feat: label the pipeline + buttons: add data source, add downstream step on hover

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/assets/AssetGraph/AddNode.svelte

@@ -16,6 +16,7 @@
 	import type { ScriptLang } from '$lib/gen'
 	import type { NativeTriggerKind } from './types'
 	import { PIPELINE_LANGUAGES } from './pipelineLanguages'
+	import { NODE } from '$lib/components/graph/util'
 	import type { PipelineOutputKind } from './pipelineTemplates'
 
 	// Each left-column kind is just "pipeline script triggered by <trigger
@@ -58,6 +59,9 @@
 	}
 </script>
 
+<!-- The layout gives this node a full node-width slot; centering the pill in
+     it lines it up with the nodes below whatever its label's width. -->
+<div class="flex justify-center" style="width: {NODE.width}px;">
 <PipelineInsertMenu
 	kinds={[
 		{
@@ -143,13 +147,14 @@
 	{#snippet trigger()}
 		<!-- Quiet insert affordance, mirroring the flow editor's inline +
 		     buttons (bg-surface + gray border + secondary text) — a filled
-		     accent circle outweighed every real node on the canvas. -->
+		     accent pill would outweigh every real node on the canvas. -->
 		<button
 			type="button"
-			class="w-8 h-8 rounded-full flex items-center justify-center bg-surface border border-gray-400 dark:border-gray-600 text-secondary shadow-sm hover:bg-surface-hover transition-colors cursor-pointer"
-			title="Add to pipeline"
+			class="h-8 px-3 rounded-full flex items-center gap-1.5 whitespace-nowrap bg-surface border border-gray-400 dark:border-gray-600 text-xs font-normal text-secondary shadow-sm hover:bg-surface-hover transition-colors cursor-pointer"
 		>
-			<Plus size={16} />
+			<Plus size={16} class="shrink-0" />
+			Add data source
 		</button>
 	{/snippet}
 </PipelineInsertMenu>
+</div>

frontend/src/lib/components/assets/AssetGraph/AssetGraphCanvas.svelte

@@ -31,12 +31,6 @@
 	import type { AssetKind } from '$lib/gen'
 	import { NODE } from '$lib/components/graph/util'
 
-	// Width of the + node's rendered DOM element. Sugiyama allocates a full
-	// NODE.width slot for every node, so the small round button ends up
-	// left-aligned in its slot. We compensate by shifting the + node right
-	// by half the difference so its visual center matches the slot center.
-	const ADD_NODE_WIDTH = 40
-
 	interface Props {
 		graph: AssetGraphResponse
 		selection?: AssetGraphSelection | undefined
@@ -967,9 +961,6 @@
 		const xCenter = paneWidth / 2 - bboxWidth / 2
 		return model.nodes.map<Node>((n) => {
 			const p = layoutPositions.get(n.id) ?? { x: 0, y: 0 }
-			// Compensate for the + node being narrower than its layout slot
-			// so it visually centers over the node(s) below.
-			const xShift = n.id === ADD_NODE_ID ? (NODE.width - ADD_NODE_WIDTH) / 2 : 0
 			// Activity-panel emphasis (purely visual rings, kept off `selected`
 			// which swaps the details pane). Hover wins over pin so the cursor
 			// always tracks.
@@ -1001,7 +992,7 @@
 			return {
 				id: n.id,
 				type: n.type,
-				position: { x: p.x + xCenter + xShift, y: p.y + 40 },
+				position: { x: p.x + xCenter, y: p.y + 40 },
 				data: n.data,
 				class: boundClass ?? dbtClass ?? runClass ?? assetClass,
 				selected: n.id === selectedId,

frontend/src/lib/components/assets/AssetGraph/AssetNode.svelte

@@ -425,30 +425,21 @@
 				onPick={handlePick}
 			>
 				{#snippet trigger()}
-					<!--
-						Sizing notes for the round + button:
-						  - w-6/h-6 (24px) chosen so that with border-2 (2px each
-						    side) the inner area is exactly 20px — divisible by
-						    the 16px icon to leave a 2px gap on every side. At
-						    20px / 12px before, the gap was 4px-each but the
-						    odd rounding interacted badly with svelte-flow's
-						    fractional zoom transforms and the icon drifted
-						    half a pixel off-center on certain zoom levels.
-						  - `grid place-items-center` instead of flex centering:
-						    flex's baseline alignment introduces a sub-pixel
-						    nudge on small elements that grid avoids.
-						  - `leading-none` strips the default line-height
-						    contribution that the SVG inherits via the parent's
-						    text rendering, otherwise the icon is shifted
-						    downward by ~0.5px at fractional zooms.
-					-->
+					<!-- A circle at rest; hovering widens it into a labelled pill. The
+					     label animates its max-width (width itself can't transition to
+					     auto) and never wraps, so the pill grows on one line. -->
 					<button
 						type="button"
 						onclick={(e) => e.stopPropagation()}
-						class="bg-surface border border-gray-400 dark:border-gray-600 text-secondary hover:bg-surface-hover rounded-full w-6 h-6 grid place-items-center shadow-sm leading-none"
-						title="Add downstream pipeline script"
+						class="group/add h-6 min-w-6 rounded-full flex items-center justify-center bg-surface border border-gray-400 dark:border-gray-600 text-secondary hover:text-primary hover:border-gray-500 shadow-sm leading-none overflow-hidden transition-[padding] duration-200 ease-out hover:pl-1"
+						aria-label="Add downstream step"
 					>
-						<Plus size={16} strokeWidth={2.5} />
+						<Plus size={16} strokeWidth={2.5} class="shrink-0" />
+						<span
+							class="max-w-0 opacity-0 whitespace-nowrap text-2xs font-normal transition-[max-width,opacity,margin] duration-200 ease-out group-hover/add:max-w-32 group-hover/add:opacity-100 group-hover/add:ml-1 group-hover/add:mr-2"
+						>
+							Add downstream step
+						</span>
 					</button>
 				{/snippet}
 			</PipelineInsertMenu>