diff --git a/static/js/main.js b/static/js/main.js
index 4009ce6c..80e6f331 100644
--- a/static/js/main.js
+++ b/static/js/main.js
@@ -1,5 +1,5 @@
 import {
-  playBtn, loopBtn, multitrack, totalDuration, loopEnabled, loopStart, loopEnd,
+  playBtn, loopBtn, totalDuration, loopEnabled, loopStart, loopEnd,
   setLoopStart, setLoopEnd, selectedStems, saveSelectedStems, stemSelectionReady,
   currentJobId, vocalSplitMode, vocalSplitModeReady, setVocalSplitMode,
   setAutoSectionsResetFn,
@@ -10,7 +10,7 @@ import { wireJobForm, showError } from "./job.js";
 import { initSearch } from "./search.js";
 import { wireTransportButtons } from "./transport.js";
 import { wireBeatGridUi } from "./beatgridUi.js";
-import { togglePlayPause, updateLoopRegionVisual, toggleMetronome } from "./transport.js";
+import { togglePlayPause, updateLoopRegionVisual, toggleMetronome, transport, setPlayheadTime } from "./transport.js";
 import { wireStemListControls, wireMixerToolbar } from "./mixer.js";
 import { initCatalog, collectDiagnostics } from "./catalog.js";
 import { initNotifications, notifyFailure, dismissFailuresByJobId } from "./notifications.js";
@@ -486,10 +486,14 @@ function wireFooterControls() {
   const scrub = document.getElementById("footer-scrub");
   if (scrub) {
     function seekToX(clientX) {
-      if (!multitrack || !totalDuration) return;
+      // setPlayheadTime, not multitrack.setTime: on the default chunked engine
+      // the multitrack is silent and this whole bar did nothing. It also moves
+      // the playhead marker, footer times and presence playhead, which the old
+      // call never did (#515).
+      if (!totalDuration) return;
       const rect = scrub.getBoundingClientRect();
       const frac = Math.max(0, Math.min(1, (clientX - rect.left) / rect.width));
-      multitrack.setTime(frac * totalDuration);
+      setPlayheadTime(frac * totalDuration);
     }
     let _scrubbing = false;
     scrub.addEventListener("mousedown", (e) => {
@@ -645,32 +649,36 @@ function wireAppShellControls() {
 // ─── Keyboard shortcuts ───
 
 document.addEventListener("keydown", (e) => {
-  if (!multitrack) return;
-  if (e.target instanceof HTMLInputElement) return;
+  if (!transport()) return;
+  // Textareas were not excluded, so Space in the log viewer started playback
+  // instead of scrolling.
+  if (e.target instanceof HTMLInputElement || e.target instanceof HTMLTextAreaElement) return;
   if (e.code === "Space") {
     e.preventDefault();
     togglePlayPause();
   } else if (e.code === "BracketLeft") {
     e.preventDefault();
-    multitrack.setTime(Math.max(0, multitrack.getCurrentTime() - 5));
+    // setPlayheadTime clamps to [0, totalDuration] itself, so the Math.max /
+    // Math.min the multitrack version needed are gone with it.
+    setPlayheadTime(transport().getCurrentTime() - 5);
   } else if (e.code === "BracketRight") {
     e.preventDefault();
-    multitrack.setTime(
-      Math.min(multitrack.getDuration(), multitrack.getCurrentTime() + 5),
-    );
+    setPlayheadTime(transport().getCurrentTime() + 5);
   } else if (e.code === "KeyL") {
     e.preventDefault();
     loopBtn.click();
   } else if (e.code === "KeyK") {
     e.preventDefault();
     toggleMetronome();
-  } else if (e.code === "KeyI" && loopEnabled && multitrack) {
+  } else if (e.code === "KeyI" && loopEnabled) {
     e.preventDefault();
-    setLoopStart(Math.min(multitrack.getCurrentTime(), loopEnd - 0.5));
+    // multitrack.getCurrentTime() is pinned at 0 on the engine path, so "set
+    // loop in at playhead" always wrote 0 regardless of where the playhead was.
