feat: audit phase 6 (T4) — node allocation, the Path of Exile payoff

The site borrowed PoE's visual language — passive-tree layout, plasma
connections, an RPG stats panel — without any of its mechanic. Nodes were
purely decorative. This is the interaction the concept was promising.

- New utils/allocation.ts: path-to-root walking, allocate/deallocate, edge
  state, and URL encode/decode. Pure, 17 unit tests.
- Allocation is path-connected like the game: allocating a leaf brings its
  whole path, and deallocating a node removes its descendants so nothing is
  ever orphaned. pathToRoot is cycle-safe, and a test asserts every real node
  reaches the origin.
- New pixi/allocation.ts: the path reads as "lit" by dimming everything else
  rather than brightening the selection — the tree is already near its
  brightness ceiling, so recession is the only headroom. Nodes dim via alpha
  (nothing tweens it after the entrance); connections dim via tint, because
  their alpha is driven by the permanent plasma pulse and writing to it would
  fight the animation every frame.
- Shareable via ?build=. Encoded as node ids, not indices: a bitset would be
  shorter, but any edit to data.ts would silently re-point every previously
  shared link at the wrong nodes. Decoding re-derives each path, so a
  hand-edited or partially-stale link can't produce a broken build, and
  unknown ids are dropped rather than throwing.
- Allocation hangs off a button in the modal rather than the node click,
  which already opens that modal. BuildBar shows the count with share/reset;
  share falls back to rewriting the address bar when the clipboard is blocked.

Two bugs found while verifying:
- Both deep links (?build and ?tour) had ended up nested inside the
  first-visit coach-hint setTimeout, so a shared link did nothing at all for
  a returning visitor and waited out the whole intro for everyone else —
  backwards, since a shared link is precisely the cold-arrival case. Hoisted
  to run immediately, unconditionally. A ?tour link now also skips the intro.
- A restored ?build= was wiped by the entrance, which tweens every node's
  alpha to 1 after the deep link applies. The result was a full-brightness
  tree with a counter claiming 4 allocated. Now re-applied once the entrance
  finishes.

Verified in the production build: allocating TypeScript lights
origin -> Skills -> Languages -> TypeScript and dims the rest; the counter
reads 4; the generated link restores exactly that state on a cold load; Reset
clears it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lib/components/BuildBar.svelte

@@ -0,0 +1,81 @@
+<script lang="ts">
+	// Controls for the allocated path: how many nodes, share, reset.
+	const {
+		count = 0,
+		onReset,
+		onShare
+	}: {
+		count?: number;
+		onReset: () => void;
+		onShare: () => Promise<boolean> | boolean;
+	} = $props();
+
+	let copied = $state(false);
+
+	async function share() {
+		copied = await onShare();
+		if (copied) setTimeout(() => (copied = false), 2000);
+	}
+</script>
+
+{#if count > 0}
+	<div class="build-bar" role="status" aria-live="polite">
+		<span class="count"><strong>{count}</strong> allocated</span>
+		<button onclick={share}>{copied ? '✓ Link copied' : 'Share build'}</button>
+		<button class="reset" onclick={onReset}>Reset</button>
+	</div>
+{/if}
+
+<style>
+	.build-bar {
+		position: fixed;
+		top: var(--space-5);
+		right: var(--space-5);
+		z-index: var(--z-panel-toggle);
+		display: flex;
+		align-items: center;
+		gap: var(--space-2);
+		padding: var(--space-2) var(--space-3);
+		border: 1px solid rgba(255, 215, 0, 0.4);
+		border-radius: var(--radius-pill);
+		background: rgba(10, 10, 20, 0.85);
+		font-size: 0.78rem;
+	}
+
+	.count {
+		color: var(--text-muted);
+	}
+
+	.count strong {
+		color: var(--color-gold);
+		font-variant-numeric: tabular-nums;
+	}
+
+	button {
+		padding: 0.25rem 0.6rem;
+		border: 1px solid rgba(255, 255, 255, 0.2);
+		border-radius: var(--radius-pill);
+		background: transparent;
+		color: var(--text-primary);
+		font: inherit;
+		font-size: 0.72rem;
+		cursor: pointer;
+	}
+
+	button:hover {
+		border-color: var(--color-gold);
+	}
+
+	.reset {
+		border-color: transparent;
+		color: var(--text-subtle);
+	}
+
+	@media (max-width: 767px) {
+		.build-bar {
+			top: auto;
+			bottom: calc(var(--space-5) + 3.2rem);
+			right: var(--space-2);
+		}
+	}
+</style>

