diff --git a/docs/INCOMPATIBLE_PHP_FEATURES.md b/docs/INCOMPATIBLE_PHP_FEATURES.md
index 80941bdb..4388a966 100644
--- a/docs/INCOMPATIBLE_PHP_FEATURES.md
+++ b/docs/INCOMPATIBLE_PHP_FEATURES.md
@@ -48,6 +48,7 @@
 - 禁止子类用同名 `private` 属性隐藏父类私有属性；`public` / `protected` 同名声明视为同一个继承 property slot，仍须满足类型、可见性和 `readonly` 兼容性要求。
 - 为避免 typed property 写入路径引入额外动态检查，native typed property 在右值类型不确定或与属性类型不一致时会退化为 `setProperty()`；部分标量赋值可能遵循 Zend 弱类型转换，而不是 AOT 默认 strict 语义。
 - constructor property promotion 的运行时属性可用，但 `ReflectionProperty::isPromoted()` 目前不返回标准 PHP 结果。
+- `readonly` 使用“初始化窗口”语义，而不是 PHP 的“一次赋值”语义：属性只能在声明类自己的 `__construct()` 或 `__clone()` 中通过直接 `$this` 写入，且窗口内允许重复修改；其他方法、子类初始化方法、嵌套闭包、其他对象、引用和 `unset()` 均不可写。`__construct()` / `__clone()` 不能作为普通方法调用，合法的 `parent::__construct()` / `parent::__clone()` 初始化链除外。
 
 ## 表达式与控制流
 
diff --git a/docs/PHP_INCOMPATIBILITY_CLASSIFICATION.md b/docs/PHP_INCOMPATIBILITY_CLASSIFICATION.md
index 0eb378bb..f5e888c5 100644
--- a/docs/PHP_INCOMPATIBILITY_CLASSIFICATION.md
+++ b/docs/PHP_INCOMPATIBILITY_CLASSIFICATION.md
@@ -76,6 +76,7 @@ These items should be documented with the exact boundary.
 | Reserved keyword methods such as `toArray()` | Intentional Rule | Conversion keywords are resolved before ordinary object methods to keep conversion lowering static and predictable. |
 | Zero-initialized fixed typed property slots | Intentional Rule / Partial | Native fixed-layout slots use their type's zero value instead of preserving every Zend uninitialized-property transition. |
 | Structural mutation of `std` containers during `foreach` | Intentional Rule | Native C++ iterators may be invalidated by append, insertion, erase or whole-container replacement. TypePHP rejects these operations inside the active loop while allowing non-structural element updates. |
+| `readonly` initialization window | Intentional Rule | A readonly property is writable only through direct `$this` access in its declaring class' `__construct()` or `__clone()`. Repeated initialization writes are allowed there; after either initialization path it is frozen. Ordinary calls to these lifecycle methods are rejected, while lexical parent initialization chains remain valid. |
 
