restored from $backup"
+  if wait_for_verdict "$LOG" "$mark2" "$WAIT_SECONDS"; then
+    case "$VERDICT_KIND" in
+      refused) warn "the RESTORE was also refused by the daemon: $VERDICT_LINE" ;;
+      *)       ok "restore confirmed: $VERDICT_LINE" ;;
+    esac
+  else
+    warn "the restore is on disk, but no confirming verdict line appeared within ${WAIT_SECONDS}s"
+    warn "cannot confirm the restore reloaded cleanly — check $LOG by hand"
+  fi
+  return 0
+}
+
+# The four-outcome decision. Echoed as a function so run_edit/restore_mode share one place that
+# can return 0/3/4/5 — never duplicated, never re-worded between the two callers.
+report_outcome() {
+  local mark="$1" backup="$2" kind line
+
+  say "waiting for the daemon's verdict (up to ${WAIT_SECONDS}s)"
+  if wait_for_verdict "$LOG" "$mark" "$WAIT_SECONDS"; then
+    kind="$VERDICT_KIND"; line="$VERDICT_LINE"
+  else
+    kind="none"
+  fi
+
+  case "$kind" in
+    clean)
+      ok "daemon verdict: $line"
+      say "result: applied cleanly"
+      return 0 ;;
+    needs-restart)
+      ok "daemon verdict: $line"
+      say "result: applied — a restart is needed for the change(s) named above"
+      return 3 ;;
+    refused)
+      warn "daemon verdict: $line"
+      say "result: REFUSED — restoring the backup"
+      restore_and_confirm "$backup"
+      return 4 ;;
+    none)
+      warn "no verdict line appeared within ${WAIT_SECONDS}s after $LOG line $mark"
+      warn "CANNOT TELL whether the daemon applied this edit, refused it, or is simply down."
+      warn "Nothing was restored — the edit is still on disk at $CONFIG."
+      echo
+      echo "   backup: $backup"
+      echo "   to restore it by hand:"
+      echo "       $(restore_command_line)"
+      return 5 ;;
+  esac
+}
+
+# ------------------------------------------------------------------------------------- the modes
+check_mode() {
+  say "config-edit --check"
+  if [ -f "$CONFIG" ]; then
+    if parse_check "$CONFIG"; then
+      ok "config parses: $CONFIG"
+    else
+      warn "config does NOT parse as valid YAML: $CONFIG"
+    fi
+  else
+    warn "no config file at $CONFIG"
+  fi
+
+  local port
+  port="$(resolve_port "$CONFIG")"
+  if daemon_listening "$port"; then
+    ok "daemon is listening on 127.0.0.1:$port"
+  else
+    warn "no daemon detected listening on 127.0.0.1:$port"
+  fi
+
+  ok "watch interval assumed: $(( $(default_wait_seconds "$LOG") / 4 ))s (derives --wait-seconds default of $(default_wait_seconds "$LOG")s)"
+
+  local verdict
+  verdict="$(last_verdict_line "$LOG")"
+  if [ -n "$verdict" ]; then
+    ok "last verdict in log: $verdict"
+  else
+    warn "no reload verdict line found in $LOG"
+  fi
+
+  local backup
+  backup="$(newest_backup "$CONFIG")"
+  if [ -n "$backup" ]; then
+    ok "newest backup: $backup"
+  else
+    warn "no backups found for $CONFIG"
+  fi
+
+  if command -v yq >/dev/null 2>&1; then
+    ok "yq: $(yq --version 2>&1)"
+  else
+    warn "yq not found on PATH"
+  fi
+
+  return 0
+}
+
+# Shared by --set and --from: backup, build, parse-check, redacted diff, install, await verdict.
+run_edit() {
+  local builder="$1"
+  [ -f "$CONFIG" ] || die "no config at $CONFIG — nothing to edit"
+
+  local mark orig_mode
+  mark="$(log_mark "$LOG")"
+  orig_mode="$(file_mode "$CONFIG")"
+
+  say "probe"
+  local port
+  port="$(resolve_port "$CONFIG")"
+  if daemon_listening "$port"; then
+    ok "daemon appears to be listening on 127.0.0.1:$port"
+  else
+    warn "no daemon detected listening on 127.0.0.1:$port — a verdict may never appear"
+  fi
+
+  say "backup"
+  local backup
+  backup="$(backup_config "$CONFIG")"
+  ok "backup: $backup"
+
+  say "candidate"
+  local cand
+  CAND="$(mktemp "$(dirname "$CONFIG")/.config-edit.XXXXXX")" \
+    || die "could not create a candidate temp file next to $CONFIG"
+  cand="$CAND"
+  if ! "$builder" "$cand"; then
+    rm -f "$cand"; CAND=""
+    die "could not build the candidate — nothing was installed. The live config at $CONFIG is unchanged."