+    setLoopStart(Math.min(transport().getCurrentTime(), loopEnd - 0.5));
     updateLoopRegionVisual();
-  } else if (e.code === "KeyO" && loopEnabled && multitrack) {
+  } else if (e.code === "KeyO" && loopEnabled) {
     e.preventDefault();
-    setLoopEnd(Math.max(multitrack.getCurrentTime(), loopStart + 0.5));
+    setLoopEnd(Math.max(transport().getCurrentTime(), loopStart + 0.5));
     updateLoopRegionVisual();
   }
 });
diff --git a/static/js/transport.js b/static/js/transport.js
index 7b6e92fc..826456e8 100644
--- a/static/js/transport.js
+++ b/static/js/transport.js
@@ -70,7 +70,18 @@ function timeFromClientX(clientX) {
   return frac * totalDuration;
 }
 
-function setPlayheadTime(sec) {
+/// The clock that actually owns playback.
+///
+/// engineMode() defaults to "chunked", where audioEngine drives audio and the
+/// multitrack is mounted with url: null for visuals only -- so operating on
+/// `multitrack` directly moves nothing and reads 0. Everything in this module
+/// already went through `audioEngine ?? multitrack`; exporting it stops other
+/// modules re-deriving it and drifting (#515).
+export function transport() {
+  return audioEngine ?? multitrack;
+}
+
+export function setPlayheadTime(sec) {
   const tx = audioEngine ?? multitrack;
   if (!tx || !totalDuration) return;
   const next = Math.max(0, Math.min(totalDuration, sec));
diff --git a/tests/js/transport-clock.test.mjs b/tests/js/transport-clock.test.mjs
new file mode 100644
index 00000000..61bf6f06
--- /dev/null
+++ b/tests/js/transport-clock.test.mjs
@@ -0,0 +1,72 @@
+// main.js drove `multitrack` directly while audioEngine owns the clock (#515).
+//
+// engineMode() defaults to "chunked", where the multitrack is mounted with
+// url: null for visuals only. So the footer scrub bar did nothing at all, and
+// "set loop in at playhead" always wrote 0 because multitrack.getCurrentTime()
+// is pinned there.
+//
+// A structural check rather than a DOM one: the bug was not a wrong value from
+// a function, it was reaching for the wrong object. Anything that reintroduces
+// a bare multitrack playback call in main.js fails here.
+
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const root = join(dirname(fileURLToPath(import.meta.url)), '..', '..');
+const mainSrc = readFileSync(join(root, 'static/js/main.js'), 'utf8');
+const transportSrc = readFileSync(join(root, 'static/js/transport.js'), 'utf8');
+
+let passed = 0;
+let failed = 0;
+
+function check(name, condition, detail = '') {
+  if (condition) {
+    passed++;
+    console.log(`PASS  ${name}`);
+  } else {
+    failed++;
+    console.log(`FAIL  ${name}${detail ? `  -- ${detail}` : ''}`);
+  }
+}
+
+// Strip comments so the explanatory ones below don't count as usage.
+const code = mainSrc.replace(/\/\/.*$/gm, '').replace(/\/\*[\s\S]*?\*\//g, '');
+
+for (const call of ['multitrack.setTime', 'multitrack.getCurrentTime', 'multitrack.getDuration']) {
+  check(
+    `main.js does not call ${call}`,
+    !code.includes(call),
+    'the multitrack is silent on the default chunked engine',
+  );
+}
+
+check(
+  'transport.js exports the accessor',
+  /export function transport\(\)/.test(transportSrc),
+);
+
+check(
+  'the accessor prefers the audio engine',
+  /return audioEngine \?\? multitrack;/.test(transportSrc),
+);
+
+check(
+  'transport.js exports setPlayheadTime',
+  /export function setPlayheadTime\(/.test(transportSrc),
+);
+
+check(
+  'main.js imports both rather than re-deriving them',
+  /import \{[^}]*\btransport\b[^}]*\} from "\.\/transport\.js"/.test(mainSrc) &&
+    /import \{[^}]*\bsetPlayheadTime\b[^}]*\} from "\.\/transport\.js"/.test(mainSrc),
+);
+
+check(
+  'the keyboard guard excludes textareas',
+  code.includes('HTMLTextAreaElement'),
+  'Space in the log viewer used to start playback instead of scrolling',
+);
+
+console.log(`\n${passed}/${passed + failed} checks passed`);
+process.exit(failed === 0 ? 0 : 1);