Merge remote-tracking branch 'origin/main'

# Conflicts:
#	AGENTS.md
#	README.md
#	index.html
#	package.json
#	src/data/buildings.js
#	src/data/grid.js
#	src/data/pavement.js
#	src/data/plants.js
#	src/data/yard.js
#	src/lib/feature-types.js
#	src/lib/yard-features.js
#	src/main.js
#	styles.css

vendor/checkbox-tree/README.md

@@ -0,0 +1,137 @@
+# Checkbox Tree
+
+A dependency-free, instance-based checkbox tree for browser ES modules. It
+supports cascading selection, indeterminate parent states, expandable branches,
+multiple independent instances, optional local-storage persistence, and compact
+shareable URL state backed by an append-only node manifest.
+
+## Install
+
+```sh
+npm install @aaronaxvig/checkbox-tree
+```
+
+The package is not published yet. During local development, install it by path:
+
+```sh
+npm install ../checkbox-tree
+```
+
+## Usage
+
+```js
+import { CheckboxTree } from "@aaronaxvig/checkbox-tree";
+import "@aaronaxvig/checkbox-tree/styles.css";
+
+const tree = new CheckboxTree(document.querySelector("#example-tree"), {
+  initiallySelected: true,
+  storageKey: "example-tree-state",
+  onSelectionChange({ selectedIds, selectedNodes }) {
+    console.log(selectedIds, selectedNodes);
+  },
+});
+
+tree.setData([
+  {
+    id: "fruit",
+    label: "Fruit",
+    children: [
+      { id: "apple", label: "Apple", metadata: { color: "red" } },
+      { id: "pear", label: "Pear", metadata: { color: "green" } },
+    ],
+  },
+]);
+```
+
+For applications without a bundler, serve or copy the `src/` directory and use
+relative URLs. The main module imports its state-codec modules alongside it:
+
+```html
+<link rel="stylesheet" href="./checkbox-tree.css">
+<script type="module">
+  import { CheckboxTree } from "./checkbox-tree.js";
+</script>
+```
+
+Every node requires unique string `id` and `label` properties. Nodes may also
+have `children`, application-owned `metadata`, and `selectable` or `disabled`
+flags.
+
+## API
+
+- `new CheckboxTree(container, options)` creates an independent instance.
+- `setData(nodes)` validates and renders nodes, then restores saved state.
+- `getSelectedIds()` returns selected node IDs.
+- `getSelectedNodes()` returns selected source node objects.
+- `setSelectedIds(ids, { notify })` replaces the selection.
+- `restoreState()` restores selection and expansion state.
+- `destroy()` removes listeners, markup, and the root CSS class.
+- `serializeStateToFragment(manifest)` returns `#v=1&c=...&x=...` state.
+- `restoreStateFromLocation(manifest, location)` safely applies URL state.
+- `validateManifest(manifest)` reports unregistered and missing paths.
+
+Options:
+
+- `initiallyCollapsed` defaults to `true`.
+- `initiallySelected` defaults to `false`.
+- `storageKey` defaults to `null`, which disables persistence.
+- `onSelectionChange` receives `{ selectedIds, selectedNodes }`.
+- `manifest` optionally supplies a parsed manifest and automatically restores
+  state from `window.location.hash` after `setData()`.
+- `stateEncoding` selects `"adaptive"` (the default), `"dense"`, or `"tiered"`.
+  The website's configured value is the URL-format contract and is not embedded
+  in the fragment.
+
+## Shareable URL state
+
+Create a JSON manifest whose array positions are permanent slots. Canonical node
+paths join ancestor IDs with `>`:
+
+```json
+{ "schema": 1, "nodes": ["fruit", "fruit>apple", "fruit>pear", null] }
+```
+
+Import `loadManifest`, pass its result as the `manifest` option, and call
+`tree.serializeStateToFragment()` when creating a share link. Existing entries
+must never be reordered. Append new paths, replace removed paths with `null`, and
+edit a path in place for a logical rename or move. Node IDs therefore cannot
+contain `>`.
+
+The fragment adaptively encodes checked (`c`) and expanded (`x`) state using the
+shortest of a dense bitset, sparse enabled slots, or sparse disabled slots.
+Sparse slot numbers are delta-encoded variable-length integers. A coverage value
+in the disabled-slot form ensures nodes appended later still default to unchecked
+and collapsed. Malformed or unsupported state is ignored.
+The helpers `encodeTreeState`, `decodeTreeState`, `applyTreeState`, and
+`restoreStateFromLocation` are also exported for custom integrations.
+Use `validateManifestEvolution(previous, next)` in a build check to reject
+removed slots and tombstone reuse; path changes are reported for deliberate
+rename/move review.
+
+With `stateEncoding: "tiered"`, `c1` stores root checked state and each deeper
+`cN` field stores nodes whose checked state differs from their parent. Expansion
+does not inherit: every `xN` stores the actual expanded branches at that depth,
+with collapsed as the baseline. Each tier field uses the adaptive codec. The
+`n` field records manifest coverage so nodes appended later still default to
+false. A non-selectable parent supplies a false checked baseline. With
+`stateEncoding: "dense"`, `c` and `x` contain trimmed
+least-significant-bit-first bitsets.