 ## Implementable but Currently Unsupported
 
diff --git a/phpunit/code/clone-direct-method-call.php b/phpunit/code/clone-direct-method-call.php
new file mode 100644
index 00000000..98e85b49
--- /dev/null
+++ b/phpunit/code/clone-direct-method-call.php
@@ -0,0 +1,13 @@
+<?php
+
+class CloneDirectMethodCall
+{
+    public function __clone(): void
+    {
+    }
+
+    public function invoke(): void
+    {
+        $this->__clone();
+    }
+}
diff --git a/phpunit/code/clone-direct-static-call.php b/phpunit/code/clone-direct-static-call.php
new file mode 100644
index 00000000..7ca1be23
--- /dev/null
+++ b/phpunit/code/clone-direct-static-call.php
@@ -0,0 +1,13 @@
+<?php
+
+class CloneDirectStaticCall
+{
+    public function __clone(): void
+    {
+    }
+
+    public function invoke(): void
+    {
+        self::__clone();
+    }
+}
diff --git a/phpunit/code/constructor-direct-method-call.php b/phpunit/code/constructor-direct-method-call.php
new file mode 100644
index 00000000..40c4c5ec
--- /dev/null
+++ b/phpunit/code/constructor-direct-method-call.php
@@ -0,0 +1,10 @@
+<?php
+class ConstructorDirectMethodCall
+{
+    public function __construct() {}
+}
+
+function invoke_constructor(ConstructorDirectMethodCall $object): void
+{
+    $object->__construct();
+}
diff --git a/phpunit/code/constructor-direct-static-call.php b/phpunit/code/constructor-direct-static-call.php
new file mode 100644
index 00000000..5344feb5
--- /dev/null
+++ b/phpunit/code/constructor-direct-static-call.php
@@ -0,0 +1,10 @@
+<?php
+class ConstructorDirectStaticCall
+{
+    public function __construct() {}
+
+    public function invoke(): void
+    {
+        self::__construct();
+    }
+}
diff --git a/phpunit/code/readonly-property-no-native-ref.php b/phpunit/code/readonly-property-no-native-ref.php
new file mode 100644
index 00000000..08197b79
--- /dev/null
+++ b/phpunit/code/readonly-property-no-native-ref.php
@@ -0,0 +1,17 @@
+<?php
+
+use native_types;
+
+class ReadonlyPropertyNoNativeRef
+{
+    public readonly int $integer;
+    public readonly float $floating;
+
+    public function __construct(int $integer, float $floating)
+    {
+        $this->integer = $integer;
+        $this->floating = $floating;
+        $this->integer += 1;
+        $this->floating += 1.5;
+    }
+}
diff --git a/phpunit/code/readonly-reference-assignment.php b/phpunit/code/readonly-reference-assignment.php
new file mode 100644
index 00000000..ccaeb962
--- /dev/null
+++ b/phpunit/code/readonly-reference-assignment.php
@@ -0,0 +1,10 @@
+<?php
+class ReadonlyReferenceAssignment
+{
+    public readonly int $value;
+
+    public function __construct(int &$source)
+    {
+        $this->value =& $source;
+    }
+}
diff --git a/phpunit/code/readonly-reference-call-argument.php b/phpunit/code/readonly-reference-call-argument.php
new file mode 100644
index 00000000..457c9783
--- /dev/null
+++ b/phpunit/code/readonly-reference-call-argument.php
@@ -0,0 +1,16 @@
+<?php
+function mutate_readonly_argument(int &$value): void
+{
+    $value++;
+}
+
+class ReadonlyReferenceCallArgument
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+        mutate_readonly_argument($this->value);
+    }
+}
diff --git a/phpunit/code/readonly-reference-fetch.php b/phpunit/code/readonly-reference-fetch.php
new file mode 100644
index 00000000..2b2bc7e7
--- /dev/null
+++ b/phpunit/code/readonly-reference-fetch.php
@@ -0,0 +1,11 @@
+<?php
+class ReadonlyReferenceFetch
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+        $reference =& $this->value;
+    }
+}
diff --git a/phpunit/code/readonly-write-array-dim.php b/phpunit/code/readonly-write-array-dim.php
new file mode 100644
index 00000000..8c64750e
--- /dev/null
+++ b/phpunit/code/readonly-write-array-dim.php
@@ -0,0 +1,7 @@
+<?php
+class ReadonlyArrayDimWrite
+{
+    public readonly array $value;
+    public function __construct() { $this->value = []; }
+    public function change(): void { $this->value[] = 1; }
+}
diff --git a/phpunit/code/readonly-write-child-clone.php b/phpunit/code/readonly-write-child-clone.php
new file mode 100644
index 00000000..fdfa0b27
--- /dev/null
+++ b/phpunit/code/readonly-write-child-clone.php
@@ -0,0 +1,19 @@
+<?php
+
+class ReadonlyCloneParent
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+    }
+}
+
+class ReadonlyCloneChild extends ReadonlyCloneParent
+{
+    public function __clone(): void
+    {
+        $this->value = 2;
+    }
+}
diff --git a/phpunit/code/readonly-write-child-constructor.php b/phpunit/code/readonly-write-child-constructor.php
new file mode 100644
index 00000000..80711c3a
--- /dev/null
+++ b/phpunit/code/readonly-write-child-constructor.php
@@ -0,0 +1,13 @@
+<?php
+class ReadonlyParent
+{
+    protected readonly int $value;
+}
+
+class ReadonlyChild extends ReadonlyParent
+{
+    public function __construct()