+  fi
+
+  if ! parse_check "$cand"; then
+    rm -f "$cand"; CAND=""
+    die "candidate does not parse as valid YAML — nothing was installed. The live config at $CONFIG is unchanged."
+  fi
+  ok "candidate parses"
+
+  apply_mode "$cand" "$orig_mode"
+
+  say "change (redacted)"
+  diff -u "$backup" "$cand" | redact || true
+
+  say "install"
+  install_candidate "$cand" "$CONFIG" \
+    || die "could not install the candidate onto $CONFIG — the live config was NOT changed. The validated candidate is sitting at $cand; investigate before retrying."
+  CAND=""
+  ok "installed: $CONFIG"
+
+  local rc=0
+  report_outcome "$mark" "$backup" || rc=$?
+  return "$rc"
+}
+
+dry_run_diff() {
+  local builder="$1"
+  [ -f "$CONFIG" ] || die "no config at $CONFIG — nothing to diff against"
+  local cand
+  CAND="$(mktemp "$(dirname "$CONFIG")/.config-edit.XXXXXX")" \
+    || die "could not create a candidate temp file next to $CONFIG"
+  cand="$CAND"
+  if ! "$builder" "$cand"; then
+    rm -f "$cand"; CAND=""
+    die "could not build the candidate — this was a --dry-run, nothing would have been installed either"
+  fi
+  if ! parse_check "$cand"; then
+    rm -f "$cand"; CAND=""
+    die "candidate does not parse as valid YAML — this was a --dry-run, nothing would have been installed either"
+  fi
+  say "dry run — diff (redacted), nothing installed"
+  diff -u "$CONFIG" "$cand" | redact || true
+  rm -f "$cand"; CAND=""
+  return 0
+}
+
+restore_mode() {
+  [ -f "$CONFIG" ] || die "no config at $CONFIG to restore onto"
+  local backup dir base
+  backup="$(newest_backup "$CONFIG")"
+  if [ -z "$backup" ]; then
+    # fleetd #635 follow-up (ticket comment 17664) — this message must name the directory the
+    # code actually searches (backup_dir_for, same as newest_backup), not the old beside-the-
+    # config glob. A backup written the OLD way is real and NOT searched any more — say so and
+    # give the one-line recovery command — but do NOT make the search itself look there; that
+    # would be a behaviour change nobody asked for. The message is the only thing being fixed.
+    dir="$(backup_dir_for "$CONFIG")"
+    base="$(basename "$CONFIG")"
+    die "no backup found matching ${dir}/${base}.bak.* — nothing to restore.
+        A backup written the OLD way, directly beside the config (${CONFIG}.bak.*), is NOT
+        searched — that location was retired so a backup of a file that must never be committed
+        cannot sit next to a tracked directory. If one exists there, recover it by hand:
+        cp ${CONFIG}.bak.<timestamp>.<pid> $CONFIG"
+  fi
+  [ -f "$backup" ] || die "backup candidate $backup vanished"
+
+  say "restore"
+  ok "restoring $backup onto $CONFIG"
+  local mark orig_mode
+  mark="$(log_mark "$LOG")"
+  orig_mode="$(file_mode "$CONFIG")"
+  cp "$backup" "$CONFIG" || die "could not copy $backup onto $CONFIG"
+  apply_mode "$CONFIG" "$orig_mode"
+  ok "installed: $CONFIG"
+
+  local rc=0
+  report_outcome "$mark" "$backup" || rc=$?
+  return "$rc"
+}
+
+# -------------------------------------------------------------------------------------- dispatch
+
+if [ -n "$WAIT_SECONDS_OVERRIDE" ]; then
+  WAIT_SECONDS="$WAIT_SECONDS_OVERRIDE"
+else
+  WAIT_SECONDS="$(default_wait_seconds "$LOG")"
+fi
+
+RC=0
+case "$MODE" in
+  check)
+    check_mode || RC=$?
+    ;;
+  set)
+    [ "${#SETS[@]}" -gt 0 ] || die "--set requires at least one <yq-path>=<value>"
+    if [ "$DRY_RUN" = 1 ]; then
+      dry_run_diff build_from_set || RC=$?
+    else
+      run_edit build_from_set || RC=$?
+    fi
+    ;;
+  from)
+    [ -n "$FROM_FILE" ] || die "--from requires a candidate file path"
+    if [ "$DRY_RUN" = 1 ]; then
+      dry_run_diff build_from_file || RC=$?
+    else
+      run_edit build_from_file || RC=$?
+    fi
+    ;;
+  restore)
+    restore_mode || RC=$?