+
+Styling is namespaced under `.checkbox-tree`. Override the custom properties
+`--checkbox-tree-indent`, `--checkbox-tree-toggle-size`, and
+`--checkbox-tree-hover-color` in the consuming application.
+
+## Development
+
+```sh
+npm install
+npm test
+npm run pack:check
+```
+
+## Future demo ideas
+
+- Add population metadata to the country, state, and county nodes and display the
+  total population represented by the current selection. Define the aggregation
+  rule carefully so checked ancestors and their checked descendants are not
+  counted twice; one option is to total only the most specific checked nodes.

vendor/checkbox-tree/checkbox-tree.css

@@ -0,0 +1,82 @@
+.checkbox-tree {
+    --checkbox-tree-indent: 18px;
+    --checkbox-tree-toggle-size: 18px;
+    --checkbox-tree-hover-color: #2c3e50;
+    font-size: 14px;
+    line-height: 1.4;
+}
+
+.checkbox-tree__item {
+    margin: 1px 0;
+}
+
+.checkbox-tree__row {
+    display: flex;
+    align-items: center;
+    min-height: 24px;
+}
+
+.checkbox-tree__toggle,
+.checkbox-tree__toggle-spacer {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    flex: 0 0 var(--checkbox-tree-toggle-size);
+    width: var(--checkbox-tree-toggle-size);
+    height: var(--checkbox-tree-toggle-size);
+    margin-right: 2px;
+}
+
+.checkbox-tree__toggle {
+    padding: 0;
+    border: 0;
+    background: transparent;
+    color: inherit;
+    cursor: pointer;
+    font: inherit;
+}
+
+.checkbox-tree__toggle[aria-expanded="true"] {
+    transform: rotate(90deg);
+}
+
+.checkbox-tree__toggle:focus-visible {
+    outline: 2px solid currentColor;
+    outline-offset: 1px;
+}
+
+.checkbox-tree__label {
+    display: inline-flex;
+    align-items: center;
+    padding: 2px 0;
+    cursor: pointer;
+    user-select: none;
+}
+
+.checkbox-tree__item:has(> .checkbox-tree__children) > .checkbox-tree__row > .checkbox-tree__label {
+    font-weight: 500;
+}
+
+.checkbox-tree__label:hover {
+    color: var(--checkbox-tree-hover-color);
+}
+
+.checkbox-tree__checkbox {
+    flex-shrink: 0;
+    width: 16px;
+    height: 16px;
+    margin: 0 4px 0 0;
+    cursor: pointer;
+}
+
+.checkbox-tree__checkbox:indeterminate {
+    accent-color: #f39c12;
+}
+
+.checkbox-tree__children {
+    margin-left: var(--checkbox-tree-indent);
+}
+
+.checkbox-tree__children[hidden] {
+    display: none;
+}

vendor/checkbox-tree/checkbox-tree.js

@@ -0,0 +1,355 @@
+// Dependency-free checkbox tree widget. State serialization lives in focused sibling modules.
+import {
+    PATH_DELIMITER,
+    assertStateEncoding
+} from './state-codec.js';
+import {
+    restoreStateFromLocation,
+    serializeStateToFragment,
+    validateManifest
+} from './tree-state.js';
+
+export {
+    PATH_DELIMITER,
+    SERIALIZATION_VERSION,
+    base64UrlToBytes,
+    bytesToBase64Url,
+    decodeAdaptiveBitset,
+    encodeAdaptiveBitset,
+    getBit,
+    loadManifest,
+    setBit
+} from './state-codec.js';
+export {
+    applyTreeState,
+    decodeTreeState,
+    encodeTreeState,
+    restoreStateFromLocation,
+    serializeStateToFragment,
+    validateManifest,
+    validateManifestEvolution
+} from './tree-state.js';
+
+const DEFAULT_OPTIONS = {
+    initiallyCollapsed: true,
+    initiallySelected: false,
+    storageKey: null,
+    onSelectionChange: null,
+    manifest: null,
+    stateEncoding: 'adaptive'
+};
+
+export class CheckboxTree {
+    constructor(container, options = {}) {
+        if (!(container instanceof Element)) {
+            throw new TypeError('CheckboxTree requires a container element.');
+        }
+
+        this.container = container;
+        this.options = { ...DEFAULT_OPTIONS, ...options };
+        assertStateEncoding(this.options.stateEncoding);
+        this.nodesById = new Map();
+        this.nodesByPath = new Map();
+        this.itemsById = new Map();
+        this.rootNodes = [];
+        this.handleChange = this.handleChange.bind(this);
+        this.handleClick = this.handleClick.bind(this);
+
+        this.container.classList.add('checkbox-tree');
+        this.container.addEventListener('change', this.handleChange);
+        this.container.addEventListener('click', this.handleClick);
+    }
+
+    setData(nodes) {
+        if (!Array.isArray(nodes)) {
+            throw new TypeError('CheckboxTree data must be an array of nodes.');
+        }
+
+        this.nodesById.clear();
+        this.nodesByPath.clear();
+        this.itemsById.clear();
+        this.rootNodes = nodes;
+        this.indexNodes(nodes);
+        this.render();
+        this.updateAllParentCheckboxes();
+        this.restoreState();
+        if (this.options.manifest) this.restoreStateFromLocation();
+    }
+
+    getSelectedIds() {
+        return this.getSelectedNodes().map(node => node.id);
+    }
+
+    getSelectedNodes() {
+        return Array.from(this.container.querySelectorAll(
+            '.checkbox-tree__checkbox:checked[data-selectable="true"]'
+        )).map(checkbox => this.nodesById.get(checkbox.dataset.nodeId)).filter(Boolean);
+    }
+
+    setSelectedIds(ids, { notify = false } = {}) {
+        const selectedIds = new Set(ids);
