diff --git a/docs/DESIRED-STATE.md b/docs/DESIRED-STATE.md
index 030325bc..759704f7 100644
--- a/docs/DESIRED-STATE.md
+++ b/docs/DESIRED-STATE.md
@@ -103,6 +103,8 @@ GitHub App and runner-group creation remain the bootstrap responsibility tracked
 
 ## Install a fresh controller
 
+The managed installer supports Debian 12 or newer. Before reading configuration or changing the host, it verifies Docker Engine and Compose v2, Git, curl, jq, the system CA bundle, direct Docker-socket access, and that the Docker filesystem is below the documented 80% warning threshold. It rejects alternate Docker endpoints and contexts, then pins every lifecycle command to the verified local Unix socket. Rollback and uninstall require only their recovery tools, not Git, tar, cmp, host-release metadata, CA bootstrap, or capacity checks.
+
 Run the command from a reviewed checkout of ci-fleet on the target Linux Docker machine:
 
 ```bash
diff --git a/scripts/cleanup.sh b/scripts/cleanup.sh
index 6ddcd4b9..b1f6682a 100755
--- a/scripts/cleanup.sh
+++ b/scripts/cleanup.sh
@@ -1,6 +1,11 @@
 #!/usr/bin/env bash
 set -Eeuo pipefail
 
+repo_root=$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)
+# shellcheck disable=SC1091
+source "$repo_root/scripts/docker-local-env.sh"
+use_local_docker
+
 apply=false
 instance="${CI_FLEET_INSTANCE:-}"
 
@@ -18,6 +23,8 @@ while (($#)); do
   shift
 done
 
+use_local_docker
+
 command -v docker >/dev/null || { echo "ERROR docker is unavailable" >&2; exit 1; }
 docker info >/dev/null
 
diff --git a/scripts/docker-local-env.sh b/scripts/docker-local-env.sh
new file mode 100644
index 00000000..96da247e
--- /dev/null
+++ b/scripts/docker-local-env.sh
@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+
+use_local_docker() {
+  local socket=${CI_FLEET_DOCKER_SOCKET:-${CI_FLEET_ROOT_PREFIX:-}/var/run/docker.sock}
+  [[ -n "$socket" ]] || socket=/var/run/docker.sock
+  [[ -z ${DOCKER_HOST:-} || ${DOCKER_HOST} == "unix://$socket" ]] || {
+    printf 'ERROR: alternate Docker endpoints are not supported; use the local Docker socket\n' >&2
+    return 1
+  }
+  [[ -z ${DOCKER_CONTEXT:-} || ${DOCKER_CONTEXT} == default ]] || {
+    printf 'ERROR: alternate Docker contexts are not supported; use the local Docker socket\n' >&2
+    return 1
+  }
+  export DOCKER_HOST="unix://$socket"
+  export DOCKER_CONTEXT=default
+  unset DOCKER_TLS_VERIFY DOCKER_CERT_PATH DOCKER_CONFIG XDG_RUNTIME_DIR
+}
diff --git a/scripts/healthcheck.sh b/scripts/healthcheck.sh
index c06bf63f..e02c40cf 100755
--- a/scripts/healthcheck.sh
+++ b/scripts/healthcheck.sh
@@ -1,6 +1,8 @@
 #!/usr/bin/env bash
 set -Eeuo pipefail
 repo_root=$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)
+# shellcheck disable=SC1091
+source "$repo_root/scripts/docker-local-env.sh"
 environment=/etc/ci-fleet/ci-fleet.env
 args=(local)
 if [[ ${CI_FLEET_TESTING:-0} == 1 && -n ${CI_FLEET_ROOT_PREFIX:-} ]]; then
@@ -13,4 +15,5 @@ if [[ -r $environment ]]; then
   . "$environment"
   set +a
 fi
+use_local_docker
 exec python3 "$repo_root/scripts/health.py" "${args[@]}" "$@"
diff --git a/scripts/install-worker-controller.sh b/scripts/install-worker-controller.sh
index ad156566..639f36d3 100755
--- a/scripts/install-worker-controller.sh
+++ b/scripts/install-worker-controller.sh
@@ -135,12 +135,36 @@ cleanup_temporary() {
 trap cleanup_temporary EXIT
 
 require_commands() {
-  local command
-  for command in git python3 docker tar install cmp readlink systemctl stat awk grep date flock mktemp; do
+  local command docker_root disk_used os_id os_release os_version socket
+  local -a required=(python3 docker install readlink systemctl stat awk grep date flock mktemp)
+  if [[ "$mode" != rollback && "$mode" != uninstall ]]; then required+=(git tar cmp); fi
+  for command in "${required[@]}"; do
