RustPython
diff --git a/Lib/test/test_compile.py b/Lib/test/test_compile.py
@@ -1012,7 +1012,7 @@ def return_genexp():
         code_lines = self.get_code_lines(genexp_code)
         self.assertEqual(genexp_lines, code_lines)
 
-    # TODO: RUSTPYTHON
+    # TODO: RUSTPYTHON; implicit return line number after async for
     @unittest.expectedFailure
     def test_line_number_implicit_return_after_async_for(self):
 

diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
@@ -401,7 +401,6 @@ def test_setrecursionlimit_to_depth(self):
         finally:
             sys.setrecursionlimit(old_limit)
 
-    @unittest.expectedFailure # TODO: RUSTPYTHON
     def test_getwindowsversion(self):
         # Raise SkipTest if sys doesn't have getwindowsversion attribute
         test.support.get_attribute(sys, "getwindowsversion")
@@ -851,7 +850,6 @@ def test_subinterp_intern_singleton(self):
                     '''))
                 self.assertTrue(sys._is_interned(s))
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; needs update for context_aware_warnings
     def test_sys_flags(self):
         self.assertTrue(sys.flags)
         attrs = ("debug",
@@ -880,7 +878,7 @@ def test_sys_flags_no_instantiation(self):
     def test_sys_version_info_no_instantiation(self):
         self.assert_raise_on_new_sys_type(sys.version_info)
 
-    @unittest.expectedFailure # TODO: RUSTPYTHON
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; TypeError not raised for getwindowsversion instantiation
     def test_sys_getwindowsversion_no_instantiation(self):
         # Skip if not being run on Windows.
         test.support.get_attribute(sys, "getwindowsversion")
@@ -1057,12 +1055,12 @@ def check_locale_surrogateescape(self, locale):
                          'stdout: surrogateescape\n'
                          'stderr: backslashreplace\n')
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; stderr: backslashreplace
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; iso8859_1 codec not registered
     @support.requires_subprocess()
     def test_c_locale_surrogateescape(self):
         self.check_locale_surrogateescape('C')
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; stderr: backslashreplace
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; iso8859_1 codec not registered
     @support.requires_subprocess()
     def test_posix_locale_surrogateescape(self):
         self.check_locale_surrogateescape('POSIX')

diff --git a/...s/codegen/src/snapshots/rustpython_codegen__compile__tests__nested_double_async_with.snap b/...s/codegen/src/snapshots/rustpython_codegen__compile__tests__nested_double_async_with.snap
diff --git a/crates/vm/src/stdlib/io.rs b/crates/vm/src/stdlib/io.rs
@@ -2607,6 +2607,92 @@ mod _io {
         }
     }
 
