perf(extensions): collect unreachable JavaScript cycles after idle bursts

android/app/src/androidTest/kotlin/com/zarz/spotiflac/ExtensionMemoryTest.kt

@@ -0,0 +1,49 @@
+package com.zarz.spotiflac
+
+import android.os.Debug
+import android.util.Log
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.spotiflac.backend.JsExtension
+import org.json.JSONObject
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(AndroidJUnit4::class)
+class ExtensionMemoryTest {
+    @Test
+    fun liveStateAndTextDecodingSurviveIdleCollection() {
+        val source = """
+            let calls = 0;
+            const keep = {value: "Music 音楽 🎵"};
+            registerExtension({
+                allocate() {
+                    const cycle = {bytes: new Uint8Array(16 * 1024 * 1024)};
+                    cycle.self = cycle;
+                    return ++calls;
+                },
+                state() {
+                    return {calls, value: keep.value,
+                        decoded: new TextDecoder().decode(new Uint8Array([97, 226, 130, 98])),
+                        text: utils.base64Decode(utils.base64Encode(keep.value))};
+                }
+            });
+        """.trimIndent()
+        JsExtension(source, "{}", 5000uL).use { runtime ->
+            val before = Debug.getNativeHeapAllocatedSize()
+            assertEquals("1", runtime.call("allocate", "[]", null, 5000uL))
+            val retained = Debug.getNativeHeapAllocatedSize()
+            Thread.sleep(2500)
+            val afterIdle = Debug.getNativeHeapAllocatedSize()
+            // Process-wide allocator samples are diagnostic, not a flaky
+            // assertion about unrelated platform allocations or Android PSS.
+            Log.i("ExtensionMemoryTest", "native heap bytes: before=$before retained=$retained afterIdle=$afterIdle")
+            val state = JSONObject(runtime.call("state", "[]", null, 5000uL))
+            assertEquals(1, state.getInt("calls"))
+            assertEquals("Music 音楽 🎵", state.getString("value"))
+            assertEquals("Music 音楽 🎵", state.getString("text"))
+            assertEquals("a\uFFFD\uFFFDb", state.getString("decoded"))
+            assertEquals("2", runtime.call("allocate", "[]", null, 5000uL))
+        }
+    }
+}