diff --git a/docs/configuration/templates.md b/docs/configuration/templates.md
index a7df11e5..36d24004 100644
--- a/docs/configuration/templates.md
+++ b/docs/configuration/templates.md
@@ -20,6 +20,12 @@ The Advanced Camera Card uses
 Consult its documentation for the wide variety of different template values
 supported.
 
+> [!NOTE]
+> To keep the card lightweight, some template features are not available. If a
+> template feature you need is missing,
+> [open an issue](https://github.com/dermotduffy/advanced-camera-card/issues) to
+> request it.
+
 See [an example](../examples.md?id=accessing-home-assistant-state) that
 accesses Home Assistant state.
 
diff --git a/package.json b/package.json
index 35d8ba3b..c99f1b8b 100644
--- a/package.json
+++ b/package.json
@@ -31,7 +31,7 @@
     "date-fns": "^3.6.0",
     "embla-carousel": "^8.6.0",
     "embla-carousel-wheel-gestures": "^8.0.1",
-    "ha-nunjucks": "^1.3.0",
+    "ha-nunjucks": "~1.6.2",
     "home-assistant-js-websocket": "^9.4.0",
     "js-yaml": "^4.1.0",
     "keycharm": "^0.4.0",
diff --git a/rollup.config.js b/rollup.config.js
index c75712bc..d46e3ace 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -35,7 +35,16 @@ const serveopts = {
  * @type {import('rollup').RollupOptions['plugins']}
  */
 const plugins = [
-  gitInfo.default({ enableBuildDate: true, updateVersion: false }),
+  gitInfo.default(
+    // Limit git-info to the project's own package.json. Without this it also
+    // rewrites any dependency's imported package.json into ESM, which then breaks
+    // the json() plugin downstream (ha-nunjucks imports its own package.json).
+    {
+      enableBuildDate: true,
+      updateVersion: false,
+      include: 'package.json',
+    },
+  ),
   styles({
     modules: false,
     // Behavior of inject mode, without actually injecting style
diff --git a/tests/card-controller/folders/ha/media-matcher.test.ts b/tests/card-controller/folders/ha/media-matcher.test.ts
index 2014a51e..8d814475 100644
--- a/tests/card-controller/folders/ha/media-matcher.test.ts
+++ b/tests/card-controller/folders/ha/media-matcher.test.ts
@@ -8,8 +8,15 @@ import type {
   BrowseMediaMetadata,
   RichBrowseMedia,
 } from '../../../../src/ha/browse-media/types';
-import { createHASS, createMockTemplateRenderer } from '../../../test-utils';
+import {
+  createHASS,
+  createMockTemplateRenderer,
+  stubConnectedHomeAssistant,
+} from '../../../test-utils';
 
+// The `with template matcher` test loads the real ha-nunjucks engine, which
+// reads `window`/`document` at import, so this suite needs a DOM environment.
+// @vitest-environment jsdom
 describe('MediaMatcher', () => {
   // A mock renderer for the matcher plumbing, which never renders templates.
   // The `value_template` suite below uses its own real, loaded engine.
@@ -153,6 +160,7 @@ describe('MediaMatcher', () => {
       // renderer (rather than the shared mock).
       const templateManager = new TemplateManager();
       beforeAll(async () => {
+        stubConnectedHomeAssistant();
         await templateManager.loadRenderer();
       });
 
diff --git a/tests/card-controller/templates/index.test.ts b/tests/card-controller/templates/index.test.ts
index a4759d69..882904c0 100644
--- a/tests/card-controller/templates/index.test.ts
+++ b/tests/card-controller/templates/index.test.ts
@@ -1,9 +1,19 @@
-import { describe, expect, it, vi } from 'vitest';
+import { beforeAll, describe, expect, it, vi } from 'vitest';
 
 import { TemplateManager } from '../../../src/card-controller/templates/index';
-import { createConfig, createHASS, createStateEntity } from '../../test-utils';
+import {
+  createConfig,
+  createHASS,
+  createStateEntity,
+  stubConnectedHomeAssistant,
+} from '../../test-utils';
 
