diff --git a/src/codegen/lower_inst/objects.rs b/src/codegen/lower_inst/objects.rs
index 1fc999ca5c..e627b515e9 100644
--- a/src/codegen/lower_inst/objects.rs
+++ b/src/codegen/lower_inst/objects.rs
@@ -783,7 +783,7 @@ fn lower_builtin_throwable_new(
     class_name: &str,
     class_id: u64,
 ) -> Result<()> {
-    if inst.operands.len() > 2 {
+    if inst.operands.len() > 3 {
         return Err(CodegenIrError::unsupported(format!(
             "{}::__construct with {} EIR operands",
             class_name,
@@ -794,6 +794,9 @@ fn lower_builtin_throwable_new(
     preserve_throwable_for_init(ctx);
     emit_throwable_message_fields(ctx, inst.operands.first().copied())?;
     emit_throwable_code_field(ctx, inst.operands.get(1).copied())?;
+    // Operand 2 is PHP's `$previous`: its expression was evaluated (side effects preserved),
+    // but the compact throwable payload has no previous slot — `getPrevious()` is synthesized
+    // as null — so the value is intentionally not stored.
     restore_throwable_after_init(ctx);
     store_if_result(ctx, inst)
 }
diff --git a/src/parser/stmt/mod.rs b/src/parser/stmt/mod.rs
index 6befd9cda1..0b828b0633 100644
--- a/src/parser/stmt/mod.rs
+++ b/src/parser/stmt/mod.rs
@@ -502,6 +502,13 @@ pub(crate) fn parse_name(
                 parts.push(name.clone());
                 *pos += 1;
             }
+            // `enum` is only a soft keyword: `Enum` is a legal class name and name segment
+            // (`new Enum`, `extends Enum`, `MabeEnum\Enum`). Statement-position `enum`
+            // dispatches to the enum-declaration parser before parse_name is consulted.
+            Some(Token::Enum) => {
+                parts.push("Enum".to_string());
+                *pos += 1;
+            }
             _ if parts.is_empty() => return Err(CompileError::new(span, first_error)),
             _ => {
                 return Err(CompileError::new(
diff --git a/src/parser/stmt/namespace_use.rs b/src/parser/stmt/namespace_use.rs
index e9ede8ebfa..1698530873 100644
--- a/src/parser/stmt/namespace_use.rs
+++ b/src/parser/stmt/namespace_use.rs
@@ -254,6 +254,35 @@ fn parse_group_use_items(
 /// the name kind is `FullyQualified`; otherwise it is `Unqualified` or `Qualified`
 /// depending on whether an intermediate `\ ` was seen. Stops when a trailing `\`
 /// followed by `{` is encountered (the opening brace is consumed by the caller).
+/// Canonical import spelling for constant-like tokens the lexer eagerly tokenizes.
+///
+/// `use const PHP_INT_MAX;` is legal PHP, but `PHP_INT_MAX` never reaches the parser as an
+/// identifier — the lexer emits a dedicated token (expressions lower these to literals
+/// directly, so the import itself is inert). Accepting them here keeps such use
+/// declarations parseable.
+fn token_as_import_name(token: &Token) -> Option<String> {
+    let name = match token {
+        Token::PhpIntMax => "PHP_INT_MAX",
+        Token::PhpIntMin => "PHP_INT_MIN",
+        Token::PhpFloatMax => "PHP_FLOAT_MAX",
+        Token::PhpFloatMin => "PHP_FLOAT_MIN",
+        Token::PhpFloatEpsilon => "PHP_FLOAT_EPSILON",
+        Token::Inf => "INF",
+        Token::Nan => "NAN",
+        Token::MPi => "M_PI",
+        Token::ME => "M_E",
+        Token::MSqrt2 => "M_SQRT2",
+        Token::MPi2 => "M_PI_2",
+        Token::MPi4 => "M_PI_4",
+        Token::MLog2e => "M_LOG2E",
+        Token::MLog10e => "M_LOG10E",
+        Token::Stdin => "STDIN",
+        Token::Stdout => "STDOUT",
+        _ => return None,
+    };
+    Some(name.to_string())
+}
+
 fn parse_use_prefix(
     tokens: &[(Token, Span)],
     pos: &mut usize,
@@ -272,6 +301,12 @@ fn parse_use_prefix(
                 parts.push(name.clone());
                 *pos += 1;
             }
+            Some(token) if token_as_import_name(token).is_some() => {
+                if let Some(name) = token_as_import_name(token) {
+                    parts.push(name);
+                }
+                *pos += 1;
+            }
             _ if parts.is_empty() => {
                 return Err(CompileError::new(
                     span,
diff --git a/src/parser/stmt/oop/declarations.rs b/src/parser/stmt/oop/declarations.rs
index bb1be87f66..539aa72663 100644
--- a/src/parser/stmt/oop/declarations.rs
+++ b/src/parser/stmt/oop/declarations.rs
@@ -39,6 +39,12 @@ pub(in crate::parser::stmt) fn parse_class_decl(
             *pos += 1;
             n
         }
+        // `enum` is only a soft keyword — `class Enum {}` is legal PHP (vendor precedent:
+        // marc-mabe/php-enum). The lexer always tokenizes the word, so accept it here.
