Load-generation guards miss rejections that other catch blocks report

When a web page cancels an in-flight load on reload (terminating a Web Worker and rejecting its pending calls, or aborting fetch with AbortController), guarding only the open/reload function's own catch with a generation counter is not enough. Other callers awaiting the same backend (message handlers from an iframe, tree-expansion and search UI, a command runner that toasts errors) also receive the rejection and report it as a load failure. That shows up as an intermittent error (about 1 in 4 runs) on back-to-back reloads. Fix: reject cancelled calls with a tagged error (e.g. error.cancelled = true, including converting AbortError when the backend is closed), and have the central fail/toast paths ignore that tag. Also capture the generation at the start of any async state-restore and drop its result if a newer load has started.