[grade=A urn:ump:qszwspay7vhx7wcpqekkkidni3ehhgidvze5qk2y22fvg2wqz3ja] fix(DC-170): reliability batch — hangs, atomicity, fail-closed, SW (audit batch 6)

8 reliability fixes across 8 files (AUDIT-2026-10-27.md findings
9/11/12/13/14/16/20 + calendar credential item):

- dns.js check-update/update HANGS: bare returns + empty else/catch
  branches left requests hanging until client timeout; every path now
  answers (502 with message); upstream JSON.parse wrapped (non-JSON ->
  502)
- calendar.js ICS fetch timeout actually applies: fetchT ignores
  opts.timeout (undici) — was running at 5s default, not the intended
  15s; now timeoutMs third arg
- calendar.js PUT /sources: updating pass no longer nulls the stored
  token (and vice versa) — existing credential record loaded, only the
  provided field overwritten
- state-manager.js ATOMIC WRITES: _atomicWrite = tmp file + fs.rename
  (POSIX-atomic); write()/update() no longer truncate-then-write the
  live file (crash mid-write corrupted services.json/config.json with
  no recovery path). Test mock extended to the tmp+rename contract
- dashboard-ws.js auth fallback FAIL-CLOSED: missing authVerifier used
  to accept any non-empty session cookie (DC-061 footgun on unwired
  boot paths); now rejects + loud CRITICAL log
- middleware.js tailscale gate: new tailscale.failClosed config (default
  off = unchanged); when set, outages/errors deny (503) instead of
  silently disabling the gate; fail-open path now logs the exact key
- sw.js: offline fallback actually works ((await match) || (await
  match) — old Promise||Promise was always truthy); only 2xx cached
  (5xx pages were stored and served as the app shell); install is
  per-URL tolerant (one bad asset kept the stale SW alive forever)
- config/settings.js GET /config (public): corrupt config.json degrades
  to {setupComplete:false, corrupt:true} instead of 500 on every load

SCOPE CORRECTION: audit finding #10 (7 reversed-arg errorResponse
sites) was a FALSE POSITIVE — those files alias message-first error();
see lesson #14. Full suite 173/173 suites, 3740/3740 tests.

dashcaddy-api/src/websocket/dashboard-ws.js

@@ -75,13 +75,12 @@ function createDashboardWS(server, deps = {}) {
   const authVerifier = typeof deps.authVerifier === 'function'
     ? deps.authVerifier
     : (req) => {
-        // Last-resort fallback: presence-only check on a non-empty
-        // session-cookie value. Used only when the caller didn't inject
-        // a real verifier (e.g. tests, unusual boot paths). Production
-        // wires the real one from app.locals.ctx.session.isValid.
-        const parsed = parseCookieHeader(req && req.headers && req.headers.cookie);
-        const raw = parsed.dashcaddy_session || parsed.sid;
-        return typeof raw === 'string' && raw.length > 0;
+        // DC-170 FAIL-CLOSED (audit 2026-10-27): the old fallback accepted ANY
+        // non-empty session cookie — the exact DC-061 footgun, resurfacing on
+        // boot paths that miss the verifier wiring. A missing verifier is a
+        // wiring bug: refuse everything and say so loudly.
+        process.stderr.write('[dashboard-ws] CRITICAL: no authVerifier injected — rejecting WS connection (fail closed). Wire ctx.session.isValid into deps.authVerifier.\n');
+        return false;
       };
 
   // Track connected clients and their subscriptions