"Six features that reuse four layers is a product. Six features with six private engines is a swamp."
The Shape on Screen
Before the abstractions, picture the window. A customizable toolbar on top. A collapsible left rail: a Selection Basket drop stack above a source list of devices, shared volumes, favorites, and recent items. Then the browser split — Pane A and Pane B, each with its own tab strip, breadcrumb, list-or-icon browser, and a resizable Preview/Info inspector dock. Exactly one pane is active; exactly one tab is active in each pane. That geometry is fixed. It doesn't rearrange itself, and users can't bolt panels onto it.
Six Families, Four Layers
The 1.x roadmap adds six fixed feature families: source-list ergonomics, named workspace presets, Batch Rename, the Selection Basket, the Size Browser, and Finder tag/color-label editing. Here's the discipline that keeps them from metastasizing: each one is a new client of the same four canonical layers — workspace, location reference, enumeration, and the operation engine — and never a new engine of its own.
What That Buys
Batch Rename doesn't invent a rename path; it submits normal immutable operation plans. The Selection Basket doesn't stage bytes; it stores ordered location references. The Size Browser doesn't build a second directory catalog; it derives a cancellable scan. Presets don't cache directory contents; they snapshot references. Because everything routes through the same audited layers, a bug fixed in the operation engine is fixed for all six features at once — and none of them can lose a file in a way the core can't.