VAULT — EDITING, WITH BACKLINKS
Three panes, file tree on the left, backlinks on the right, Markdown in the middle. Nothing here is reinvented. The only differences are in what can appear in a link: questions and source stubs are first-class objects in the tree, in autocomplete, and in the backlinks panel, alongside ordinary notes.
TAG BROWSER — SLASH-SEPARATED, PARSED INTO A TREE
The one change to a familiar control: #ml/interpretability/probing is a path, not a string. Selecting a parent includes everything beneath it, and the count on a parent row is the inclusive count — the exclusive count is shown beside it so the difference is never a guess.
SOURCE STUB versus SOURCE WITH A FILE
Both are sources and both are linkable. The distinction is carried by one glyph, a dashed outline, and the absence of the page apparatus — so it is legible in the tree, in autocomplete, in backlinks, and on the page itself. Attaching a PDF is a drop target and a single command, and everything already linked to the stub keeps pointing at it.
GRAPH — PRESENT, NOT PROMOTED
It exists because it is expected, it is honest about what it shows, and it is not the front door. The relational view that earns its place is the Question Map, which is a different surface. Filters are the usual ones plus the two object kinds this vault adds.