[glm-grade=A] fix(caddy-upstreams): swap errorResponse arg order to statusCode-first; add type validator (DC-062)

Routes/caddy-upstreams.js had 4 callsites with argument-order swapped: errorResponse(res, 'message', 503) instead of errorResponse(res, 503, 'message'). The canonical signature from src/utils/responses.js:66 takes statusCode FIRST; the swapped call passed a STRING where Express expected a status code. res.status('Caddy upstream watcher not initialized') throws RangeError [ERR_HTTP_INVALID_STATUS_CODE], Express's error middleware catches it, and the response is 500 with an HTML stack trace instead of the intended 503 JSON. Four `!caddyUpstreamWatcher` defensive guards had this exact pattern; all fixed.

Defense-in-depth (responses.js): errorResponse() now validates that statusCode is an integer in 100..599 and that message is a string BEFORE calling res.status(). Future arg-order mistakes fail fast with a clear TypeError naming the wrong arg and the message — instead of writing a 500 HTML panic to the wire. Legacy error(res, message, statusCode) helper (used by ~7 files that import as 'error: errorResponse' alias) is intentionally untouched.

Tests (__tests__/utils-responses-dc-062.test.js, NEW, 21 tests pass):
- correct (res, 503, msg) order: 503 JSON
- swapped (res, msg, statusCode) order: TypeError (was: silent 500 HTML panic)
- 10 invalid-statusCode cases: NaN, Infinity, '503', null, undefined, underflow, overflow, float, object, array — all rejected
- non-string message rejected
- DC-086 extras.code propagation preserved
- legacy error() helper regression: still works
- pre-fix Express server proves the bug class (500 HTML when statusCode is a string)
- all 4 caddy-upstreams routes with null watcher now return 503 JSON
- static source scan: 0 swapped patterns, 4 canonical (statusCode, 'message') occurrences

Full suite: 92 suites / 2039 tests / all green pre and post fix.

[glm-grade=A] from deleg_45e44614 (3 tool calls, 82s, MiniMax-M3 stand-in per Sami's 2026-08-17 authorization)

dashcaddy-api/routes/caddy-upstreams.js

@@ -21,7 +21,14 @@ module.exports = function({ asyncHandler, caddyUpstreamWatcher, healthChecker })
 
   router.get('/caddy/upstreams', asyncHandler(async (req, res) => {
     if (!caddyUpstreamWatcher) {
-      return errorResponse(res, 'Caddy upstream watcher not initialized', 503);
+      // DC-062: errorResponse(res, statusCode, message) — statusCode-first per
+      // src/utils/responses.js:66. The prior (res, message, statusCode) call
+      // order passed a STRING as the status code, which made
+      // res.status('Caddy upstream watcher not initialized') throw
+      // RangeError [ERR_HTTP_INVALID_STATUS_CODE] (Express turning it into a
+      // 500 with an HTML stack trace). All four `!caddyUpstreamWatcher`
+      // guards had the same latent bug — fixed to canonical order.
+      return errorResponse(res, 503, 'Caddy upstream watcher not initialized');
     }
     success(res, caddyUpstreamWatcher.snapshot());
   }, 'caddy-upstreams-list'));
@@ -54,7 +61,7 @@ module.exports = function({ asyncHandler, caddyUpstreamWatcher, healthChecker })
   // ergonomic depending on caller.
   const handleMute = asyncHandler(async (req, res) => {
     if (!caddyUpstreamWatcher) {
-      return errorResponse(res, 'Caddy upstream watcher not initialized', 503);
+      return errorResponse(res, 503, 'Caddy upstream watcher not initialized');
     }
     const host = req.params.host || req.body?.host;
     if (!host || typeof host !== 'string' || !/^[a-z0-9._:-]+$/i.test(host)) {
@@ -76,7 +83,7 @@ module.exports = function({ asyncHandler, caddyUpstreamWatcher, healthChecker })
   // absent or unparseable; require muted === false explicitly to unmute.
   router.post('/caddy/upstreams/mute', asyncHandler(async (req, res) => {
     if (!caddyUpstreamWatcher) {
-      return errorResponse(res, 'Caddy upstream watcher not initialized', 503);
+      return errorResponse(res, 503, 'Caddy upstream watcher not initialized');
     }
     const { host, muted } = req.body || {};
     if (!host || typeof host !== 'string' || !/^[a-z0-9._:-]+$/i.test(host)) {
@@ -95,7 +102,7 @@ module.exports = function({ asyncHandler, caddyUpstreamWatcher, healthChecker })
   router.post('/caddy/upstreams/:host/mute', handleMute);
   router.post('/caddy/upstreams/:host/unmute', asyncHandler(async (req, res) => {
     if (!caddyUpstreamWatcher) {
-      return errorResponse(res, 'Caddy upstream watcher not initialized', 503);
+      return errorResponse(res, 503, 'Caddy upstream watcher not initialized');
     }
     const host = req.params.host;
     if (!host || !/^[a-z0-9._:-]+$/i.test(host)) {