src/lib/components/NodeModal.svelte

@@ -6,8 +6,13 @@
 		node,
 		visible,
 		onClose,
-		onDismiss
+		onDismiss,
+		allocated = false,
+		onToggleAllocate
 	}: {
+		allocated?: boolean;
+		/** Allocate/remove this node and its path. */
+		onToggleAllocate?: (id: string) => void;
 		node: TreeNode;
 		visible: boolean;
 		/** Explicit close (✕ button) — always immediate. */
@@ -84,6 +89,19 @@
 	>
 		<button class="close-btn" onclick={onClose} aria-label="Close dialog">✕</button>
 
+		{#if onToggleAllocate}
+			<!-- Allocation lives on a button rather than the node click, which
+			     already opens this dialog. -->
+			<button
+				class="allocate-btn"
+				class:on={allocated}
+				onclick={() => onToggleAllocate(node.id)}
+				aria-pressed={allocated}
+			>
+				{allocated ? '✓ Allocated' : '⊕ Allocate path'}
+			</button>
+		{/if}
+
 		<h2 id="modal-title">
 			{#if node.icon}
 				<img src={node.icon} alt="" class="modal-icon" />
@@ -275,6 +293,29 @@
 		backdrop-filter: blur(4px);
 	}
 
+	.allocate-btn {
+		display: inline-flex;
+		align-items: center;
+		gap: 0.35rem;
+		margin-bottom: var(--space-3);
+		padding: 0.3rem 0.75rem;
+		border: 1px solid rgba(255, 215, 0, 0.45);
+		border-radius: var(--radius-pill);
+		background: transparent;
+		color: var(--color-gold);
+		font: inherit;
+		font-size: 0.75rem;
+		cursor: pointer;
+	}
+
+	.allocate-btn:hover {
+		background: rgba(255, 215, 0, 0.12);
+	}
+
+	.allocate-btn.on {
+		background: rgba(255, 215, 0, 0.18);
+	}
+
 	.modal:focus {
 		outline: none;
 	}

src/lib/components/SkillTree.svelte

@@ -14,6 +14,9 @@
 	import CoachHint from './CoachHint.svelte';
 	import SearchPalette from './SearchPalette.svelte';
 	import JourneyMode from './JourneyMode.svelte';
+	import BuildBar from './BuildBar.svelte';
+	import { allocate, deallocate, encodeBuild, decodeBuild } from '$lib/utils/allocation';
+	import { updateAllocation } from '$lib/pixi/allocation';
 	import { getJourneyStops, findStopIndex } from '$lib/utils/journey';
 	import { MOBILE_BREAKPOINT, prefersReducedMotion } from '$lib/config';
 	import {
@@ -55,6 +58,34 @@
 	let journeyActive = $state(false);
 	let journeyStartIndex = $state(0);
 