+    #[pyclass(module = "_io", name, no_attr)]
+    #[derive(Debug, PyPayload)]
+    struct StatelessIncrementalEncoder {
+        encode: PyObjectRef,
+        errors: Option<PyStrRef>,
+        name: Option<PyStrRef>,
+    }
+
+    #[pyclass]
+    impl StatelessIncrementalEncoder {
+        #[pymethod]
+        fn encode(
+            &self,
+            input: PyObjectRef,
+            _final: OptionalArg<bool>,
+            vm: &VirtualMachine,
+        ) -> PyResult {
+            let mut args: Vec<PyObjectRef> = vec![input];
+            if let Some(errors) = &self.errors {
+                args.push(errors.to_owned().into());
+            }
+            let res = self.encode.call(args, vm)?;
+            let tuple: PyTupleRef = res.try_into_value(vm)?;
+            if tuple.len() != 2 {
+                return Err(vm.new_type_error("encoder must return a tuple (object, integer)"));
+            }
+            Ok(tuple[0].clone())
+        }
+
+        #[pymethod]
+        fn reset(&self) {}
+
+        #[pymethod]
+        fn setstate(&self, _state: PyObjectRef) {}
+
+        #[pymethod]
+        fn getstate(&self, vm: &VirtualMachine) -> PyObjectRef {
+            vm.ctx.new_int(0).into()
+        }
+
+        #[pygetset]
+        fn name(&self) -> Option<PyStrRef> {
+            self.name.clone()
+        }
-    #[pyclass(module = "_io", name, no_attr)]
-    #[derive(Debug, PyPayload)]
-    struct StatelessIncrementalEncoder {
-        encode: PyObjectRef,
-        errors: Option<PyStrRef>,
-        name: Option<PyStrRef>,
-    }
-
-    #[pyclass]
-    impl StatelessIncrementalEncoder {
-        #[pymethod]
-        fn encode(
-            &self,
-            input: PyObjectRef,
-            _final: OptionalArg<bool>,
-            vm: &VirtualMachine,
-        ) -> PyResult {
-            let mut args: Vec<PyObjectRef> = vec![input];
-            if let Some(errors) = &self.errors {
-                args.push(errors.to_owned().into());
-            }
-            let res = self.encode.call(args, vm)?;
-            let tuple: PyTupleRef = res.try_into_value(vm)?;
-            if tuple.len() != 2 {
-                return Err(vm.new_type_error("encoder must return a tuple (object, integer)"));
-            }
-            Ok(tuple[0].clone())
-        }
-
-        #[pymethod]
-        fn reset(&self) {}
-
-        #[pymethod]
-        fn setstate(&self, _state: PyObjectRef) {}
-
-        #[pymethod]
-        fn getstate(&self, vm: &VirtualMachine) -> PyObjectRef {
-            vm.ctx.new_int(0).into()
-        }
-
-        #[pygetset]
-        fn name(&self) -> Option<PyStrRef> {
-            self.name.clone()
-        }
+    #[pyclass(module = "_io", name, no_attr)]
+    #[derive(Debug, PyPayload)]
+    struct StatelessIncrementalEncoder {
+        encode: PyObjectRef,
+        errors: Option<PyStrRef>,
+        name: Option<PyStrRef>,
+    }
+
+    #[pyclass]
+    impl StatelessIncrementalEncoder {
+        #[pymethod]
+        fn encode(
+            &self,
+            input: PyObjectRef,
+            _final: OptionalArg<bool>,
+            vm: &VirtualMachine,
+        ) -> PyResult {
+            let mut args: Vec<PyObjectRef> = vec![input];
+            if let Some(errors) = &self.errors {
+                args.push(errors.to_owned().into());
+            }
+            let res = self.encode.call(args, vm)?;
+            let tuple: PyTupleRef = res.try_into_value(vm)?;
+            if tuple.len() != 2 {
+                return Err(vm.new_type_error("encoder must return a tuple (object, integer)"));
+            }
+            let _consumed: isize = isize::try_from_object(vm, tuple[1].clone()).map_err(|_| {
+                vm.new_type_error("encoder must return a tuple (object, integer)")
+            })?;
+            Ok(tuple[0].clone())
+        }
+
+        #[pymethod]
+        fn reset(&self) {}
+
+        #[pymethod]
+        fn setstate(&self, _state: PyObjectRef) {}
+
+        #[pymethod]
+        fn getstate(&self, vm: &VirtualMachine) -> PyObjectRef {
+            vm.ctx.new_int(0).into()
+        }
+
+        #[pygetset]
+        fn name(&self) -> Option<PyStrRef> {
+            self.name.clone()
+        }
-    #[pyclass(module = "_io", name, no_attr)]
-    #[derive(Debug, PyPayload)]
-    struct StatelessIncrementalEncoder {
-        encode: PyObjectRef,
-        errors: Option<PyStrRef>,
-        name: Option<PyStrRef>,
-    }
-
-    #[pyclass]
-    impl StatelessIncrementalEncoder {
-        #[pymethod]
-        fn encode(
-            &self,
-            input: PyObjectRef,
-            _final: OptionalArg<bool>,
-            vm: &VirtualMachine,
-        ) -> PyResult {
-            let mut args: Vec<PyObjectRef> = vec![input];
-            if let Some(errors) = &self.errors {
-                args.push(errors.to_owned().into());
-            }
-            let res = self.encode.call(args, vm)?;
-            let tuple: PyTupleRef = res.try_into_value(vm)?;
-            if tuple.len() != 2 {
-                return Err(vm.new_type_error("encoder must return a tuple (object, integer)"));
-            }
-            Ok(tuple[0].clone())
-        }
-
-        #[pymethod]
-        fn reset(&self) {}
-
-        #[pymethod]
-        fn setstate(&self, _state: PyObjectRef) {}
-
-        #[pymethod]
-        fn getstate(&self, vm: &VirtualMachine) -> PyObjectRef {
-            vm.ctx.new_int(0).into()
-        }
-
-        #[pygetset]
-        fn name(&self) -> Option<PyStrRef> {
-            self.name.clone()
-        }
+    #[pyclass(module = "_io", name, no_attr)]
+    #[derive(Debug, PyPayload)]
+    struct StatelessIncrementalEncoder {
+        encode: PyObjectRef,
+        errors: Option<PyStrRef>,
+        name: Option<PyStrRef>,
+    }
+
+    #[pyclass]
+    impl StatelessIncrementalEncoder {
+        #[pymethod]
+        fn encode(
+            &self,
+            input: PyObjectRef,
+            _final: OptionalArg<bool>,
+            vm: &VirtualMachine,
+        ) -> PyResult {
+            let mut args: Vec<PyObjectRef> = vec![input];
+            if let Some(errors) = &self.errors {
+                args.push(errors.to_owned().into());
+            }
+            let res = self.encode.call(args, vm)?;
+            let tuple: PyTupleRef = res.try_into_value(vm)?;
+            if tuple.len() != 2 {
+                return Err(vm.new_type_error("encoder must return a tuple (object, integer)"));
+            }
+            let _consumed: isize = isize::try_from_object(vm, tuple[1].clone()).map_err(|_| {
+                vm.new_type_error("encoder must return a tuple (object, integer)")
+            })?;
+            Ok(tuple[0].clone())
+        }
+
+        #[pymethod]
+        fn reset(&self) {}
+
+        #[pymethod]
+        fn setstate(&self, _state: PyObjectRef) {}
+
+        #[pymethod]
+        fn getstate(&self, vm: &VirtualMachine) -> PyObjectRef {
+            vm.ctx.new_int(0).into()
+        }
+
+        #[pygetset]
+        fn name(&self) -> Option<PyStrRef> {
+            self.name.clone()
+        }
+    }
+
+    #[pyclass(module = "_io", name, no_attr)]
+    #[derive(Debug, PyPayload)]
+    struct StatelessIncrementalDecoder {
+        decode: PyObjectRef,
+        errors: Option<PyStrRef>,
+    }
+
+    #[pyclass]
+    impl StatelessIncrementalDecoder {
+        #[pymethod]
+        fn decode(
+            &self,
+            input: PyObjectRef,
+            _final: OptionalArg<bool>,
+            vm: &VirtualMachine,
+        ) -> PyResult {
+            let mut args: Vec<PyObjectRef> = vec![input];
+            if let Some(errors) = &self.errors {
+                args.push(errors.to_owned().into());
+            }
+            let res = self.decode.call(args, vm)?;
+            let tuple: PyTupleRef = res.try_into_value(vm)?;
+            if tuple.len() != 2 {
+                return Err(vm.new_type_error("decoder must return a tuple (object, integer)"));
+            }
+            Ok(tuple[0].clone())
+        }
+
+        #[pymethod]
+        fn getstate(&self, vm: &VirtualMachine) -> (PyBytesRef, u64) {
+            (vm.ctx.empty_bytes.to_owned(), 0)
+        }
+
+        #[pymethod]
+        fn setstate(&self, _state: PyTupleRef, _vm: &VirtualMachine) {}
+
+        #[pymethod]
+        fn reset(&self) {}
+    }
+
     #[pyattr]
     #[pyclass(name = "TextIOWrapper", base = _TextIOBase)]
     #[derive(Debug, Default)]
@@ -2830,7 +2916,25 @@ mod _io {
 