     command -v "$command" >/dev/null || die "$command is required"
   done
+  socket=$(root_path /var/run/docker.sock)
+  [[ -z ${DOCKER_CONTEXT:-} || ${DOCKER_CONTEXT} == default ]] || die 'alternate Docker contexts are not supported; use the local Docker socket'
+  [[ -z ${DOCKER_HOST:-} || ${DOCKER_HOST} == "unix://$socket" ]] || die 'alternate Docker endpoints are not supported; use the local Docker socket'
+  DOCKER_HOST=unix://$socket
+  export DOCKER_HOST
+  unset DOCKER_CONTEXT DOCKER_TLS_VERIFY DOCKER_CERT_PATH
   docker info >/dev/null 2>&1 || die 'Docker daemon is unavailable'
   docker compose version >/dev/null 2>&1 || die 'Docker Compose v2 is unavailable'
+  [[ "$mode" == rollback || "$mode" == uninstall ]] && return
+
+  for command in curl jq df openssl; do command -v "$command" >/dev/null || die "$command is required"; done
+  os_release=$(root_path /etc/os-release)
+  [[ -r "$os_release" ]] || die 'supported Linux release metadata is unavailable'
+  os_id=$(awk -F= '$1 == "ID" {gsub(/"/, "", $2); print $2}' "$os_release")
+  os_version=$(awk -F= '$1 == "VERSION_ID" {gsub(/"/, "", $2); print $2}' "$os_release")
+  [[ "$os_id" == debian && "$os_version" =~ ^[0-9]+$ ]] || die 'supported Linux is Debian 12 or newer'
+  ((10#$os_version >= 12)) || die 'supported Linux is Debian 12 or newer'
+  [[ -r $(root_path /etc/ssl/certs/ca-certificates.crt) ]] || die 'CA certificate bundle is unavailable'
+  [[ -S "$socket" && -r "$socket" && -w "$socket" || "$testing" == 1 && -e "$socket" ]] || die 'Docker socket is unavailable or inaccessible'
+  docker_root=$(docker info --format '{{.DockerRootDir}}' 2>/dev/null) || die 'Docker root directory is unavailable'
+  [[ "$docker_root" == /* ]] || die 'Docker root directory is invalid'
+  disk_used=$(df -P "$docker_root" 2>/dev/null | awk 'NR == 2 {gsub(/%/, "", $5); print $5}')
+  [[ "$disk_used" =~ ^[0-9]{1,3}$ ]] || die 'Docker disk capacity could not be determined'
+  ((disk_used < 80)) || die 'Docker filesystem must remain below 80% utilization'
 }
 
 validate_common_arguments() {
diff --git a/scripts/test-install-worker-controller.sh b/scripts/test-install-worker-controller.sh
index 2b4c6043..11d96935 100755
--- a/scripts/test-install-worker-controller.sh
+++ b/scripts/test-install-worker-controller.sh
@@ -16,6 +16,8 @@ export REAL_TAR
 REAL_TAR=$(command -v tar)
 export REAL_GIT
 REAL_GIT=$(command -v git)
+export REAL_DF
+REAL_DF=$(command -v df)
 
 cat >"$fake_bin/docker" <<'EOF'
 #!/usr/bin/env bash
@@ -23,8 +25,18 @@ set -u
 state=${FAKE_DOCKER_STATE:?}
 status_file=${FAKE_CONTROLLER_STATUS_FILE:-}
 paused_state=${FAKE_PAUSED_STATE:-}
+if [[ -n ${FAKE_REQUIRE_LOCAL_DOCKER_ENDPOINT:-} ]]; then
+  expected_socket=${CI_FLEET_ROOT_PREFIX:-}/var/run/docker.sock
+  [[ ${DOCKER_HOST:-} == "unix://$expected_socket" ]] || {
+    printf 'expected local Docker socket %s, got %s\n' "unix://$expected_socket" "${DOCKER_HOST:-<unset>}" >&2
+    exit 91
+  }
+fi
 case "${1:-}" in
-  info) exit 0 ;;
+  info)
+    [[ "$*" != *DockerRootDir* ]] || printf '%s\n' "${CI_FLEET_DOCKER_ROOT:?}"
+    exit 0
+    ;;
   inspect)
     [[ -f "$state" ]] || exit 1
     if [[ "$*" == *'.Config.Env'* ]]; then
@@ -185,7 +197,35 @@ exec "$REAL_GIT" "$@"
 EOF
 chmod 700 "$fake_bin/git"
 
+cat >"$fake_bin/df" <<'EOF'
+#!/usr/bin/env bash
+if [[ -n ${FAKE_DISK_USED_PERCENT:-} ]]; then
+  printf 'Filesystem 1024-blocks Used Available Capacity Mounted on\n'
+  printf 'fixture 100 90 10 %s%% /fixture\n' "$FAKE_DISK_USED_PERCENT"
+  exit 0
+fi
+exec "$REAL_DF" "$@"
+EOF
+chmod 700 "$fake_bin/df"
+
 export PATH="$fake_bin:$PATH"
+
+# Build a PATH that mirrors the real one but omits openssl, so the
+# installer's command-presence preflight can be exercised for the
+# remote-reconciliation dependency without disturbing the rest of the test.