+    ;;
+esac
+
+exit "$RC"
diff --git a/scripts/test-config-edit.sh b/scripts/test-config-edit.sh
new file mode 100755
index 0000000..3518771
--- /dev/null
+++ b/scripts/test-config-edit.sh
@@ -0,0 +1,585 @@
+#!/usr/bin/env bash
+# Self-contained checks for scripts/config-edit.sh — fleetd ticket #635.
+#
+# Drives the REAL config-edit.sh as a subprocess against a FIXTURE config and a FIXTURE log in a
+# throwaway temp directory this file creates and removes. Never touches fleetd/fleetd.yaml or
+# fleetd/fleetd.out, and never starts, stops, or contacts a daemon — there is no daemon here, so
+# each test PLAYS the daemon: it starts config-edit.sh in the background (it is waiting on the
+# log), appends the verdict line it wants, then collects the real exit code.
+
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+EDIT="$ROOT/scripts/config-edit.sh"
+TMP="$(mktemp -d "$ROOT/.config-edit-test.XXXXXX")"
+trap 'rm -rf "$TMP"' EXIT
+
+fail() {
+  printf 'FAIL: %s\n' "$*" >&2
+  return 1
+}
+
+assert_equals() {
+  local expected="$1" actual="$2" description="$3"
+  [ "$expected" = "$actual" ] || fail "$description: expected $expected, got $actual"
+}
+
+assert_contains() {
+  local needle="$1" text="$2" description="$3"
+  printf '%s' "$text" | grep -qF -- "$needle" || fail "$description: missing [$needle]"
+}
+
+assert_not_contains() {
+  local needle="$1" text="$2" description="$3"
+  if printf '%s' "$text" | grep -qF -- "$needle"; then
+    fail "$description: must NOT contain [$needle], but it does"
+  fi
+  return 0
+}
+
+# A fresh fixture pair per test: $1/fleetd.yaml (the config) and $1/fleetd.out (the log), plus a
+# small wait-seconds budget so no test takes long. Returns the fixture dir via stdout.
+new_fixture() {
+  local dir
+  dir="$(mktemp -d "$TMP/fixture.XXXXXX")"
+  cat > "$dir/fleetd.yaml" <<'YAML'
+bind:
+  host: 127.0.0.1
+  port: 19999
+broker:
+  uri: amqp://user:hunter2@host/vhost
+profiles:
+  sonnet:
+    weight: 3
+    maxLoad: 5
+YAML
+  : > "$dir/fleetd.out"
+  printf '%s' "$dir"
+}
+
+# Runs config-edit.sh in the background against $dir's fixtures, with the given extra args, and
+# a short --wait-seconds. Sets RUN_PID. Caller appends to $dir/fleetd.out (or not, for the
+# silence test) and then calls collect_run to block for the exit code.
+start_run() {
+  local dir="$1" wait_s="$2"; shift 2
+  (
+    # config-edit.sh deliberately exits 3/4/5 on several of these tests. This subshell inherits
+    # the parent's `set -e`, and without disabling it here the FIRST nonzero exit would kill the
+    # subshell before the `echo $? > rc` line ever ran — the real code would never reach the file.
+    set +e
+    "$EDIT" --config "$dir/fleetd.yaml" --log "$dir/fleetd.out" --wait-seconds "$wait_s" "$@" \
+      > "$dir/stdout.log" 2>&1
+    echo $? > "$dir/rc"
+  ) &
+  RUN_PID=$!
+}
+
+collect_run() {
+  local dir="$1"
+  # wait echoes back the backgrounded subshell's own exit status (here, deliberately 3/4/5 on
+  # several tests) — under `set -e` a bare nonzero `wait` would abort this whole test script, so
+  # it is neutralized with `|| true`; the real code is read from $dir/rc right after.
+  wait "$RUN_PID" || true
+  RUN_OUTPUT="$(cat "$dir/stdout.log")"
+  RUN_RC="$(cat "$dir/rc")"
+}
+
+# -------------------------------------------------------------- acceptance criterion 1: refusal
+test_refusal_restores_byte_for_byte() {
+  local dir
+  dir="$(new_fixture)"
+  cp "$dir/fleetd.yaml" "$dir/pre-edit.yaml"
+
+  start_run "$dir" 5 --set '.broker.uri=amqp://changed@host/x'
+  sleep 1
+  printf 'config reload refused — these keys cannot change under a running daemon: broker. Restart fleetd to apply them.\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 4 "$RUN_RC" "refusal exit code"
+  cmp -s "$dir/fleetd.yaml" "$dir/pre-edit.yaml" \
+    || fail "refusal must restore the config byte for byte onto the pre-edit backup"
+}
+
+# -------------------------------------------------------------- acceptance criterion 2: clean
+test_clean_reload_keeps_the_edit() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.weight=7'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "clean reload exit code"
+  assert_equals "7" "$(yq eval '.profiles.sonnet.weight' "$dir/fleetd.yaml")" "clean reload live value"
+}
+
+# ----------------------------------------------------- acceptance criterion 3: deferred != clean
+test_deferred_reload_is_told_apart_from_clean() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.weight=9'
+  sleep 1
+  printf 'config reloaded; these changes need a restart to take effect: profiles\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 3 "$RUN_RC" "deferred reload exit code"
+  [ "$RUN_RC" != 0 ] || fail "deferred reload must not report exit 0"
+  assert_contains "profiles" "$RUN_OUTPUT" "deferred reload names the key"
+  assert_contains "restart" "$RUN_OUTPUT" "deferred reload says a restart is needed"
+}
+
+# -------------------------------------------------------------- acceptance criterion 4: silence
+test_silence_is_its_own_answer() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 2 --set '.profiles.sonnet.weight=11'
+  # Feed the log nothing.