             let encoder = if vm.call_method(buffer, "writable", ())?.try_to_bool(vm)? {
                 let incremental_encoder =
-                    codec.get_incremental_encoder(Some(errors.to_owned()), vm)?;
+                    match codec.get_incremental_encoder(Some(errors.to_owned()), vm) {
+                        Ok(encoder) => encoder,
+                        Err(err)
+                            if err.fast_isinstance(vm.ctx.exceptions.type_error)
+                                || err.fast_isinstance(vm.ctx.exceptions.attribute_error) =>
+                        {
+                            let name = vm
+                                .get_attribute_opt(codec.as_tuple().to_owned().into(), "name")?
+                                .and_then(|obj| obj.downcast::<PyStr>().ok());
+                            StatelessIncrementalEncoder {
+                                encode: codec.get_encode_func().to_owned(),
+                                errors: Some(errors.to_owned()),
+                                name,
+                            }
+                            .into_ref(&vm.ctx)
+                            .into()
+                        }
+                        Err(err) => return Err(err),
+                    };
                 let encoding_name = vm.get_attribute_opt(incremental_encoder.clone(), "name")?;
                 let encode_func = encoding_name.and_then(|name| {
                     let name = name.downcast_ref::<PyStr>()?;
@@ -2845,7 +2949,21 @@ mod _io {
             };
 
