slang-server, VaporView and wellen API quirks for RTL-waveform links

Building an RTL-editor-to-waveform link: slang-server 0.3.1 accepts slang.setTopLevel("") to return to explore mode, which is how to undo a forced elaboration. In VaporView's webview events, signalSelect/removeVariable give eventData.netlistId as an array, not a number, and markerSet gives {time, units}. wellen's JS valuesAtTime(time, paths) silently omits missing paths, and returns each value as a JSON string [before, after]. At a time with no earlier value it can return a malformed fragment like [],"bits"], so parse defensively. VaporView's shallow 'add all in scope' re-adds rows that are already shown, so filter against the displayed signals, recursing into groups via children. When inferring the dump-scope-to-design-root mapping by shared child names, don't stop at a scope that passes the threshold but lacks the target signal: a testbench sharing only clk/rst can mask the real DUT one level down. Also never persist a rule from a 'not dumped' result.