+  collect_run "$dir"
+
+  assert_equals 5 "$RUN_RC" "silence exit code"
+  assert_equals "11" "$(yq eval '.profiles.sonnet.weight' "$dir/fleetd.yaml")" "the edited value must still be on disk"
+  assert_contains '--restore' "$RUN_OUTPUT" "silence prints the --restore command"
+
+  local backup restore_cmd
+  backup="$(ls -t "$dir"/.config-backups/fleetd.yaml.bak.* | head -1)"
+  [ -n "$backup" ] || fail "silence must still have taken a backup"
+
+  restore_cmd="$(printf '%s\n' "$RUN_OUTPUT" | grep -F -- '--restore --config' | sed -E 's/^[[:space:]]*//')"
+  [ -n "$restore_cmd" ] || fail "could not find the printed --restore invocation in the output"
+  # Running this --restore invocation installs the backup, then itself waits for a confirming
+  # verdict that this fixture never feeds — so it legitimately exits 5 ("cannot tell") here, same
+  # as any edit with no daemon on the other end. Only a usage/internal error (1 or 2) is a real
+  # failure of the command itself; the actual assertion is the byte-for-byte cmp below.
+  local restore_rc=0
+  eval "$restore_cmd" > "$dir/restore.log" 2>&1 || restore_rc=$?
+  case "$restore_rc" in
+    0|3|4|5) : ;;
+    *) fail "the printed --restore command errored out (exit $restore_rc): $(cat "$dir/restore.log")" ;;
+  esac
+
+  cmp -s "$dir/fleetd.yaml" "$backup" \
+    || fail "running the printed --restore command must put the file back to the original backup"
+}
+
+# --------------------------------------------------------- acceptance criterion 5: bad candidate
+test_broken_candidate_never_reaches_live_path() {
+  local dir rc=0
+  dir="$(new_fixture)"
+  printf 'foo: [unclosed\n' > "$dir/broken.yaml"
+
+  "$EDIT" --from "$dir/broken.yaml" --config "$dir/fleetd.yaml" --log "$dir/fleetd.out" --wait-seconds 2 \
+    > "$dir/stdout.log" 2>&1 || rc=$?
+
+  [ "$rc" -ne 0 ] || fail "a broken --from candidate must exit non-zero"
+  cmp -s "$dir/fleetd.yaml" <(new_fixture_yaml) \
+    || fail "the broken candidate must never reach the live fixture config"
+}
+new_fixture_yaml() {
+  cat <<'YAML'
+bind:
+  host: 127.0.0.1
+  port: 19999
+broker:
+  uri: amqp://user:hunter2@host/vhost
+profiles:
+  sonnet:
+    weight: 3
+    maxLoad: 5
+YAML
+}
+
+# -------------------------------------------------------------------- acceptance criterion 6
+test_marker_skips_lines_before_it() {
+  local dir
+  dir="$(new_fixture)"
+  printf 'config reload refused — something ancient\n' > "$dir/fleetd.out"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.weight=5'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "a stale refusal before the marker must not be read as this edit's verdict"
+}
+
+# ------------------------------------------------------------------- acceptance criterion 7 (+13)
+# fleetd #635 follow-up (ticket comment 17659) — the two assertions below this comment were the
+# WHOLE test before the follow-up, and both are negative-only: they pass just as happily when the
+# diff is never printed at all as when it is printed and correctly redacted. A mutant that deletes
+# `diff -u "$backup" "$cand" | redact` from the edit path survives them, because an absent output
+# contains neither "hunter2" nor "user:" either — see the mutation-and-revert proof in the reply.
+# Criterion 13 is the fix: a LOUD positive control that only passes when a diff was demonstrably
+# printed AND the redaction demonstrably ran on real content, not merely that nothing leaked.