+    {
+        $this->value = 1;
+    }
+}
diff --git a/phpunit/code/readonly-write-clone-closure.php b/phpunit/code/readonly-write-clone-closure.php
new file mode 100644
index 00000000..b54583fc
--- /dev/null
+++ b/phpunit/code/readonly-write-clone-closure.php
@@ -0,0 +1,19 @@
+<?php
+
+class ReadonlyCloneClosure
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+    }
+
+    public function __clone(): void
+    {
+        $write = function (): void {
+            $this->value = 2;
+        };
+        $write();
+    }
+}
diff --git a/phpunit/code/readonly-write-coalesce.php b/phpunit/code/readonly-write-coalesce.php
new file mode 100644
index 00000000..9f785115
--- /dev/null
+++ b/phpunit/code/readonly-write-coalesce.php
@@ -0,0 +1,7 @@
+<?php
+class ReadonlyCoalesceWrite
+{
+    public readonly ?int $value;
+    public function __construct() { $this->value = null; }
+    public function change(): void { $this->value ??= 1; }
+}
diff --git a/phpunit/code/readonly-write-compound.php b/phpunit/code/readonly-write-compound.php
new file mode 100644
index 00000000..e01ca545
--- /dev/null
+++ b/phpunit/code/readonly-write-compound.php
@@ -0,0 +1,7 @@
+<?php
+class ReadonlyCompoundWrite
+{
+    public readonly int $value;
+    public function __construct() { $this->value = 1; }
+    public function change(): void { $this->value += 1; }
+}
diff --git a/phpunit/code/readonly-write-constructor-closure.php b/phpunit/code/readonly-write-constructor-closure.php
new file mode 100644
index 00000000..697b8c39
--- /dev/null
+++ b/phpunit/code/readonly-write-constructor-closure.php
@@ -0,0 +1,13 @@
+<?php
+class ReadonlyConstructorClosure
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $writer = function (): void {
+            $this->value = 1;
+        };
+        $writer();
+    }
+}
diff --git a/phpunit/code/readonly-write-foreach.php b/phpunit/code/readonly-write-foreach.php
new file mode 100644
index 00000000..28260962
--- /dev/null
+++ b/phpunit/code/readonly-write-foreach.php
@@ -0,0 +1,10 @@
+<?php
+class ReadonlyForeachWrite
+{
+    public readonly int $value;
+    public function __construct() { $this->value = 1; }
+    public function change(): void
+    {
+        foreach ([2] as $this->value) {}
+    }
+}
diff --git a/phpunit/code/readonly-write-increment.php b/phpunit/code/readonly-write-increment.php
new file mode 100644
index 00000000..11d5469d
--- /dev/null
+++ b/phpunit/code/readonly-write-increment.php
@@ -0,0 +1,7 @@
+<?php
+class ReadonlyIncrementWrite
+{
+    public readonly int $value;
+    public function __construct() { $this->value = 1; }
+    public function change(): void { ++$this->value; }
+}
diff --git a/phpunit/code/readonly-write-list.php b/phpunit/code/readonly-write-list.php
new file mode 100644
index 00000000..6a574822
--- /dev/null
+++ b/phpunit/code/readonly-write-list.php
@@ -0,0 +1,7 @@
+<?php
+class ReadonlyListWrite
+{
+    public readonly int $value;
+    public function __construct() { $this->value = 1; }
+    public function change(): void { [$this->value] = [2]; }
+}
diff --git a/phpunit/code/readonly-write-other-instance-clone.php b/phpunit/code/readonly-write-other-instance-clone.php
new file mode 100644
index 00000000..ecd79b5f
--- /dev/null
+++ b/phpunit/code/readonly-write-other-instance-clone.php
@@ -0,0 +1,17 @@
+<?php
+
+class ReadonlyCloneOtherInstance
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+    }
+
+    public function __clone(): void
+    {
+        $other = new self();
+        $other->value = 2;
+    }
+}
diff --git a/phpunit/code/readonly-write-other-instance-constructor.php b/phpunit/code/readonly-write-other-instance-constructor.php
new file mode 100644
index 00000000..c22906ae
--- /dev/null
+++ b/phpunit/code/readonly-write-other-instance-constructor.php
@@ -0,0 +1,10 @@
+<?php
+class ReadonlyOtherInstance
+{
+    public readonly int $value;
+
+    public function __construct(ReadonlyOtherInstance $other)
+    {
+        $other->value = 1;
+    }
+}
diff --git a/phpunit/code/readonly-write-outside-constructor.php b/phpunit/code/readonly-write-outside-constructor.php
new file mode 100644
index 00000000..bcf1a9ba
--- /dev/null
+++ b/phpunit/code/readonly-write-outside-constructor.php
@@ -0,0 +1,15 @@
+<?php
+class ReadonlyWriteOutsideConstructor
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+    }
+
+    public function change(): void
+    {
+        $this->value = 2;
+    }
+}
diff --git a/phpunit/src/NativePropertyTest.php b/phpunit/src/NativePropertyTest.php
index 49b0b842..c730abee 100644
--- a/phpunit/src/NativePropertyTest.php
+++ b/phpunit/src/NativePropertyTest.php
@@ -60,6 +60,21 @@ class NativePropertyTest extends \BaseTest
         $this->assertStringNotContainsString('box.attr(php_get_prop(0, _literal_strings[0], 0, _literal_strings[1]), true) +=', $code);
     }
 