+        Some(Token::Enum) => {
+            *pos += 1;
+            "Enum".to_string()
+        }
         _ => return Err(CompileError::new(span, "Expected class name after 'class'")),
     };
 
diff --git a/src/types/checker/builtin_types/exception.rs b/src/types/checker/builtin_types/exception.rs
index 33523e1c0b..e8269a4ae6 100644
--- a/src/types/checker/builtin_types/exception.rs
+++ b/src/types/checker/builtin_types/exception.rs
@@ -70,6 +70,15 @@ pub(super) fn builtin_exception_constructor_method() -> ClassMethod {
                 )),
                 false,
             ),
+            // PHP's third parameter, `?Throwable $previous = null`. Accepted (positionally and
+            // as the `previous:` named argument) but not stored: the compact throwable payload
+            // has no previous slot and `getPrevious()` is already synthesized as null.
+            (
+                "previous".to_string(),
+                None,
+                Some(Expr::new(ExprKind::Null, crate::span::Span::dummy())),
+                false,
+            ),
         ],
         variadic: None,
         variadic_type: None,
diff --git a/src/types/checker/schema/classes/interfaces.rs b/src/types/checker/schema/classes/interfaces.rs
index dcd5d55af3..23adb7d301 100644
--- a/src/types/checker/schema/classes/interfaces.rs
+++ b/src/types/checker/schema/classes/interfaces.rs
@@ -362,7 +362,28 @@ fn validate_interface_method(
             )?;
         }
     }
+    // Covariant self-return: PHP accepts an implementation returning a NARROWER type than the
+    // interface declares. The common shape — `withX(): static`/`self`/the class itself against
+    // an interface-typed return (PSR-7's immutability methods) — cannot go through
+    // `type_accepts`, because the class under validation is not registered in
+    // `checker.classes` yet (its interface list is invisible mid-construction). Accept it from
+    // the facts at hand: this function IS the proof that `class` implements `interface_name`,
+    // so a self-typed return conforms when the declared return is that interface (or one it
+    // extends), or any interface the class itself declares (or one those extend).
+    let self_return_conforms = match (&required_sig.return_type, &actual_sig.return_type) {
+        (PhpType::Object(expected_name), PhpType::Object(actual_name)) => {
+            actual_name == &class.name
+                && (expected_name == interface_name
+                    || checker.interface_extends_interface(interface_name, expected_name)
+                    || class.implements.iter().any(|declared| {
+                        declared == expected_name
+                            || checker.interface_extends_interface(declared, expected_name)
+                    }))
+        }
+        _ => false,
+    };
     if required_sig.declared_return
+        && !self_return_conforms
         && !declared_return_type_compatible(
             checker,
             &required_sig.return_type,
diff --git a/src/types/checker/stmt_check/control_flow.rs b/src/types/checker/stmt_check/control_flow.rs
index 92d4929d80..a1d67b9432 100644
--- a/src/types/checker/stmt_check/control_flow.rs
+++ b/src/types/checker/stmt_check/control_flow.rs
@@ -65,7 +65,16 @@ impl Checker {
                 let arr_ty = self.infer_type_with_assignment_effects(array, env)?;
                 if let PhpType::Array(elem_ty) = &arr_ty {
                     if let Some(k) = key_var {
-                        env.insert(k.clone(), PhpType::Int);
+                        // A genuinely packed array has int keys; an UNKNOWN-element array (an
+                        // `array`-hinted param/property, elements known only to phpdoc) may be
+                        // associative at runtime, so its keys are Mixed (ward-http's
+                        // `foreach ($headers as $name => $values)` with string keys).
+                        let key_ty = if matches!(elem_ty.as_ref(), PhpType::Mixed) {
+                            PhpType::Mixed
+                        } else {
+                            PhpType::Int
+                        };
+                        env.insert(k.clone(), key_ty);
                         self.clear_foreach_callable_metadata(k);
                     }
                     let value_ty = *elem_ty.clone();
diff --git a/tests/codegen/control_flow/functions.rs b/tests/codegen/control_flow/functions.rs
index 799ca30a02..768c86d9d8 100644
--- a/tests/codegen/control_flow/functions.rs
+++ b/tests/codegen/control_flow/functions.rs
@@ -167,3 +167,14 @@ fn test_property_throw_guard_narrowing() {
     );
     assert_eq!(out, "x");
 }
+
+/// foreach KEYS over an unknown-element array (an `array`-hinted param — elements known only
+/// to phpdoc) are Mixed, not Int: the value may be associative at runtime (header-map shape
+/// with string keys into a `string $name` parameter). Byte-parity vs PHP 8.5.
