fulcrum: convert to a role, de-Uptime-Kuma the health check

685-line playbook becomes 33 lines plus a 426-line role
(install/service/healthcheck phases, six templates, one handler).
fulcrum_vars.yml is deleted; its content is the role's defaults.

Verified: fulcrum untouched - active since 2026-07-29 (no restart), 192G datadir,
height 966842, bitcoind and db_mem unchanged on disk. Second run changed=1 (the
arming run, changed_when: false aside). vipy changed=0.

THREE PRE-EXISTING LANDMINES the check-mode diff caught, any of which a faithful
extraction would have detonated:

- bitcoin_rpc_host was "192.168.1.140", commented "IP of knots_box_local". But
  .140 is fulcrum-box ITSELF; knots-box is .135. The DHCP leases had reshuffled -
  the fifth instance of this same disease in this estate. The live config had
  been hand-corrected to knots-box; running the playbook would have reverted it
  and pointed Fulcrum at itself. Now addressed by Tailscale name.

- The `Restart fulcrum` handler was guarded by uptime_kuma_enabled, so the three
  tasks that notify it (SSL cert, fulcrum.conf, systemd unit) could not restart
  anything. A config change applied to disk, reported success, and silently never
  took effect. That is worse than the other banner casualties: it makes the
  deployment itself lie. Ungated.

- db_mem was about to go 2048 -> 4448 (75% of 5931MB RAM), leaving ~1.4GB for the
  OS and Fulcrum's non-cache memory. The live value had been hand-tuned down.
  fulcrum_db_mem_mb_override pins it. Note set_fact outranks role defaults, so
  the calculation itself has to honour the override.

MY OWN ERROR, third instance: retyping `copy:` as `template:` lost `owner:` on
the banner and on fulcrum.conf. Rather than keep catching these by eye, every
managed path's owner/group/mode is now compared against `git show HEAD:`
mechanically - 12/12 match.

The health check timer had not fired since 2026-02-17 while reporting `active`
and `enabled`. It is OnBootSec + OnUnitActiveSec with no OnCalendar: OnBootSec
elapses once, and OnUnitActiveSec needs the SERVICE to have run this boot to have
anything to schedule from. Restarting the timer does not supply that; running the
service does, so the role now runs the check once after enabling. Also dropped
`Requires=fulcrum.service` from the timer - on a timer that means "stop watching
when the watched thing stops".

Diagnostic note: NextElapseUSecRealtime is always empty for a monotonic timer, so
it reads as broken even when healthy. I misread it once and wrongly called the
timer dead. Use NextElapseUSecMonotonic or systemctl list-timers.

fulcrum_ssl_port and fulcrum_tailscale_hostname moved to services_config.yml -
the socket-proxy play on the edge host needs them and a role default cannot reach
a second play.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ansible/roles/fulcrum/README.md

