[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/routes/calendar.js

@@ -142,8 +142,21 @@ module.exports = function createCalendarRoutes({
     if (req.body.user !== undefined) updates.user = req.body.user || null;
     if (updates.name !== undefined) updates.name = String(updates.name).slice(0, 120);
     if (req.body.pass !== undefined || req.body.token !== undefined) {
+      // DC-170: preserve the credential TYPE not being updated — the old write
+      // stored {pass: body.pass ?? null, token: body.token ?? null}, so
+      // updating pass on a token-authenticated source (or vice versa) nulled
+      // the other field and broke the source's stored credential.
+      let existingCreds = {};
+      try {
+        const raw = await credentialManager.retrieve(`calendar:source:${existing.id}`);
+        if (raw) existingCreds = JSON.parse(raw);
+      } catch (_) { /* start from empty */ }
+      const next = {
+        pass: req.body.pass !== undefined ? req.body.pass : (existingCreds.pass ?? null),
+        token: req.body.token !== undefined ? req.body.token : (existingCreds.token ?? null),
+      };
       await credentialManager.store(`calendar:source:${existing.id}`,
-        JSON.stringify({ pass: req.body.pass ?? null, token: req.body.token ?? null }),
+        JSON.stringify(next),
         { label: `Calendar source ${existing.name}`, updatedAt: new Date().toISOString() });
     }
     await calendarStateManager.updateItem(existing.id, updates);
@@ -174,7 +187,9 @@ module.exports = function createCalendarRoutes({
 
     const results = await Promise.allSettled(wanted.map(async (source) => {
       if (source.type === 'ics') {
-        const resp = await fetchT(source.url, { timeout: 15000 });
+        // DC-170: fetchT ignores opts.timeout (undici) — the 15s intent ran at
+        // the 5s HTTP_DEFAULT. Pass it as the third arg (timeoutMs).
+        const resp = await fetchT(source.url, {}, 15000);
         if (!resp.ok) throw new Error(`ICS fetch HTTP ${resp.status}`);
         // Bounded read (judge r3 blocker): same 5 MiB cap as the CalDAV path —
         // a misbehaving feed must not balloon API memory.

dashcaddy-api/routes/config/settings.js

@@ -28,7 +28,15 @@ module.exports = function({ configStateManager: _configStateManager, asyncHandle
       return res.json({ setupComplete: false });
     }
     const data = await fsp.readFile(ctx.CONFIG_FILE, 'utf8');
-    const config = JSON.parse(data);
+    let config;
+    try {
+      config = JSON.parse(data);
+    } catch (_) {
+      // DC-170: a corrupt/partial config.json (e.g. non-atomic write crash)
+      // previously 500'd this PUBLIC endpoint on every dashboard load.
+      // Degrade to the setup wizard instead of an error page.
+      return res.json({ setupComplete: false, corrupt: true });
+    }
     res.json(config);
   }, 'config-get'));
 

dashcaddy-api/routes/dns.js

@@ -718,11 +718,17 @@ module.exports = function({
 
       const text = await response.text();
 
+      // DC-170: every path must answer — bare returns left requests hanging
       if (!text || text.trim() === '') {
-        return // Error handled by middleware
+        return errorResponse(res, 'Empty response from DNS server update check', 502);
       }
 
-      const result = JSON.parse(text);
+      let result;
+      try {
+        result = JSON.parse(text);
+      } catch (_) {
+        return errorResponse(res, 'DNS server returned a non-JSON update response', 502);
+      }
 
       if (result.status === 'ok') {
         success(res, {
@@ -735,11 +741,11 @@ module.exports = function({
           instructionsLink: result.response.instructionsLink || null
         });
       } else {
-        // Error handled by middleware
+        return errorResponse(res, `DNS server update check failed: ${result.message || result.status}`, 502);
       }
     } catch (error) {
       log.error('dns', error, null, { note: 'DNS update check error' });
-      // Error handled by middleware
+      return errorResponse(res, safeErrorMessage(error), error.statusCode || 502);
     }
   }, 'dns-check-update'));
 
@@ -776,12 +782,17 @@ module.exports = function({
 
       const checkText = await checkResponse.text();
       if (!checkText || checkText.trim() === '') {
-        return // Error handled by middleware
+        return errorResponse(res, 'Empty response from DNS server update check', 502);
+      }
+      let checkResult;
+      try {
+        checkResult = JSON.parse(checkText);
+      } catch (_) {
+        return errorResponse(res, 'DNS server returned a non-JSON update response', 502);
       }
-      const checkResult = JSON.parse(checkText);
 
       if (checkResult.status !== 'ok') {
-        return // Error handled by middleware
+        return errorResponse(res, `DNS server update check failed: ${checkResult.message || checkResult.status}`, 502);
       }
 
       if (!checkResult.response.updateAvailable) {
@@ -807,7 +818,7 @@ module.exports = function({
       });
     } catch (error) {
       log.error('dns', error, null, { note: 'DNS update error' });
-      // Error handled by middleware
+      return errorResponse(res, safeErrorMessage(error), error.statusCode || 502);
     }
   }, 'dns-update'));