fix(windows): force UTF-8 encoding for all spawned child processes

- Set UTF-8 environment variables (PYTHONUTF8, PYTHONIOENCODING, LANG,
  LC_ALL) on all child processes via process.rs helpers
- Configure PTY terminals per shell flavor: chcp 65001 for cmd.exe,
  [Console]::OutputEncoding for PowerShell, LANG=C.UTF-8 for Git Bash
- Use /K and -NoExit for interactive shells to avoid nested processes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/src/process.rs

@@ -13,6 +13,7 @@ pub fn configure_std_command(command: &mut Command) -> &mut Command {
     {
         use std::os::windows::process::CommandExt;
         command.creation_flags(CREATE_NO_WINDOW);
+        set_utf8_env(command);
     }
 
     command
@@ -33,11 +34,47 @@ pub fn configure_tokio_command(
     #[cfg(windows)]
     {
         command.creation_flags(CREATE_NO_WINDOW);
+        set_utf8_env(command);
     }
 
     command
 }
 
+/// Hint child processes to produce UTF-8 output on Windows.
+///
+/// Sets environment variables recognised by common runtimes (Python, MSYS2/Git
+/// Bash, .NET console apps).  Not all programs honour these, but they cover the
+/// most frequent sources of mojibake in practice.
+#[cfg(windows)]
+fn set_utf8_env<C: SetEnv>(command: &mut C) {
+    // Python
+    command.env("PYTHONUTF8", "1");
+    command.env("PYTHONIOENCODING", "utf-8");
+    // MSYS2 / Git-for-Windows / POSIX-layer tools
+    command.env("LANG", "C.UTF-8");
+    command.env("LC_ALL", "C.UTF-8");
+}
+
+/// Abstraction over the `.env()` method shared by std and tokio Command types.
+#[cfg(windows)]
+trait SetEnv {
+    fn env(&mut self, key: &str, val: &str) -> &mut Self;
+}
+
+#[cfg(windows)]
+impl SetEnv for Command {
+    fn env(&mut self, key: &str, val: &str) -> &mut Self {
+        Command::env(self, key, val)
+    }
+}
+
+#[cfg(windows)]
+impl SetEnv for tokio::process::Command {
+    fn env(&mut self, key: &str, val: &str) -> &mut Self {
+        tokio::process::Command::env(self, key, val)
+    }
+}
+
 #[cfg(windows)]
 fn maybe_windows_cmd_shim(program: &OsStr) -> Option<OsString> {
     let path = Path::new(program);

src-tauri/src/terminal/manager.rs

@@ -92,11 +92,19 @@ fn detect_windows_shell_flavor(shell: &str) -> WindowsShellFlavor {
 fn configure_shell_command(cmd: &mut CommandBuilder, shell: &str, initial_command: Option<&str>) {
     #[cfg(target_os = "windows")]
     {
+        // Force UTF-8 output for all Windows shell flavors
+        cmd.env("PYTHONUTF8", "1");
+        cmd.env("PYTHONIOENCODING", "utf-8");
+
         match detect_windows_shell_flavor(shell) {
             WindowsShellFlavor::Cmd => {
                 if let Some(command) = initial_command {
                     cmd.env("CODEG_CMD", command);
-                    cmd.args(["/D", "/S", "/C", "%CODEG_CMD%"]);
+                    // Set UTF-8 code page before running the actual command
+                    cmd.args(["/D", "/S", "/C", "chcp 65001 >nul & %CODEG_CMD%"]);
+                } else {
+                    // /K runs the command then stays open for interactive use
+                    cmd.args(["/D", "/S", "/K", "chcp 65001 >nul"]);
                 }
             }
             WindowsShellFlavor::PowerShell => {
@@ -106,16 +114,24 @@ fn configure_shell_command(cmd: &mut CommandBuilder, shell: &str, initial_comman
                         "-NoLogo",
                         "-NoProfile",
                         "-Command",
-                        "$ErrorActionPreference = 'Stop'; Invoke-Expression $env:CODEG_CMD",
+                        "[Console]::OutputEncoding = [System.Text.Encoding]::UTF8; $ErrorActionPreference = 'Stop'; Invoke-Expression $env:CODEG_CMD",
                     ]);
                 } else {
-                    cmd.args(["-NoLogo", "-NoProfile"]);
+                    // -NoExit runs the command then stays open for interactive use
+                    cmd.args([
+                        "-NoLogo",
+                        "-NoProfile",
+                        "-NoExit",
+                        "-Command",
+                        "[Console]::OutputEncoding = [System.Text.Encoding]::UTF8; $host.UI.RawUI.WindowTitle = 'codeg'",
+                    ]);
                 }
             }
             WindowsShellFlavor::Posix => {
                 cmd.env("TERM", "xterm-256color");
                 cmd.env("COLORTERM", "truecolor");
                 cmd.env("TERM_PROGRAM", "codeg");
+                cmd.env("LANG", "C.UTF-8");
                 if let Some(command) = initial_command {
                     cmd.env("CODEG_CMD", command);
                     cmd.args(["-l", "-i", "-c", "eval \"$CODEG_CMD\""]);