+    public function testReadonlyPropertiesDoNotUseNativeScalarReferences(): void
+    {
+        try {
+            $outputFile = $this->compileNativeProperty('readonly-property-no-native-ref.php');
+        } catch (TestError $e) {
+            $this->fail($e->getMessage());
+        }
+
+        $code = file_get_contents($outputFile);
+        $this->assertStringNotContainsString('typephp_static_int_ref(', $code);
+        $this->assertStringNotContainsString('typephp_static_float_ref(', $code);
+        $this->assertStringNotContainsString('_object_prop_', $code);
+        $this->assertStringContainsString('.attr(', $code);
+    }
+
     public function testNativeIntPropertyAssignOpConvertsBitwiseNotClassConst(): void
     {
         try {
diff --git a/phpunit/src/ReadonlyPropertyTest.php b/phpunit/src/ReadonlyPropertyTest.php
new file mode 100644
index 00000000..30721c7f
--- /dev/null
+++ b/phpunit/src/ReadonlyPropertyTest.php
@@ -0,0 +1,77 @@
+<?php
+
+class ReadonlyPropertyTest extends \BaseTest
+{
+    public function testConstructorCannotBeCalledAsOrdinaryMethod(): void
+    {
+        $this->exec('Constructor __construct() can only be invoked by new', 'constructor-direct-method-call.php');
+        $this->exec('Constructor __construct() can only be invoked by new', 'constructor-direct-static-call.php');
+    }
+
+    public function testCloneCannotBeCalledAsOrdinaryMethod(): void
+    {
+        $this->exec('Clone method __clone() can only be invoked by clone', 'clone-direct-method-call.php');
+        $this->exec('Clone method __clone() can only be invoked by clone', 'clone-direct-static-call.php');
+    }
+
+    public function testWriteOutsideConstructorIsRejected(): void
+    {
+        $this->exec('Readonly property `ReadonlyWriteOutsideConstructor::$value` can only be modified in its declaring `__construct` or `__clone` method', 'readonly-write-outside-constructor.php');
+    }
+
+    public function testChildConstructorCannotWriteParentReadonlyProperty(): void
+    {
+        $this->exec('Readonly property `ReadonlyParent::$value` can only be modified in its declaring `__construct` or `__clone` method', 'readonly-write-child-constructor.php');
+    }
+
+    public function testConstructorCannotWriteReadonlyPropertyOnAnotherObject(): void
+    {
+        $this->exec('Readonly property `ReadonlyOtherInstance::$value` can only be modified on `$this`', 'readonly-write-other-instance-constructor.php');
+    }
+
+    public function testClosureInsideConstructorCannotWriteReadonlyProperty(): void
+    {
+        $this->exec('Readonly property `ReadonlyConstructorClosure::$value` can only be modified directly in `__construct` or `__clone`', 'readonly-write-constructor-closure.php');
+    }
+
+    public function testReadonlyCloneWriteRetainsLexicalRestrictions(): void
+    {
+        $this->exec(
+            'Readonly property `ReadonlyCloneParent::$value` can only be modified in its declaring `__construct` or `__clone` method',
+            'readonly-write-child-clone.php'
+        );
+        $this->exec(
+            'Readonly property `ReadonlyCloneClosure::$value` can only be modified directly in `__construct` or `__clone`',
+            'readonly-write-clone-closure.php'
+        );
+        $this->exec(
+            'Readonly property `ReadonlyCloneOtherInstance::$value` can only be modified on `$this`',
+            'readonly-write-other-instance-clone.php'
+        );
+    }
+
+    public function testReadonlyPropertyCannotBeAssignedByReference(): void
+    {
+        $this->exec('Cannot assign readonly property `ReadonlyReferenceAssignment::$value` by reference', 'readonly-reference-assignment.php');
+    }
+
+    public function testReadonlyPropertyCannotBeTakenByReference(): void
+    {
+        $this->exec('Cannot take reference to readonly property `ReadonlyReferenceFetch::$value`', 'readonly-reference-fetch.php');
+        $this->exec('Cannot take reference to readonly property `ReadonlyReferenceCallArgument::$value`', 'readonly-reference-call-argument.php');
+    }
+
+    public function testAllReadonlyWriteFormsOutsideConstructorAreRejected(): void
+    {
+        foreach ([
+            'readonly-write-compound.php',
+            'readonly-write-increment.php',
+            'readonly-write-array-dim.php',
+            'readonly-write-coalesce.php',
+            'readonly-write-list.php',
+            'readonly-write-foreach.php',
+        ] as $file) {
+            $this->exec('can only be modified in its declaring `__construct` or `__clone` method', $file);
+        }
+    }
+}
diff --git a/src/CompilerBase.php b/src/CompilerBase.php
index 8b148eee..def1e9ea 100644
--- a/src/CompilerBase.php
+++ b/src/CompilerBase.php
@@ -1095,6 +1095,11 @@ class CompilerBase implements PropertyAccessContext
         return $this->method === '__construct';
     }
 