+test_redaction_holds() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.weight=4'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "redaction-case reload exit code"
+  assert_not_contains "hunter2" "$RUN_OUTPUT" "full output must never contain the password"
+  assert_not_contains "user:" "$RUN_OUTPUT" "full output must never contain the userinfo"
+  # acceptance criterion 13 — positive control: the diff's default 3-line context around the
+  # changed "weight" key also covers the fixture's "uri:" line, so a genuinely-printed, genuinely-
+  # redacted diff must contain BOTH the redaction marker and the changed key's name. A test that
+  # only ever asserts absence cannot tell "redacted" from "never printed" apart; this can.
+  assert_contains "<redacted>" "$RUN_OUTPUT" "the redaction must be PROVEN to have run on real content, not merely absent"
+  assert_contains "weight" "$RUN_OUTPUT" "a diff must have been demonstrably printed at all"
+}
+
+# ------------------------------------------------------- acceptance criterion 9: forgotten value
+# `--set .a.b=` is a plausible typo (the value simply forgotten), and it must be refused outright
+# rather than silently nulling the field — a null numeric field falls back to its default, which
+# widens capacity instead of failing loudly. No background verdict feeder here: a refused --set
+# must never even reach the daemon, so this never starts a background run at all.
+test_forgotten_value_refuses_and_installs_nothing() {
+  local dir rc=0
+  dir="$(new_fixture)"
+  cp "$dir/fleetd.yaml" "$dir/pre-edit.yaml"
+
+  "$EDIT" --set '.profiles.sonnet.maxLoad=' \
+    --config "$dir/fleetd.yaml" --log "$dir/fleetd.out" --wait-seconds 2 \
+    > "$dir/stdout.log" 2>&1 || rc=$?
+  RUN_OUTPUT="$(cat "$dir/stdout.log")"
+
+  [ "$rc" -ne 0 ] || fail "an empty --set value must exit non-zero, got 0"
+  cmp -s "$dir/fleetd.yaml" "$dir/pre-edit.yaml" \
+    || fail "an empty --set value must install nothing — the live fixture changed"
+  assert_contains "EMPTY value" "$RUN_OUTPUT" "the refusal must name the empty value"
+}
+
+# ---------------------------------------------------------- acceptance criterion 10: explicit null
+# `--set .a.b=null` is the deliberate-clear spelling, and it must write a REAL yaml null, never
+# the string "''" — those are different values to the daemon's loader (fleetd ticket #635's
+# follow-up comment measured `""` reading back as a null field anyway, which is exactly why the
+# two forms must not collapse onto each other: `--set path=` refuses instead of silently reaching
+# this same null outcome through the back door). Read the RAW line with grep, never only through
+# `yq` — `yq eval` reports `null` for both an actual null and a missing/absent key, so it cannot
+# tell "wrote null" apart from "wrote nothing"; only the literal line on disk can.
+test_explicit_null_writes_bare_null_not_empty_string() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.maxLoad=null'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "explicit null clear exit code"
+  local raw_line
+  raw_line="$(grep -E 'maxLoad' "$dir/fleetd.yaml")"
+  assert_contains "null" "$raw_line" "the installed line must spell a bare null"
+  assert_not_contains '""' "$raw_line" "the installed line must NOT be a quoted empty string"
+}
+
+# ------------------------------------------------------- acceptance criterion 11: backup never committable
+# A backup of fleetd.yaml inherits fleetd.yaml's own "never commit this" requirement (fleetd #635
+# follow-up, ticket comment 17655). Proves two things: the backup lands somewhere `git
+# check-ignore` reports as ignored (equivalently, a path `git status --porcelain` never lists as
+# untracked), AND that --restore still finds and uses it from that location.
+test_backup_is_never_committable() {
+  local dir backup
+  dir="$(new_fixture)"
+  cp "$dir/fleetd.yaml" "$dir/pre-edit.yaml"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.weight=55'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+  assert_equals 0 "$RUN_RC" "setup edit exit code"
+
+  backup="$(ls -t "$dir"/.config-backups/fleetd.yaml.bak.* 2>/dev/null | head -1)"
+  [ -n "$backup" ] || fail "no backup found under .config-backups/ — did the location change?"