@@ -0,0 +1,65 @@
+# `fulcrum`
+
+Deploys [Fulcrum](https://github.com/cculianu/Fulcrum), an Electrum server
+indexing the Bitcoin Knots node, on `fulcrum-box`. The second play in the
+calling playbook publishes its SSL port from the edge host via `socket_proxy`.
+
+Converted from `deploy_fulcrum_playbook.yml` (685 lines) under Plan 6. The
+playbook is now 33 lines.
+
+## The index is the expensive thing
+
+`{{ fulcrum_db_dir }}` is ~192 GB and takes days to rebuild. Nothing in this role
+touches it beyond `state: directory` with the ownership it already has
+(`fulcrum:fulcrum 0755`). Restarting Fulcrum re-opens the database; it does not
+reindex.
+
+## Three things this conversion fixed, all pre-existing
+
+**`bitcoind` pointed at the wrong machine.** The vars file carried
+`bitcoin_rpc_host: "192.168.1.140"` commented "IP of knots_box_local", but `.140`
+is **fulcrum-box itself** — knots-box is `.135`. The DHCP leases had reshuffled.
+The live config had already been hand-corrected to `knots-box`; running the
+playbook would have reverted it and broken indexing. Now addressed by Tailscale
+name, like everything else in this repo.
+
+**The restart handler was inert.** It carried
+`when: uptime_kuma_enabled | default(false)`, so the three tasks that notify it
+(SSL certificate, `fulcrum.conf`, systemd unit) could not restart anything. A
+configuration change would write to disk, report success, and silently never take
+effect. Ungated.
+
+**`db_mem` was about to quadruple.** The role computes a share of RAM; on this
+5931 MB host 75% is 4448 MB, leaving ~1.4 GB for the OS and Fulcrum's non-cache
+memory. The live value had been hand-tuned to 2048. `fulcrum_db_mem_mb_override`
+pins it. Note `set_fact` outranks role defaults, so the *calculation* has to
+honour the override — pinning it in `defaults/` alone is silently ignored.
+
+## The health check timer, and how to read it
+
+The timer is `OnBootSec` + `OnUnitActiveSec` with no `OnCalendar`. That
+combination has a failure mode worth knowing: `OnBootSec` is monotonic and
+elapses once; `OnUnitActiveSec` schedules relative to the **service** last being
+active. If the service does not run in a given boot, there is no reference to
+schedule from and the timer sits `active` and `enabled` doing nothing. That is
+exactly what had happened here — last trigger **2026-02-17**, seven months of no
+health check, with every surface-level indicator green.
+
+Restarting the timer does not supply that reference; running the service does.
+So the role runs the check once after enabling the timer, which is both the fix
+and a smoke test.
+
+**Diagnosing this is easy to get wrong**: `NextElapseUSecRealtime` is always
+empty for a monotonic timer, so it looks broken even when it is fine. Read
+`NextElapseUSecMonotonic`, or just use `systemctl list-timers`.
+
+The timer also no longer carries `Requires=fulcrum.service`. On a timer that
+means "stop watching when the watched thing stops", which is backwards for a
+health check.
+
+## Monitoring: one variable, no product knowledge
+
+The check tests the Electrum TCP port and records the answer in its exit code,
+which systemd keeps: `systemctl is-failed fulcrum-healthcheck.service`. To report
+elsewhere set `healthcheck_push_url` to any endpoint accepting an HTTP ping. The
+Uptime Kuma API calls, monitor creation and token handling are gone.