+// ha-nunjucks reads `window`/`document` at import and renders via a
+// `window.haNunjucks` global, so the renderer needs a DOM environment.
+// @vitest-environment jsdom
 describe('TemplateManager', () => {
+  beforeAll(() => stubConnectedHomeAssistant());
+
   describe('loadRenderer', () => {
     it('should render a template raw before the engine is loaded', () => {
       const manager = new TemplateManager();
diff --git a/tests/condition-trigger/common/time-period.test.ts b/tests/condition-trigger/common/time-period.test.ts
index 23f21132..b7f564f0 100644
--- a/tests/condition-trigger/common/time-period.test.ts
+++ b/tests/condition-trigger/common/time-period.test.ts
@@ -6,6 +6,7 @@ import {
   createHASS,
   createMockTemplateRenderer,
   createStateEntity,
+  stubConnectedHomeAssistant,
 } from '../../test-utils';
 
 // @vitest-environment jsdom
@@ -66,6 +67,7 @@ describe('renderTimePeriodToSeconds', () => {
     const templateManager = new TemplateManager();
 
     beforeAll(async () => {
+      stubConnectedHomeAssistant();
       await templateManager.loadRenderer();
     });
 
diff --git a/tests/condition-trigger/conditions/conditions-manager.test.ts b/tests/condition-trigger/conditions/conditions-manager.test.ts
index 063d30b3..75024a94 100644
--- a/tests/condition-trigger/conditions/conditions-manager.test.ts
+++ b/tests/condition-trigger/conditions/conditions-manager.test.ts
@@ -7,6 +7,7 @@ import {
   createHASS,
   createMockTemplateRenderer,
   createStateEntity,
+  stubConnectedHomeAssistant,
 } from '../../test-utils';
 
 // A mock renderer for the orchestration tests, which never render templates.
@@ -198,6 +199,7 @@ describe('ConditionsManager', () => {
     // loaded for the synchronous renderer (rather than the shared mock).
     const templateManager = new TemplateManager();
     beforeAll(async () => {
+      stubConnectedHomeAssistant();
       await templateManager.loadRenderer();
     });
 
diff --git a/tests/condition-trigger/conditions/conditions/numeric-state.test.ts b/tests/condition-trigger/conditions/conditions/numeric-state.test.ts
index e2da0b53..77fcc827 100644
--- a/tests/condition-trigger/conditions/conditions/numeric-state.test.ts
+++ b/tests/condition-trigger/conditions/conditions/numeric-state.test.ts
@@ -6,6 +6,7 @@ import {
   createHASS,
   createMockTemplateRenderer,
   createStateEntity,
+  stubConnectedHomeAssistant,
 } from '../../../test-utils';
 import { createEvaluatorContext } from './test-utils';
 
@@ -131,6 +132,7 @@ describe('numeric state condition', () => {
     // This case renders a real value_template, so load the lazily-imported
     // engine for the synchronous renderer.
     const templateManager = new TemplateManager();
+    stubConnectedHomeAssistant();
     await templateManager.loadRenderer();
 
     const evaluator = createConditionEvaluator(
diff --git a/tests/condition-trigger/conditions/conditions/state.test.ts b/tests/condition-trigger/conditions/conditions/state.test.ts
index 37e7e9fa..6c7dce22 100644
--- a/tests/condition-trigger/conditions/conditions/state.test.ts
+++ b/tests/condition-trigger/conditions/conditions/state.test.ts
@@ -2,7 +2,11 @@ import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
 import { TemplateManager } from '../../../../src/card-controller/templates';
 import { createConditionEvaluator } from '../../../../src/condition-trigger/conditions/factory';
-import { createHASS, createStateEntity } from '../../../test-utils';
+import {
+  createHASS,
+  createStateEntity,
+  stubConnectedHomeAssistant,
+} from '../../../test-utils';
 import { createEvaluatorContext } from './test-utils';
 
