fix(format): don't overwrite freshly-refreshed cache on slow API resolve

Sourcery flagged a race in loadWorkspaceTimezone: if the user updated
the timezone via Settings → refreshWorkspaceTimezone while the initial
GET /settings/workspace was still in flight, the eventual resolution
of that GET would overwrite cachedTz (and localStorage) with the stale
server value, silently reverting the user's change until the next
reload.

Fix: in both the success and failure handlers, only write if cachedTz
is still null. If anything else claimed the cache in the meantime,
keep the fresher value.

Reported-by: sourcery-ai[bot] on PR #59

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

Author: lsoldado

dashboard/frontend/src/lib/format.ts

@@ -38,22 +38,33 @@ export function getTimezoneSync(): string {
   return browserTz()
 }
 
-/** Fetch from API and cache. Subsequent callers reuse the in-flight promise. */
+/** Fetch from API and cache. Subsequent callers reuse the in-flight promise.
+ *
+ * Race-safe with `refreshWorkspaceTimezone`: if the user updates the setting
+ * (or any other code path populates the cache) while this fetch is in flight,
+ * the resolved value is dropped — we never overwrite a fresher cache value
+ * with the stale server response. */
 export async function loadWorkspaceTimezone(): Promise<string> {
   if (cachedTz) return cachedTz
   if (inflight) return inflight
   inflight = api
     .get('/settings/workspace')
     .then((data: any) => {
       const tz: string = data?.workspace?.timezone || browserTz()
-      cachedTz = tz
-      try { window.localStorage.setItem(STORAGE_KEY, tz) } catch { /* noop */ }
-      return tz
+      // Only write if nothing else claimed the cache in the meantime
+      // (e.g. a concurrent refreshWorkspaceTimezone from Settings save).
+      if (cachedTz == null) {
+        cachedTz = tz
+        try { window.localStorage.setItem(STORAGE_KEY, tz) } catch { /* noop */ }
+      }
+      return cachedTz!
     })
     .catch(() => {
       const fallback = browserTz()
-      cachedTz = fallback
-      return fallback
+      if (cachedTz == null) {
+        cachedTz = fallback
+      }
+      return cachedTz!
     })
     .finally(() => { inflight = null })
   return inflight