ansible/roles/fulcrum/defaults/main.yml

@@ -0,0 +1,78 @@
+# Fulcrum Configuration Variables
+
+# Version - Pinned to specific release
+fulcrum_version: "2.1.0"  # Fulcrum version to install
+
+# Directories
+fulcrum_db_dir: /mnt/fulcrum_data/fulcrum_db  # Database directory (heavy data on special mount)
+fulcrum_config_dir: /etc/fulcrum  # Config file location (standard OS path)
+fulcrum_lib_dir: /var/lib/fulcrum  # Other data files (banner, etc.) on OS disk
+fulcrum_binary_path: /usr/local/bin/Fulcrum
+
+# Network - Bitcoin RPC connection
+# Bitcoin Knots is on a different host (knots_box_local)
+# Using RPC user/password authentication (credentials from infra_secrets.yml)
+# Addressed by Tailscale name, never a LAN IP. This was
+#   bitcoin_rpc_host: "192.168.1.140"  # IP of knots_box_local
+# but .140 is fulcrum-box ITSELF - knots-box is .135. The DHCP leases had
+# reshuffled (the same drift that transposed the inventory), so running this
+# playbook would have pointed Fulcrum at itself and broken indexing. The live
+# config had already been hand-corrected to knots-box; this makes the repo
+# agree with it.
+bitcoin_rpc_host: "knots-box"
+bitcoin_rpc_port: 8332  # Bitcoin Knots RPC port
+# Note: bitcoin_rpc_user and bitcoin_rpc_password are loaded from infra_secrets.yml
+
+# Network - Fulcrum server
+fulcrum_tcp_port: 50001
+# Shared with the socket-proxy play on the edge host, so it lives in
+# services_config.yml rather than only here.
+fulcrum_ssl_port: "{{ service_settings.fulcrum.ssl_port }}"
+# Binding address for Fulcrum TCP/SSL server:
+#   - "127.0.0.1" = localhost only (use when Caddy is on the same box)
+#   - "0.0.0.0" = all interfaces (use when Caddy is on a different box)
+#   - Specific IP = bind to specific network interface
+fulcrum_tcp_bind: "0.0.0.0"  # Default: localhost (change to "0.0.0.0" if Caddy is on different box)
+fulcrum_ssl_bind: "0.0.0.0"  # Binding address for SSL port
+# If Caddy is on a different box, set this to the IP address that Caddy will use to connect
+
+# SSL/TLS Configuration
+fulcrum_ssl_enabled: true
+fulcrum_ssl_cert_path: "{{ fulcrum_config_dir }}/fulcrum.crt"
+fulcrum_ssl_key_path: "{{ fulcrum_config_dir }}/fulcrum.key"
+fulcrum_ssl_cert_days: 3650  # 10 years validity for self-signed cert
+
+# Port forwarding configuration (for public access via VPS)
+fulcrum_tailscale_hostname: "{{ service_settings.fulcrum.tailscale_hostname }}"
+
+# Performance
+# db_mem will be calculated as 75% of available RAM automatically in playbook
+# db_mem is computed as this share of RAM unless fulcrum_db_mem_mb is set
+# explicitly. On a 5931 MB host 75% is 4448 MB, which leaves ~1.4 GB for the
+# OS and for Fulcrum's non-cache memory; the live config had been hand-tuned
+# down to 2048 and that setting is respected below.
+fulcrum_db_mem_percent: 0.75  # 75% of RAM for database cache
+
+# Configuration options
+fulcrum_anon_logs: true  # Anonymize client IPs and TxIDs in logs
+fulcrum_peering: false  # Disable peering with other Fulcrum servers
+fulcrum_zmq_allow_hashtx: true  # Allow ZMQ hashtx notifications
+
+# Service user
+fulcrum_user: fulcrum
+fulcrum_group: fulcrum
+
+
+# --- Health check -----------------------------------------------------------
+# Checks the Electrum TCP port and records the answer in its exit code, which
+# systemd keeps: `systemctl is-failed fulcrum-healthcheck.service`.
+#
+# WHERE TO REPORT HEALTH — the one place to plug in monitoring. Empty means
+# check, exit honestly, report nowhere. Any endpoint accepting an HTTP ping
+# works; nothing here is specific to a monitoring product.
+healthcheck_push_url: ""
+
+# Explicit db_mem in MB. When set it wins over fulcrum_db_mem_percent; empty
+# means compute from RAM. Set here because the live host had been hand-tuned to
+# 2048 and a silent jump to 4448 is not something a refactor should do.
+fulcrum_db_mem_mb_override: 2048

ansible/roles/fulcrum/handlers/main.yml

@@ -0,0 +1,15 @@
+---
+# Ungated on purpose. The hand-written handler carried
+#   when: uptime_kuma_enabled | default(false)
+# so it has been inert since the decommissioning: three tasks notify it (the SSL
+# certificate, fulcrum.conf and the systemd unit), and none of them could
+# actually restart Fulcrum. A configuration change therefore applied to disk and
+# silently never took effect — the worst kind of quiet failure, because the
+# playbook reports success and the running service keeps its old settings.
+#
+# Restarting Fulcrum re-opens its database; it does not reindex.
+- name: Restart fulcrum
+  systemd:
+    name: fulcrum
+    state: restarted
+    daemon_reload: yes