+    protected function isCurrentCloneMethod(): bool
+    {
+        return $this->method === '__clone';
+    }
+
     protected function getCurrentMethodDisplayName(): string
     {
         return $this->getFullClassName() . '::' . $this->method;
diff --git a/src/Entity/MethodDef.php b/src/Entity/MethodDef.php
index 93eca879..cbf52344 100644
--- a/src/Entity/MethodDef.php
+++ b/src/Entity/MethodDef.php
@@ -25,6 +25,9 @@ class MethodDef
     /** Source trait, retained only for diagnostics and the __TRAIT__ constant. */
     public string $traitOrigin = '';
 
+    /** Original trait method name before a use-site alias is applied. */
+    public string $traitMethod = '';
+
     public function __construct(int $flags, string $name)
     {
         $this->flags = $flags;
diff --git a/src/Generator/CallArgumentGenerator.php b/src/Generator/CallArgumentGenerator.php
index 5a36c7ec..0bb15b29 100644
--- a/src/Generator/CallArgumentGenerator.php
+++ b/src/Generator/CallArgumentGenerator.php
@@ -418,6 +418,9 @@ trait CallArgumentGenerator
                 $namedArgs[$arg->name->name] = true;
                 $byRef = ($funcName && $this->isReferenceNamedArgument($funcName, $className, $arg->name->name))
                     || ($preserveExistingReferences && $this->isExistingReferenceCallArg($arg));
+                if ($byRef) {
+                    $this->assertReadonlyPropertyReferenceForbidden($arg->value, $arg, false);
+                }
                 $value = ($byRef || $this->isRefvalCall($arg->value) || $this->isToRefCall($arg->value))
                     ? $this->parseReferenceCallArgValue($arg)
                     : $this->parseCallArgValue($arg);
@@ -438,6 +441,9 @@ trait CallArgumentGenerator
             }
             $byRef = ($funcName && $this->isReferenceArgument($funcName, $className, $i))
                 || ($preserveExistingReferences && $this->isExistingReferenceCallArg($arg));
+            if ($byRef) {
+                $this->assertReadonlyPropertyReferenceForbidden($arg->value, $arg, false);
+            }
             if (($funcName === 'call_user_func' || $funcName === 'call_user_func_array') && $i === 0) {
                 $callback = $this->parseScopedCallbackArg($arg);
                 if ($callback !== null) {
diff --git a/src/Parser/ArrayExpressionTrait.php b/src/Parser/ArrayExpressionTrait.php
index 819cf8cf..1a1186c4 100644
--- a/src/Parser/ArrayExpressionTrait.php
+++ b/src/Parser/ArrayExpressionTrait.php
@@ -106,6 +106,11 @@ trait ArrayExpressionTrait
         }
 
         if ($expr instanceof Expr\PropertyFetch) {
+            // Keep the write-policy check at the common writable-expression
+            // boundary as well as at assignment lowering sites. This covers
+            // destructuring, foreach targets, and future write forms that use
+            // parseWritableIdentifier() directly.
+            $this->preparePropertyWriteTarget($expr);
             return $this->parsePropertyFetchUpdate($expr);
         }
 
diff --git a/src/Parser/AssignOpTrait.php b/src/Parser/AssignOpTrait.php
index 593477ba..1fe2da86 100644
--- a/src/Parser/AssignOpTrait.php
+++ b/src/Parser/AssignOpTrait.php
@@ -624,6 +624,12 @@ trait AssignOpTrait
         if ($def === null) {
             return null;
         }
+        if ($def->isReadonly()) {
+            // A native scalar reference mutates the property zval directly and
+            // bypasses Zend's readonly checks. Keep readonly properties on the
+            // normal attr() path so no raw scalar reference escapes the wrapper.
+            return null;
+        }
 
         $rightType = $this->detectTypeOfExpr($node->expr);
         if ($this->isFixedObjectProp($def) && $rightType !== Type::VAR && !$this->canAssignStaticTypeToObjectProperty($def, $rightType)) {
@@ -782,6 +788,12 @@ trait AssignOpTrait
             $this->fatalError($expr->expr, 'Cannot take reference of a nullsafe chain');
         }
 
+        // A reference would outlive the constructor-only write window and
+        // make later mutations invisible to the compiler. It is therefore
+        // forbidden on either side even inside the declaring constructor.
+        $this->assertReadonlyPropertyReferenceForbidden($expr->var, $expr, true);
+        $this->assertReadonlyPropertyReferenceForbidden($expr->expr, $expr, false);
+
         $left = $this->parseWritableIdentifier($expr->var);
         // Keep this write-context form for every RHS kind. Re-parsing it as a
         // read later breaks append and missing-key targets such as
diff --git a/src/Parser/ForeachTrait.php b/src/Parser/ForeachTrait.php
index 1e0ce341..9b1db1d5 100644
--- a/src/Parser/ForeachTrait.php
+++ b/src/Parser/ForeachTrait.php
@@ -91,7 +91,9 @@ trait ForeachTrait
             return $this->getIndent() . "{$array}.offsetSet({$dim}, {$valueExpr});";
         }
 
-        $valueVar = $this->parseIdentifier($node->valueVar);
+        $valueVar = $this->isPropertyFetch($node->valueVar)
+            ? $this->parseWritableIdentifier($node->valueVar)
+            : $this->parseIdentifier($node->valueVar);
         if ($node->byRef) {
             if (!$this->hasVar($valueVar)) {
                 $this->addLocalVar($valueVar, Type::REF);
diff --git a/src/Parser/MethodCallTrait.php b/src/Parser/MethodCallTrait.php
index 3bc1d4c3..b767d437 100644
--- a/src/Parser/MethodCallTrait.php
+++ b/src/Parser/MethodCallTrait.php
@@ -276,6 +276,25 @@ trait MethodCallTrait
             }
             return $this->genRuntimeFunctionCall($callable, $expr->args, $method, $parentClass);
         }
+        if ($method === '__construct') {
+            if (!$this->isConstructorImplementationContext() || $this->context->inClosure) {
+                $this->fatalError($expr, 'Constructor __construct() can only be invoked by new');
+            }
+            if (empty($expr->args)) {
+                return 'typephp_call_parent_constructor(this_, ' . $methodPtr . ')';
+            }
+            return 'typephp_call_parent_constructor(this_, ' . $methodPtr . ', '
+                . $this->parseCallArgs($expr->args, $method, $parentClass) . ')';
+        }
+        if ($method === '__clone') {
+            if (!$this->isCurrentCloneMethod() || $this->context->inClosure) {
+                $this->fatalError($expr, 'Clone method __clone() can only be invoked by clone');
+            }
+            if (!empty($expr->args)) {
+                $this->fatalError($expr, 'Clone method __clone() does not accept arguments');
+            }
+            return 'typephp_call_parent_clone(this_, ' . $methodPtr . ')';
+        }
         if (empty($expr->args)) {
             return 'this_.call(' . $methodPtr . ')';
         }
@@ -303,6 +322,15 @@ trait MethodCallTrait
 
