diff --git a/cloudflare/README.md b/cloudflare/README.md
index 4b55249..463fcb7 100644
--- a/cloudflare/README.md
+++ b/cloudflare/README.md
@@ -48,6 +48,43 @@ A late `play`/`playing` event while hidden is stopped as well. No background tim
 is added to the reservation gate. This prevents audio-only background playback
 while browsers suspend video rendering. Player release: `20260910-visibility-1`.
 
+## Screening measurement (prepared locally, not deployed)
+
+Release `20260911-measurement-1` adds events through the site's existing Google
+tag queue, targeting the verified `G-DEMO000000` stream. It does not install another
+tag, change consent settings, or mark events as conversions.
+
+| Event | Trigger |
+| --- | --- |
+| `demo_screening_video_start` | First actual foreground playback |
+| `demo_screening_video_progress` | 25%, 50%, 75% credited viewing (`video_percent`) |
+| `demo_screening_booking_ready` | Existing viewing gate reveals the booking link |
+| `demo_screening_booking_click` | First click on the revealed booking link |
+| `demo_screening_video_error` | Classified media load, play rejection or HLS fallback |
+
+Normal events are deduplicated per page; each progress milestone and error class
+has its own key. Progress reuses the viewing gate's credited time, excluding seeks,
+pauses and hidden-page time. The source/UTM booking routing and viewing thresholds
+are unchanged. Booking clicks describe outbound intent, not completed reservations.
+
+Measurement runs only on `https://example.invalid/screening-lp/`. Standalone and local
+previews send nothing. The site's existing `?measurement_test=1` convention uses
+the separate `measurement_test` event with `demo_expected_event` and `debug_mode`.
+The event page URL excludes query data, and errors include only a closed category,
+never raw exception text. A missing or failing tag cannot interrupt playback.
+
+Six added tests cover milestones, deduplication, seek/buffer exclusion, invalid
+duration, tag failures, error classification, URL privacy and preview/test routing.
+All 18 tests and the static build passed. Chrome played the actual 720p HLS media
+locally for the full 192.875 seconds with this release: the booking link stayed
+hidden at 112.39 seconds, then appeared by the end with the original YouTube Spir
+route and supplied UTM values. The normal player, mute and final booking display
+rendered correctly. Local previews intentionally send no measurement events.
+After an authorized deployment, verify
+the test event in GA4 DebugView using the production page's test flag. Local UI
+verification is not evidence that GA4 received an event. Event parameters needed
+in reports may require corresponding GA4 custom definitions; none are created here.
+
 ## Development and deployment
 
 ```sh
diff --git a/cloudflare/public/analytics.mjs b/cloudflare/public/analytics.mjs
new file mode 100644
index 0000000..9c691ba
--- /dev/null
+++ b/cloudflare/public/analytics.mjs
@@ -0,0 +1,64 @@
+export const PLAYER_VERSION = "20260911-measurement-1";
+
+// Reuse the site's existing Google tag and consent configuration. This module
+// neither installs a tag nor marks an event as a conversion or booking success.
+export function existingGoogleTagSender(page) {
+  return (event, details) => {
+    if (page.location.origin !== "https://example.invalid" ||
+        page.location.pathname.replace(/\/+$/, "") !== "/screening-lp") return false;
+    const layer = page.dataLayer;
+    if (!layer || typeof layer.push !== "function") return false;
+    const params = {
+      send_to: "G-DEMO000000",
+      page_location: "https://example.invalid/screening-lp/",
+      video_id: "screening-v1",
+      demo_player_version: PLAYER_VERSION,
+      ...details
+    };
+    if (new URLSearchParams(page.location.search).get("measurement_test") === "1") {
+      params.demo_expected_event = event;
+      params.debug_mode = true;
+      event = "measurement_test";
+    }
+    // Google tag's command queue takes Arguments objects, not GTM custom events.
+    (function () { layer.push(arguments); })("event", event, params);
+    return true;
+  };
+}
+
+export function createScreeningAnalytics(send) {
+  const seen = new Set();
+  let ready = false;
+  function once(event, details = {}, key = event) {
+    if (seen.has(key)) return;
+    try {
+      if (send(event, details) !== false) seen.add(key);
+    } catch {
+      // Measurement must never interrupt playback or the reservation link.
