core: prevent scope parent-chain cycles when reusing pooled frames

- Scope.resetForReuse: fully detach before re-parenting (clear state, parent=null, new frameId), then validate with ensureNoCycle and assign parent/args/pos/thisObj
- ScopePool.borrow (JVM/Android/JS/Native/Wasm): defensive fallback to fresh Scope allocation if resetForReuse detects a cycle
- docs: add docs/fix-scope-parent-cycle.md describing the change and expectations
- test: add ScopeCycleRegressionTest to ensure instance method call pattern does not crash and returns "ok"

lynglib/src/commonTest/kotlin/ScopeCycleRegressionTest.kt

@@ -0,0 +1,34 @@
+/*
+ * Regression test for scope parent-chain cycle when reusing pooled frames
+ */
+
+import kotlinx.coroutines.test.runTest
+import net.sergeych.lyng.eval
+import kotlin.test.Test
+
+class ScopeCycleRegressionTest {
+    @Test
+    fun instanceMethodCallDoesNotCycle() = runTest {
+        eval(
+            (
+                """
+                class Whatever {
+                    fun something() {
+                        trace("something")
+                    }
+                }
+
+                fun ll() { Whatever() }
+
+                fun callTest1() {
+                    val l = ll()
+                    l.something()
+                    "ok"
+                }
+
+                assertEquals("ok", callTest1())
+                """
+                ).trimIndent()
+        )
+    }
+}