     protected function parseMethodCall(Expr\MethodCall $expr): string
     {
+        if ($this->isNamedMethod($expr->name)) {
+            $methodName = strtolower($expr->name->toString());
+            if ($methodName === '__construct') {
+                $this->fatalError($expr, 'Constructor __construct() can only be invoked by new');
+            }
+            if ($methodName === '__clone') {
+                $this->fatalError($expr, 'Clone method __clone() can only be invoked by clone');
+            }
+        }
         if ($this->containsNullsafeChain($expr->var)) {
             return $this->parseNullsafeExpr($expr);
         }
@@ -510,6 +538,12 @@ trait MethodCallTrait
         }
     }
 
+    private function isConstructorImplementationContext(): bool
+    {
+        return $this->isCurrentConstructor()
+            || strtolower($this->methodDef?->traitMethod ?? '') === '__construct';
+    }
+
     private function isDefinitelyObjectReceiver(
         Expr $receiver,
         string $object,
@@ -573,6 +607,25 @@ trait MethodCallTrait
         $rtClass = '';
         $class = $this->parseIdentifier($expr->class);
 
+        if ($this->isIdExpr($expr->name) && strtolower($expr->name->toString()) === '__construct') {
+            $isParentConstructor = $this->isNameExpr($expr->class)
+                && $class === 'parent'
+                && $this->isConstructorImplementationContext()
+                && !$this->context->inClosure;
+            if (!$isParentConstructor) {
+                $this->fatalError($expr, 'Constructor __construct() can only be invoked by new');
+            }
+        }
+        if ($this->isIdExpr($expr->name) && strtolower($expr->name->toString()) === '__clone') {
+            $isParentClone = $this->isNameExpr($expr->class)
+                && $class === 'parent'
+                && $this->isCurrentCloneMethod()
+                && !$this->context->inClosure;
+            if (!$isParentClone) {
+                $this->fatalError($expr, 'Clone method __clone() can only be invoked by clone');
+            }
+        }
+
         // parent::$method() still has a lexical parent class even when the
         // method name itself is dynamic. Handle it before the generic dynamic
         // static-call branch below.
diff --git a/src/Parser/PropertyAccessTrait.php b/src/Parser/PropertyAccessTrait.php
index 68a0f025..54d2b3b8 100644
--- a/src/Parser/PropertyAccessTrait.php
+++ b/src/Parser/PropertyAccessTrait.php
@@ -147,6 +147,9 @@ trait PropertyAccessTrait
 
     protected function emitDynamicPropertyFetchAppendArray(Expr\PropertyFetch $expr, string $value, ?PropertyWriteTarget $target = null): string
     {
+        if ($this->isNativePropertyAccess($expr)) {
+            return $this->parseWritableIdentifier($expr) . ".newItem() = {$value}";
+        }
         if ($this->canEmitDynamicPropertyTarget($target)) {
             return $this->emitDynamicPropertyTargetAppendArray($target, $value);
         }
@@ -160,6 +163,9 @@ trait PropertyAccessTrait
 
     protected function emitDynamicPropertyFetchUpdateArray(Expr\PropertyFetch $expr, string $dim, string $value, ?PropertyWriteTarget $target = null): string
     {
+        if ($this->isNativePropertyAccess($expr)) {
+            return $this->parseWritableIdentifier($expr) . ".item({$dim}, true) = {$value}";
+        }
         if ($this->canEmitDynamicPropertyTarget($target)) {
             return $this->emitDynamicPropertyTargetUpdateArray($target, $dim, $value);
         }
@@ -437,7 +443,7 @@ trait PropertyAccessTrait
         $this->assertCanAssignObjectProperty($left, $right, 'static property');
     }
 
-    protected function preparePropertyWriteTarget(NodeAbstract $left): ?PropertyWriteTarget
+    protected function preparePropertyWriteTarget(NodeAbstract $left, bool $checkReadonlyWrite = true): ?PropertyWriteTarget
     {
         if ($left instanceof Expr\PropertyFetch) {
             $objectExpr = null;
@@ -449,6 +455,9 @@ trait PropertyAccessTrait
             if ($this->isIdExpr($left->name)) {
                 $this->getPropertyIdentifier($left, $left->var, $left->name);
                 $this->assertPropertySetVisibility($left);
+                if ($checkReadonlyWrite) {
+                    $this->assertReadonlyPropertyWriteContext($left);
+                }
             }
             return new PropertyWriteTarget($left, 'object property', $objectExpr, $propertyExpr);
         }
@@ -464,6 +473,71 @@ trait PropertyAccessTrait
         return null;
     }
 