+        this.container.querySelectorAll('.checkbox-tree__checkbox').forEach(checkbox => {
+            checkbox.checked = checkbox.dataset.selectable === 'true' && selectedIds.has(checkbox.dataset.nodeId);
+            checkbox.indeterminate = false;
+        });
+        this.updateAllParentCheckboxes();
+        this.saveState();
+
+        if (notify) {
+            this.notifySelectionChange();
+        }
+    }
+
+    destroy() {
+        this.container.removeEventListener('change', this.handleChange);
+        this.container.removeEventListener('click', this.handleClick);
+        this.container.classList.remove('checkbox-tree');
+        this.container.replaceChildren();
+        this.nodesById.clear();
+        this.nodesByPath.clear();
+        this.itemsById.clear();
+    }
+
+    indexNodes(nodes, parentPath = '') {
+        nodes.forEach(node => {
+            if (!node || typeof node.id !== 'string' || !node.id || typeof node.label !== 'string') {
+                throw new TypeError('Each CheckboxTree node requires non-empty string id and label properties.');
+            }
+            if (this.nodesById.has(node.id)) {
+                throw new Error(`Duplicate CheckboxTree node id: ${node.id}`);
+            }
+
+            if (node.id.includes(PATH_DELIMITER)) {
+                throw new Error(`CheckboxTree node id cannot contain "${PATH_DELIMITER}": ${node.id}`);
+            }
+
+            this.nodesById.set(node.id, node);
+            const path = parentPath ? `${parentPath}${PATH_DELIMITER}${node.id}` : node.id;
+            this.nodesByPath.set(path, node);
+            if (node.children !== undefined) {
+                if (!Array.isArray(node.children)) {
+                    throw new TypeError(`CheckboxTree node children must be an array: ${node.id}`);
+                }
+                this.indexNodes(node.children, path);
+            }
+        });
+    }
+
+    render() {
+        const fragment = document.createDocumentFragment();
+        this.rootNodes.forEach(node => fragment.appendChild(this.createNodeElement(node)));
+        this.container.replaceChildren(fragment);
+    }
+
+    createNodeElement(node) {
+        const item = document.createElement('div');
+        item.className = 'checkbox-tree__item';
+        item.dataset.nodeId = node.id;
+        this.itemsById.set(node.id, item);
+
+        const row = document.createElement('div');
+        row.className = 'checkbox-tree__row';
+        const hasChildren = Array.isArray(node.children) && node.children.length > 0;
+
+        if (hasChildren) {
+            const toggle = document.createElement('button');
+            toggle.type = 'button';
+            toggle.className = 'checkbox-tree__toggle';
+            toggle.dataset.action = 'toggle';
+            toggle.setAttribute('aria-label', `Expand ${node.label}`);
+            toggle.setAttribute('aria-expanded', 'false');
+            toggle.textContent = '▶';
+            row.appendChild(toggle);
+        } else {
+            const spacer = document.createElement('span');
+            spacer.className = 'checkbox-tree__toggle-spacer';
+            spacer.setAttribute('aria-hidden', 'true');
+            row.appendChild(spacer);
+        }
+
+        const label = document.createElement('label');
+        label.className = 'checkbox-tree__label';
+        if (node.selectable !== false) {
+            const checkbox = document.createElement('input');
+            checkbox.type = 'checkbox';
+            checkbox.className = 'checkbox-tree__checkbox';
+            checkbox.dataset.nodeId = node.id;
+            checkbox.dataset.selectable = 'true';
+            checkbox.disabled = node.disabled === true;
+            checkbox.checked = this.options.initiallySelected && !checkbox.disabled;
+            label.appendChild(checkbox);
+        }
+        label.appendChild(document.createTextNode(node.label));
+        row.appendChild(label);
+        item.appendChild(row);
+
+        if (hasChildren) {
+            const children = document.createElement('div');
+            children.className = 'checkbox-tree__children';
+            children.hidden = this.options.initiallyCollapsed;
+            node.children.forEach(child => children.appendChild(this.createNodeElement(child)));
+            item.appendChild(children);
+
+            if (!this.options.initiallyCollapsed) {
+                this.setExpanded(item, true);
+            }
+        }
+
+        return item;
+    }
+
+    handleClick(event) {
+        const toggle = event.target.closest('.checkbox-tree__toggle[data-action="toggle"]');
+        if (!toggle || !this.container.contains(toggle)) {
+            return;
+        }
+
+        const item = toggle.closest('.checkbox-tree__item');
+        this.setExpanded(item, toggle.getAttribute('aria-expanded') !== 'true');
+        this.saveState();
+    }
+
+    handleChange(event) {
+        const checkbox = event.target.closest('.checkbox-tree__checkbox');
+        if (!checkbox || !this.container.contains(checkbox)) {
+            return;
+        }
+