             let decoder = if vm.call_method(buffer, "readable", ())?.try_to_bool(vm)? {
-                let decoder = codec.get_incremental_decoder(Some(errors.to_owned()), vm)?;
+                let decoder = match codec.get_incremental_decoder(Some(errors.to_owned()), vm) {
+                    Ok(decoder) => decoder,
+                    Err(err)
+                        if err.fast_isinstance(vm.ctx.exceptions.type_error)
+                            || err.fast_isinstance(vm.ctx.exceptions.attribute_error) =>
+                    {
+                        StatelessIncrementalDecoder {
+                            decode: codec.get_decode_func().to_owned(),
+                            errors: Some(errors.to_owned()),
+                        }
+                        .into_ref(&vm.ctx)
+                        .into()
+                    }
+                    Err(err) => return Err(err),
+                };
                 if let Newlines::Universal | Newlines::Passthrough = newline {
                     let args = IncrementalNewlineDecoderArgs {
                         decoder,

diff --git a/crates/vm/src/stdlib/sys.rs b/crates/vm/src/stdlib/sys.rs
@@ -73,7 +73,7 @@ mod sys {
         RUST_MULTIARCH.replace("-unknown", "")
     }
 
-    #[pyclass(no_attr, name = "_BootstrapStderr", module = "sys")]
+    #[pyclass(no_attr, name = "_BootstrapStderr")]
     #[derive(Debug, PyPayload)]
     pub(super) struct BootstrapStderr;
 
@@ -95,7 +95,7 @@ mod sys {
 
     /// Lightweight stdio wrapper for sandbox mode (no host_env).
     /// Directly uses Rust's std::io for stdin/stdout/stderr without FileIO.
-    #[pyclass(no_attr, name = "_SandboxStdio", module = "sys")]
+    #[pyclass(no_attr, name = "_SandboxStdio")]
     #[derive(Debug, PyPayload)]
     pub struct SandboxStdio {
         pub fd: i32,
@@ -1565,10 +1565,6 @@ mod sys {
         safe_path: bool,
         /// -X warn_default_encoding, PYTHONWARNDEFAULTENCODING
         warn_default_encoding: u8,
-        /// -X thread_inherit_context, whether new threads inherit context from parent
-        thread_inherit_context: bool,
-        /// -X context_aware_warnings, whether warnings are context aware
-        context_aware_warnings: bool,
     }
 
     impl FlagsData {
@@ -1592,13 +1588,11 @@ mod sys {
                 int_max_str_digits: settings.int_max_str_digits,
                 safe_path: settings.safe_path,
                 warn_default_encoding: settings.warn_default_encoding as u8,
-                thread_inherit_context: settings.thread_inherit_context,
-                context_aware_warnings: settings.context_aware_warnings,
             }
         }
     }
 