 // @vitest-environment jsdom
@@ -340,6 +344,7 @@ describe('state condition', () => {
       // This case renders a real templated `for`, so load the lazily-imported
       // engine for the synchronous renderer.
       const templateManager = new TemplateManager();
+      stubConnectedHomeAssistant();
       await templateManager.loadRenderer();
 
       const evaluator = createConditionEvaluator(
diff --git a/tests/condition-trigger/conditions/conditions/template.test.ts b/tests/condition-trigger/conditions/conditions/template.test.ts
index 26e4511a..ca05cb11 100644
--- a/tests/condition-trigger/conditions/conditions/template.test.ts
+++ b/tests/condition-trigger/conditions/conditions/template.test.ts
@@ -2,13 +2,18 @@ import { beforeAll, describe, expect, it } from 'vitest';
 
 import { TemplateManager } from '../../../../src/card-controller/templates';
 import { createConditionEvaluator } from '../../../../src/condition-trigger/conditions/factory';
-import { createHASS, createStateEntity } from '../../../test-utils';
+import {
+  createHASS,
+  createStateEntity,
+  stubConnectedHomeAssistant,
+} from '../../../test-utils';
 import { createEvaluatorContext } from './test-utils';
 
 // @vitest-environment jsdom
 describe('template condition', () => {
   const templateManager = new TemplateManager();
   beforeAll(async () => {
+    stubConnectedHomeAssistant();
     await templateManager.loadRenderer();
   });
 
diff --git a/tests/condition-trigger/triggers/manager.test.ts b/tests/condition-trigger/triggers/manager.test.ts
index 12ab581a..1f0ac9f8 100644
--- a/tests/condition-trigger/triggers/manager.test.ts
+++ b/tests/condition-trigger/triggers/manager.test.ts
@@ -9,6 +9,7 @@ import {
   createHASSManager,
   createMockTemplateRenderer,
   createStateEntity,
+  stubConnectedHomeAssistant,
 } from '../../test-utils';
 
 const templateManager = createMockTemplateRenderer();
@@ -126,6 +127,7 @@ describe('TriggersManager', () => {
     // loaded for the synchronous renderer (rather than the shared mock).
     const templateManager = new TemplateManager();
     beforeAll(async () => {
+      stubConnectedHomeAssistant();
       await templateManager.loadRenderer();
     });
 
diff --git a/tests/condition-trigger/triggers/triggers/numeric-state.test.ts b/tests/condition-trigger/triggers/triggers/numeric-state.test.ts
index a48fffa8..16a3e02d 100644
--- a/tests/condition-trigger/triggers/triggers/numeric-state.test.ts
+++ b/tests/condition-trigger/triggers/triggers/numeric-state.test.ts
@@ -8,7 +8,11 @@ import {
 import { ConditionStateManager } from '../../../../src/condition-trigger/conditions/state-manager';
 import { NumericStateTrigger } from '../../../../src/condition-trigger/triggers/triggers/numeric-state';
 import type { TriggerOfType } from '../../../../src/condition-trigger/triggers/triggers/types';
-import { createHASS, createStateEntity } from '../../../test-utils';
+import {
+  createHASS,
+  createStateEntity,
+  stubConnectedHomeAssistant,
+} from '../../../test-utils';
 import { createTriggerEvaluatorContext } from './test-utils';
 
 const SENSOR = 'sensor.temperature';
@@ -163,6 +167,7 @@ describe('NumericStateTrigger', () => {
 
   it('should match the rendered value_template', async () => {
     const templateManager = new TemplateManager();
+    stubConnectedHomeAssistant();
     await templateManager.loadRenderer();
 
     const { trigger, stateManager, callback } = create(
diff --git a/tests/condition-trigger/triggers/triggers/template.test.ts b/tests/condition-trigger/triggers/triggers/template.test.ts
index 738505a7..b6567e32 100644
--- a/tests/condition-trigger/triggers/triggers/template.test.ts
+++ b/tests/condition-trigger/triggers/triggers/template.test.ts
@@ -13,11 +13,16 @@ import { TemplateManager } from '../../../../src/card-controller/templates';
 import { ConditionStateManager } from '../../../../src/condition-trigger/conditions/state-manager';
 import { TemplateTrigger } from '../../../../src/condition-trigger/triggers/triggers/template';
 import type { TriggerOfType } from '../../../../src/condition-trigger/triggers/triggers/types';
-import { createHASS, createStateEntity } from '../../../test-utils';
+import {
+  createHASS,
+  createStateEntity,
+  stubConnectedHomeAssistant,
+} from '../../../test-utils';
 import { createTriggerEvaluatorContext } from './test-utils';
 