+        const item = checkbox.closest('.checkbox-tree__item');
+        const children = this.directChildrenContainer(item);
+        if (children) {
+            children.querySelectorAll('.checkbox-tree__checkbox:not(:disabled)').forEach(child => {
+                child.checked = checkbox.checked;
+                child.indeterminate = false;
+            });
+        }
+
+        checkbox.indeterminate = false;
+        this.updateAncestorCheckboxes(item);
+        this.saveState();
+        this.notifySelectionChange();
+    }
+
+    notifySelectionChange() {
+        if (typeof this.options.onSelectionChange === 'function') {
+            this.options.onSelectionChange({
+                selectedIds: this.getSelectedIds(),
+                selectedNodes: this.getSelectedNodes()
+            });
+        }
+    }
+
+    setExpanded(item, expanded) {
+        if (!item) return;
+        const toggle = item.querySelector(':scope > .checkbox-tree__row > .checkbox-tree__toggle');
+        const children = this.directChildrenContainer(item);
+        if (!toggle || !children) {
+            return;
+        }
+
+        children.hidden = !expanded;
+        toggle.setAttribute('aria-expanded', String(expanded));
+        const label = this.nodesById.get(item.dataset.nodeId)?.label ?? 'branch';
+        toggle.setAttribute('aria-label', `${expanded ? 'Collapse' : 'Expand'} ${label}`);
+    }
+
+    directChildrenContainer(item) {
+        return item.querySelector(':scope > .checkbox-tree__children');
+    }
+
+    directCheckbox(item) {
+        return item.querySelector(':scope > .checkbox-tree__row .checkbox-tree__checkbox');
+    }
+
+    itemForNode(id) {
+        return this.itemsById.get(id) ?? null;
+    }
+
+    updateAncestorCheckboxes(item) {
+        let parentItem = item.parentElement?.closest('.checkbox-tree__item');
+        while (parentItem && this.container.contains(parentItem)) {
+            this.updateParentCheckbox(parentItem);
+            parentItem = parentItem.parentElement?.closest('.checkbox-tree__item');
+        }
+    }
+
+    updateAllParentCheckboxes() {
+        const parents = Array.from(this.container.querySelectorAll('.checkbox-tree__item'))
+            .filter(item => this.directChildrenContainer(item));
+        parents.reverse().forEach(item => this.updateParentCheckbox(item));
+    }
+
+    updateParentCheckbox(item) {
+        const checkbox = this.directCheckbox(item);
+        const children = this.directChildrenContainer(item);
+        if (!checkbox || !children) {
+            return;
+        }
+
+        const childCheckboxes = Array.from(children.querySelectorAll(
+            ':scope > .checkbox-tree__item > .checkbox-tree__row .checkbox-tree__checkbox'
+        )).filter(child => !child.disabled);
+        const hasSelection = childCheckboxes.some(child => child.checked || child.indeterminate);
+        const allSelected = childCheckboxes.length > 0 && childCheckboxes.every(child => child.checked);
+        checkbox.checked = allSelected;
+        checkbox.indeterminate = hasSelection && !allSelected;
+    }
+
+    saveState() {
+        if (!this.options.storageKey) {
+            return;
+        }
+
+        const collapsedIds = Array.from(this.container.querySelectorAll('.checkbox-tree__children[hidden]'))
+            .map(children => children.parentElement.dataset.nodeId);
+        try {
+            localStorage.setItem(this.options.storageKey, JSON.stringify({
+                version: 1,
+                selectedIds: this.getSelectedIds(),
+                collapsedIds
+            }));
+        } catch {
+            // Persistence is optional; storage may be disabled or full.
+        }
+    }
+
+    restoreState() {
+        if (!this.options.storageKey) {
+            return;
+        }
+
+        let state;
+        try {
+            state = JSON.parse(localStorage.getItem(this.options.storageKey));
+        } catch {
+            return;
+        }
+        if (!state || typeof state !== 'object') {
+            return;
+        }
+
+        if (Array.isArray(state.selectedIds)) {
+            this.setSelectedIds(state.selectedIds);
+        }
+        if (Array.isArray(state.collapsedIds)) {
+            const collapsedIds = new Set(state.collapsedIds);
+            this.container.querySelectorAll('.checkbox-tree__item').forEach(item => {
+                if (this.directChildrenContainer(item)) {
+                    this.setExpanded(item, !collapsedIds.has(item.dataset.nodeId));
+                }
+            });
+        }
+    }
+
+    validateManifest(manifest = this.options.manifest) {
+        return validateManifest(manifest, this);
+    }
+
+    serializeStateToFragment(manifest = this.options.manifest) {
+        return serializeStateToFragment(this, manifest);
+    }
+
+    restoreStateFromLocation(manifest = this.options.manifest, location = window.location) {
+        return restoreStateFromLocation(this, manifest, location);
+    }
+}

vendor/checkbox-tree/state-codec.js

@@ -0,0 +1,206 @@
+// Manifest parsing and binary codecs. This module has no DOM dependencies.