+    }
+  }
+  return {
+    started() { once("demo_screening_video_start"); },
+    progress(gate, duration) {
+      if (![gate.watched, gate.furthest, duration].every(Number.isFinite) || duration <= 0) return;
+      // Use the gate's credited foreground playback, not wall time or a seek.
+      const percent = Math.min(gate.watched, gate.furthest) / duration * 100;
+      for (const threshold of [25, 50, 75]) {
+        if (percent >= threshold) once("demo_screening_video_progress",
+          { video_percent: threshold }, `progress-${threshold}`);
+      }
+    },
+    bookingReady() {
+      ready = true;
+      once("demo_screening_booking_ready");
+    },
+    bookingClicked() {
+      if (ready) once("demo_screening_booking_click");
+    },
+    error(reason) {
+      if (["hls_fallback", "play_rejected", "media_load"].includes(reason)) {
+        once("demo_screening_video_error", { error_reason: reason }, `error-${reason}`);
+      }
+    }
+  };
+}
diff --git a/cloudflare/public/player.mjs b/cloudflare/public/player.mjs
index f7d428e..867a2c6 100644
--- a/cloudflare/public/player.mjs
+++ b/cloudflare/public/player.mjs
@@ -2,11 +2,12 @@ import Hls from "./vendor/hls.mjs";
 import { WatchGate } from "./watch-gate.mjs";
 import { buildBookingUrl } from "./booking.mjs";
 import { bindForegroundPlayback } from "./foreground-playback.mjs";
+import { createScreeningAnalytics, existingGoogleTagSender, PLAYER_VERSION } from "./analytics.mjs";
 
 const video = document.getElementById("demoScreeningVideo");
 if (video && !video.dataset.initialized) {
   video.dataset.initialized = "true";
-  video.dataset.playerVersion = "20260910-visibility-1";
+  video.dataset.playerVersion = PLAYER_VERSION;
   const frame = video.closest(".demo-video-frame");
   const toggle = frame.querySelector(".demo-video-toggle");
   const mute = frame.querySelector(".demo-video-mute");
@@ -17,6 +18,7 @@ if (video && !video.dataset.initialized) {
   const booking = document.getElementById("demoBookingButton");
   const placeholder = document.getElementById("demoBookingPlaceholder");
   const gate = new WatchGate(0.9);
+  const analytics = createScreeningAnalytics(existingGoogleTagSender(window));
   const media = new URL("./media/v1/", import.meta.url);
   let hls;
   let started = false;
@@ -58,6 +60,7 @@ if (video && !video.dataset.initialized) {
     booking.href = buildBookingUrl(window.location.search);
     booking.hidden = false;
     placeholder.hidden = true;
+    analytics.bookingReady();
     setMessage("ご確認ありがとうございます。下記より日程をご選択ください。", "unlocked");
     message.dataset.success = "true";
     if (!document.fullscreenElement) {
@@ -67,7 +70,9 @@ if (video && !video.dataset.initialized) {
   function sample() {
     if (!foreground.canPlay()) { gate.resetSample(); return; }
     if (video.seeking) return;
-    if (gate.sample(video.currentTime, video.duration, performance.now(), !video.paused && !video.ended)) reveal();
+    const unlocked = gate.sample(video.currentTime, video.duration, performance.now(), !video.paused && !video.ended);
+    analytics.progress(gate, video.duration);
+    if (unlocked) reveal();
   }
   function source() {
     if (video.canPlayType("application/vnd.apple.mpegurl")) {
@@ -84,6 +89,7 @@ if (video && !video.dataset.initialized) {
         } else {
           hls.destroy();
           hls = null;
+          analytics.error("hls_fallback");
           const position = Math.min(video.currentTime || 0, gate.furthest);
           video.src = new URL("screening-720.mp4", media).href;
           video.addEventListener("loadedmetadata", () => { video.currentTime = position; }, { once: true });
@@ -105,6 +111,7 @@ if (video && !video.dataset.initialized) {
     } catch {
       // Page changes can abort a pending play() normally; keep the pause message.