+	// Allocated path. SvelteSet so mutation is tracked — a plain Set is not
+	// proxied by $state, the same trap that silently broke the stats panel.
+	const allocated = new SvelteSet<string>();
+
+	function toggleAllocate(id: string) {
+		const next = allocated.has(id) ? deallocate(allocated, id) : allocate(allocated, id);
+		allocated.clear();
+		for (const nodeId of next) allocated.add(nodeId);
+	}
+
+	function resetBuild() {
+		allocated.clear();
+	}
+
+	async function shareBuild(): Promise<boolean> {
+		const url = new URL(window.location.href);
+		url.searchParams.set('build', encodeBuild(allocated));
+		try {
+			await navigator.clipboard.writeText(url.toString());
+			return true;
+		} catch {
+			// Clipboard can be blocked (insecure origin, permissions). Put the link
+			// in the address bar so it is still copyable by hand.
+			history.replaceState(null, '', url);
+			return false;
+		}
+	}
+
 	function startJourney(index = 0) {
 		journeyStartIndex = index;
 		journeyActive = true;
@@ -362,18 +393,43 @@
 					// mount instead would flag someone who bounced after a second as
 					// having seen it, and they'd never get it.
 					markVisited();
-
-					// ?tour=peraton deep-links straight into that stop of the journey.
-					const tourParam = new URLSearchParams(window.location.search).get('tour');
-					if (tourParam !== null) {
-						const stops = getJourneyStops();
-						const found = findStopIndex(stops, tourParam);
-						// A bare ?tour starts from the beginning.
-						startJourney(found === -1 ? 0 : found);
-					}
 				}, entrance.durationMs + 300);
 				life.add(() => clearTimeout(hintTimer));
 			}
+
+			// Deep links, applied immediately and regardless of whether this is a
+			// first or return visit. These were previously nested inside the
+			// first-visit hint timer, so a shared ?build= or ?tour= link did nothing
+			// for a returning visitor and waited out the whole intro for everyone
+			// else — backwards, since a shared link is exactly the cold-arrival case.
+			const params = new URLSearchParams(window.location.search);
+
+			// ?build=... restores a shared allocation.
+			const shared = decodeBuild(params.get('build'));
+			if (shared.size) {
+				for (const id of shared) allocated.add(id);
+				updateAllocation(controller, allocated);
+
+				// The entrance tweens every node's alpha to 1, which lands after this
+				// and wipes the dimming. Re-apply once it has finished, or the shared
+				// build shows a full-brightness tree with a counter that disagrees.
+				const repaint = setTimeout(
+					() => updateAllocation(controller, allocated),
+					entrance.durationMs + 100
+				);
+				life.add(() => clearTimeout(repaint));
+			}
+
+			// ?tour=peraton deep-links straight into that stop of the journey.
+			const tourParam = params.get('tour');
+			if (tourParam !== null) {
+				const stops = getJourneyStops();
+				const found = findStopIndex(stops, tourParam);
+				// A bare ?tour starts from the beginning.
+				startJourney(found === -1 ? 0 : found);
+				// Don't make someone who followed a tour link sit through the intro.
+				skipIntro();
+			}
 		} catch (err) {
 			// No WebGL, or a texture failed to load. Don't strand the user on a
 			// spinner that never resolves — reveal the text version instead.
@@ -391,6 +447,13 @@
 		return () => life.dispose();
 	});
 
+	// Repaint allocation styling whenever the build changes.
+	$effect(() => {
+		// Touch .size so this re-runs on every mutation of the SvelteSet.
+		void allocated.size;
+		if (controllerRef) updateAllocation(controllerRef, allocated);
+	});
+
 	// Live tooltip element, so flip decisions use its real measured size rather
 	// than a hardcoded 280x120 guess (descriptions vary in length, so the old
 	// height constant mis-flipped tall tooltips near the viewport bottom).
@@ -445,6 +508,8 @@
 <!-- Persistent identity: name, title and the one-line hook, always on screen -->
 <Hud showSkip={introPlaying} onSkip={skipIntro} onStartJourney={() => startJourney(0)} />
 
+<BuildBar count={allocated.size} onReset={resetBuild} onShare={shareBuild} />
+
 <JourneyMode
 	active={journeyActive}
 	startIndex={journeyStartIndex}
@@ -499,6 +564,8 @@
 		visible={modalVisible}
 		onClose={closeModal}
 		onDismiss={dismissModal}
+		allocated={allocated.has(selectedNode.id)}
+		onToggleAllocate={toggleAllocate}
 	/>
 {/if}
 

src/lib/pixi/allocation.ts

@@ -0,0 +1,40 @@
+// Visual treatment for allocated nodes.
+//
+// The path reads as "lit" by dimming everything else rather than brightening
+// the selection — the tree is already near its brightness ceiling, so
+// recession is the only headroom available.
+import { isEdgeAllocated } from '$lib/utils/allocation';
+import type { SkillTreeController } from './controller';
+
+/** Alpha for nodes outside the current build. */
+const DIMMED_NODE_ALPHA = 0.22;
+/** Tint applied to connections outside the current build. */
+const DIMMED_LINE_TINT = 0x2a2a35;
+
+/**
+ * Apply (or clear) allocation styling.
+ *
+ * Nodes are dimmed via `alpha`, which nothing tweens after the entrance
+ * finishes. Connections are dimmed via `tint` instead — their alpha is driven
+ * by the permanent plasma-beam pulse, so writing to it here would fight the
+ * animation every frame.
+ */
+export function updateAllocation(ctrl: SkillTreeController, allocated: ReadonlySet<string>) {
+	const active = allocated.size > 0;
+
+	for (const obj of ctrl.nodeObjects) {
+		const lit = !active || allocated.has(obj.node.id);
+		const alpha = lit ? 1 : DIMMED_NODE_ALPHA;
+		obj.graphics.alpha = alpha;
+		obj.glowGraphics.alpha = lit ? 1 : DIMMED_NODE_ALPHA * 0.5;
+		if (obj.label) obj.label.alpha = alpha;
+	}
+
+	for (const line of ctrl.lineObjects) {
+		const lit = !active || isEdgeAllocated(allocated, line.node);
+		const tint = lit ? 0xffffff : DIMMED_LINE_TINT;
+		line.graphics.tint = tint;
+		line.glowGraphics.tint = tint;
+		line.plasmaBeam.tint = tint;
+	}
+}