ansible/roles/fulcrum/tasks/healthcheck.yml

@@ -0,0 +1,62 @@
+---
+# Everything here answers "is Fulcrum healthy" and records the answer. The
+# Uptime Kuma specifics that used to follow — an embedded Python script creating
+# monitors over the API, a /tmp credentials file, push-URL extraction and a
+# systemd Environment= rewrite — are gone. Where it reports is now one variable,
+# healthcheck_push_url. See the role README.
+- name: Create Fulcrum health check script
+  ansible.builtin.template:
+    src: healthcheck.sh.j2
+    dest: /usr/local/bin/fulcrum-healthcheck-push.sh
+    owner: root
+    group: root
+    mode: '0755'
+    validate: "bash -n %s"
+
+- name: Create systemd service for Fulcrum health check
+  ansible.builtin.template:
+    src: healthcheck.service.j2
+    dest: /etc/systemd/system/fulcrum-healthcheck.service
+    owner: root
+    group: root
+    mode: '0644'
+
+- name: Create systemd timer for Fulcrum health check
+  ansible.builtin.template:
+    src: healthcheck.timer.j2
+    dest: /etc/systemd/system/fulcrum-healthcheck.timer
+    owner: root
+    group: root
+    mode: '0644'
+
+- name: Reload systemd daemon for health check
+  systemd:
+    daemon_reload: yes
+
+# state: restarted, not started. The hand-written timer had got itself stuck
+# `active` with no next elapse and had not fired since 2026-02-17; `started` on
+# an already-active timer is a no-op and would have left it stuck. Restarting
+# re-arms it. See the note in healthcheck.timer.j2.
+- name: Enable and restart the Fulcrum health check timer
+  systemd:
+    name: fulcrum-healthcheck.timer
+    enabled: yes
+    state: restarted
+    daemon_reload: yes
+
+# Run the check once, which is both a smoke test and the thing that actually
+# arms the timer.
+#
+# This timer is OnBootSec + OnUnitActiveSec with no OnCalendar. OnBootSec is
+# monotonic and had long since elapsed; OnUnitActiveSec schedules relative to the
+# SERVICE last being active, and the service had not run since 2026-02-17 — so
+# there was no reference to schedule from and the timer sat `active` and
+# `enabled` with NextElapseUSecMonotonic=infinity. Restarting the timer alone
+# does not supply that reference; running the service does.
+#
+# (Diagnosing this is easy to get wrong: NextElapseUSecRealtime is always empty
+# for a monotonic timer, so it looks broken even when it is fine. Read
+# NextElapseUSecMonotonic, or just use `systemctl list-timers`.)
+- name: Run the Fulcrum health check once to arm the timer
+  command: systemctl start fulcrum-healthcheck.service
+  changed_when: false