+    /**
+     * TypePHP intentionally gives readonly an initialization-phase meaning:
+     * only the declaring class' __construct or __clone body may write its own
+     * property. This check is lexical; a nested closure is a different
+     * function and must not inherit the write privilege.
+     */
+    private function assertReadonlyPropertyWriteContext(Expr\PropertyFetch $property): void
+    {
+        $access = $this->getNativePropertyAccess($property);
+        if ($access === null || !$access->getPropertyDef()->isReadonly()) {
+            return;
+        }
+
+        $declaringClass = $access->resolution->declaringClass;
+        $propertyName = $this->parseIdentifier($property->name);
+        $display = $declaringClass . '::$' . $propertyName;
+
+        if ($this->context->inClosure) {
+            $this->fatalError(
+                $property,
+                "Readonly property `{$display}` can only be modified directly in `__construct` or `__clone`"
+            );
+        }
+
+        if ((!$this->isCurrentConstructor() && !$this->isCurrentCloneMethod())
+            || !$this->isSameClassName($this->getFullClassName(), $declaringClass)) {
+            $this->fatalError(
+                $property,
+                "Readonly property `{$display}` can only be modified in its declaring `__construct` or `__clone` method"
+            );
+        }
+
+        if (!$this->isVarExpr($property->var) || $this->parseIdentifier($property->var) !== 'this_') {
+            $this->fatalError(
+                $property,
+                "Readonly property `{$display}` can only be modified on `\$this`"
+            );
+        }
+    }
+
+    protected function assertReadonlyPropertyReferenceForbidden(
+        NodeAbstract $expr,
+        NodeAbstract $errorNode,
+        bool $assignmentTarget,
+    ): void {
+        while ($expr instanceof Expr\ArrayDimFetch) {
+            $expr = $expr->var;
+        }
+        if (!$expr instanceof Expr\PropertyFetch || !$this->isIdExpr($expr->name)) {
+            return;
+        }
+
+        $this->getPropertyIdentifier($expr, $expr->var, $expr->name);
+        $access = $this->getNativePropertyAccess($expr);
+        if ($access === null || !$access->getPropertyDef()->isReadonly()) {
+            return;
+        }
+
+        $display = $access->resolution->declaringClass . '::$' . $this->parseIdentifier($expr->name);
+        $message = $assignmentTarget
+            ? "Cannot assign readonly property `{$display}` by reference"
+            : "Cannot take reference to readonly property `{$display}`";
+        $this->fatalError($errorNode, $message);
+    }
+
     private function assertPropertySetVisibility(NodeAbstract $property): void
     {
         if ($this->isPropertyHookBackingAccess($property)) {
@@ -730,7 +804,9 @@ trait PropertyAccessTrait
                     $lines[] = $array . '.offsetUnset(' . $dim . ');';
                 }
             } elseif ($this->isPropertyFetch($var)) {
-                $propertyWriteTarget = $this->preparePropertyWriteTarget($var);
+                // unset has its own unconditional readonly diagnostic below;
+                // it is forbidden even while __construct is running.
+                $propertyWriteTarget = $this->preparePropertyWriteTarget($var, false);
                 $object = $this->getDynamicPropertyFetchObjectExpr($var, $propertyWriteTarget);
                 $restoreDefault = null;
                 if ($this->isIdExpr($var->name)) {
diff --git a/src/Translator.php b/src/Translator.php
index bb0e5090..3de716a5 100644
--- a/src/Translator.php
+++ b/src/Translator.php
@@ -4630,6 +4630,7 @@ CODE;
         $methodDef = new MethodDef($flags, $name);
         $methodDef->node = $methodStmt;
         $methodDef->traitOrigin = (string) $methodStmt->getAttribute(self::TRAIT_ORIGIN_ATTRIBUTE, '');
+        $methodDef->traitMethod = (string) $methodStmt->getAttribute(self::TRAIT_METHOD_ATTRIBUTE, '');
 