+
+  git -C "$ROOT" check-ignore -q -- "$backup" \
+    || fail "the backup at $backup is NOT gitignored — it would survive a git add -A"
+  if git -C "$ROOT" status --porcelain -- "$backup" 2>/dev/null | grep -q '^??'; then
+    fail "git status still lists the backup as untracked: $backup"
+  fi
+
+  start_run "$dir" 5 --restore
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+  assert_equals 0 "$RUN_RC" "--restore after the backup-location change exit code"
+  cmp -s "$dir/fleetd.yaml" "$dir/pre-edit.yaml" \
+    || fail "--restore from the new backup location must still put the file back byte for byte"
+}
+
+# --------------------------------------------------------- acceptance criterion 12: file mode
+# `mv` from a mktemp candidate carries mktemp's 0600 forever, and a plain `cp` onto an existing
+# file keeps the DESTINATION's mode rather than the source's, so a restore does not undo the
+# narrowing either (fleetd #635 follow-up, ticket comment 17657). Proves the mode survives an edit
+# AND a subsequent restore, from two different starting points — 644 is the common case, 600
+# proves the fix PRESERVES whatever mode was there rather than hardcoding 644.
+test_file_mode_survives_edit_and_restore() {
+  local dir want got
+  for want in 644 600; do
+    dir="$(new_fixture)"
+    chmod "$want" "$dir/fleetd.yaml"
+
+    start_run "$dir" 5 --set ".profiles.sonnet.weight=${want}"
+    sleep 1
+    printf 'config reloaded\n' >> "$dir/fleetd.out"
+    collect_run "$dir"
+    assert_equals 0 "$RUN_RC" "mode-preservation setup edit exit code ($want)"
+    got="$(stat -f '%Lp' "$dir/fleetd.yaml" 2>/dev/null || stat -c '%a' "$dir/fleetd.yaml")"
+    assert_equals "$want" "$got" "mode must survive a --set ($want)"
+
+    start_run "$dir" 5 --restore
+    sleep 1
+    printf 'config reloaded\n' >> "$dir/fleetd.out"
+    collect_run "$dir"
+    assert_equals 0 "$RUN_RC" "mode-preservation restore exit code ($want)"
+    got="$(stat -f '%Lp' "$dir/fleetd.yaml" 2>/dev/null || stat -c '%a' "$dir/fleetd.yaml")"
+    assert_equals "$want" "$got" "mode must survive a --restore ($want)"
+  done
+}
+
+# ----------------------------------------- acceptance criterion 14: restore message names the real directory
+# fleetd #635 follow-up (ticket comment 17664, defect 6) — the --restore "no backup found"
+# message used to print the OLD beside-the-config glob even though newest_backup had already
+# moved to searching the managed directory. Proves BOTH directions: the not-found message names
+# the directory actually searched (not merely that it says SOMETHING), and that a real backup
+# sitting in that directory still lets --restore succeed — otherwise the fix could regress into
+# a message that is always printed regardless of whether a backup exists.
+test_restore_message_names_the_searched_directory() {
+  local dir rc=0
+
+  # Direction 1: no backup anywhere — the message must name .config-backups/, not the bare
+  # beside-the-config glob the OLD code printed.
+  dir="$(new_fixture)"
+  "$EDIT" --restore --config "$dir/fleetd.yaml" --log "$dir/fleetd.out" --wait-seconds 2 \
+    > "$dir/stdout.log" 2>&1 || rc=$?
+  RUN_OUTPUT="$(cat "$dir/stdout.log")"
+
+  assert_equals 1 "$rc" "--restore with no backup anywhere exit code"
+  assert_contains ".config-backups/fleetd.yaml.bak.*" "$RUN_OUTPUT" \
+    "the not-found message must name the directory actually searched, not the old beside-the-config glob"
+
+  # Direction 2: a real backup IS present in .config-backups/ — --restore must still succeed, so
+  # the message fix cannot have turned into one that prints regardless of whether a backup exists.
+  dir="$(new_fixture)"
+  cp "$dir/fleetd.yaml" "$dir/pre-edit.yaml"
+  start_run "$dir" 5 --set '.profiles.sonnet.weight=77'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+  assert_equals 0 "$RUN_RC" "setup edit exit code for criterion 14's second half"
+
+  start_run "$dir" 5 --restore
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+  assert_equals 0 "$RUN_RC" "--restore with a real backup present must still succeed"
+  cmp -s "$dir/fleetd.yaml" "$dir/pre-edit.yaml" \
+    || fail "--restore with a real backup present must put the file back byte for byte"
+}
+
+# ------------------------- acceptance criterion 15a: block-scalar continuation lines are redacted
+# fleetd #635 follow-up (ticket comment 17670, defect 7) — redact() used to look only AT the key
+# line. A YAML block scalar (`|`) puts its value on the lines that FOLLOW the key, each indented
+# deeper than it, so the real secret flowed through untouched while the key line right above it
+# printed a reassuring "<redacted>" — worse than no redaction, because the marker stops a reader
+# from looking further. The edited key here ("retries") sits directly next to the block scalar,
+# well inside diff -u's default 3-line context window, so the printed hunk is GUARANTEED to
+# include the secret's lines — placing the edit further away would let this pass today even
+# without the fix, proving nothing (the ticket comment's own warning, from the lead's first
+# reproduction attempt). The positive control runs FIRST: without it, "the secret never entered
+# the diff at all" would pass identically to "it entered and was correctly redacted".
