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

892-line playbook becomes 40 lines plus a role with install/build/configure/
service/healthcheck phases, five templates and one handler. bitcoin_knots_vars.yml
is deleted; its content is the role's defaults.

Verified after a real run: bitcoind still active since 2026-08-19 (NO restart),
chain at 966844 blocks / 875 GB, DATUM config intact, dbcache still 200, health
check timer firing again. changed=3, all health-check. vipy changed=0.

⚠ THE BIG ONE: the playbook would have deleted the mining integration.

bitcoin.conf on the node carries a section that was hand-added and was missing
from the template entirely:

    blockmaxsize=3985000
    blockmaxweight=3985000
    blocknotify=killall -USR1 datum_gateway
    maxmempool=1000
    blockreconstructionextratxn=1000000

blocknotify is how datum_gateway learns a new block landed. Running the old
playbook would have stripped all of it and solo mining would have carried on
against a stale template - a silent failure that costs money rather than raising
an error. Also dbcache 200 -> 3528 (hand-tuned down; the calculation wants 90% of
RAM) and logging moved off the file. All now reconciled, dbcache behind
bitcoin_dbcache_mb_override.

bitcoin-knots and datum-gateway are ONE SYSTEM. Noted in the README.

AND MY OWN FIX MADE IT MORE DANGEROUS. The `Restart bitcoind` handler was guarded
by uptime_kuma_enabled, so it had been inert: bitcoin.conf and the systemd unit
both notify it and neither could restart anything - a config change applied to
disk, reported success, and never took effect. Ungating that is right, but it
converts "wrong config sitting inertly on disk" into "node restarted onto a
config that breaks mining". The ungating had to land WITH the template
reconciliation, not before it.

It also raises the bar permanently: any residual template/live difference now
restarts a Bitcoin node on every run. Four rounds of --check --diff to reach
changed=0 - the DATUM section, an explanatory comment that was rendering into the
deployed config (now a {# #} Jinja comment), a "# Pruning (optional)" comment the
live file had, and one trailing blank line.

The build path is 32 tasks all guarded by `not bitcoind_binary_exists.stat.exists`,
so a converged host skips the 30-60 minute compile and both `state: absent`
deletions. Those target /opt/bitcoin-knots/{source,bitcoin-<version>}; the chain
is in /mnt/knots_data and is never touched. Signature-verification tasks copied
verbatim.

The health check timer had last fired 2026-08-09 while reporting active/enabled -
same OnBootSec + OnUnitActiveSec dead chain as fulcrum. The role runs the check
once after enabling to supply the reference the timer schedules from.

Ownership parity checked mechanically against `git show HEAD:`, keyed by TASK
NAME rather than path - keying by path gave a false positive, because
bitcoin_knots_source_dir is created with ownership and later removed with
state: absent, so whichever task comes last wins and that differs between one
file and five. 13/13 match.

bitcoin_p2p_port and the tailscale hostname moved to services_config.yml for the
socket-proxy play on the edge host.

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

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

@@ -0,0 +1,11 @@
+[Unit]
+Description=Bitcoin Knots Health Check Timer
+Requires=bitcoind.service
+
+[Timer]
+OnBootSec=1min
+OnUnitActiveSec=1min
+Persistent=true
+
+[Install]
+WantedBy=timers.target