diff --git a/changelog.d/1522-zoom-out-runaway.md b/changelog.d/1522-zoom-out-runaway.md
new file mode 100644
index 000000000..1e9c61a78
--- /dev/null
+++ b/changelog.d/1522-zoom-out-runaway.md
@@ -0,0 +1,5 @@
+- Keep the globe on screen when zooming out from a tilted view. User zoom is
+  capped at 40,000 km, and above 300 km outward zoom pitches the view down so
+  Earth stays framed. Correction finishes when zoom stops, respects tilt
+  gestures and stricter host limits, and yields to other camera actions
+  (asturksever, #1522).
diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index da72c1041..256db0530 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -44,6 +44,27 @@ pinching traverses globe and street scales with fewer gestures. Cesium retains
 its distance-aware zoom, collision handling and minimum/maximum distance limits.
 Fine-pointer desktop mouse and trackpad sensitivity is unchanged.
 
+User zoom is capped at 40,000 km (or a stricter host limit). Explicit camera
+flight, share-link and story destinations can go farther; from there, user zoom
+can't climb any higher and zooms in gradually from the current height, with no
+jump to the cap. Cesium can still use the limit when it computes an automatic
+bounding-sphere framing distance.
+Above 300 km, outward movement from the controller's configured zoom bindings
+(wheel, pinch distance and unmodified right-drag by default) pitches the camera
+down towards 8° below the Earth's limb. Large steps reach the limb immediately;
+the remaining margin eases into place, including after zooming stops or reaches
+the ceiling. Continuous outward inertia remains guarded without a time cutoff.
+Two-finger tilts, modifier-specific tilts and other camera gestures cancel the
+correction. A two-finger gesture counts as a pinch zoom only while the finger
+spacing changes more than the fingers move up or down, so spacing drift during
+a tilt is ignored. Explicit navigation handoffs, including toolbar tilt,
+cancel it before animation begins. Zooming in, disabled zoom/input, non-3D modes, tracked
+transforms and flights also cancel it; external pose changes cancel stationary
+settling. Oblique views below 300 km are left alone.
+
+`QA_BASE_URL=http://localhost:4173 node scripts/qa-zoom-out-guard.mjs` exercises
+the real browser controller at desktop and phone widths with keyless fixtures.
+
 Analyst region queries resolve unique Natural Earth names offline without
 geocoding, so Gold Coast and Ivory Coast name the West African natural regions.
 Duplicate names require a geocoded containment anchor; when several entries for
diff --git a/scripts/format-scope.json b/scripts/format-scope.json
index 860fa10ce..afe2e153c 100644
--- a/scripts/format-scope.json
+++ b/scripts/format-scope.json
@@ -57,6 +57,9 @@
   "src/app/mapLifecycle.test.mjs",
   "src/app/startupCamera.test.mjs",
   "src/app/viewer.js",
+  "src/app/zoomOutGuard.test.mjs",
+  "src/app/controls.test.mjs",
+  "scripts/qa-zoom-out-guard.mjs",
   "src/app/atmosphereCompat.test.mjs",
   "src/standalone/application.js",
   "src/standalone/controls.js",
diff --git a/scripts/package-boundaries.json b/scripts/package-boundaries.json
index 8ed8b859a..a5c43b973 100644
--- a/scripts/package-boundaries.json
+++ b/scripts/package-boundaries.json
@@ -2274,6 +2274,7 @@
       "src/app/layers/traffic.js",
       "src/app/operations.js",
       "src/app/scene.js",
+      "src/app/zoomOutGuard.js",
       "src/sources/sourceSlot.js",
       "src/app/sources.js",
       "src/app/startupChrome.js",
diff --git a/scripts/qa-zoom-out-guard.mjs b/scripts/qa-zoom-out-guard.mjs
new file mode 100644
index 000000000..770a4148d
--- /dev/null
+++ b/scripts/qa-zoom-out-guard.mjs
@@ -0,0 +1,333 @@
+#!/usr/bin/env node
+/** Real-app zoom and tilt regression. Start a dev server, then run this file. */
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import path from 'node:path';
+import puppeteer from 'puppeteer';
+
+const origin = process.env.QA_BASE_URL || 'http://localhost:4173';
+const browser = await puppeteer.launch({
+  headless: true,
+  args: [
+    '--no-sandbox',
+    ...(process.platform === 'darwin'
+      ? ['--use-angle=metal', '--enable-gpu']
+      : [
+          '--use-gl=angle',
+          '--use-angle=swiftshader',
+          '--enable-unsafe-swiftshader',
+        ]),
+  ],
+  protocolTimeout: 120_000,
+});
+const errors = [];
+try {
+  const page = await browser.newPage();
+  page.on('pageerror', (error) => errors.push(error.message));
+  await page.setViewport({ width: 1200, height: 800 });
+  await page.goto(`${origin}/?welcome=0`, { waitUntil: 'domcontentloaded' });
+  await page.waitForFunction(
+    () =>
+      window.__godsEyeView?.viewer &&
+      window.__godsEyeView.viewer.scene.screenSpaceCameraController
+        .enableInputs &&
+      document.getElementById('loading-screen')?.classList.contains('hidden'),
+    { timeout: 90_000 },
+  );
+  const renderer = await page.evaluate(async () => {
+    const C = await import('/node_modules/cesium/Build/Cesium/index.js');
+    const { maxPitchForHeight } = await import('/src/app/zoomOutGuard.js');
+    const { readCameraTargetFrame } =
+      await import('/src/ui/cameraOrientationControls.js');
+    const viewer = window.__godsEyeView.viewer;
+    viewer.camera.cancelFlight();
+    viewer.trackedEntity = undefined;
+    // Explicit real renders make each gesture independent of host frame rate.
+    viewer.useDefaultRenderLoop = false;
+    const controller = viewer.scene.screenSpaceCameraController;
+    controller.inertiaZoom = 0;
+    controller.inertiaSpin = 0;
+    const original = viewer.camera.setView.bind(viewer.camera);
+    const qa = {
+      viewer,
+      guardWrites: 0,
+      targetPitch: () => readCameraTargetFrame(viewer)?.pitch,
+      history: [],
+      frame() {
+        viewer.scene.requestRender();
+        viewer.render();
+        qa.history.push({
+          height: viewer.camera._positionCartographic.height,
+          guardWrites: qa.guardWrites,
+          position: { ...viewer.camera.position },
+        });
+        if (qa.history.length > 80) qa.history.shift();
+      },
+      pose() {
+        return {
+          height: viewer.camera.positionCartographic.height,
+          pitch: viewer.camera.pitch,
+          maxPitch: maxPitchForHeight(
+            viewer.camera.positionCartographic.height,
+          ),
+          guardWrites: qa.guardWrites,
+        };
+      },
+      reset(height = 1_000_000, pitch = -35) {
+        viewer.camera.cancelFlight();
+        viewer.camera.lookAtTransform(C.Matrix4.IDENTITY);
+        original({
+          destination: C.Cartesian3.fromDegrees(0, 0, height),
+          orientation: { heading: 0, pitch: C.Math.toRadians(pitch), roll: 0 },
+        });
+        qa.frame();
+        qa.guardWrites = 0;
+      },
+    };
+    viewer.camera.setView = (options) => {
+      // Cesium itself also calls setView while processing touch movement.