+new_fixture_block_scalar() {
+  local dir
+  dir="$(mktemp -d "$TMP/fixture.XXXXXX")"
+  cat > "$dir/fleetd.yaml" <<'YAML'
+bind:
+  host: 127.0.0.1
+  port: 19999
+broker:
+  uri: amqp://user:hunter2@host/vhost
+auth:
+  token: |
+    FAKELEAK-BLOCK-SCALAR
+  retries: 1
+profiles:
+  sonnet:
+    weight: 3
+    maxLoad: 5
+YAML
+  : > "$dir/fleetd.out"
+  printf '%s' "$dir"
+}
+
+test_block_scalar_continuation_is_redacted() {
+  local dir
+  dir="$(new_fixture_block_scalar)"
+
+  start_run "$dir" 5 --set '.auth.retries=2'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "block-scalar case reload exit code"
+  # Positive control FIRST: the key's own (masked) line must really be in the printed diff, or the
+  # negative assertion right after proves nothing — see the comment above this test.
+  assert_contains "token:" "$RUN_OUTPUT" "block-scalar case: the key's line must be in the printed diff"
+  assert_contains "<redacted>" "$RUN_OUTPUT" "block-scalar case: redaction must be proven to have run on real content"
+  assert_not_contains "FAKELEAK-BLOCK-SCALAR" "$RUN_OUTPUT" "block-scalar case: the block scalar's VALUE must never leak"
+}
+
+# ------------------------------------- acceptance criterion 15b: "passphrase" is also recognised
+# "passphrase" was in none of TOKEN|SECRET|PASSWORD|PASSWD|CREDENTIAL|URI|_KEY (ticket comment
+# 17670). This is a plain key:value line, not a block scalar — kept in its OWN fixture and OWN
+# function, separate from criterion 15a, so that a failure in one case can never mask a failure in
+# the other (a single combined test would abort under `set -e` at its first failing assertion,
+# and the second case would then never even run).
+new_fixture_passphrase() {
+  local dir
+  dir="$(mktemp -d "$TMP/fixture.XXXXXX")"
+  cat > "$dir/fleetd.yaml" <<'YAML'
+bind:
+  host: 127.0.0.1
+  port: 19999
+broker:
+  uri: amqp://user:hunter2@host/vhost
+auth:
+  passphrase: FAKELEAK-PASSPHRASE
+  retries: 1
+profiles:
+  sonnet:
+    weight: 3
+    maxLoad: 5
+YAML
+  : > "$dir/fleetd.out"
+  printf '%s' "$dir"
+}
+
+test_passphrase_key_is_redacted() {
+  local dir
+  dir="$(new_fixture_passphrase)"
+
+  start_run "$dir" 5 --set '.auth.retries=2'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "passphrase case reload exit code"
+  assert_contains "passphrase:" "$RUN_OUTPUT" "passphrase case: the key's line must be in the printed diff"
+  assert_contains "<redacted>" "$RUN_OUTPUT" "passphrase case: redaction must be proven to have run on real content"
+  assert_not_contains "FAKELEAK-PASSPHRASE" "$RUN_OUTPUT" "passphrase case: the passphrase VALUE must never leak"
+}
+
+# ----------------------------------- acceptance criterion 16: a failing --set must not echo value
+# fleetd #635 follow-up (ticket comment 17673, defect 8) — apply_set_pairs used to echo the FULL
+# "$kv" (path=value, exactly as typed) in its yq-failure messages, so a broken --set with a
+# secret-looking value printed that value right back out. The path alone is what the positive
+# control proves is still there — it is what the operator needs to fix their command — and the
+# negative assertion proves the value itself never appears. Kept to exactly this one failure
+# shape (an invalid yq path/expression), matching the ticket's own reproduction.
+test_failing_set_does_not_echo_its_value() {
+  local dir rc=0
+  dir="$(new_fixture)"
+  cp "$dir/fleetd.yaml" "$dir/pre-edit.yaml"
+
+  "$EDIT" --dry-run --set '.broker.["bad=FAKELEAK-SETVALUE' \
+    --config "$dir/fleetd.yaml" --log "$dir/fleetd.out" --wait-seconds 2 \
+    > "$dir/stdout.log" 2>&1 || rc=$?
+  RUN_OUTPUT="$(cat "$dir/stdout.log")"
+
+  [ "$rc" -ne 0 ] || fail "a --set with an invalid yq expression must exit non-zero, got 0"
+  cmp -s "$dir/fleetd.yaml" "$dir/pre-edit.yaml" \
+    || fail "a failing --set must install nothing — the live fixture changed"
+  # Positive control FIRST: the path must still be in the message, or the negative assertion right
+  # after proves nothing (the message could simply have disappeared entirely).
