The rate is internal/fx: a free, no-key endpoint (open.er-api.com/v6/latest/USD), cached in memory and in a small file beside magpie's other caches (XDG_CACHE_HOME/magpie/fxrate.json) for 12h, refetched only once that's stale, and falling back to the last rate it ever had — or a fixed 7.2 — while offline; the currency row's tooltip names the rate and when it was learned. usage.FormatCost carries the $/¥ formatting (2 decimals above $1, 3 below, whole numbers above 100) that usage_cli.go and internal/tui/pages.go used to each have their own copy of; both now read Settings' currency once per command/redraw rather than per row. internal/gui/api.go exposes the rate on /api/settings always and on /api/state only when cny is actually chosen, so usd users' hot path never touches the network for a rate nothing shows with.
Tested with new internal/fx/fx_test.go (a fake server: fetches and caches, answers from memory then from the cache file with no further calls, refetches once stale, falls back to a stale cache or Fallback when offline, ignores a reply with no CNY rate), TestFXInState in internal/gui/fx_test.go, TestFmtCostShowsChosenCurrency in internal/tui/usage_test.go, and a new internal/gui/tests/currency.test.cjs in Chromium and WebKit, English and Chinese (the Usage page's $ by default and ¥12.34×7.2 once cny is picked, the currency row's labels/state/tooltip, a real wheel scroll deep into Settings left alone by picking a currency, the choice surviving a reload). go build -tags nogui, GOOS=linux and GOOS=windows builds, and go test -tags nogui -count=1 ./... all pass clean.
A fetch that failed is not tried again for 10 minutes (the stale or fixed rate shown at once meanwhile), so offline each state() does not wait up to 4s on the network: TestGetDoesNotRetryAFailedFetchAtOnce.
yetone
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