+      if (new Error().stack.includes('/src/app/zoomOutGuard.js'))
+        qa.guardWrites++;
+      return original(options);
+    };
+    window.__zoomGuardQa = qa;
+    const gl = viewer.scene.context._gl;
+    const debug = gl.getExtension('WEBGL_debug_renderer_info');
+    return gl.getParameter(debug ? debug.UNMASKED_RENDERER_WEBGL : gl.RENDERER);
+  });
+  console.log(`[INFO] WebGL renderer: ${renderer}`);
+  const frame = (count = 1) =>
+    page.evaluate(async (n) => {
+      for (let i = 0; i < n; i++) {
+        window.__zoomGuardQa.frame();
+        await new Promise((resolve) => setTimeout(resolve, 0));
+      }
+      return window.__zoomGuardQa.pose();
+    }, count);
+  const reset = (height, pitch) =>
+    page.evaluate((h, p) => window.__zoomGuardQa.reset(h, p), height, pitch);
+  const session = await page.createCDPSession();
+  for (const viewport of [
+    { width: 1200, height: 800 },
+    { width: 390, height: 844 },
+  ]) {
+    await page.setViewport(viewport);
+    await page.evaluate(() => window.__zoomGuardQa.viewer.resize());
+    const x = Math.round(viewport.width / 2);
+    const y = Math.round(viewport.height / 2);
+    await reset(1_000_000, -25);
+    await page.mouse.move(x, y);
+    await page.evaluate(
+      ({ x, y }) => {
+        window.__zoomGuardQa.viewer.canvas.dispatchEvent(
+          new WheelEvent('wheel', {
+            deltaY: 2400,
+            clientX: x,
+            clientY: y,
+            bubbles: true,
+            cancelable: true,
+          }),
+        );
+      },
+      { x, y },
+    );
+    const first = await frame();
+    console.log(`[INFO] ${viewport.width}px wheel delivered`);
+    const settled = await frame(40);
+    assert.ok(first.height > 1_000_000, 'wheel must move the real camera');
+    assert.ok(settled.guardWrites > 0, 'zoom guard must run');
+    assert.ok(
+      settled.pitch <= settled.maxPitch + 1e-6,
+      `stationary pitch must finish easing: ${JSON.stringify(settled)}`,
+    );
+    for (let i = 0; i < 12; i++) {
+      await page.evaluate(
+        ({ x, y }) => {
+          window.__zoomGuardQa.viewer.canvas.dispatchEvent(
+            new WheelEvent('wheel', {
+              deltaY: 2400,
+              clientX: x,
+              clientY: y,
+              bubbles: true,
+              cancelable: true,
+            }),
+          );
+        },
+        { x, y },
+      );
+      await frame();
+    }
+    const ceiling = await frame(40);
+    assert.ok(ceiling.height <= 40_000_001, 'user zoom respects the ceiling');
+    assert.ok(
+      ceiling.height > 39_000_000,
+      'exercise the ceiling, not a low orbit',
+    );
+    assert.ok(
+      ceiling.pitch <= ceiling.maxPitch + 1e-6,
+      `ceiling must settle: ${JSON.stringify(await page.evaluate(() => window.__zoomGuardQa.history))}`,
+    );
+    console.log(
+      `[PASS] ${viewport.width}px wheel, stationary easing and ceiling`,
+    );
+    if (process.env.QA_SCREENSHOT_DIR) {
+      fs.mkdirSync(process.env.QA_SCREENSHOT_DIR, { recursive: true });
+      await page.screenshot({
+        path: path.join(
+          process.env.QA_SCREENSHOT_DIR,
+          `zoom-ceiling-${viewport.width}.png`,
+        ),
+      });
+    }
+
+    await reset();
+    await page.mouse.move(x, y);
+    await page.keyboard.down('Control');
+    await page.mouse.down({ button: 'right' });
+    for (let i = 1; i <= 6; i++) {
+      await page.mouse.move(x, y + i * 3);
+      await frame();
+    }
+    await page.mouse.up({ button: 'right' });
+    await page.keyboard.up('Control');
+    const tilted = await frame(3);
+    assert.equal(
+      tilted.guardWrites,
+      0,
+      'Ctrl+right tilt must not trigger guard',
+    );
+    assert.ok(Math.abs(tilted.height - 1_000_000) > 1, 'tilt must move camera');
+
+    await reset();
+    const touches = (dy) => [
+      { x: x - 60, y: y + dy, id: 1 },
+      { x: x + 60, y: y + dy, id: 2 },
+    ];
+    await session.send('Input.dispatchTouchEvent', {
+      type: 'touchStart',
+      touchPoints: touches(0),
+    });
+    await frame();
+    for (let i = 1; i <= 6; i++) {
+      await session.send('Input.dispatchTouchEvent', {
+        type: 'touchMove',
+        touchPoints: touches(i * 3),
+      });
+      await frame();
+    }
+    await session.send('Input.dispatchTouchEvent', {
+      type: 'touchEnd',
+      touchPoints: [],
+    });
+    const translated = await frame(3);
+    assert.equal(
+      translated.guardWrites,
+      0,
+      'parallel two-finger tilt must not trigger guard',
+    );
+    assert.ok(
+      Math.abs(translated.height - 1_000_000) > 1,
+      'touch tilt must move camera',
+    );
+    console.log(
+      `[PASS] ${viewport.width}px Ctrl+right and parallel touch tilt`,
+    );
+    await reset(1_000_000, -35);
+    await page.evaluate(
+      ({ x, y }) => {
+        window.__zoomGuardQa.viewer.canvas.dispatchEvent(
+          new WheelEvent('wheel', {
+            deltaY: 120,
+            clientX: x,
+            clientY: y,
+            bubbles: true,
+            cancelable: true,
+          }),
+        );
+      },
+      { x, y },
+    );
+    const beforeTilt = await frame();
+    assert.ok(
+      beforeTilt.guardWrites > 0,
+      'wheel correction must be pending before UI tilt',
+    );
+    const targetPitchBeforeClick = await page.evaluate(() =>
+      window.__zoomGuardQa.targetPitch(),
+    );
+    assert.ok(
+      Number.isFinite(targetPitchBeforeClick),
+      'UI tilt fixture must have a ground target under the canvas center',
+    );
+    // Programmatic fixture resets precede moveEnd, so the button's published
+    // aria state may still describe the previous view. The action toggles the
+    // current target frame: angles shallower than -60 degrees are tilted.
+    const wasTilted = targetPitchBeforeClick > -Math.PI / 3;
+    await page.click('#tilt-map-view');
+    const uiTilt = await page.evaluate(
+      async (desiredDegrees) => {
+        const qa = window.__zoomGuardQa;
+        const desired = (desiredDegrees * Math.PI) / 180;
+        const started = performance.now();
+        const deadline = started + 3000;
+        while (performance.now() < deadline) {
+          qa.frame();
+          // The 650 ms animator can be numerically near its destination
+          // before it releases preUpdate. Finish its lifetime before resetting.