+export const SERIALIZATION_VERSION = 1;
+export const PATH_DELIMITER = '>';
+const STATE_ENCODINGS = new Set(['adaptive', 'dense', 'tiered']);
+
+export function loadManifest(source) {
+    let records;
+    let schema = 1;
+
+    if (typeof source === 'string') {
+        records = source.split(/\r?\n/)
+            .map(line => line.trim())
+            .filter(line => line && !line.startsWith('#'))
+            .map(line => line === '!deleted' ? null : line);
+    } else if (source && typeof source === 'object' && Array.isArray(source.nodes)) {
+        schema = source.schema;
+        records = source.nodes;
+    } else if (source && Array.isArray(source.slots)) {
+        return normalizeManifest(source.schema, source.slots.map(slot => slot?.deleted ? null : slot?.path));
+    } else {
+        throw new TypeError('CheckboxTree manifest must be text or an object with a nodes array.');
+    }
+
+    return normalizeManifest(schema, records);
+}
+
+function normalizeManifest(schema, records) {
+    if (schema !== 1) {
+        throw new Error(`Unsupported CheckboxTree manifest schema: ${schema}`);
+    }
+
+    const pathToSlot = new Map();
+    const slots = records.map((record, index) => {
+        if (record === null || record === '!deleted') {
+            return { path: null, deleted: true };
+        }
+        if (typeof record !== 'string' || !record || record.trim() !== record) {
+            throw new TypeError(`Invalid CheckboxTree manifest entry at slot ${index}.`);
+        }
+        if (pathToSlot.has(record)) {
+            throw new Error(`Duplicate CheckboxTree manifest path: ${record}`);
+        }
+        pathToSlot.set(record, index);
+        return { path: record, deleted: false };
+    });
+
+    return { schema: 1, slots, pathToSlot };
+}
+
+export function setBit(bytes, bitIndex, value) {
+    const byteIndex = Math.floor(bitIndex / 8);
+    const mask = 1 << (bitIndex % 8);
+    if (value) bytes[byteIndex] |= mask;
+    else bytes[byteIndex] &= ~mask;
+}
+
+export function getBit(bytes, bitIndex) {
+    const byteIndex = Math.floor(bitIndex / 8);
+    return byteIndex < bytes.length && (bytes[byteIndex] & (1 << (bitIndex % 8))) !== 0;
+}
+
+export function bytesToBase64Url(bytes) {
+    let binary = '';
+    for (const byte of bytes) binary += String.fromCharCode(byte);
+    return btoa(binary).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/g, '');
+}
+
+export function base64UrlToBytes(value, maximumLength = Infinity) {
+    if (typeof value !== 'string' || !/^[A-Za-z0-9_-]*$/.test(value) || value.length % 4 === 1) {
+        throw new Error('Invalid Base64URL value.');
+    }
+    if (Number.isFinite(maximumLength) && value.length > Math.ceil(maximumLength * 4 / 3) + 2) {
+        throw new Error('Encoded tree state exceeds the manifest size.');
+    }
+    const base64 = value.replace(/-/g, '+').replace(/_/g, '/');
+    const binary = atob(base64 + '='.repeat((4 - base64.length % 4) % 4));
+    if (binary.length > maximumLength) throw new Error('Encoded tree state exceeds the manifest size.');
+    return Uint8Array.from(binary, character => character.charCodeAt(0));
+}
+
+function trimTrailingZeroBytes(bytes) {
+    let end = bytes.length;
+    while (end && bytes[end - 1] === 0) end--;
+    return bytes.slice(0, end);
+}
+
+function encodeUnsignedVarint(value) {
+    const bytes = [];
+    do {
+        let byte = value & 0x7f;
+        value = Math.floor(value / 128);
+        if (value) byte |= 0x80;
+        bytes.push(byte);
+    } while (value);
+    return bytes;
+}
+
+function decodeUnsignedVarint(bytes, offset) {
+    let value = 0;
+    let multiplier = 1;
+    for (let index = offset; index < bytes.length && index < offset + 8; index++) {
+        const byte = bytes[index];
+        value += (byte & 0x7f) * multiplier;
+        if ((byte & 0x80) === 0) return { value, offset: index + 1 };
+        multiplier *= 128;
+        if (!Number.isSafeInteger(value) || !Number.isSafeInteger(multiplier)) break;
+    }
+    throw new Error('Invalid adaptive tree-state integer.');
+}
+
+function encodeSparseIndexes(indexes) {
+    const bytes = [];
+    let previous = -1;
+    for (const index of indexes) {
+        bytes.push(...encodeUnsignedVarint(index - previous - 1));
+        previous = index;
+    }
+    return bytes;
+}
+
+function decodeSparseIndexes(bytes, offset, limit) {
+    const indexes = new Set();
+    let previous = -1;
+    while (offset < bytes.length) {
+        const decoded = decodeUnsignedVarint(bytes, offset);
+        const index = previous + decoded.value + 1;
+        if (index >= limit) throw new Error('Sparse tree state contains an out-of-range slot.');
+        indexes.add(index);
+        previous = index;
+        offset = decoded.offset;
+    }
+    return indexes;
+}
+
+export function encodeAdaptiveBitset(values, slotCount) {
+    const enabled = [];
+    const disabled = [];
+    const denseBytes = new Uint8Array(Math.ceil(slotCount / 8));
+    for (const [slot, value] of values) {
+        (value ? enabled : disabled).push(slot);