ansible/roles/fulcrum/tasks/install.yml

@@ -0,0 +1,146 @@
+---
+- name: Calculate db_mem as a share of system RAM
+  set_fact:
+    fulcrum_db_mem_mb: "{{ (ansible_memtotal_mb | float * fulcrum_db_mem_percent) | int }}"
+  when: fulcrum_db_mem_mb_override | string | length == 0
+
+- name: Use the explicit db_mem override
+  set_fact:
+    fulcrum_db_mem_mb: "{{ fulcrum_db_mem_mb_override }}"
+  when: fulcrum_db_mem_mb_override | string | length > 0
+  changed_when: false
+
+- name: Display calculated db_mem value
+  debug:
+    msg: "Setting db_mem to {{ fulcrum_db_mem_mb }} MB ({{ (fulcrum_db_mem_percent * 100) | int }}% of {{ ansible_memtotal_mb }} MB total RAM)"
+
+- name: Display Fulcrum version to install
+  debug:
+    msg: "Installing Fulcrum version {{ fulcrum_version }}"
+
+- name: Install required packages
+  apt:
+    name:
+      - curl
+      - wget
+      - openssl
+    state: present
+    update_cache: yes
+
+- name: Create fulcrum group
+  group:
+    name: "{{ fulcrum_group }}"
+    system: yes
+    state: present
+
+- name: Create fulcrum user
+  user:
+    name: "{{ fulcrum_user }}"
+    group: "{{ fulcrum_group }}"
+    system: yes
+    shell: /usr/sbin/nologin
+    home: /home/{{ fulcrum_user }}
+    create_home: yes
+    state: present
+
+- name: Create Fulcrum database directory (heavy data on special mount)
+  file:
+    path: "{{ fulcrum_db_dir }}"
+    state: directory
+    owner: "{{ fulcrum_user }}"
+    group: "{{ fulcrum_group }}"
+    mode: '0755'
+
+- name: Create Fulcrum config directory
+  file:
+    path: "{{ fulcrum_config_dir }}"
+    state: directory
+    owner: root
+    group: "{{ fulcrum_group }}"
+    mode: '0755'
+
+- name: Create Fulcrum lib directory (for banner and other data files)
+  file:
+    path: "{{ fulcrum_lib_dir }}"
+    state: directory
+    owner: "{{ fulcrum_user }}"
+    group: "{{ fulcrum_group }}"
+    mode: '0755'
+
+# ===========================================
+# SSL Certificate Generation
+# ===========================================
+- name: Check if SSL certificate already exists
+  stat:
+    path: "{{ fulcrum_ssl_cert_path }}"
+  register: fulcrum_ssl_cert_exists
+  when: fulcrum_ssl_enabled | default(false)
+
+- name: Generate self-signed SSL certificate for Fulcrum
+  command: >
+    openssl req -x509 -newkey rsa:4096
+    -keyout {{ fulcrum_ssl_key_path }}
+    -out {{ fulcrum_ssl_cert_path }}
+    -sha256 -days {{ fulcrum_ssl_cert_days }}
+    -nodes
+    -subj "/C=XX/ST=Decentralized/L=Bitcoin/O=Fulcrum/OU=Electrum/CN=fulcrum.local"
+  args:
+    creates: "{{ fulcrum_ssl_cert_path }}"
+  when: fulcrum_ssl_enabled | default(false)
+  notify: Restart fulcrum
+
+- name: Set SSL certificate permissions
+  file:
+    path: "{{ fulcrum_ssl_cert_path }}"
+    owner: "{{ fulcrum_user }}"
+    group: "{{ fulcrum_group }}"
+    mode: '0644'
+  when: fulcrum_ssl_enabled | default(false) and fulcrum_ssl_cert_exists.stat.exists | default(false) or fulcrum_ssl_enabled | default(false)
+
+- name: Set SSL key permissions
+  file:
+    path: "{{ fulcrum_ssl_key_path }}"
+    owner: "{{ fulcrum_user }}"
+    group: "{{ fulcrum_group }}"
+    mode: '0600'
+  when: fulcrum_ssl_enabled | default(false)
+
+- name: Check if Fulcrum binary already exists
+  stat:
+    path: "{{ fulcrum_binary_path }}"
+  register: fulcrum_binary_exists
+  changed_when: false
+
+- name: Download Fulcrum binary tarball
+  get_url:
+    url: "https://github.com/cculianu/Fulcrum/releases/download/v{{ fulcrum_version }}/Fulcrum-{{ fulcrum_version }}-x86_64-linux.tar.gz"
+    dest: "/tmp/Fulcrum-{{ fulcrum_version }}-x86_64-linux.tar.gz"
+    mode: '0644'
+  when: not fulcrum_binary_exists.stat.exists
+
+- name: Extract Fulcrum binary
+  unarchive:
+    src: "/tmp/Fulcrum-{{ fulcrum_version }}-x86_64-linux.tar.gz"
+    dest: "/tmp"
+    remote_src: yes
+  when: not fulcrum_binary_exists.stat.exists
+
+- name: Install Fulcrum binary
+  copy:
+    src: "/tmp/Fulcrum-{{ fulcrum_version }}-x86_64-linux/Fulcrum"
+    dest: "{{ fulcrum_binary_path }}"
+    owner: root
+    group: root
+    mode: '0755'
+    remote_src: yes
+  when: not fulcrum_binary_exists.stat.exists
+
+- name: Verify Fulcrum binary installation
+  command: "{{ fulcrum_binary_path }} --version"
+  register: fulcrum_version_check
+  changed_when: false
+
+- name: Display Fulcrum version
+  debug:
+    msg: "{{ fulcrum_version_check.stdout_lines }}"
+