+          if (
+            performance.now() - started >= 700 &&
+            Math.abs(qa.targetPitch() - desired) < 1e-5
+          )
+            return { settled: true, guardWrites: qa.guardWrites };
+          await new Promise((resolve) => setTimeout(resolve, 16));
+        }
+        return {
+          settled: false,
+          guardWrites: qa.guardWrites,
+          pitch: qa.targetPitch(),
+        };
+      },
+      wasTilted ? -89 : -35,
+    );
+    assert.ok(
+      uiTilt.settled,
+      `UI tilt must reach its destination: ${JSON.stringify(uiTilt)}`,
+    );
+    assert.equal(
+      uiTilt.guardWrites,
+      beforeTilt.guardWrites,
+      'UI navigation handoff must cancel pending zoom correction',
+    );
+    console.log(
+      `[PASS] ${viewport.width}px UI tilt takes over a pending wheel correction`,
+    );
+
+    await reset(1_000_000, -25);
+    await session.send('Input.dispatchTouchEvent', {
+      type: 'touchStart',
+      touchPoints: touches(0),
+    });
+    await frame();
+    await session.send('Input.dispatchTouchEvent', {
+      type: 'touchMove',
+      touchPoints: [
+        { x: x - 35, y, id: 1 },
+        { x: x + 35, y, id: 2 },
+      ],
+    });
+    await frame();
+    await session.send('Input.dispatchTouchEvent', {
+      type: 'touchEnd',
+      touchPoints: [],
+    });
+    const pinched = await frame(40);
+    assert.ok(pinched.height > 1_000_000, 'pinch-out must move camera outward');
+    assert.ok(pinched.guardWrites > 0, 'pinch-out must trigger the guard');
+    assert.ok(pinched.pitch <= pinched.maxPitch + 1e-6);
+    console.log(`[PASS] ${viewport.width}px pinch-out settles below the limb`);
+  }
+  assert.deepEqual(errors, [], 'no JavaScript page errors');
+  console.log('[PASS] no JavaScript page errors');
+} finally {
+  await browser.close();
+}
diff --git a/src/app/controls.js b/src/app/controls.js
index ecf52f302..99bc2555f 100644
--- a/src/app/controls.js
+++ b/src/app/controls.js
@@ -1,6 +1,7 @@
 import { catalogControlServices } from './catalog.js';
 import { StyleManager } from '../ui/composition.js';
 import { flyToAustin } from '../camera.js';
+import { installZoomOutGuard } from './zoomOutGuard.js';
 import { initCockpitCloudEffects } from '../cockpitCloudEffects.js';
 import { t } from '../i18n/index.js';
 
@@ -41,6 +42,12 @@ export function createApplicationControls({
   defer(() => styleManager.orbitController.stop());
   defer(() => styleManager.hud.destroy());
   defer(() => styleManager.dispose());
+  defer(
+    installZoomOutGuard(viewer, {
+      subscribeCameraHandoff: (listener) =>
+        styleManager.subscribeCameraHandoff?.(listener),
+    }),
+  );
   // The previous multi-canvas weather compositor remains disabled. Cockpit
   // clouds use a separate, capped low-resolution GPU pass that never attaches
   // Cesium fog or post-process stages and is fully stopped in map mode.
diff --git a/src/app/controls.test.mjs b/src/app/controls.test.mjs
new file mode 100644
index 000000000..3db3b7d8b
--- /dev/null
+++ b/src/app/controls.test.mjs
@@ -0,0 +1,68 @@
+import test, { after, before } from 'node:test';
+import assert from 'node:assert/strict';
+import * as Cesium from 'cesium';
+import '../testSupport/stubMgrs.mjs';
+import { installVueDom } from '../testSupport/vueDom.mjs';
+import { MAXIMUM_ZOOM_DISTANCE_M } from './zoomOutGuard.js';
+
+const { createApplicationControls } = await import('./controls.js');
+
+let uninstallDom;
+before(() => {
+  uninstallDom = installVueDom();
+});
+after(() => uninstallDom());
+
+test('application controls install the zoom-out guard and remove it on teardown', () => {
+  const canvas = document.createElement('canvas');
+  const controller = { maximumZoomDistance: Infinity };
+  const scene = {
+    mode: Cesium.SceneMode.SCENE3D,
+    screenSpaceCameraController: controller,
+    preRender: new Cesium.Event(),
+    postUpdate: new Cesium.Event(),
+  };
+  const camera = {
+    position: Cesium.Cartesian3.fromDegrees(0, 0, 1_000_000),
+    positionCartographic: { height: 1_000_000 },
+  };
+  const viewer = { scene, camera, canvas };
+  const handoffs = new Set();
+  class Controls {
+    hasShareState = true;
+    orbitController = { stop() {} };
+    hud = { destroy() {} };
+    dispose() {}
+    subscribeCameraHandoff(listener) {
+      handoffs.add(listener);
+      return () => handoffs.delete(listener);
+    }
+  }
+  const cleanups = [];
+  createApplicationControls({
+    scene: {
+      viewer,
+      mapStackController: {},
+      operations: {
+        surface: { controlServices: {} },
+        searchAndFlyTo() {},
+        requests: { regional: {}, weather: {} },
+      },
+    },
+    loaderStatus: {},
+    Controls,
+    catalog: { get: (id) => ({ id }) },
+    defer: (cleanup) => cleanups.push(cleanup),
+  });
+
+  assert.equal(controller.maximumZoomDistance, MAXIMUM_ZOOM_DISTANCE_M);
+  assert.equal(scene.preRender.numberOfListeners, 1);
+  assert.equal(scene.postUpdate.numberOfListeners, 1);
+  assert.equal(handoffs.size, 1);
+
+  for (const cleanup of cleanups.reverse()) cleanup();
+  assert.equal(controller.maximumZoomDistance, Infinity);
+  assert.equal(scene.preRender.numberOfListeners, 0);
+  assert.equal(scene.postUpdate.numberOfListeners, 0);
+  assert.equal(handoffs.size, 0);
+});
diff --git a/src/app/zoomOutGuard.js b/src/app/zoomOutGuard.js
new file mode 100644
index 000000000..51d2fdfcd
--- /dev/null
+++ b/src/app/zoomOutGuard.js
@@ -0,0 +1,241 @@
+import * as Cesium from 'cesium';
+import { governorRequestRender } from '../renderGovernor.js';
+
+/** Whole-Earth input limit; explicit camera destinations can go farther. */
+export const MAXIMUM_ZOOM_DISTANCE_M = 40_000_000;
+/** Below this, oblique browsing is left alone. */
+export const PITCH_CLAMP_MIN_HEIGHT_M = 300_000;
+/** Look this far below the Earth's limb, so the globe stays on screen. */
+export const LIMB_MARGIN_RAD = Cesium.Math.toRadians(8);
+const PITCH_EASE = 0.35;
+const PITCH_SNAP_RAD = Cesium.Math.toRadians(0.1);
+const HEIGHT_EPSILON_M = 0.0001;
+const EARTH_RADIUS_M = 6_371_000;
+const INPUT_BINDINGS = Object.values(Cesium.CameraEventType).flatMap((type) =>
+  [undefined, ...Object.values(Cesium.KeyboardEventModifier)].map(
+    (modifier) => ({
+      type,
+      modifier,
+    }),
+  ),
+);
+
+/**
+ * The shallowest pitch (radians, negative is down) that still keeps the Earth
+ * framed from height `h`, or null where tilted views are left alone.
+ * The limb sits acos(R / (R + h)) below the local horizontal.