+        setBit(denseBytes, slot, value);
+    }
+    enabled.sort((left, right) => left - right);
+    disabled.sort((left, right) => left - right);
+    if (enabled.length === 0) return new Uint8Array();
+
+    const candidates = [
+        Uint8Array.from([0, ...trimTrailingZeroBytes(denseBytes)]),
+        Uint8Array.from([1, ...encodeSparseIndexes(enabled)]),
+        Uint8Array.from([2, ...encodeUnsignedVarint(slotCount), ...encodeSparseIndexes(disabled)])
+    ];
+    return candidates.reduce((shortest, candidate) =>
+        candidate.length < shortest.length ? candidate : shortest
+    );
+}
+
+export function decodeAdaptiveBitset(bytes, slotCount) {
+    if (bytes.length === 0) return () => false;
+    const mode = bytes[0];
+    if (mode === 0) {
+        const dense = bytes.slice(1);
+        if (dense.length > Math.ceil(slotCount / 8)) {
+            throw new Error('Dense tree state exceeds the manifest size.');
+        }
+        return slot => getBit(dense, slot);
+    }
+    if (mode === 1) {
+        const enabled = decodeSparseIndexes(bytes, 1, slotCount);
+        return slot => enabled.has(slot);
+    }
+    if (mode === 2) {
+        const coverage = decodeUnsignedVarint(bytes, 1);
+        if (coverage.value > slotCount) throw new Error('Tree-state coverage exceeds the manifest size.');
+        const disabled = decodeSparseIndexes(bytes, coverage.offset, coverage.value);
+        return slot => slot < coverage.value && !disabled.has(slot);
+    }
+    throw new Error('Unknown adaptive tree-state mode.');
+}
+
+
+export function encodeDenseBitset(values, slotCount) {
+    const bytes = new Uint8Array(Math.ceil(slotCount / 8));
+    for (const [slot, value] of values) setBit(bytes, slot, value);
+    return trimTrailingZeroBytes(bytes);
+}
+
+export function decodeDenseBitset(bytes, slotCount) {
+    if (bytes.length > Math.ceil(slotCount / 8)) {
+        throw new Error('Dense tree state exceeds the manifest size.');
+    }
+    return slot => getBit(bytes, slot);
+}
+
+export function maximumEncodedLength(slotCount) {
+    return Math.max(Math.ceil(slotCount / 8) + 1, slotCount * 2 + 10);
+}
+
+export function assertStateEncoding(encoding) {
+    if (!STATE_ENCODINGS.has(encoding)) {
+        throw new Error(`Unsupported CheckboxTree state encoding: ${encoding}`);
+    }
+}
+
+export function asManifestSource(manifest) {
+    return manifest?.pathToSlot instanceof Map ? manifest : loadManifest(manifest);
+}

vendor/checkbox-tree/tree-state.js

@@ -0,0 +1,310 @@
+// Adapts pure state codecs to CheckboxTree's rendered node model and URL format.
+import {
+    PATH_DELIMITER,
+    SERIALIZATION_VERSION,
+    asManifestSource as asManifest,
+    assertStateEncoding,
+    base64UrlToBytes,
+    bytesToBase64Url,
+    decodeAdaptiveBitset,
+    decodeDenseBitset,
+    encodeAdaptiveBitset,
+    encodeDenseBitset,
+    maximumEncodedLength
+} from './state-codec.js';
+
+export function validateManifest(manifest, tree) {
+    const normalized = asManifest(manifest);
+    const treePaths = new Set(tree.nodesByPath.keys());
+    return {
+        valid: Array.from(treePaths).every(path => normalized.pathToSlot.has(path)),
+        unregisteredPaths: Array.from(treePaths).filter(path => !normalized.pathToSlot.has(path)),
+        missingPaths: normalized.slots
+            .filter(slot => !slot.deleted && !treePaths.has(slot.path))
+            .map(slot => slot.path)
+    };
+}
+
+export function validateManifestEvolution(previous, next) {
+    const oldManifest = asManifest(previous);
+    const newManifest = asManifest(next);
+    const errors = [];
+
+    if (newManifest.slots.length < oldManifest.slots.length) {
+        errors.push('Manifest slots cannot be removed; use tombstones.');
+    }
+    oldManifest.slots.forEach((oldSlot, index) => {
+        const newSlot = newManifest.slots[index];
+        if (!newSlot) return;
+        if (oldSlot.deleted && !newSlot.deleted) {
+            errors.push(`Tombstoned slot ${index} cannot be reused.`);
+        }
+        if (!oldSlot.deleted && !newSlot.deleted && oldSlot.path !== newSlot.path) {
+            errors.push(`Slot ${index} changed path; confirm this is a logical rename or move.`);
+        }
+    });
+
+    return { valid: errors.length === 0, errors };
+}
+
+function collectTreeValues(tree, manifest) {
+    const normalized = asManifest(manifest);
+    const checkedValues = new Map();
+    const expandedValues = new Map();
+
+    for (const [path, node] of tree.nodesByPath) {
+        const slot = normalized.pathToSlot.get(path);
+        if (slot === undefined) continue;
+        const item = tree.itemForNode(node.id);
+        const checkbox = item && tree.directCheckbox(item);
+        const toggle = item?.querySelector(':scope > .checkbox-tree__row > .checkbox-tree__toggle');
+        checkedValues.set(slot, Boolean(checkbox?.checked));
+        expandedValues.set(slot, toggle?.getAttribute('aria-expanded') === 'true');
+    }
+
+    return { normalized, checkedValues, expandedValues };
+}
+
+function nodeState(tree, node) {