+#[test]
+fn test_foreach_key_over_unknown_element_array() {
+    let out = compile_and_run(
+        "<?php final class H { private array $headers = []; public function setHeader(string $name, string $value): void { $this->headers[$name] = $value; } public function all(array $headers): string { $out = ''; foreach ($headers as $name => $value) { $this->setHeader($name, $value); $out .= $name . '=' . $value . ';'; } return $out; } } function main(): void { echo (new H())->all(['a' => '1', 'b' => '2']); } main();",
+    );
+    assert_eq!(out, "a=1;b=2;");
+}
diff --git a/tests/codegen/exceptions.rs b/tests/codegen/exceptions.rs
index 58e17e9f99..11bb421121 100644
--- a/tests/codegen/exceptions.rs
+++ b/tests/codegen/exceptions.rs
@@ -624,3 +624,15 @@ try { echo $c->foo(); echo 'no'; } catch (Error $e) { echo 'err'; }
     );
     assert_eq!(out, "err");
 }
+
+/// The builtin exception constructors accept PHP's third `$previous` parameter (positional or
+/// the `previous:` named argument). It is not stored — `getPrevious()` remains synthesized as
+/// null — but wrap-and-rethrow code compiles and the message/code round-trip is byte-identical
+/// to PHP 8.5.
+#[test]
+fn test_exception_constructor_accepts_previous() {
+    let out = compile_and_run(
+        "<?php function f(): string { try { try { throw new \\ValueError('inner'); } catch (\\ValueError $e) { throw new \\InvalidArgumentException('outer: ' . $e->getMessage(), $e->getCode(), previous: $e); } } catch (\\InvalidArgumentException $x) { return $x->getMessage() . '/' . $x->getCode(); } } echo f();",
+    );
+    assert_eq!(out, "outer: inner/0");
+}
diff --git a/tests/codegen/namespaces.rs b/tests/codegen/namespaces.rs
index 5b5e8a7e93..a9a041d48e 100644
--- a/tests/codegen/namespaces.rs
+++ b/tests/codegen/namespaces.rs
@@ -480,3 +480,22 @@ echo \App\C\K::mk()->t->p;
     );
     assert_eq!(out, "/");
 }
+
+/// `use const PHP_INT_MAX;` — the lexer eagerly tokenizes such constants, so the
+/// use-declaration parser must accept the dedicated tokens as import names (the import itself
+/// is inert; expression uses lower to literals).
+#[test]
+fn test_use_const_of_lexer_tokenized_constant() {
+    let out = compile_and_run(
+        r#"<?php
+
+namespace App;
+
+use const PHP_INT_MAX;
+use const PHP_INT_MIN;
+
+echo PHP_INT_MAX > 0 ? 'max' : '?', ':', PHP_INT_MIN < 0 ? 'min' : '?';
+"#,
+    );
+    assert_eq!(out, "max:min");
+}
diff --git a/tests/codegen/oop/interfaces.rs b/tests/codegen/oop/interfaces.rs
index dbdf52168c..0a0e2975d9 100644
--- a/tests/codegen/oop/interfaces.rs
+++ b/tests/codegen/oop/interfaces.rs
@@ -282,3 +282,15 @@ echo implode(',', C::previews());
     );
     assert_eq!(out, "a,b");
 }
+
+/// An implementation may return a NARROWER type than the interface declares — the PSR-7 shape
+/// `withX(): static` (resolving to the class) against an interface-typed return. The class
+/// under validation is mid-construction when conformance runs, so the covariance is proven
+/// from the conformance context itself. Byte-parity vs PHP 8.5.
+#[test]
+fn test_interface_covariant_self_return() {
+    let out = compile_and_run(
+        "<?php interface I { public function w(): I; } final class C implements I { public function w(): static { return $this; } } echo (new C())->w() instanceof C ? 'ok' : 'no';",
+    );
+    assert_eq!(out, "ok");
+}
diff --git a/tests/codegen/oop/misc.rs b/tests/codegen/oop/misc.rs
index 32b46055ca..0c9ac5b0d2 100644
--- a/tests/codegen/oop/misc.rs
+++ b/tests/codegen/oop/misc.rs
@@ -102,3 +102,14 @@ fn test_example_v017_trio_compiles_and_runs() {
     let out = compile_and_run(include_str!("../../../examples/v017-trio/main.php"));
     assert_eq!(out, "health:[ok]:missing");
 }
+
+/// EC-10 (#493): `enum` is only a soft keyword — `class Enum {}` is legal PHP (vendor
+/// precedent: marc-mabe/php-enum). The always-tokenizing lexer must not block the class
+/// declaration. Byte-parity vs PHP 8.5.
+#[test]
+fn test_class_named_enum_declares() {
+    let out = compile_and_run(
+        "<?php class Enum { public function tag(): string { return 'e'; } } echo (new Enum())->tag();",
+    );
+    assert_eq!(out, "e");
+}