+ */
+export function maxPitchForHeight(h) {
+  if (!(h >= PITCH_CLAMP_MIN_HEIGHT_M)) return null;
+  const limb = Math.acos(EARTH_RADIUS_M / (EARTH_RADIUS_M + h));
+  return -Math.min(limb + LIMB_MARGIN_RAD, Cesium.Math.PI_OVER_TWO);
+}
+
+function matchesZoomBinding(bindings, type, modifier) {
+  if (Array.isArray(bindings))
+    return bindings.some((binding) =>
+      matchesZoomBinding(binding, type, modifier),
+    );
+  return typeof bindings === 'number'
+    ? bindings === type && modifier === undefined
+    : bindings?.eventType === type && bindings?.modifier === modifier;
+}
+
+function readInput(aggregator, bindings) {
+  let outward = false;
+  let cancel = false;
+  for (const { type, modifier } of INPUT_BINDINGS) {
+    if (!aggregator.isMoving(type, modifier)) continue;
+    const movement = aggregator.getMovement(type, modifier);
+    const pinch = type === Cesium.CameraEventType.PINCH;
+    const distance = pinch ? movement.distance : movement;
+    const delta = distance.endPosition.y - distance.startPosition.y;
+    // Cesium tilts by the fingers' midpoint while zooming by their spacing,
+    // both in the same quarter-pixel units. Fingers rarely keep a perfectly
+    // even spacing, so the larger of the two movements decides the gesture.
+    const tilt = pinch
+      ? movement.angleAndHeight.endPosition.y -
+        movement.angleAndHeight.startPosition.y
+      : 0;
+    if (
+      matchesZoomBinding(bindings, type, modifier) &&
+      Math.abs(delta) > Math.abs(tilt)
+    ) {
+      outward ||= delta < 0;
+      cancel ||= delta > 0;
+    } else {
+      // Includes modifier-specific tilts and parallel two-finger movement.
+      cancel = true;
+    }
+  }
+  aggregator.reset();
+  return { outward, cancel };
+}
+
+/**
+ * Keep outward user zooms bounded and framed, without taking camera ownership
+ * from tilts, tracked entities or flights. Returns an idempotent disposer.
+ */
+export function installZoomOutGuard(
+  viewer,
+  {
+    requestRender = governorRequestRender,
+    subscribeCameraHandoff,
+    createAggregator = (canvas) => new Cesium.CameraEventAggregator(canvas),
+  } = {},
+) {
+  const scene = viewer?.scene;
+  const controller = scene?.screenSpaceCameraController;
+  const camera = viewer?.camera;
+  const canvas = viewer?.canvas;
+  if (
+    !controller ||
+    !camera ||
+    !canvas ||
+    !scene.preRender ||
+    !scene.postUpdate
+  )
+    throw new TypeError('A complete Cesium viewer is required');
+
+  const aggregator = createAggregator(canvas);
+  const originalMaximumZoomDistance = controller.maximumZoomDistance;
+  const ownsCeiling = originalMaximumZoomDistance > MAXIMUM_ZOOM_DISTANCE_M;
+  let maximumZoomDistance = Math.min(
+    originalMaximumZoomDistance,
+    MAXIMUM_ZOOM_DISTANCE_M,
+  );
+  controller.maximumZoomDistance = maximumZoomDistance;
+  // Cesium clamps any zoom that starts above the limit to the limit, in either
+  // direction. A camera placed higher by a flight or share link keeps its own
+  // height as the limit, so it zooms in gradually and can't climb further.
+  const followCeiling = () => {
+    if (!ownsCeiling || controller.maximumZoomDistance !== maximumZoomDistance)
+      return;
+    // While tracking, Cesium measures zoom from the target, not the Earth, so
+    // the camera's altitude would lift the ceiling with every outward step.
+    const untracked =
+      scene.mode === Cesium.SceneMode.SCENE3D &&
+      Cesium.Matrix4.equals(camera.transform, Cesium.Matrix4.IDENTITY);
+    const height = untracked ? camera.positionCartographic?.height : undefined;
+    maximumZoomDistance =
+      height > MAXIMUM_ZOOM_DISTANCE_M ? height : MAXIMUM_ZOOM_DISTANCE_M;
+    controller.maximumZoomDistance = maximumZoomDistance;
+  };
+  followCeiling();
+
+  let lastHeight = camera.positionCartographic?.height;
+  let lastPosition = Cesium.Cartesian3.clone(camera.position);
+  let lastHeading = camera.heading;
+  let lastPitch = camera.pitch;
+  let lastRoll = camera.roll;
+  let zoomingOut = false;
+  let settling = false;
+  const cancel = () => {
+    zoomingOut = false;
+    settling = false;
+  };
+  const guard = () => {
+    const input = readInput(aggregator, controller.zoomEventTypes);
+    const height = camera.positionCartographic?.height;
+    const climbing = height > lastHeight + HEIGHT_EPSILON_M;
+    const descending = height < lastHeight - HEIGHT_EPSILON_M;
+    try {
+      if (
+        scene.mode !== Cesium.SceneMode.SCENE3D ||
+        controller.enableInputs === false ||
+        controller.enableZoom === false ||
+        !Cesium.Matrix4.equals(camera.transform, Cesium.Matrix4.IDENTITY) ||
+        // Cesium has no public running-flight flag.
+        camera._currentFlight ||
+        input.cancel ||
+        (descending && !settling)
+      ) {
+        cancel();
+        return;
+      }
+      if (input.outward) {
+        zoomingOut = true;
+        // A genuine outward gesture can be blocked by the controller's ceiling.
+        settling = true;
+      }
+      if (climbing) {
+        if (!zoomingOut) return;
+        settling = true;
+      } else {
+        zoomingOut = false;
+        // Outward inertia can lower altitude when Cesium clamps slant range at
+        // the ceiling. Finish that correction; fresh inward input cancels above.
+        // A stationary correction owns only the pose it last produced.
+        if (
+          !input.outward &&
+          ((!descending &&
+            !Cesium.Cartesian3.equals(camera.position, lastPosition)) ||
+            Math.abs(Cesium.Math.negativePiToPi(camera.heading - lastHeading)) >
+              1e-10 ||
+            Math.abs(camera.pitch - lastPitch) > 1e-10 ||
+            Math.abs(Cesium.Math.negativePiToPi(camera.roll - lastRoll)) >
+              1e-10)
+        )
+          settling = false;
+        if (!settling) return;
+      }
+      const maxPitch = maxPitchForHeight(height);
+      if (maxPitch === null || !(camera.pitch > maxPitch)) {
+        settling = false;
+      } else {
+        const error = maxPitch - camera.pitch;
+        const easedPitch =
+          Math.abs(error) <= PITCH_SNAP_RAD
+            ? maxPitch
+            : camera.pitch + error * PITCH_EASE;
+        // A large wheel step must not leave the view above the limb while easing.
+        const limbPitch = -Math.acos(
+          EARTH_RADIUS_M / (EARTH_RADIUS_M + height),
+        );
+        const pitch = Math.min(easedPitch, limbPitch);
+        camera.setView({
+          orientation: { heading: camera.heading, pitch, roll: camera.roll },
+        });
+        settling = pitch > maxPitch;
+      }
+      // Observe the end of inertia too; no arbitrary timeout cuts off a long zoom.
+      if (zoomingOut || settling) requestRender('zoom-out-guard');
+    } finally {
+      lastHeight = camera.positionCartographic?.height;
+      lastPosition = Cesium.Cartesian3.clone(camera.position, lastPosition);
+      lastHeading = camera.heading;
+      lastPitch = camera.pitch;
+      lastRoll = camera.roll;
+    }
+  };
+  const removePreRender = scene.preRender.addEventListener(guard);
+  // Fires every frame, after Cesium has applied this frame's input, while
+  // preRender fires only on frames that draw. Input that didn't move the camera
+  // (such as wheel at the ceiling) would otherwise wait for an unrelated frame.