-    #[pystruct_sequence(name = "flags", module = "sys", data = "FlagsData", no_attr)]
+    #[pystruct_sequence(name = "flags", data = "FlagsData", no_attr)]
     pub(super) struct PyFlags;
 
     #[pyclass(with(PyStructSequence))]
@@ -1607,6 +1601,16 @@ mod sys {
         fn slot_new(_cls: PyTypeRef, _args: FuncArgs, vm: &VirtualMachine) -> PyResult {
             Err(vm.new_type_error("cannot create 'sys.flags' instances"))
         }
+
+        #[pygetset]
+        fn context_aware_warnings(&self, vm: &VirtualMachine) -> bool {
+            vm.state.config.settings.context_aware_warnings
+        }
+
+        #[pygetset]
+        fn thread_inherit_context(&self, vm: &VirtualMachine) -> bool {
+            vm.state.config.settings.thread_inherit_context
+        }
     }
 
     #[cfg(feature = "threading")]
@@ -1776,10 +1780,15 @@ mod sys {
         build: u32,
         platform: u32,
         service_pack: String,
+        #[pystruct_sequence(skip)]
         service_pack_major: u16,
+        #[pystruct_sequence(skip)]
         service_pack_minor: u16,
+        #[pystruct_sequence(skip)]
         suite_mask: u16,
+        #[pystruct_sequence(skip)]
         product_type: u8,
+        #[pystruct_sequence(skip)]
         platform_version: (u32, u32, u32),
     }
 

diff --git a/crates/vm/src/vm/mod.rs b/crates/vm/src/vm/mod.rs
@@ -331,6 +331,21 @@ impl VirtualMachine {
         self.state
             .codec_registry
             .register_manual("utf8", utf8_codec)?;
+
+        // Register latin-1 / iso8859-1 aliases needed very early for stdio
+        // bootstrap (e.g. PYTHONIOENCODING=latin-1).
+        if cfg!(feature = "freeze-stdlib") {
+            self.import("encodings.latin_1", 0)?;
+            let latin1_module = sys_modules.get_item("encodings.latin_1", self)?;
+            let getregentry = latin1_module.get_attr("getregentry", self)?;
+            let codec_info = getregentry.call((), self)?;
+            let latin1_codec: crate::codecs::PyCodec = codec_info.try_into_value(self)?;
+            for name in ["latin-1", "latin_1", "latin1", "iso8859-1", "iso8859_1"] {
+                self.state
+                    .codec_registry
+                    .register_manual(name, latin1_codec.clone())?;
+            }
+        }
         Ok(())
     }
 
@@ -367,8 +382,8 @@ impl VirtualMachine {
                 let io = import::import_builtin(self, "_io")?;
 
                 // Full stdio: FileIO → BufferedWriter → TextIOWrapper
-                #[cfg(feature = "host_env")]
-                let make_stdio = |name: &str, fd: i32, write: bool| {
+                #[cfg(all(feature = "host_env", feature = "stdio"))]
+                let make_stdio = |name: &str, fd: i32, write: bool| -> PyResult<PyObjectRef> {
                     let buffered_stdio = self.state.config.settings.buffered_stdio;
                     let unbuffered = write && !buffered_stdio;
                     let buf = crate::stdlib::io::open(
@@ -397,12 +412,13 @@ impl VirtualMachine {
                     let errors = if fd == 2 {
                         Some("backslashreplace")
                     } else {
-                        self.state
-                            .config
-                            .settings
-                            .stdio_errors
-                            .as_deref()
-                            .or(Some("surrogateescape"))
+                        self.state.config.settings.stdio_errors.as_deref().or(
+                            if self.state.config.settings.stdio_encoding.is_some() {
+                                Some("strict")
+                            } else {
+                                Some("surrogateescape")
+                            },
+                        )
                     };
 
                     let stdio = self.call_method(