+    const item = tree.itemForNode(node.id);
+    const checkbox = item && tree.directCheckbox(item);
+    const toggle = item?.querySelector(':scope > .checkbox-tree__row > .checkbox-tree__toggle');
+    return {
+        checked: Boolean(checkbox?.checked),
+        hasChecked: Boolean(checkbox),
+        expanded: toggle?.getAttribute('aria-expanded') === 'true',
+        hasExpanded: Boolean(toggle)
+    };
+}
+
+function encodeTieredState(tree, normalized) {
+    const checkedByDepth = new Map();
+    const expandedByDepth = new Map();
+    const statesByPath = new Map();
+
+    for (const [path, node] of tree.nodesByPath) {
+        const slot = normalized.pathToSlot.get(path);
+        if (slot === undefined) continue;
+        const depth = path.split(PATH_DELIMITER).length;
+        const parentPath = path.includes(PATH_DELIMITER)
+            ? path.slice(0, path.lastIndexOf(PATH_DELIMITER))
+            : null;
+        const parent = statesByPath.get(parentPath) ?? {
+            checked: false,
+            hasChecked: false,
+            expanded: false,
+            hasExpanded: false
+        };
+        const current = nodeState(tree, node);
+        if (current.hasChecked) {
+            checkedByDepth.set(depth, checkedByDepth.get(depth) ?? new Map());
+            checkedByDepth.get(depth).set(slot, current.checked !== (parent.hasChecked ? parent.checked : false));
+        }
+        if (current.hasExpanded) {
+            expandedByDepth.set(depth, expandedByDepth.get(depth) ?? new Map());
+            expandedByDepth.get(depth).set(slot, current.expanded);
+        }
+        statesByPath.set(path, current);
+    }
+
+    const fields = new Map([['n', String(normalized.slots.length)]]);
+    for (const [depth, values] of checkedByDepth) {
+        const encoded = bytesToBase64Url(encodeAdaptiveBitset(values, normalized.slots.length));
+        if (encoded) fields.set(`c${depth}`, encoded);
+    }
+    for (const [depth, values] of expandedByDepth) {
+        const encoded = bytesToBase64Url(encodeAdaptiveBitset(values, normalized.slots.length));
+        if (encoded) fields.set(`x${depth}`, encoded);
+    }
+    return fields;
+}
+
+export function encodeTreeState(tree, manifest, encoding = tree.options?.stateEncoding ?? 'adaptive') {
+    assertStateEncoding(encoding);
+    const { normalized, checkedValues, expandedValues } = collectTreeValues(tree, manifest);
+
+    if (encoding === 'tiered') {
+        return { version: SERIALIZATION_VERSION, encoding, fields: encodeTieredState(tree, normalized) };
+    }
+
+    const encode = encoding === 'dense' ? encodeDenseBitset : encodeAdaptiveBitset;
+    const checkedValue = bytesToBase64Url(encode(checkedValues, normalized.slots.length));
+    const expandedValue = bytesToBase64Url(encode(expandedValues, normalized.slots.length));
+    return {
+        version: SERIALIZATION_VERSION,
+        encoding,
+        checked: checkedValue || null,
+        expanded: expandedValue || null
+    };
+}
+
+function decodeField(params, name, normalized, encoding) {
+    const maximumLength = encoding === 'dense'
+        ? Math.ceil(normalized.slots.length / 8)
+        : maximumEncodedLength(normalized.slots.length);
+    const bytes = base64UrlToBytes(params.get(name) ?? '', maximumLength);
+    const decode = encoding === 'dense' ? decodeDenseBitset : decodeAdaptiveBitset;
+    decode(bytes, normalized.slots.length);
+    return bytes;
+}
+
+export function decodeTreeState(fragment, manifest, encoding = 'adaptive') {
+    assertStateEncoding(encoding);
+    const normalized = asManifest(manifest);
+    const value = fragment.startsWith('#') ? fragment.slice(1) : fragment;
+    const params = new URLSearchParams(value);
+    if (params.get('v') !== String(SERIALIZATION_VERSION)) {
+        return { applied: false, version: params.get('v'), encoding, warnings: ['Missing or unsupported serialization version.'] };
+    }
+    try {
+        if (encoding === 'tiered') {
+            if (params.has('c') || params.has('x')) {
+                throw new Error('Tiered tree state contains non-tiered fields.');
+            }
+            const maximumDepth = normalized.slots.reduce((depth, slot) =>
+                slot.deleted ? depth : Math.max(depth, slot.path.split(PATH_DELIMITER).length)
+            , 0);
+            for (const key of params.keys()) {
+                const match = /^([cx])(\d+)$/.exec(key);
+                if (match && (Number(match[2]) < 1 || Number(match[2]) > maximumDepth)) {
+                    throw new Error(`Tree state contains an invalid tier: ${key}`);
+                }
+            }
+            const coverage = Number(params.get('n'));
+            if (!Number.isSafeInteger(coverage) || coverage < 0 || coverage > normalized.slots.length) {
+                throw new Error('Tiered tree state has invalid manifest coverage.');
+            }
+            const checkedTiers = new Map();
+            const expandedTiers = new Map();
+            for (let depth = 1; depth <= maximumDepth; depth++) {