+  const removePostUpdate = scene.postUpdate.addEventListener(() => {
+    followCeiling();
+    if (
+      INPUT_BINDINGS.some(({ type, modifier }) =>
+        aggregator.isMoving(type, modifier),
+      )
+    )
+      requestRender('zoom-out-guard');
+  });
+  const removeCameraHandoff = subscribeCameraHandoff?.(() => {
+    cancel();
+    // Discard input queued before an explicit navigation action took ownership.
+    aggregator.reset();
+  });
+
+  let active = true;
+  return () => {
+    if (!active) return;
+    active = false;
+    removeCameraHandoff?.();
+    removePreRender?.();
+    removePostUpdate?.();
+    aggregator.destroy();
+    if (controller.maximumZoomDistance === maximumZoomDistance)
+      controller.maximumZoomDistance = originalMaximumZoomDistance;
+  };
+}
diff --git a/src/app/zoomOutGuard.test.mjs b/src/app/zoomOutGuard.test.mjs
new file mode 100644
index 000000000..4785cee8b
--- /dev/null
+++ b/src/app/zoomOutGuard.test.mjs
@@ -0,0 +1,764 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import * as Cesium from 'cesium';
+import {
+  installZoomOutGuard,
+  maxPitchForHeight,
+  MAXIMUM_ZOOM_DISTANCE_M,
+} from './zoomOutGuard.js';
+
+const deg = Cesium.Math.toDegrees;
+const { WHEEL, PINCH, RIGHT_DRAG, LEFT_DRAG, MIDDLE_DRAG } =
+  Cesium.CameraEventType;
+const { CTRL, SHIFT, ALT } = Cesium.KeyboardEventModifier;
+
+test('maxPitchForHeight leaves low-altitude tilt alone', () => {
+  assert.equal(maxPitchForHeight(0), null);
+  assert.equal(maxPitchForHeight(299_999), null);
+  assert.equal(maxPitchForHeight(NaN), null);
+  assert.equal(maxPitchForHeight(undefined), null);
+});
+
+test('maxPitchForHeight looks 8 degrees below the limb', () => {
+  assert.ok(Math.abs(deg(maxPitchForHeight(1_000_000)) + 38.19) < 0.01);
+  assert.equal(deg(maxPitchForHeight(1e12)), -90);
+});
+
+test('maxPitchForHeight steepens monotonically with height', () => {
+  let previous = 0;
+  for (let h = 300_000; h <= 100_000_000; h *= 1.5) {
+    const pitch = maxPitchForHeight(h);
+    assert.ok(pitch <= previous, `pitch at ${h} m`);
+    previous = pitch;
+  }
+});
+
+function guardFixture({ maximumZoomDistance = Infinity } = {}) {
+  const preRender = new Set();
+  const postUpdate = new Set();
+  const handoffs = new Set();
+  const container = new EventTarget();
+  const canvas = new EventTarget();
+  const movements = new Map();
+  const key = (type, modifier) => `${type}:${modifier}`;
+  const aggregator = {
+    resets: 0,
+    destroys: 0,
+    isMoving: (type, modifier) => movements.has(key(type, modifier)),
+    getMovement: (type, modifier) => movements.get(key(type, modifier)),
+    reset() {
+      movements.clear();
+      this.resets++;
+    },
+    destroy() {
+      this.destroys++;
+      movements.clear();
+    },
+  };
+  const camera = {
+    height: 170_000,
+    longitude: 0,
+    latitude: 0,
+    heading: 0.4,
+    pitch: Cesium.Math.toRadians(-25),
+    roll: 0,
+    transform: Cesium.Matrix4.clone(Cesium.Matrix4.IDENTITY),
+    views: [],
+    get positionCartographic() {
+      return {
+        height: this.height,
+        longitude: this.longitude,
+        latitude: this.latitude,
+      };
+    },
+    get position() {
+      return this.positionWC;
+    },
+    get positionWC() {
+      return Cesium.Cartesian3.fromRadians(
+        this.longitude,
+        this.latitude,
+        this.height,
+      );
+    },
+    setView({ orientation }) {
+      this.views.push(orientation);
+      this.heading = orientation.heading;
+      this.pitch = orientation.pitch;
+      this.roll = orientation.roll;
+    },
+  };
+  const controller = {
+    maximumZoomDistance,
+    enableInputs: true,
+    enableZoom: true,
+    zoomEventTypes: [
+      RIGHT_DRAG,
+      WHEEL,
+      PINCH,
+      { eventType: WHEEL, modifier: CTRL },
+    ],
+  };
+  const scene = {
+    mode: Cesium.SceneMode.SCENE3D,
+    screenSpaceCameraController: controller,
+    preRender: {
+      addEventListener(handler) {
+        preRender.add(handler);
+        return () => preRender.delete(handler);
+      },
+    },
+    postUpdate: {
+      addEventListener(handler) {
+        postUpdate.add(handler);
+        return () => postUpdate.delete(handler);
+      },
+    },
+  };
+  const renders = [];
+  const dispose = installZoomOutGuard(
+    { camera, container, canvas, scene },
+    {
+      subscribeCameraHandoff(listener) {
+        handoffs.add(listener);
+        return () => handoffs.delete(listener);
+      },
+      createAggregator(element) {
+        assert.equal(element, canvas);
+        return aggregator;
+      },
+      requestRender: (reason) => renders.push(reason),
+    },
+  );
+  // A frame Cesium skips drawing in request-render mode: no preRender.
+  const idleFrame = () => {
+    for (const handler of postUpdate) handler();
+  };
+  const frame = (height = camera.height) => {
+    camera.height = height;
+    idleFrame();
+    for (const handler of preRender) handler();
+  };
+  const movement = (type, deltaY, { modifier, tiltDeltaY = 0 } = {}) => {
+    const distance = {
+      startPosition: new Cesium.Cartesian2(0, 0),
+      endPosition: new Cesium.Cartesian2(0, deltaY),
+    };
+    movements.set(
+      key(type, modifier),
+      type === PINCH
+        ? {
+            distance,
+            angleAndHeight: {
+              startPosition: new Cesium.Cartesian2(0, 0),
+              endPosition: new Cesium.Cartesian2(0, tiltDeltaY),
+            },
+          }
+        : distance,
+    );
+    // Also exercise the former raw DOM path when running against the PR head.
