Chart builder: discoverable entry points — Build Chart door, dataset picker, no-datasets state

docs/spec/02-snippet-library.md

@@ -4,10 +4,14 @@ The Snippet Library is the left pane and the primary entry point to the app. A *
 
 ## The List
 
-The list shows every saved snippet and is always visible. A persistent "Create New Snippet" affordance sits at the top of the list, above all snippets, so the user can always start a new snippet regardless of scroll position.
+The list shows every saved snippet and is always visible. A persistent **creation surface** sits at the top of the list, above all snippets, so the user can always start a new chart regardless of scroll position. It offers the two ways in with a clear hierarchy:
+
+- **Build Chart** — the primary action; opens the **Chart Builder** (see _Chart Builder_), the guided no-JSON path. The builder opens on the most recently modified dataset (or its no-datasets state when the library has none) — it is not gated on first selecting a dataset.
+- **New JSON snippet** — a ghost/tertiary action beside it; creates and selects a new snippet directly in the editor (see _Snippet Operations_ → Create New), the expert path — always visible, one click, never hidden behind the guided one.
+
+When the library pane is dragged narrow, the buttons shed their labels (the long ghost label first) and keep their icons and accessible names.
 
 - The list shows all snippets, ordered newest-modified first by default (see _Sort_).
-- A "Create New Snippet" item is pinned at the top of the list; activating it creates and selects a new snippet (see _Snippet Operations_).
 - Selecting a snippet makes it the **active snippet**: it loads into the editor and preview, becomes highlighted in the list, and the URL updates to reflect the selected snippet so the state is shareable and survives a page reload (see _Application Shell & Navigation_).
 - Exactly one snippet is active at a time.
 - When no snippets match the current search, the list shows an empty-state message ("No snippets match your search", with a hint to try a different term). This is the list's only empty state: a genuinely empty library never shows the list at all (see next).
@@ -17,8 +21,9 @@ The list shows every saved snippet and is always visible. A persistent "Create N
 
 When the library is empty — on first run, or after the user deletes their last snippet — the app does **not** seed placeholder content. Instead the **onboarding canvas takes the full workspace**, replacing the pane chrome (the pane toggle strip, the library list, the editor, and the preview): with no snippets, the library's create/search/sort/storage controls and the pane toggles have nothing to act on, so the welcome gets the whole width. The user starts from a deliberate choice rather than dropped into the middle of an unfamiliar spec.
 
-- The canvas briefly identifies what Astrolabe is, then offers two ways to begin.
+- The canvas briefly identifies what Astrolabe is, then offers the ways to begin.
 - **Create your first snippet** — the primary action; starts a new snippet from the sample bar-chart template and opens it in the editor (identical to _Create New_ under _Snippet Operations_).
+- **Build a chart from your data** — the data-first door beside the primary; opens the **Chart Builder** over the canvas. With no datasets yet, the builder's no-datasets state explains itself and leads to "Add a dataset" (see _Chart Builder → Opening_) — the path never dead-ends. Opening the builder also lays the workspace out at the default split below, since creating from the builder leaves the canvas directly.
 - An **example gallery** of a few simple snippets showcasing distinct Vega-Lite capabilities (e.g. a bar chart, a time-series line, a scatter plot, a stacked area, a donut, a binned histogram). Each example shows a **live preview** of the chart and a one-line description.
   - **Add** on an example creates it as an ordinary snippet and makes it active (opening it in the editor).
   - **Add all** creates the whole set at once and makes one of them active.