+no_ssl_dir=$tmp/bin-no-ssl
+mkdir -p "$no_ssl_dir"
+IFS=: read -ra path_dirs <<< "$PATH"
+for dir in "${path_dirs[@]}"; do
+  [[ -d "$dir" ]] || continue
+  for entry in "$dir"/*; do
+    base=$(basename "$entry")
+    [[ "$base" == openssl ]] && continue
+    [[ -e "$no_ssl_dir/$base" ]] || ln -sf "$entry" "$no_ssl_dir/$base" 2>/dev/null
+  done
+done
+export NO_SSL_PATH="$no_ssl_dir"
+
 export FAKE_DOCKER_STATE=$tmp/docker-controller-running
 export FAKE_CONTROLLER_STATUS_FILE=$tmp/docker-controller-status
 export FAKE_PAUSED_STATE=$tmp/docker-controller-paused
@@ -289,7 +329,10 @@ PY
 root=$tmp/host
 export CI_FLEET_ROOT_PREFIX=$root
 export CI_FLEET_DOCKER_ROOT=$root/var/lib/docker
-mkdir -p "$root/etc/ci-fleet/secrets" "$CI_FLEET_DOCKER_ROOT"
+mkdir -p "$root/etc/ci-fleet/secrets" "$root/etc/ssl/certs" "$root/var/run" "$CI_FLEET_DOCKER_ROOT"
+printf 'ID=debian\nVERSION_ID="12"\n' >"$root/etc/os-release"
+printf 'fixture CA bundle\n' >"$root/etc/ssl/certs/ca-certificates.crt"
+: >"$root/var/run/docker.sock"
 pem=$root/etc/ci-fleet/secrets/github-app.pem
 printf 'fixture only\n' >"$pem"
 chmod 600 "$pem"
@@ -315,10 +358,32 @@ git -C "$config_repo" reset -q --hard "$ref_one"
 installer=$repo_root/scripts/install-worker-controller.sh
 base_args=(--config-repo "$config_repo" --controller example-ci-01)
 
+expect_failure 'alternate Docker endpoints are not supported' env DOCKER_HOST=tcp://example.invalid:2376 "$installer" --check "${base_args[@]}" --ref "$ref_one"
+expect_failure 'alternate Docker contexts are not supported' env DOCKER_CONTEXT=remote "$installer" --check "${base_args[@]}" --ref "$ref_one"
+printf 'ID=example\nVERSION_ID="1"\n' >"$root/etc/os-release"
+expect_failure 'supported Linux is Debian 12 or newer' "$installer" --check "${base_args[@]}" --ref "$ref_one"
+printf 'ID=debian\nVERSION_ID="12"\n' >"$root/etc/os-release"
+export FAKE_DISK_USED_PERCENT=80
+expect_failure 'Docker filesystem must remain below 80% utilization' "$installer" --check "${base_args[@]}" --ref "$ref_one"
+unset FAKE_DISK_USED_PERCENT
+
+# The installed maintenance scripts must pin the local Docker daemon themselves,
+# not just inherit it from the installer.
+export FAKE_REQUIRE_LOCAL_DOCKER_ENDPOINT=1
+expect_success "$repo_root/scripts/cleanup.sh" --apply
+unset FAKE_REQUIRE_LOCAL_DOCKER_ENDPOINT
+
+# Remote reconciliation enables the ci-fleet-reconcile timer during install,
+# and reconciliation signs the GitHub App JWT with openssl. Require openssl
+# before install/check so the enabled timer cannot fail at runtime.