ansible/roles/fulcrum/tasks/main.yml

@@ -0,0 +1,6 @@
+---
+# import_tasks, not include_tasks: static imports stay visible to --list-tasks,
+# which is how this conversion was verified against the playbook it replaced.
+- ansible.builtin.import_tasks: install.yml
+- ansible.builtin.import_tasks: service.yml
+- ansible.builtin.import_tasks: healthcheck.yml

ansible/roles/fulcrum/tasks/service.yml

@@ -0,0 +1,54 @@
+---
+- name: Create Fulcrum banner file
+  ansible.builtin.template:
+    src: banner.txt.j2
+    dest: "{{ fulcrum_lib_dir }}/fulcrum-banner.txt"
+    owner: "{{ fulcrum_user }}"
+    group: "{{ fulcrum_group }}"
+    mode: '0644'
+
+- name: Create Fulcrum configuration file
+  ansible.builtin.template:
+    src: fulcrum.conf.j2
+    dest: "{{ fulcrum_config_dir }}/fulcrum.conf"
+    owner: "{{ fulcrum_user }}"
+    group: "{{ fulcrum_group }}"
+    mode: '0640'
+  notify: Restart fulcrum
+
+- name: Create systemd service file for Fulcrum
+  ansible.builtin.template:
+    src: fulcrum.service.j2
+    dest: /etc/systemd/system/fulcrum.service
+    owner: root
+    group: root
+    mode: '0644'
+  notify: Restart fulcrum
+
+- name: Reload systemd daemon
+  systemd:
+    daemon_reload: yes
+
+- name: Enable and start Fulcrum service
+  systemd:
+    name: fulcrum
+    enabled: yes
+    state: started
+
+- name: Wait for Fulcrum to start
+  wait_for:
+    port: "{{ fulcrum_tcp_port }}"
+    host: "{{ fulcrum_tcp_bind }}"
+    delay: 5
+    timeout: 30
+  ignore_errors: yes
+
+- name: Check Fulcrum service status
+  systemd:
+    name: fulcrum
+  register: fulcrum_service_status
+  changed_when: false
+
+- name: Display Fulcrum service status
+  debug:
+    msg: "Fulcrum service is {{ 'running' if fulcrum_service_status.status.ActiveState == 'active' else 'not running' }}"

ansible/roles/fulcrum/templates/banner.txt.j2

@@ -0,0 +1,3 @@
+counterinfra
+
+PER ASPERA AD ASTRA

ansible/roles/fulcrum/templates/fulcrum.conf.j2

@@ -0,0 +1,29 @@
+# Fulcrum Configuration
+# Generated by Ansible
+
+# Bitcoin Core/Knots RPC settings
+bitcoind = {{ bitcoin_rpc_host }}:{{ bitcoin_rpc_port }}
+rpcuser = {{ bitcoin_rpc_user }}
+rpcpassword = {{ bitcoin_rpc_password }}
+
+# Fulcrum server general settings
+datadir = {{ fulcrum_db_dir }}
+tcp = {{ fulcrum_tcp_bind }}:{{ fulcrum_tcp_port }}
+peering = {{ 'true' if fulcrum_peering else 'false' }}
+zmq_allow_hashtx = {{ 'true' if fulcrum_zmq_allow_hashtx else 'false' }}
+
+# SSL/TLS Configuration
+{% if fulcrum_ssl_enabled | default(false) %}
+ssl = {{ fulcrum_ssl_bind }}:{{ fulcrum_ssl_port }}
+cert = {{ fulcrum_ssl_cert_path }}
+key = {{ fulcrum_ssl_key_path }}
+{% endif %}
+
+# Anonymize client IP addresses and TxIDs in logs
+anon_logs = {{ 'true' if fulcrum_anon_logs else 'false' }}
+
+# Max RocksDB Memory in MiB
+db_mem = {{ fulcrum_db_mem_mb }}.0
+
+# Banner
+banner = {{ fulcrum_lib_dir }}/fulcrum-banner.txt