+    const event = new Event(
+      type === WHEEL ? 'wheel' : type === PINCH ? 'touchmove' : 'pointermove',
+    );
+    Object.assign(event, {
+      buttons: type === RIGHT_DRAG ? 2 : type === MIDDLE_DRAG ? 4 : 1,
+      ctrlKey: modifier === CTRL,
+      shiftKey: modifier === SHIFT,
+      altKey: modifier === ALT,
+      touches: type === PINCH ? [1, 2] : [],
+    });
+    container.dispatchEvent(event);
+  };
+  return {
+    camera,
+    controller,
+    scene,
+    aggregator,
+    preRender,
+    postUpdate,
+    handoffs,
+    handoff: () => {
+      for (const listener of handoffs) listener();
+    },
+    renders,
+    dispose,
+    frame,
+    idleFrame,
+    movement,
+  };
+}
+
+test('a tilted wheel zoom-out pitches down and preserves heading and roll', () => {
+  const f = guardFixture();
+  f.frame();
+  f.movement(WHEEL, -10);
+  f.frame(1_000_000);
+  const target = maxPitchForHeight(1_000_000);
+  assert.ok(f.camera.pitch < Cesium.Math.toRadians(-25));
+  assert.ok(f.camera.pitch > target, 'eases rather than snapping');
+  assert.equal(f.camera.heading, 0.4);
+  assert.equal(f.camera.roll, 0);
+  for (let i = 1; i <= 40; i++) f.frame(1_000_000 + i);
+  assert.ok(
+    Math.abs(f.camera.pitch - maxPitchForHeight(f.camera.height)) < 1e-3,
+  );
+  assert.ok(f.renders.length > 0);
+});
+
+test('a large outward step immediately keeps the Earth limb in view', () => {
+  const f = guardFixture();
+  f.frame(500_000);
+  f.movement(WHEEL, -100);
+  f.frame(20_000_000);
+  const limbPitch = -Math.acos(6_371_000 / (6_371_000 + 20_000_000));
+  assert.ok(f.camera.pitch <= limbPitch);
+  assert.ok(f.camera.pitch > maxPitchForHeight(20_000_000));
+});
+
+test('pinch, right-drag and configured Ctrl+wheel can zoom out', () => {
+  for (const [type, modifier] of [[PINCH], [RIGHT_DRAG], [WHEEL, CTRL]]) {
+    const f = guardFixture();
+    f.frame(500_000);
+    f.movement(type, -10, { modifier });
+    f.frame(700_000);
+    assert.equal(f.camera.views.length, 1, `${type}:${modifier}`);
+    f.dispose();
+  }
+});
+
+test('Ctrl+right-drag tilt is left at the pose chosen by Cesium', () => {
+  const f = guardFixture();
+  f.frame(500_000);
+  f.movement(RIGHT_DRAG, 3, { modifier: CTRL });
+  // Real Cesium's orbit tilt raises altitude with no zoom movement.
+  f.camera.pitch = Cesium.Math.toRadians(-26.07722459498313);
+  f.frame(529_392.3759876974);
+  assert.equal(f.camera.views.length, 0);
+  assert.equal(deg(f.camera.pitch), -26.07722459498313);
+});
+
+test('parallel two-finger tilt is not mistaken for pinch zoom', () => {
+  const f = guardFixture();
+  f.frame(500_000);
+  f.movement(PINCH, 0, { tiltDeltaY: 3 });
+  f.frame(600_000);
+  assert.equal(f.camera.views.length, 0);
+});
+
+test('two-finger tilt with finger-spacing drift is left to Cesium', () => {
+  for (const [spacing, tilt] of [
+    [-0.01, 3],
+    [-2, 3],
+    [-3, -3],
+  ]) {
+    const f = guardFixture();
+    f.frame(500_000);
+    f.movement(PINCH, spacing, { tiltDeltaY: tilt });
+    // Real Cesium's two-finger tilt climbs and picks its own pitch.
+    f.camera.pitch = Cesium.Math.toRadians(-26.07746);
+    f.frame(529_406);
+    assert.equal(f.camera.views.length, 0, `${spacing}, ${tilt}`);
+    f.dispose();
+  }
+});
+
+test('a pinch that closes the fingers more than it moves them still zooms out', () => {
+  // One finger still, the other sliding towards it: the midpoint moves half as far.
+  const f = guardFixture();
+  f.frame(500_000);
+  f.movement(PINCH, -10, { tiltDeltaY: -5 });
+  f.frame(700_000);
+  assert.equal(f.camera.views.length, 1);
+  f.dispose();
+});
+
+test('unconfigured wheel modifiers and one-finger drag do not enable the guard', () => {
+  for (const [type, modifier] of [[WHEEL, SHIFT], [WHEEL, ALT], [LEFT_DRAG]]) {
+    const f = guardFixture();
+    f.frame(500_000);
+    f.movement(type, -10, { modifier });
+    f.frame(600_000);
+    assert.equal(f.camera.views.length, 0, `${type}:${modifier}`);
+    f.dispose();
+  }
+});
+
+test('current controller zoom bindings are honored', () => {
+  const f = guardFixture();
+  f.frame(500_000);
+  f.controller.zoomEventTypes = { eventType: MIDDLE_DRAG, modifier: ALT };
+  f.movement(WHEEL, -10);
+  f.frame(600_000);
+  assert.equal(f.camera.views.length, 0);
+  f.movement(MIDDLE_DRAG, -10, { modifier: ALT });
+  f.frame(700_000);
+  assert.equal(f.camera.views.length, 1);
+});
+
+test('programmatic height changes alone never activate the guard', () => {
+  const f = guardFixture();
+  f.frame(170_000);
+  f.frame(2_000_000);
+  f.frame(3_000_000);
+  assert.equal(f.camera.views.length, 0);
+});
+
+test('inward zoom does not activate the guard even when altitude rises', () => {
+  const f = guardFixture();
+  f.frame(500_000);
+  f.movement(WHEEL, 10);
+  f.frame(600_000);
+  assert.equal(f.camera.views.length, 0);
+});
+
+test('outward input with falling height does not alter pitch', () => {
+  const f = guardFixture();
+  f.frame(2_000_000);
+  f.movement(WHEEL, -10);
+  f.frame(1_500_000);
+  f.frame(1_500_000);
+  assert.equal(f.camera.views.length, 0);
+});
+
+test('pitch finishes settling when the zoom stops changing height', () => {
+  const f = guardFixture();
+  f.frame(500_000);
+  f.movement(WHEEL, -10);
+  f.frame(2_000_000);
+  const firstPitch = f.camera.pitch;
+  for (let i = 0; i < 40; i++) f.frame();
+  assert.ok(f.camera.pitch < firstPitch);
+  assert.ok(Math.abs(f.camera.pitch - maxPitchForHeight(2_000_000)) < 1e-10);
+  const views = f.camera.views.length;
+  f.frame();
+  assert.equal(
+    f.camera.views.length,
+    views,
+    'settled pose does not keep rendering',
+  );
+});
+
+test('completed settling does not authorize a later programmatic climb', () => {
+  const f = guardFixture();
+  f.frame(500_000);
+  f.movement(WHEEL, -10);
+  f.frame(700_000);
+  for (let i = 0; i < 40; i++) f.frame();
+  const views = f.camera.views.length;
+  f.frame(3_000_000);
+  assert.equal(f.camera.views.length, views);
+});
+
+test('a fresh inward zoom or unrelated gesture cancels pending correction', () => {
+  for (const [type, delta, options] of [
+    [WHEEL, 10, {}],
+    [RIGHT_DRAG, 3, { modifier: CTRL }],
+    [LEFT_DRAG, 3, {}],
+    [MIDDLE_DRAG, 3, {}],
+    [PINCH, 0, { tiltDeltaY: 3 }],
+  ]) {
+    const f = guardFixture();
+    f.frame(500_000);
+    f.movement(WHEEL, -10);
+    f.frame(700_000);
+    const views = f.camera.views.length;
+    f.movement(type, delta, options);
+    f.frame(800_000);
+    f.frame(900_000);
+    assert.equal(f.camera.views.length, views, `${type}:${options.modifier}`);