+expect_failure 'openssl is required' env PATH="$NO_SSL_PATH" "$installer" --check "${base_args[@]}" --ref "$ref_one"
+
 staged_checkpoint="$root/var/lib/ci-fleet/checkpoints/.checkpoint.staging.interrupted"
 mkdir -p "$staged_checkpoint"
 : >"$staged_checkpoint/.complete"
+mv "$root/etc/os-release" "$root/etc/os-release.missing"
 expect_failure 'no controller checkpoint is available' "$installer" --rollback
+mv "$root/etc/os-release.missing" "$root/etc/os-release"
 rm -rf "$staged_checkpoint"
 expect_failure 'secret-bearing files are forbidden' "$installer" --check "${base_args[@]}" --ref "$forbidden_ref"
 expect_failure 'possible committed secret detected' "$installer" --check "${base_args[@]}" --ref "$secret_ref"
@@ -328,6 +393,7 @@ unset FAKE_WRONG_HOST_CONFIG_OWNER
 expect_failure 'managed installs require the default' "$installer" --check "${base_args[@]}" --ref "$ref_one" --host-config "$tmp/custom-host.env"
 
 first=$(expect_success "$installer" --install "${base_args[@]}" --ref "$ref_one")
+expect_success env DOCKER_CONTEXT=default "$installer" --check "${base_args[@]}" --ref "$ref_one"
 grep -Fq 'CONVERGED mode=install' <<<"$first" || fail 'fresh install did not converge'
 [[ -L "$root/opt/ci-fleet/current" && -f "$root/var/lib/ci-fleet/install-state.json" ]] || fail 'fresh install state is incomplete'
 [[ $(readlink -f "$root/opt/ci-fleet/manager/current") == "$root/opt/ci-fleet/manager/releases/$engine_ref" ]] || fail 'installer manager did not activate the desired engine release'
@@ -343,9 +409,11 @@ chmod 644 "$rendered_env"
 expect_failure 'DRIFT rendered_environment' "$installer" --check "${base_args[@]}" --ref "$ref_one"
 expect_success "$installer" --install "${base_args[@]}" --ref "$ref_one" >/dev/null
 [[ $(stat -c %a "$rendered_env") == 600 ]] || fail 'convergence did not repair rendered-environment mode'
+export FAKE_REQUIRE_LOCAL_DOCKER_ENDPOINT=1
 manual_health_result=0
 "$repo_root/scripts/healthcheck.sh" >/dev/null || manual_health_result=$?
 ((manual_health_result < 2)) || fail 'manual healthcheck did not source rendered capacity'
+unset FAKE_REQUIRE_LOCAL_DOCKER_ENDPOINT
 export FAKE_WRONG_INSTALL_STATE_OWNER=$install_state
 expect_failure 'install state must be owned by root with mode 0600' env CI_FLEET_INSTALL_STATE_FILE="$install_state" CI_FLEET_INSTALLER="$installer" "$repo_root/scripts/check-installed-state.sh"
 unset FAKE_WRONG_INSTALL_STATE_OWNER
@@ -640,7 +708,10 @@ unset FAKE_RUNNER_STATE_ONCE FAKE_ALL_RUNNER_STATE
 adopt_root=$tmp/adopt-host
 export CI_FLEET_ROOT_PREFIX=$adopt_root
 export FAKE_DOCKER_STATE=$tmp/adopt-controller-running
-mkdir -p "$adopt_root/etc/ci-fleet/secrets" "$adopt_root/opt/ci-fleet/deploy" "$adopt_root/opt/ci-fleet/scripts"
+mkdir -p "$adopt_root/etc/ci-fleet/secrets" "$adopt_root/etc/ssl/certs" "$adopt_root/var/run" "$adopt_root/opt/ci-fleet/deploy" "$adopt_root/opt/ci-fleet/scripts"
+printf 'ID=debian\nVERSION_ID="12"\n' >"$adopt_root/etc/os-release"
+printf 'fixture CA bundle\n' >"$adopt_root/etc/ssl/certs/ca-certificates.crt"
+: >"$adopt_root/var/run/docker.sock"
 adopt_pem=$adopt_root/etc/ci-fleet/secrets/github-app.pem
 printf 'fixture only\n' >"$adopt_pem"
 chmod 600 "$adopt_pem"