diff --git a/.nx/version-plans/fix-promise-tracker-leak.md b/.nx/version-plans/fix-promise-tracker-leak.md
new file mode 100644
index 0000000..0308c73
--- /dev/null
+++ b/.nx/version-plans/fix-promise-tracker-leak.md
@@ -0,0 +1,5 @@
+---
+__default__: patch
+---
+
+Fixes an unbounded memory leak in the runtime promise tracker that could exhaust the JS heap (`JavaScript heap out of memory`) during long runs. Apps that keep producing work every frame (animations, `requestAnimationFrame` loops, polling, async data-binding) create a stream of promises that never settle; these were retained forever along with a captured stack, growing memory until the run crashed. Harness now releases a promise's tracking record as soon as the promise is garbage-collected and caps the number of retained records, so memory stays bounded regardless of how busy the app under test is.
diff --git a/packages/runtime/src/promise-tracker.ts b/packages/runtime/src/promise-tracker.ts
index b1e785f..382d770 100644
--- a/packages/runtime/src/promise-tracker.ts
+++ b/packages/runtime/src/promise-tracker.ts
@@ -20,10 +20,25 @@ type PromiseExecutor<T> = (
   reject: PromiseReject
 ) => void;
 
+// Backstop against unbounded growth if GC can't keep up: never-settling
+// promises created in a hot loop would otherwise OOM the heap. Diagnostics only
+// ever show a handful, so evicting the oldest (Map keeps insertion order) is safe.
+export const MAX_TRACKED_PROMISES = 10_000;
+
 const pendingPromises = new Map<number, TrackedPromiseRecord>();
 const promiseIds = new WeakMap<object, number>();
 const promiseContexts = new WeakMap<object, PromiseTrackerTestContext>();
 
+// A garbage-collected promise can never settle or hold anything pending, so drop
+// its record (and captured stack) instead of leaking it. Primary defense; the
+// size cap above covers the window before GC runs.
+const promiseFinalization =
+  typeof FinalizationRegistry === 'undefined'
+    ? null
+    : new FinalizationRegistry<number>((id) => {
+        pendingPromises.delete(id);
+      });
+
 let originalPromise: PromiseConstructor | null = null;
 let nextPromiseId = 1;
 let currentTestContext: PromiseTrackerTestContext | undefined;
@@ -64,6 +79,15 @@ const registerPromise = ():
     test,
   });
 
+  while (pendingPromises.size > MAX_TRACKED_PROMISES) {
+    const oldest = pendingPromises.keys().next().value;
+    if (oldest === undefined) {
+      break;
+    }
+
+    pendingPromises.delete(oldest);
+  }
+
   return { id, test };
 };
 
@@ -161,6 +185,7 @@ const createTrackedPromiseConstructor = (): PromiseConstructor => {
 
       if (registration.id !== null) {
         promiseIds.set(this, registration.id);
+        promiseFinalization?.register(this, registration.id);
       }
 
       if (registration.test) {