+    f.dispose();
+  }
+});
+
+test('an external pose change at fixed height cancels pending correction', () => {
+  for (const field of ['heading', 'pitch', 'roll', 'longitude', 'latitude']) {
+    const f = guardFixture();
+    f.frame(500_000);
+    f.movement(WHEEL, -10);
+    f.frame(700_000);
+    const views = f.camera.views.length;
+    f.camera[field] += 0.1;
+    f.frame();
+    f.frame(900_000);
+    assert.equal(f.camera.views.length, views, field);
+    f.dispose();
+  }
+});
+
+test('disabled controls, flights, tracked transforms and non-3D scenes cancel intent', () => {
+  const cases = [
+    (f) => {
+      f.controller.enableInputs = false;
+      return () => {
+        f.controller.enableInputs = true;
+      };
+    },
+    (f) => {
+      f.controller.enableZoom = false;
+      return () => {
+        f.controller.enableZoom = true;
+      };
+    },
+    (f) => {
+      f.camera._currentFlight = {};
+      return () => {
+        delete f.camera._currentFlight;
+      };
+    },
+    (f) => {
+      f.camera.transform = Cesium.Matrix4.fromTranslation(
+        new Cesium.Cartesian3(1, 2, 3),
+      );
+      return () => {
+        f.camera.transform = Cesium.Matrix4.clone(Cesium.Matrix4.IDENTITY);
+      };
+    },
+    (f) => {
+      f.scene.mode = Cesium.SceneMode.SCENE2D;
+      return () => {
+        f.scene.mode = Cesium.SceneMode.SCENE3D;
+      };
+    },
+  ];
+  for (const block of cases) {
+    const f = guardFixture();
+    f.frame(500_000);
+    f.movement(WHEEL, -10);
+    f.frame(700_000);
+    const views = f.camera.views.length;
+    const restore = block(f);
+    f.movement(WHEEL, -10);
+    f.frame(800_000);
+    restore();
+    f.frame(900_000);
+    assert.equal(f.camera.views.length, views);
+    f.movement(WHEEL, -10);
+    f.frame(1_000_000);
+    assert.equal(f.camera.views.length, views + 1);
+    f.dispose();
+  }
+});
+
+test('installer sets the ceiling and disposer releases aggregator and frame listener', () => {
+  const f = guardFixture();
+  assert.equal(f.controller.maximumZoomDistance, MAXIMUM_ZOOM_DISTANCE_M);
+  assert.equal(f.preRender.size, 1);
+  assert.equal(f.postUpdate.size, 1);
+  f.frame();
+  assert.ok(f.aggregator.resets > 0);
+  f.dispose();
+  f.dispose();
+  assert.equal(f.controller.maximumZoomDistance, Infinity);
+  assert.equal(f.aggregator.destroys, 1);
+  assert.equal(f.preRender.size, 0);
+  assert.equal(f.postUpdate.size, 0);
+  assert.equal(f.handoffs.size, 0);
+});
+
+test('installer preserves a stricter host zoom ceiling', () => {
+  const f = guardFixture({ maximumZoomDistance: 123 });
+  assert.equal(f.controller.maximumZoomDistance, 123);
+  f.dispose();
+  assert.equal(f.controller.maximumZoomDistance, 123);
+});
+
+test('disposer keeps a ceiling someone else changed later', () => {
+  const f = guardFixture();
+  f.controller.maximumZoomDistance = 5;
+  f.dispose();
+  assert.equal(f.controller.maximumZoomDistance, 5);
+});
+
+test('installer rejects an incomplete viewer', () => {
+  assert.throws(() => installZoomOutGuard({}), TypeError);
+});
+
+test('outward input at the ceiling reframes a deliberately tilted camera', () => {
+  const f = guardFixture();
+  f.frame(MAXIMUM_ZOOM_DISTANCE_M);
+  f.movement(WHEEL, -10);
+  f.frame();
+  for (let i = 0; i < 40; i++) f.frame();
+  assert.ok(
+    Math.abs(f.camera.pitch - maxPitchForHeight(MAXIMUM_ZOOM_DISTANCE_M)) <
+      1e-10,
+  );
+  f.dispose();
+});
+
+test('input that leaves the camera still requests a frame to read it', () => {
+  const f = guardFixture();
+  f.frame(MAXIMUM_ZOOM_DISTANCE_M);
+  f.idleFrame();
+  assert.deepEqual(f.renders, [], 'an idle scene stays idle');
+  // At the ceiling Cesium doesn't move the camera, so nothing would draw.
+  f.movement(WHEEL, -10);
+  f.idleFrame();
+  assert.deepEqual(f.renders, ['zoom-out-guard']);
+  f.frame();
+  assert.ok(f.camera.pitch < Cesium.Math.toRadians(-25), 'read that frame');
+  f.dispose();
+});
+
+test('equivalent heading and roll wraps do not cancel stationary settling', () => {
+  const f = guardFixture();
+  f.frame(500_000);
+  f.movement(WHEEL, -10);
+  f.frame(2_000_000);
+  f.camera.heading += Cesium.Math.TWO_PI;
+  f.camera.roll += Cesium.Math.TWO_PI;
+  for (let i = 0; i < 40; i++) f.frame();
+  assert.ok(Math.abs(f.camera.pitch - maxPitchForHeight(2_000_000)) < 1e-10);
+  f.dispose();
+});
+
+test('a real Cesium camera settles across the north heading wrap at Istanbul', () => {
+  const scene = {
+    canvas: { clientWidth: 1200, clientHeight: 800, width: 1200, height: 800 },
+    drawingBufferWidth: 1200,
+    drawingBufferHeight: 800,
+    mapProjection: new Cesium.GeographicProjection(),
+    globe: { ellipsoid: Cesium.Ellipsoid.WGS84 },
+    mapMode2D: Cesium.MapMode2D.INFINITE_SCROLL,
+    mode: Cesium.SceneMode.SCENE3D,
+    pixelRatio: 1,
+    preRender: new Cesium.Event(),
+    postUpdate: new Cesium.Event(),
+    screenSpaceCameraController: {
+      maximumZoomDistance: Infinity,
+      enableInputs: true,
+      zoomEventTypes: [WHEEL],
+    },
+  };
+  const camera = new Cesium.Camera(scene);
+  scene.camera = camera;
+  const setHeight = (height) =>
+    camera.setView({
+      destination: Cesium.Cartesian3.fromDegrees(28.9784, 41.0082, height),
+      orientation: { heading: 0, pitch: Cesium.Math.toRadians(-25), roll: 0 },
+    });
+  setHeight(1_000_000);
+  let outward = false;
+  const dispose = installZoomOutGuard(
+    { scene, camera, canvas: scene.canvas },
+    {
+      createAggregator: () => ({
+        isMoving: (type, modifier) =>
+          outward && type === WHEEL && modifier === undefined,
+        getMovement: () => ({
+          startPosition: { y: 0 },
+          endPosition: { y: -10 },
+        }),
+        reset: () => {
+          outward = false;
+        },
+        destroy() {},
+      }),
+      requestRender() {},
+    },
+  );
+  try {
+    setHeight(MAXIMUM_ZOOM_DISTANCE_M);
+    outward = true;
+    for (let i = 0; i < 40; i++) scene.preRender.raiseEvent(scene);
+    assert.ok(
+      Math.abs(
+        camera.pitch - maxPitchForHeight(camera.positionCartographic.height),
+      ) < 1e-8,
+    );
+  } finally {
+    dispose();
+  }
+});
+
+test('an outward inertia ceiling adjustment can descend while pitch settles', () => {
+  const f = guardFixture();
+  f.frame(39_000_000);
+  f.movement(WHEEL, -10);
+  f.frame(39_999_999);
+  const before = f.camera.pitch;
+  // Cesium limits slant range on an inertial pick, slightly below the altitude cap.