+                checkedTiers.set(depth, decodeField(params, `c${depth}`, normalized, 'adaptive'));
+                expandedTiers.set(depth, decodeField(params, `x${depth}`, normalized, 'adaptive'));
+            }
+            return {
+                applied: true,
+                version: SERIALIZATION_VERSION,
+                encoding,
+                coverage,
+                checkedTiers,
+                expandedTiers,
+                warnings: []
+            };
+        }
+
+        for (const key of params.keys()) {
+            if (key === 'n' || /^[cx]\d+$/.test(key)) {
+                throw new Error('Tree state contains tiered fields for a non-tiered encoding.');
+            }
+        }
+
+        const checked = decodeField(params, 'c', normalized, encoding);
+        const expanded = decodeField(params, 'x', normalized, encoding);
+        return {
+            applied: true,
+            version: SERIALIZATION_VERSION,
+            encoding,
+            checked,
+            expanded,
+            warnings: []
+        };
+    } catch (error) {
+        return { applied: false, version: SERIALIZATION_VERSION, encoding, warnings: [error.message] };
+    }
+}
+
+export function applyTreeState(tree, manifest, state) {
+    if (!state?.applied) return false;
+    const normalized = asManifest(manifest);
+    if (state.encoding === 'tiered') return applyTieredTreeState(tree, normalized, state);
+    let isChecked;
+    let isExpanded;
+    try {
+        const decode = state.encoding === 'dense' ? decodeDenseBitset : decodeAdaptiveBitset;
+        isChecked = decode(state.checked, normalized.slots.length);
+        isExpanded = decode(state.expanded, normalized.slots.length);
+    } catch {
+        return false;
+    }
+    for (const [path, node] of tree.nodesByPath) {
+        const slot = normalized.pathToSlot.get(path);
+        if (slot === undefined) continue;
+        const item = tree.itemForNode(node.id);
+        const checkbox = item && tree.directCheckbox(item);
+        if (checkbox && !checkbox.disabled) checkbox.checked = isChecked(slot);
+        tree.setExpanded(item, isExpanded(slot));
+    }
+    tree.updateAllParentCheckboxes();
+    return true;
+}
+
+function applyTieredTreeState(tree, normalized, state) {
+    const resolvedByPath = new Map();
+    const checkedDecoders = new Map();
+    const expandedDecoders = new Map();
+    try {
+        for (const [depth, bytes] of state.checkedTiers) {
+            checkedDecoders.set(depth, decodeAdaptiveBitset(bytes, normalized.slots.length));
+        }
+        for (const [depth, bytes] of state.expandedTiers) {
+            expandedDecoders.set(depth, decodeAdaptiveBitset(bytes, normalized.slots.length));
+        }
+    } catch {
+        return false;
+    }
+
+    for (const [path, node] of tree.nodesByPath) {
+        const slot = normalized.pathToSlot.get(path);
+        if (slot === undefined) continue;
+        const depth = path.split(PATH_DELIMITER).length;
+        const parentPath = path.includes(PATH_DELIMITER)
+            ? path.slice(0, path.lastIndexOf(PATH_DELIMITER))
+            : null;
+        const parent = resolvedByPath.get(parentPath) ?? {
+            checked: false,
+            hasChecked: false,
+            expanded: false,
+            hasExpanded: false
+        };
+        const item = tree.itemForNode(node.id);
+        const checkbox = item && tree.directCheckbox(item);
+        const toggle = item?.querySelector(':scope > .checkbox-tree__row > .checkbox-tree__toggle');
+        const isCovered = slot < state.coverage;
+        const checked = checkbox && isCovered
+            ? (parent.hasChecked ? parent.checked : false) !== checkedDecoders.get(depth)(slot)
+            : false;
+        const expanded = Boolean(toggle && isCovered && expandedDecoders.get(depth)(slot));
+        if (checkbox && !checkbox.disabled) checkbox.checked = checked;
+        tree.setExpanded(item, expanded);
+        resolvedByPath.set(path, {
+            checked,
+            hasChecked: Boolean(checkbox),
+            expanded,
+            hasExpanded: Boolean(toggle)
+        });
+    }
+    tree.updateAllParentCheckboxes();
+    return true;
+}
+
+export function serializeStateToFragment(tree, manifest, encoding = tree.options?.stateEncoding ?? 'adaptive') {
+    const state = encodeTreeState(tree, manifest, encoding);
+    const params = new URLSearchParams({ v: String(state.version) });
+    if (state.encoding === 'tiered') {
+        for (const [name, value] of state.fields) params.set(name, value);
+    } else {
+        if (state.checked) params.set('c', state.checked);
+        if (state.expanded) params.set('x', state.expanded);
+    }
+    return `#${params}`;
+}
+
+export function restoreStateFromLocation(
+    tree,
+    manifest,
+    location = window.location,
+    encoding = tree.options?.stateEncoding ?? 'adaptive'
+) {
+    const state = decodeTreeState(location.hash ?? '', manifest, encoding);
+    if (state.applied) applyTreeState(tree, manifest, state);
+    return state;
+}