src/lib/utils/allocation.test.ts

@@ -0,0 +1,116 @@
+import { describe, it, expect } from 'vitest';
+import {
+	pathToRoot,
+	allocate,
+	deallocate,
+	isEdgeAllocated,
+	encodeBuild,
+	decodeBuild
+} from './allocation';
+import { treeNodes, type TreeNode } from '$lib/data';
+
+const node = (id: string, parentId: string | null): TreeNode =>
+	({
+		id,
+		label: id,
+		description: '',
+		x: 0,
+		y: 0,
+		parentId,
+		category: 'skills',
+		size: 'small'
+	}) as TreeNode;
+
+const chain = [node('root', null), node('mid', 'root'), node('leaf', 'mid')];
+
+describe('pathToRoot', () => {
+	it('walks a leaf up to the root inclusive', () => {
+		expect(pathToRoot('leaf', chain)).toEqual(['leaf', 'mid', 'root']);
+	});
+
+	it('returns just the root for the root', () => {
+		expect(pathToRoot('root', chain)).toEqual(['root']);
+	});
+
+	it('returns nothing for an unknown id', () => {
+		expect(pathToRoot('nope', chain)).toEqual([]);
+	});
+
+	it('terminates on a cyclic parent chain', () => {
+		const cyclic = [node('a', 'b'), node('b', 'a')];
+		expect(pathToRoot('a', cyclic).length).toBe(2);
+	});
+
+	it('reaches the origin for every real node', () => {
+		for (const n of treeNodes) {
+			expect(pathToRoot(n.id).at(-1)).toBe('origin');
+		}
+	});
+});
+
+describe('allocate / deallocate', () => {
+	it('allocating a leaf brings its whole path', () => {
+		expect([...allocate([], 'leaf', chain)].sort()).toEqual(['leaf', 'mid', 'root']);
+	});
+
+	it('is idempotent', () => {
+		const once = allocate([], 'leaf', chain);
+		expect([...allocate(once, 'leaf', chain)].sort()).toEqual([...once].sort());
+	});
+
+	it('deallocating removes descendants so nothing is orphaned', () => {
+		const full = allocate([], 'leaf', chain);
+		expect([...deallocate(full, 'mid', chain)]).toEqual(['root']);
+	});
+
+	it('deallocating a leaf leaves its ancestors alone', () => {
+		const full = allocate([], 'leaf', chain);
+		expect([...deallocate(full, 'leaf', chain)].sort()).toEqual(['mid', 'root']);
+	});
+
+	it('does not mutate the input', () => {
+		const start = new Set(['root']);
+		allocate(start, 'leaf', chain);
+		expect([...start]).toEqual(['root']);
+	});
+});
+
+describe('isEdgeAllocated', () => {
+	it('is true only when both ends are allocated', () => {
+		const allocated = new Set(['root', 'mid']);
+		expect(isEdgeAllocated(allocated, chain[1])).toBe(true);
+		expect(isEdgeAllocated(allocated, chain[2])).toBe(false);
+	});
+
+	it('is false for a root node, which has no edge', () => {
+		expect(isEdgeAllocated(new Set(['root']), chain[0])).toBe(false);
+	});
+});
+
+describe('encodeBuild / decodeBuild', () => {
+	it('round-trips', () => {
+		const build = allocate([], 'lang-typescript');
+		expect(decodeBuild(encodeBuild(build))).toEqual(build);
+	});
+
+	it('is order-independent, so the same build is always the same link', () => {
+		expect(encodeBuild(['b', 'a', 'c'])).toBe(encodeBuild(['c', 'b', 'a']));
+	});
+
+	it('returns an empty build for empty or missing input', () => {
+		expect(decodeBuild(null).size).toBe(0);
+		expect(decodeBuild('').size).toBe(0);
+	});
+
+	it('discards ids that no longer exist', () => {
+		expect(decodeBuild('lang-typescript~was-deleted').has('was-deleted')).toBe(false);
+		expect(decodeBuild('lang-typescript~was-deleted').has('lang-typescript')).toBe(true);
+	});
+
+	it('repairs a hand-edited link that skips ancestors', () => {
+		// Only the leaf in the URL — the path must come back with it.
+		const decoded = decodeBuild('lang-typescript');
+		expect(decoded.has('origin')).toBe(true);
+		expect(decoded.has('languages')).toBe(true);
+	});
+});