ansible/roles/fulcrum/templates/fulcrum.service.j2

@@ -0,0 +1,24 @@
+# MiniBolt: systemd unit for Fulcrum
+# /etc/systemd/system/fulcrum.service
+
+[Unit]
+Description=Fulcrum
+After=network.target
+
+StartLimitBurst=2
+StartLimitIntervalSec=20
+
+[Service]
+ExecStart={{ fulcrum_binary_path }} {{ fulcrum_config_dir }}/fulcrum.conf
+
+User={{ fulcrum_user }}
+Group={{ fulcrum_group }}
+
+# Process management
+####################
+Type=simple
+KillSignal=SIGINT
+TimeoutStopSec=300
+
+[Install]
+WantedBy=multi-user.target

ansible/roles/fulcrum/templates/healthcheck.service.j2

@@ -0,0 +1,14 @@
+[Unit]
+Description=Fulcrum Health Check
+After=network.target fulcrum.service
+
+[Service]
+Type=oneshot
+User=root
+ExecStart=/usr/local/bin/fulcrum-healthcheck-push.sh
+Environment=HEALTHCHECK_PUSH_URL={{ healthcheck_push_url }}
+StandardOutput=journal
+StandardError=journal
+
+[Install]
+WantedBy=multi-user.target

ansible/roles/fulcrum/templates/healthcheck.sh.j2

@@ -0,0 +1,34 @@
+#!/bin/bash
+# Fulcrum health check — managed by Ansible (roles/fulcrum)
+#
+# Checks that Fulcrum's Electrum TCP port is accepting connections, and records
+# the answer in the exit code, which systemd keeps:
+#     systemctl is-failed fulcrum-healthcheck.service
+# That is a complete answer with no monitoring system involved. Reporting
+# elsewhere is optional and generic — set healthcheck_push_url.
+
+FULCRUM_HOST="{{ fulcrum_tcp_bind }}"
+FULCRUM_PORT={{ fulcrum_tcp_port }}
+PUSH_URL="${HEALTHCHECK_PUSH_URL:-}"
+
+check_fulcrum() {
+    timeout 5 bash -c "echo > /dev/tcp/${FULCRUM_HOST}/${FULCRUM_PORT}" 2>/dev/null
+}
+
+report() {
+    local status=$1 msg=$2
+    # No push URL is normal, not an error: the exit code below is still a
+    # complete answer for anything reading unit state.
+    [ -n "$PUSH_URL" ] || return 0
+    curl -s --max-time 10 --retry 2 -o /dev/null \
+        "${PUSH_URL}?status=${status}&msg=${msg// /%20}&ping=" || true
+}
+
+if check_fulcrum; then
+    report "up" "OK"
+    exit 0
+else
+    echo "Fulcrum TCP port ${FULCRUM_PORT} not responding"
+    report "down" "Fulcrum TCP port not responding"
+    exit 1
+fi

ansible/roles/fulcrum/templates/healthcheck.timer.j2

@@ -0,0 +1,17 @@
+[Unit]
+Description=Fulcrum Health Check Timer
+# NOTE: this deliberately does NOT carry `Requires=fulcrum.service`, which the
+# hand-written unit had. Requires on a timer means the timer is stopped when the
+# required unit stops — i.e. "if the thing I am watching goes down, stop
+# watching it", which is backwards for a health check and leaves nothing to
+# re-arm the timer when the service returns. The live timer had been `active`
+# and `enabled` with NextElapseUSecMonotonic=infinity and a last trigger of
+# 2026-02-17: seven months with no health check and no outward sign of it.
+
+[Timer]
+OnBootSec=1min
+OnUnitActiveSec=1min
+Persistent=true
+
+[Install]
+WantedBy=timers.target