+  f.frame(39_997_258);
+  for (let i = 0; i < 40; i++) f.frame();
+  assert.ok(f.camera.pitch < before);
+  assert.ok(
+    Math.abs(f.camera.pitch - maxPitchForHeight(f.camera.height)) < 1e-10,
+  );
+  f.dispose();
+});
+
+test('a descending programmatic tilt cancels pending correction', () => {
+  const f = guardFixture();
+  f.frame(39_000_000);
+  f.movement(WHEEL, -10);
+  f.frame(39_999_999);
+  const count = f.camera.views.length;
+  f.camera.pitch += 0.1;
+  f.frame(39_997_258);
+  for (let i = 0; i < 40; i++) f.frame();
+  assert.equal(f.camera.views.length, count);
+  f.dispose();
+});
+
+test('explicit navigation cancels outward inertia before a climbing UI tilt', () => {
+  const f = guardFixture();
+  f.movement(WHEEL, -10);
+  f.frame(1_000_000);
+  f.movement(WHEEL, -10);
+  f.handoff();
+  const writes = f.camera.views.length;
+  f.camera.pitch = Cesium.Math.toRadians(-25);
+  f.frame(1_100_000);
+  f.frame(1_200_000);
+  assert.equal(f.camera.views.length, writes);
+  assert.equal(deg(f.camera.pitch), -25);
+  // A subsequent user zoom starts a new correction normally.
+  f.movement(WHEEL, -10);
+  f.frame(1_300_000);
+  assert.ok(f.camera.views.length > writes);
+  f.dispose();
+});
+
+// A real Cesium camera and controller, fed by DOM wheel events on the canvas.
+function realControllerScene(startHeight) {
+  const canvas = Object.assign(new EventTarget(), {
+    clientWidth: 1200,
+    clientHeight: 800,
+    width: 1200,
+    height: 800,
+    style: {},
+    // Keep Cesium's input handler off the missing `document`.
+    disableRootEvents: true,
+    onwheel: null,
+    getBoundingClientRect: () => ({
+      left: 0,
+      top: 0,
+      width: 1200,
+      height: 800,
+    }),
+  });
+  const scene = {
+    canvas,
+    drawingBufferWidth: 1200,
+    drawingBufferHeight: 800,
+    mapProjection: new Cesium.GeographicProjection(),
+    ellipsoid: Cesium.Ellipsoid.WGS84,
+    mapMode2D: Cesium.MapMode2D.INFINITE_SCROLL,
+    mode: Cesium.SceneMode.SCENE3D,
+    pixelRatio: 1,
+    verticalExaggeration: 1,
+    verticalExaggerationRelativeHeight: 0,
+    preRender: new Cesium.Event(),
+    postUpdate: new Cesium.Event(),
+  };
+  const camera = new Cesium.Camera(scene);
+  scene.camera = camera;
+  const controller = new Cesium.ScreenSpaceCameraController(scene);
+  controller.inertiaZoom = 0;
+  scene.screenSpaceCameraController = controller;
+  const setHeight = (h) =>
+    camera.setView({
+      destination: Cesium.Cartesian3.fromDegrees(28.9784, 41.0082, h),
+      orientation: { heading: 0, pitch: -Cesium.Math.PI_OVER_TWO, roll: 0 },
+    });
+  setHeight(startHeight);
+  const dispose = installZoomOutGuard(
+    { scene, camera, canvas },
+    { requestRender() {} },
+  );
+  // Scene.render order: the controller applies input, then postUpdate, then
+  // preRender on frames that draw.
+  const frame = () => {
+    controller.update();
+    scene.postUpdate.raiseEvent(scene);
+    scene.preRender.raiseEvent(scene);
+  };
+  const wheel = (deltaY) =>
+    canvas.dispatchEvent(
+      Object.assign(new Event('wheel'), {
+        deltaY,
+        deltaMode: 0,
+        clientX: 600,
+        clientY: 400,
+      }),
+    );
+  const height = () => camera.positionCartographic.height;
+  return {
+    scene,
+    camera,
+    controller,
+    setHeight,
+    frame,
+    wheel,
+    height,
+    dispose,
+  };
+}
+
+test('a camera placed above the ceiling cannot zoom out and zooms in without a jump', () => {
+  const s = realControllerScene(60_000_000);
+  try {
+    s.frame();
+    s.wheel(1);
+    s.frame();
+    assert.ok(Math.abs(s.height() - 60_000_000) < 1, `${s.height()} m`);
+    s.wheel(-1);
+    s.frame();
+    const firstStep = s.height();
+    assert.ok(firstStep < 60_000_000, 'zooms in');
+    assert.ok(firstStep > 50_000_000, `${firstStep} m is gradual`);
+    // The camera can no longer climb back above where it has descended to.
+    s.wheel(1);
+    s.frame();
+    assert.ok(Math.abs(s.height() - firstStep) < 1, `${s.height()} m`);
+    for (let i = 0; i < 40; i++) {
+      s.wheel(-100);
+      s.frame();
+    }
+    assert.ok(s.height() < MAXIMUM_ZOOM_DISTANCE_M);
+    assert.equal(s.controller.maximumZoomDistance, MAXIMUM_ZOOM_DISTANCE_M);
+    for (let i = 0; i < 80; i++) {
+      s.wheel(100);
+      s.frame();
+    }
+    assert.ok(Math.abs(s.height() - MAXIMUM_ZOOM_DISTANCE_M) < 1_000);
+  } finally {
+    s.dispose();
+  }
+  assert.equal(s.controller.maximumZoomDistance, Infinity);
+});
+
+test('a share-link view restored above the ceiling is honoured by later frames', () => {
+  const s = realControllerScene(1_000_000);
+  try {
+    s.frame();
+    s.setHeight(97_679_259);
+    s.frame();
+    s.wheel(100);
+    s.frame();
+    assert.ok(Math.abs(s.height() - 97_679_259) < 1, `${s.height()} m`);
+  } finally {
+    s.dispose();
+  }
+});
+
+test('a tracked camera cannot climb past the ceiling from its target', () => {
+  const s = realControllerScene(1_000_000);
+  try {
+    s.frame();
+    // In look-at mode Cesium measures zoom from the target, not the Earth.
+    s.camera.lookAt(
+      Cesium.Cartesian3.fromDegrees(0, 0, 35_786_000),
+      new Cesium.HeadingPitchRange(0, -0.5, 5_000_000),
+    );
+    for (let i = 0; i < 20; i++) {
+      s.wheel(100);
+      s.frame();
+    }
+    const range = Cesium.Cartesian3.magnitude(s.camera.position);
+    assert.ok(range <= MAXIMUM_ZOOM_DISTANCE_M + 1_000, `${range} m`);
+    assert.equal(s.controller.maximumZoomDistance, MAXIMUM_ZOOM_DISTANCE_M);
+  } finally {
+    s.dispose();
+  }
+});