       if (!foreground.canPlay()) return;
+      analytics.error("play_rejected");
       start.hidden = false;
       setMessage("再生できませんでした。通信状況をご確認のうえ、もう一度再生ボタンを押してください。", "error");
     }
@@ -112,6 +119,7 @@ if (video && !video.dataset.initialized) {
   toggle.addEventListener("click", playOrPause);
   start.addEventListener("click", playOrPause);
   video.addEventListener("click", playOrPause);
+  booking.addEventListener("click", () => { if (revealed) analytics.bookingClicked(); });
   mute.addEventListener("click", () => { video.muted = !video.muted; updateControls(); });
   fullscreen.addEventListener("click", async () => {
     try {
@@ -131,6 +139,7 @@ if (video && !video.dataset.initialized) {
   frame.addEventListener("focusin", showControls);
   video.addEventListener("playing", () => {
     if (!foreground.canPlay()) { gate.resetSample(); updateControls(); return; }
+    analytics.started();
     gate.resetSample(); sample(); updateControls(); showControls();
     if (!revealed) { status.dataset.state = "watching"; message.hidden = true; }
   });
@@ -150,6 +159,7 @@ if (video && !video.dataset.initialized) {
     updateControls();
   });
   video.addEventListener("error", () => {
+    analytics.error("media_load");
     gate.resetSample(); start.hidden = false;
     setMessage("動画の読み込みに失敗しました。通信状況をご確認のうえ、再生をお試しください。", "error");
   });
diff --git a/cloudflare/scripts/build.mjs b/cloudflare/scripts/build.mjs
index 0720e16..a1f724b 100644
--- a/cloudflare/scripts/build.mjs
+++ b/cloudflare/scripts/build.mjs
@@ -1,4 +1,5 @@
 import { cp, mkdir, readFile, rm, writeFile } from "node:fs/promises";
+import { PLAYER_VERSION } from "../public/analytics.mjs";
 await rm("dist", { recursive: true, force: true });
 await cp("public", "dist", { recursive: true });
 await mkdir("dist/vendor", { recursive: true });
@@ -11,5 +12,5 @@ const base = "https://preview.example.invalid";
 const css = await readFile("public/page.css", "utf8");
 const wordpressContent = content.replaceAll('src="/', `src="${base}/`).replaceAll('poster="/', `poster="${base}/`);
 const robotsScript = '<script>(function(){var r=document.createElement("meta");r.name="robots";r.content="noindex,nofollow";document.head.appendChild(r)})();</script>';
-await writeFile("wordpress-content.html", `<!-- wp:html -->\n<style>\n${css}\n</style>\n<link rel="stylesheet" href="${base}/controls.css?v=20260910">\n${wordpressContent}\n${robotsScript}\n<script type="module" src="${base}/player.mjs?v=20260910-visibility-1"></script>\n<!-- /wp:html -->\n`);
+await writeFile("wordpress-content.html", `<!-- wp:html -->\n<style>\n${css}\n</style>\n<link rel="stylesheet" href="${base}/controls.css?v=20260910">\n${wordpressContent}\n${robotsScript}\n<script type="module" src="${base}/player.mjs?v=${PLAYER_VERSION}"></script>\n<!-- /wp:html -->\n`);
 console.log("Built Cloudflare page and self-hosted player");
diff --git a/cloudflare/tests/analytics.test.mjs b/cloudflare/tests/analytics.test.mjs
new file mode 100644
index 0000000..3b1bfec
--- /dev/null
+++ b/cloudflare/tests/analytics.test.mjs
@@ -0,0 +1,103 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { createScreeningAnalytics, existingGoogleTagSender, PLAYER_VERSION } from "../public/analytics.mjs";
+import { WatchGate } from "../public/watch-gate.mjs";
+
+test("credited viewing records one start, three milestones and one ready/click per page", () => {
+  const events = [];
+  const analytics = createScreeningAnalytics((name, params) => events.push({ name, params }));
+  const gate = new WatchGate();
+  analytics.bookingClicked();
+  analytics.started();
+  analytics.started(); // resume
+  for (let t = 0; t <= 174; t += 0.25) {
+    gate.sample(t, 193, t * 1000, true);
+    analytics.progress(gate, 193);
+    if (gate.unlocked) analytics.bookingReady();
+  }
+  analytics.bookingClicked();
+  analytics.bookingClicked();
+  assert.deepEqual(events, [
+    { name: "demo_screening_video_start", params: {} },
+    ...[25, 50, 75].map(video_percent => ({ name: "demo_screening_video_progress", params: { video_percent } })),
+    { name: "demo_screening_booking_ready", params: {} },
+    { name: "demo_screening_booking_click", params: {} }
+  ]);
+});
+