         $this->method = $name;
         $this->methodDef = $methodDef;
diff --git a/src/TypeSystem/NativeTypeCompatibilityTrait.php b/src/TypeSystem/NativeTypeCompatibilityTrait.php
index 4fd9c467..c1dda088 100644
--- a/src/TypeSystem/NativeTypeCompatibilityTrait.php
+++ b/src/TypeSystem/NativeTypeCompatibilityTrait.php
@@ -162,6 +162,7 @@ trait NativeTypeCompatibilityTrait
         if ($argInfo->byRef) {
             if ($this->isReferenceWrapperCall($arg->value)) {
                 $inner = $this->unwrapReferenceWrapperCall($arg->value, $arg);
+                $this->assertReadonlyPropertyReferenceForbidden($inner, $arg, false);
                 if ($this->isVarExpr($inner)) {
                     $arg->value = $inner;
                 } else {
@@ -171,6 +172,8 @@ trait NativeTypeCompatibilityTrait
                     }
                     $this->fatalError($arg, 'The refval function only accepts a variable, array element, or object property');
                 }
+            } else {
+                $this->assertReadonlyPropertyReferenceForbidden($arg->value, $arg, false);
             }
             if ($this->isVarExpr($arg->value)) {
                 $var = $this->parseVariable($arg->value);
diff --git a/tests/compiler/object_property/readonly-clone-initialization.phpt b/tests/compiler/object_property/readonly-clone-initialization.phpt
new file mode 100644
index 00000000..bd44add7
--- /dev/null
+++ b/tests/compiler/object_property/readonly-clone-initialization.phpt
@@ -0,0 +1,68 @@
+--TEST--
+TypePHP readonly properties may be updated while cloning
+--FILE--
+<?php
+
+use native_types;
+
+class ReadonlyCloneBase
+{
+    public readonly int $base;
+
+    public function __construct()
+    {
+        $this->base = 1;
+    }
+
+    public function __clone(): void
+    {
+        $this->base++;
+        $this->base += 3;
+    }
+}
+
+class ReadonlyCloneValue extends ReadonlyCloneBase
+{
+    public readonly string $name;
+    public readonly array $items;
+
+    public function __construct()
+    {
+        parent::__construct();
+        $this->name = 'original';
+        $this->items = [1];
+    }
+
+    public function __clone(): void
+    {
+        parent::__clone();
+        $this->name = 'clone';
+        $this->name .= 'd';
+        $this->items[] = 2;
+        $this->items[0] = 10;
+    }
+}
+
+function main(): void
+{
+    $original = new ReadonlyCloneValue();
+    $copy = clone $original;
+    var_dump($original->base, $original->name, $original->items);
+    var_dump($copy->base, $copy->name, $copy->items);
+}
+?>
+--EXPECT--
+int(1)
+string(8) "original"
+array(1) {
+  [0]=>
+  int(1)
+}
+int(5)
+string(6) "cloned"
+array(2) {
+  [0]=>
+  int(10)
+  [1]=>
+  int(2)
+}
diff --git a/tests/compiler/object_property/readonly-constructor-only.phpt b/tests/compiler/object_property/readonly-constructor-only.phpt
new file mode 100644
index 00000000..be429575
--- /dev/null
+++ b/tests/compiler/object_property/readonly-constructor-only.phpt
@@ -0,0 +1,42 @@
+--TEST--
+TypePHP readonly properties are mutable only during their declaring constructor
+--FILE--
+<?php
+
+use native_types;
+
+class ReadonlyConstructorOnly
+{
+    public readonly int $number;
+    public readonly string $text;
+    public readonly array $items;
+
+    public function __construct()
+    {
+        $this->number = 1;
+        $this->number = 2;
+        $this->number += 3;
+        ++$this->number;
+
+        $this->text = 'a';
+        $this->text .= 'b';
+
+        $this->items = [];
+        $this->items[] = 10;
+        $this->items[0] = 20;
+    }
+}
+
+function main(): void
+{
+    $value = new ReadonlyConstructorOnly();
+    var_dump($value->number, $value->text, $value->items);
+}
+?>
+--EXPECT--
+int(6)
+string(2) "ab"
+array(1) {
+  [0]=>
+  int(20)
+}
diff --git a/tests/compiler/object_property/readonly-dynamic-clone-call.phpt b/tests/compiler/object_property/readonly-dynamic-clone-call.phpt
new file mode 100644
index 00000000..00fd7a9b
--- /dev/null
+++ b/tests/compiler/object_property/readonly-dynamic-clone-call.phpt
@@ -0,0 +1,35 @@
+--TEST--
+Readonly clone method cannot be called dynamically
+--FILE--
+<?php
+
+class ReadonlyDynamicCloneCall
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+    }
+
+    public function __clone(): void
+    {
+        $this->value = 2;
+    }
+}
+
+function main(): void
+{
+    $value = new ReadonlyDynamicCloneCall();
+    $method = '__clone';
+    try {
+        $value->$method();
+    } catch (Error $error) {
+        echo $error->getMessage(), "\n";
+    }
+    var_dump($value->value);
+}
+?>
+--EXPECT--
+Clone method ReadonlyDynamicCloneCall::__clone() can only be invoked by clone
+int(1)
diff --git a/tests/compiler/object_property/readonly-dynamic-constructor-call.phpt b/tests/compiler/object_property/readonly-dynamic-constructor-call.phpt
new file mode 100644
index 00000000..f95e07cd
--- /dev/null
+++ b/tests/compiler/object_property/readonly-dynamic-constructor-call.phpt
@@ -0,0 +1,30 @@
+--TEST--
+Readonly constructor cannot be called dynamically after construction
+--FILE--
+<?php
+
+class ReadonlyDynamicConstructorCall
+{
+    public readonly int $value;
+
+    public function __construct(int $value)
+    {
+        $this->value = $value;
+    }
+}
+
+function main(): void
+{
+    $value = new ReadonlyDynamicConstructorCall(1);
+    $method = '__construct';
+    try {
+        $value->$method(2);
+    } catch (Error $error) {
+        echo $error->getMessage(), "\n";
+    }
+    var_dump($value->value);
+}
+?>
+--EXPECT--
+Constructor ReadonlyDynamicConstructorCall::__construct() can only be invoked by new
+int(1)