src/lib/utils/allocation.ts

@@ -0,0 +1,93 @@
+// ==========================================================================
+// ALLOCATION — Path-of-Exile style node allocation. Pure; no DOM, no PixiJS.
+// ==========================================================================
+
+import { treeNodes, type TreeNode } from '$lib/data';
+
+/**
+ * Every node from `id` up to the root, inclusive.
+ *
+ * Allocation is path-connected like the game it borrows from: you cannot
+ * light a leaf without the branch that reaches it. Cycle-safe — a malformed
+ * parent chain terminates rather than looping forever.
+ */
+export function pathToRoot(id: string, nodes: TreeNode[] = treeNodes): string[] {
+	const byId = new Map(nodes.map((n) => [n.id, n]));
+	const path: string[] = [];
+	const seen = new Set<string>();
+
+	let current = byId.get(id);
+	while (current && !seen.has(current.id)) {
+		seen.add(current.id);
+		path.push(current.id);
+		current = current.parentId ? byId.get(current.parentId) : undefined;
+	}
+
+	return path;
+}
+
+/**
+ * Allocate a node: adds it and its whole path to the root.
+ * Returns a new set — callers hold reactive state.
+ */
+export function allocate(allocated: Iterable<string>, id: string, nodes = treeNodes): Set<string> {
+	const next = new Set(allocated);
+	for (const nodeId of pathToRoot(id, nodes)) next.add(nodeId);
+	return next;
+}
+
+/**
+ * Deallocate a node and everything downstream of it, since orphaned children
+ * would violate path-connectedness.
+ */
+export function deallocate(
+	allocated: Iterable<string>,
+	id: string,
+	nodes = treeNodes
+): Set<string> {
+	const next = new Set(allocated);
+
+	// Collect descendants breadth-first.
+	const doomed = [id];
+	while (doomed.length) {
+		const current = doomed.pop() as string;
+		next.delete(current);
+		for (const node of nodes) {
+			if (node.parentId === current && next.has(node.id)) doomed.push(node.id);
+		}
+	}
+
+	return next;
+}
+
+/** Is this edge (child → its parent) fully allocated? */
+export function isEdgeAllocated(allocated: ReadonlySet<string>, node: TreeNode): boolean {
+	return !!node.parentId && allocated.has(node.id) && allocated.has(node.parentId);
+}
+
+/**
+ * Encode for a shareable URL.
+ *
+ * Node ids rather than indices: a bitset would be shorter, but any edit to
+ * data.ts would silently re-point every previously shared link at the wrong
+ * nodes. Ids only break if an id itself is renamed, which is both rarer and
+ * fails loudly (the node is simply skipped).
+ */
+export function encodeBuild(allocated: Iterable<string>): string {
+	return [...allocated].sort().join('~');
+}
+
+/** Decode a ?build= value, discarding anything that no longer exists. */
+export function decodeBuild(value: string | null, nodes: TreeNode[] = treeNodes): Set<string> {
+	if (!value) return new Set();
+	const valid = new Set(nodes.map((n) => n.id));
+	const result = new Set<string>();
+
+	for (const id of value.split('~')) {
+		if (!valid.has(id)) continue;
+		// Re-derive the path so a hand-edited link can't produce a broken build.
+		for (const nodeId of pathToRoot(id, nodes)) result.add(nodeId);
+	}
+
+	return result;
+}