Unify URL resolution, add health checker sync, and make modules optional

- Add url-resolver.js with single resolveServiceUrl() used by all 5 consumers
  (probes, health routes, health checker auto-config)
- Health checker now does full sync (add/update/remove) instead of add-only,
  and re-syncs automatically after every services.json mutation
- docker-maintenance and log-digest are now optional imports with try/catch,
  preventing container crashes when these files are absent
- Add null guards in routes/logs.js for graceful 503 responses

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dashcaddy-api/startup-validator.js

@@ -10,6 +10,7 @@ const path = require('path');
 const http = require('http');
 const https = require('https');
 const { exists, isAccessible } = require('./fs-helpers');
+const { resolveServiceUrl } = require('./url-resolver');
 
 /**
  * Validate startup configuration and environment.
@@ -146,17 +147,19 @@ async function validateStartupConfig({ log, CADDYFILE_PATH, SERVICES_FILE, CONFI
 }
 
 /**
- * Auto-configure health checker from services.json + top-card services.
+ * Full-sync health checker from services.json + top-card services.
+ * Adds missing, updates changed URLs, removes deleted services.
  *
  * @param {Object} deps
  * @param {Function} deps.log - structured logger
  * @param {string} deps.SERVICES_FILE
  * @param {Object} deps.servicesStateManager - StateManager instance
  * @param {Object} deps.healthChecker - health checker module
- * @param {Function} deps.buildDomain - builds domain from subdomain
+ * @param {Function} deps.buildServiceUrl - canonical URL builder
+ * @param {Object} deps.siteConfig - site config (dnsServers, etc.)
  * @param {Object} deps.APP - app constants (USER_AGENTS)
  */
-async function syncHealthCheckerServices({ log, SERVICES_FILE, servicesStateManager, healthChecker, buildDomain, APP }) {
+async function syncHealthCheckerServices({ log, SERVICES_FILE, servicesStateManager, healthChecker, buildServiceUrl, siteConfig, APP }) {
   try {
     const topCardServices = [
       { id: 'dns1', name: 'DNS1' },
@@ -164,6 +167,11 @@ async function syncHealthCheckerServices({ log, SERVICES_FILE, servicesStateMana
       { id: 'internet', name: 'Internet' },
     ];
 
+    // Add dns3 if it exists in dnsServers config
+    if (siteConfig?.dnsServers?.dns3) {
+      topCardServices.push({ id: 'dns3', name: 'DNS3' });
+    }
+
     let appServices = [];
     if (await exists(SERVICES_FILE)) {
       const data = await servicesStateManager.read();
@@ -171,38 +179,47 @@ async function syncHealthCheckerServices({ log, SERVICES_FILE, servicesStateMana
     }
 
     const allServices = [...topCardServices, ...appServices];
-    const configuredIds = new Set(Object.keys(healthChecker.config.services || {}));
-    let added = 0;
+    const desiredIds = new Set();
+    let added = 0, updated = 0, removed = 0;
 
     for (const svc of allServices) {
       const id = svc.id || svc.name?.toLowerCase();
-      if (!id || configuredIds.has(id)) continue;
+      if (!id) continue;
+      desiredIds.add(id);
 
-      let url;
-      if (id === 'internet') {
-        url = 'https://www.google.com';
-      } else if (svc.isExternal && svc.externalUrl) {
-        url = svc.externalUrl;
-      } else {
-        url = `https://${buildDomain(id)}`;
+      const url = resolveServiceUrl(id, svc, siteConfig, buildServiceUrl);
+      const existing = healthChecker.config.services?.[id];
+
+      if (!existing) {
+        healthChecker.configureService(id, {
+          name: svc.name || id,
+          url,
+          method: 'HEAD',
+          timeout: 5000,
+          expectedStatusCodes: [200, 201, 204, 301, 302, 303, 307, 308, 401, 403],
+          headers: { 'User-Agent': APP.USER_AGENTS.HEALTH },
+        });
+        added++;
+      } else if (existing.url !== url) {
+        healthChecker.configureService(id, { ...existing, url });
+        updated++;
       }
-
-      healthChecker.configureService(id, {
-        name: svc.name || id,
-        url,
-        method: 'HEAD',
-        timeout: 5000,
-        expectedStatusCodes: [200, 201, 204, 301, 302, 303, 307, 308, 401, 403],
-        headers: { 'User-Agent': APP.USER_AGENTS.HEALTH },
-      });
-      added++;
     }
 
-    if (added > 0) {
-      log.info('health', 'Auto-configured services from services.json', { count: added });
+    // Remove services no longer in the desired set
+    const configuredIds = Object.keys(healthChecker.config.services || {});
+    for (const id of configuredIds) {
+      if (!desiredIds.has(id)) {
+        healthChecker.removeService(id);
+        removed++;
+      }
+    }
+
+    if (added > 0 || updated > 0 || removed > 0) {
+      log.info('health', 'Health checker synced', { added, updated, removed });
     }
   } catch (error) {
-    log.error('health', 'Error syncing services', { error: error.message });
+    log.error('health', 'Error syncing health checker', { error: error.message });
   }
 }