 const templateManager = new TemplateManager();
 beforeAll(async () => {
+  stubConnectedHomeAssistant();
   await templateManager.loadRenderer();
 });
 
diff --git a/tests/test-utils.ts b/tests/test-utils.ts
index 84d45dda..115cd56b 100644
--- a/tests/test-utils.ts
+++ b/tests/test-utils.ts
@@ -758,6 +758,36 @@ export const createMockTemplateRenderer = (): TemplateManager => {
   return renderer;
 };
 
+// At import the real ha-nunjucks engine waits for a connected `home-assistant`
+// element before finishing initialization, retrying on a timer that can outlive
+// the test (and throw `document is not defined` once the environment is torn
+// down). Test suites that load the real engine call this first, in a jsdom
+// environment, so it initializes immediately as it does in a real Home
+// Assistant frontend. Idempotent.
+//
+// Workaround for an upstream bug; remove once it is fixed:
+// https://github.com/Nerwyn/ha-nunjucks/issues/11
+export const stubConnectedHomeAssistant = (): void => {
+  if (document.querySelector('home-assistant')) {
+    return;
+  }
+  const ha = document.createElement('home-assistant');
+  Object.assign(ha, {
+    hass: {
+      // The readiness gate the engine polls for.
+      connected: true,
+      connection: {
+        connected: true,
+        // Awaited by the engine's label-registry fetch during init.
+        sendMessagePromise: () => Promise.resolve([]),
+      },
+      language: 'en',
+      states: {},
+    },
+  });
+  document.body.appendChild(ha);
+};
+
 export const createCardAPI = (): CardController => {
   const api = mock<CardController>();
 
diff --git a/yarn.lock b/yarn.lock
index 41df4b59..fbf032ec 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2662,7 +2662,7 @@ __metadata:
     eslint-config-airbnb-base: "npm:^15.0.0"
     eslint-config-prettier: "npm:^9.1.0"
     eslint-plugin-import: "npm:^2.29.1"
-    ha-nunjucks: "npm:^1.3.0"
+    ha-nunjucks: "npm:~1.6.2"
     home-assistant-js-websocket: "npm:^9.4.0"
     js-yaml: "npm:^4.1.0"
     jsdom: "npm:^21.1.2"
@@ -5786,14 +5786,15 @@ __metadata:
   languageName: node
   linkType: hard
 
-"ha-nunjucks@npm:^1.3.0":
-  version: 1.3.0
-  resolution: "ha-nunjucks@npm:1.3.0"
+"ha-nunjucks@npm:~1.6.2":
+  version: 1.6.2
+  resolution: "ha-nunjucks@npm:1.6.2"
   dependencies:
     home-assistant-js-websocket: "npm:latest"
     nunjucks: "npm:latest"
+    slugify: "npm:latest"
     ts-py-datetime: "npm:latest"
-  checksum: 10c0/9c346ee9866f748b41d98dbefefd46ddb0a43f7d563e4456e000047e273e5441e5a15321ba8684325a81d746a9e9c32c5c0f4f1a58637291babebcae45329442
+  checksum: 10c0/f3953be5de5f27e7cf5c111bb9fc969e2e7a7732547c0549c88a5fed2480c12bdb058feff81e68059570831b1464cf26bf356df6f60dfcc904d16d2c6f844ee8
   languageName: node
   linkType: hard
 
@@ -10283,6 +10284,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"slugify@npm:latest":
+  version: 1.6.9
+  resolution: "slugify@npm:1.6.9"
+  checksum: 10c0/8473c566ae00c5db26bfbf6182a4a9478ab3c912a9c926e1fdb410736a77228bfca4fdc5c755b46fafa7d2d9900de482fd7a9bd5e5c91128c4743c2c072d88da
+  languageName: node
+  linkType: hard
+
 "smart-buffer@npm:^4.2.0":
   version: 4.2.0
   resolution: "smart-buffer@npm:4.2.0"