+  assert_contains '.broker.["bad' "$RUN_OUTPUT" "the failure message must still name the PATH"
+  assert_not_contains "FAKELEAK-SETVALUE" "$RUN_OUTPUT" "the failure message must NEVER echo the VALUE"
+}
+
+# dry-run must never touch the live file and must still redact.
+test_dry_run_never_installs_and_redacts() {
+  local dir before
+  dir="$(new_fixture)"
+  before="$(cat "$dir/fleetd.yaml")"
+
+  "$EDIT" --dry-run --set '.profiles.sonnet.weight=99' \
+    --config "$dir/fleetd.yaml" --log "$dir/fleetd.out" --wait-seconds 2 \
+    > "$dir/stdout.log" 2>&1
+  local rc=$?
+  RUN_OUTPUT="$(cat "$dir/stdout.log")"
+
+  assert_equals 0 "$rc" "dry-run exit code"
+  assert_equals "$before" "$(cat "$dir/fleetd.yaml")" "dry-run must never write the live config"
+  assert_not_contains "hunter2" "$RUN_OUTPUT" "dry-run diff must also be redacted"
+  assert_contains "99" "$RUN_OUTPUT" "dry-run diff must show the candidate value"
+  # Same positive-control reasoning as acceptance criterion 13, applied to the dry-run diff path.
+  assert_contains "<redacted>" "$RUN_OUTPUT" "the dry-run diff's redaction must be PROVEN to have run, not merely absent"
+}
+
+# --check is read-only and always exits 0, even against a dead "daemon".
+test_check_is_read_only_and_exits_zero() {
+  local dir before rc=0
+  dir="$(new_fixture)"
+  before="$(cat "$dir/fleetd.yaml")"
+
+  "$EDIT" --check --config "$dir/fleetd.yaml" --log "$dir/fleetd.out" \
+    > "$dir/stdout.log" 2>&1 || rc=$?
+
+  assert_equals 0 "$rc" "--check exit code"
+  assert_equals "$before" "$(cat "$dir/fleetd.yaml")" "--check must never modify the config"
+}
+
+test_refusal_shape_from_parse_failure_wording_is_recognised() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.weight=6'
+  sleep 1
+  printf 'config reload from %s refused, keeping the running config: boom\n' "$dir/fleetd.yaml" >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 4 "$RUN_RC" "the parse-failure refusal shape must also exit 4, not be read as silence"
+}
+
+echo "== acceptance criterion 1: refusal restores byte for byte =="
+test_refusal_restores_byte_for_byte
+echo "== acceptance criterion 2: clean reload keeps the edit =="
+test_clean_reload_keeps_the_edit
+echo "== acceptance criterion 3: deferred reload told apart from clean =="
+test_deferred_reload_is_told_apart_from_clean
+echo "== acceptance criterion 4: silence is its own answer =="
+test_silence_is_its_own_answer
+echo "== acceptance criterion 5: broken candidate never reaches the live path =="
+test_broken_candidate_never_reaches_live_path
+echo "== acceptance criterion 6: the marker works =="
+test_marker_skips_lines_before_it
+echo "== acceptance criterion 7 (+13: redaction is proven to have run) =="
+test_redaction_holds
+echo "== acceptance criterion 9: a forgotten value refuses and installs nothing =="
+test_forgotten_value_refuses_and_installs_nothing
+echo "== acceptance criterion 10: an explicit clear writes a bare null =="
+test_explicit_null_writes_bare_null_not_empty_string
+echo "== acceptance criterion 11: a backup is never committable =="
+test_backup_is_never_committable
+echo "== acceptance criterion 12: the file mode survives an edit and a restore =="
+test_file_mode_survives_edit_and_restore
+echo "== acceptance criterion 14: the restore message names the directory actually searched =="
+test_restore_message_names_the_searched_directory
+echo "== acceptance criterion 15a: a block scalar's continuation lines are redacted =="
+test_block_scalar_continuation_is_redacted
+echo "== acceptance criterion 15b: a passphrase key is also recognised =="
+test_passphrase_key_is_redacted
+echo "== acceptance criterion 16: a failing --set must not echo its value =="
+test_failing_set_does_not_echo_its_value
+echo "== extra: dry-run never installs, and redacts =="
+test_dry_run_never_installs_and_redacts
+echo "== extra: --check is read-only and always exits 0 =="
+test_check_is_read_only_and_exits_zero
+echo "== extra: the parse-failure refusal shape is also recognised =="
+test_refusal_shape_from_parse_failure_wording_is_recognised
+
+printf 'PASS: config-edit acceptance criteria\n'