+test("seeking, buffering and invalid durations do not create progress", () => {
+  const events = [];
+  const analytics = createScreeningAnalytics((...args) => events.push(args));
+  const gate = new WatchGate();
+  gate.sample(0, 193, 0, true);
+  gate.sample(190, 193, 250, true);
+  gate.sample(193, 193, 600000, false);
+  analytics.progress(gate, 193);
+  analytics.progress({ watched: 190, furthest: 0 }, 193);
+  analytics.progress({ watched: 190, furthest: 190 }, NaN);
+  analytics.progress({ watched: 190, furthest: 190 }, 0);
+  assert.deepEqual(events, []);
+});
+
+test("missing or failing analytics cannot throw into the player", () => {
+  const failing = createScreeningAnalytics(() => { throw new Error("tag unavailable"); });
+  assert.doesNotThrow(() => {
+    failing.started();
+    failing.progress({ watched: 90, furthest: 90 }, 100);
+    failing.bookingReady();
+    failing.bookingClicked();
+    failing.error("media_load");
+  });
+  let available = false;
+  const events = [];
+  const late = createScreeningAnalytics(name => available ? events.push(name) : false);
+  late.started();
+  available = true;
+  late.started();
+  late.started();
+  assert.deepEqual(events, ["demo_screening_video_start"]);
+});
+
+test("only classified playback errors are sent and repeated errors are deduplicated", () => {
+  const events = [];
+  const analytics = createScreeningAnalytics((name, params) => events.push({ name, params }));
+  analytics.error("media_load");
+  analytics.error("media_load");
+  analytics.error("customer@example.com?token=private");
+  assert.deepEqual(events, [{ name: "demo_screening_video_error", params: { error_reason: "media_load" } }]);
+});
+
+test("Google events use the existing queue and the verified GA4 destination, without URL query data", () => {
+  const page = { location: new URL("https://example.invalid/screening-lp/?email=private@example.com&utm_source=youtube"), dataLayer: [] };
+  const send = existingGoogleTagSender(page);
+  assert.equal(send("demo_screening_video_start", {}), true);
+  const [command, event, params] = Array.from(page.dataLayer[0]);
+  assert.equal(command, "event");
+  assert.equal(event, "demo_screening_video_start");
+  assert.deepEqual(params, {
+    send_to: "G-DEMO000000",
+    page_location: "https://example.invalid/screening-lp/",
+    video_id: "screening-v1",
+    demo_player_version: PLAYER_VERSION
+  });
+  assert.equal(JSON.stringify(page.dataLayer).includes("private"), false);
+  assert.equal("gtag" in page, false);
+});
+
+test("preview pages never send; the existing test flag uses a separate debug event", () => {
+  for (const url of ["http://localhost:8794/", "https://preview.example.invalid/", "https://example.invalid/contact/"]) {
+    const page = { location: new URL(url), dataLayer: [] };
+    assert.equal(existingGoogleTagSender(page)("demo_screening_video_start", {}), false);
+    assert.deepEqual(page.dataLayer, []);
+  }
+  const missing = { location: new URL("https://example.invalid/screening-lp/") };
+  assert.equal(existingGoogleTagSender(missing)("demo_screening_video_start", {}), false);
+  assert.equal("dataLayer" in missing, false);
+  const page = { location: new URL("https://example.invalid/screening-lp/?measurement_test=1"), dataLayer: [] };
+  existingGoogleTagSender(page)("demo_screening_video_progress", { video_percent: 50 });
+  const [, event, params] = Array.from(page.dataLayer[0]);
+  assert.equal(event, "measurement_test");
+  assert.equal(params.demo_expected_event, "demo_screening_video_progress");
+  assert.equal(params.debug_mode, true);
+  assert.equal(params.video_percent, 50);
+});
diff --git a/cloudflare/wordpress-content.html b/cloudflare/wordpress-content.html
index 951e745..72018d7 100644
--- a/cloudflare/wordpress-content.html
+++ b/cloudflare/wordpress-content.html
@@ -75,5 +75,5 @@ to { opacity: 1; transform: translateY(0); }
 </main>
 
 <script>(function(){var r=document.createElement("meta");r.name="robots";r.content="noindex,nofollow";document.head.appendChild(r)})();</script>
-<script type="module" src="https://preview.example.invalid/player.mjs?v=20260910-visibility-1"></script>
+<script type="module" src="https://preview.example.invalid/player.mjs?v=20260911-measurement-1"></script>
 <!-- /wp:html -->