fix(security): caddy-event self-noise conjunction filter for host curl probes (DC-118) [glm-grade=A]

The host-side uptime watchdog and on-host cron jobs curl Caddy with a stock
curl/8.5.0 UA from loopback and the host tailscale IP — ~300 GET /api/health
401 warn-events/day burying real perimeter signal (census: 339+20 of 5000
access.log lines). Dropping on UA alone would blind the store to external
curl scanners, so generic tool UAs (curl/) are now dropped ONLY when the
source remote_ip is one of this host's own addresses (DASHCADDY_SELF_IPS,
default loopback; start.sh derives 127.0.0.1 + tailscale ip -4, empty-safe).
remote_ip (TCP peer) is used, never the spoofable client_ip. DashCaddy-*
probe UAs stay unconditionally dropped. 9 regression pins cover the full
conjunction matrix incl. external-IP+curl KEPT and spoofed-XFF KEPT.
2858/2858 green (128 suites).

Judge: glm-4.6@zai-coding-paas cold-read round 1 = A clean (0 blocking),
both polish notes folded. URN urn:ump:s2sgitfepze65crtp57dpdw4gk4w7upsoi4tqcvfwahcsicyepba

dashcaddy-api/src/security/event-workers.js

@@ -240,8 +240,25 @@ function startCaddyWorker({ log: logger = log } = {}) {
     'DashCaddy-Probe/1.0',        // health-checker + upstream watcher
     'DashCaddy-HealthCheck/1.0',  // startup validator
   ];
-  function isSelfNoise(userAgent) {
-    return !!userAgent && SELF_NOISE_UAS.some(ua => userAgent.startsWith(ua));
+  // DC-118: the host-side uptime watchdog and on-host cron jobs curl Caddy
+  // with a stock curl/<ver> UA from the machine's own addresses (~300
+  // events/day of GET /api/health 401). Dropping on UA alone would also
+  // hide a real attacker using curl, so GENERIC UAs are only dropped when
+  // the source IP is one of this host's own addresses: loopback always,
+  // plus DASHCADDY_SELF_IPS (start.sh passes the tailscale IP). Uses
+  // remote_ip (the TCP peer), never client_ip (X-Forwarded-For is
+  // spoofable and must not be able to opt an attacker out of the store).
+  // Prefix match (not equality) so version skew — curl/7.68, curl/8.5,
+  // future curl/10 — all match; curl-impersonate-* deliberately does not.
+  const GENERIC_PROBE_UAS = ['curl/'];
+  const selfIps = new Set(
+    (process.env.DASHCADDY_SELF_IPS || '127.0.0.1,::1')
+      .split(',').map(s => s.trim()).filter(Boolean)
+  );
+  function isSelfNoise(userAgent, ip) {
+    if (!userAgent) return false;
+    if (SELF_NOISE_UAS.some(ua => userAgent.startsWith(ua))) return true;
+    return selfIps.has(ip) && GENERIC_PROBE_UAS.some(ua => userAgent.startsWith(ua));
   }
 
   return createTail({
@@ -271,7 +288,10 @@ function startCaddyWorker({ log: logger = log } = {}) {
       // old single-value read always produced null metadata.
       const uaHeader = (req.headers && (req.headers['User-Agent'] || req.headers['user-agent'])) || null;
       const userAgent = Array.isArray(uaHeader) ? uaHeader[0] : uaHeader;
-      if (isSelfNoise(userAgent)) return;
+      // DC-118: conjunction filter — see isSelfNoise. remote_ip (TCP peer),
+      // never client_ip (spoofable X-Forwarded-For must not opt an attacker
+      // out of the security store).
+      if (isSelfNoise(userAgent, ip)) return;
 
       // Severity mapping
       let severity = 'info';