fix(desktop): agent shells inherit a UTF-8 locale on macOS

apps/desktop/src/shell/DesktopShellEnvironment.test.ts

@@ -152,6 +152,108 @@ describe("DesktopShellEnvironment", () => {
     }),
   );
 
+  it.effect("hydrates the locale from the login shell on macOS", () =>
+    Effect.gen(function* () {
+      const env: NodeJS.ProcessEnv = {
+        SHELL: "/bin/zsh",
+        PATH: "/usr/bin",
+      };
+
+      yield* runShellEnvironment({
+        env,
+        platform: "darwin",
+        handler: () =>
+          envOutput({
+            PATH: "/opt/homebrew/bin:/usr/bin",
+            LANG: "de_DE.UTF-8",
+          }),
+      });
+
+      assert.equal(env.LANG, "de_DE.UTF-8");
+    }),
+  );
+
+  it.effect("preserves an inherited locale over the login shell on macOS", () =>
+    Effect.gen(function* () {
+      const env: NodeJS.ProcessEnv = {
+        SHELL: "/bin/zsh",
+        PATH: "/usr/bin",
+        LANG: "en_US.UTF-8",
+      };
+
+      yield* runShellEnvironment({
+        env,
+        platform: "darwin",
+        handler: () =>
+          envOutput({
+            PATH: "/opt/homebrew/bin:/usr/bin",
+            LANG: "de_DE.UTF-8",
+          }),
+      });
+
+      assert.equal(env.LANG, "en_US.UTF-8");
+    }),
+  );
+
+  it.effect("does not mix login-shell locale categories into an inherited locale", () =>
+    Effect.gen(function* () {
+      const env: NodeJS.ProcessEnv = {
+        SHELL: "/bin/zsh",
+        PATH: "/usr/bin",
+        LANG: "en_US.UTF-8",
+      };
+
+      yield* runShellEnvironment({
+        env,
+        platform: "darwin",
+        handler: () =>
+          envOutput({
+            PATH: "/opt/homebrew/bin:/usr/bin",
+            LC_ALL: "de_DE.UTF-8",
+          }),
+      });
+
+      assert.equal(env.LANG, "en_US.UTF-8");
+      assert.equal(env.LC_ALL, undefined);
+    }),
+  );
+
+  it.effect("falls back to a UTF-8 LC_CTYPE when no locale is available on macOS", () =>
+    Effect.gen(function* () {
+      const env: NodeJS.ProcessEnv = {
+        SHELL: "/bin/zsh",
+        PATH: "/usr/bin",
+      };
+
+      yield* runShellEnvironment({
+        env,
+        platform: "darwin",
+        handler: () => envOutput({ PATH: "/opt/homebrew/bin:/usr/bin" }),
+      });
+
+      assert.equal(env.LANG, undefined);
+      assert.equal(env.LC_ALL, undefined);
+      assert.equal(env.LC_CTYPE, "en_US.UTF-8");
+    }),
+  );
+
+  it.effect("does not apply the locale fallback on linux", () =>
+    Effect.gen(function* () {
+      const env: NodeJS.ProcessEnv = {
+        SHELL: "/bin/zsh",
+        PATH: "/usr/bin",
+      };
+
+      yield* runShellEnvironment({
+        env,
+        platform: "linux",
+        handler: () => envOutput({ PATH: "/home/linuxbrew/.linuxbrew/bin:/usr/bin" }),
+      });
+
+      assert.equal(env.LANG, undefined);
+    }),
+  );
+
   it.effect("hydrates PATH and missing SSH_AUTH_SOCK from the login shell on linux", () =>
     Effect.gen(function* () {
       const env: NodeJS.ProcessEnv = {

apps/desktop/src/shell/DesktopShellEnvironment.ts

@@ -71,6 +71,9 @@ const LOGIN_SHELL_ENV_NAMES = [
   "PATH",
   "DBUS_SESSION_BUS_ADDRESS",
   "DISPLAY",
+  "LANG",
+  "LC_ALL",
+  "LC_CTYPE",
   "SSH_AUTH_SOCK",
   "HOMEBREW_PREFIX",
   "HOMEBREW_CELLAR",
@@ -84,6 +87,8 @@ const LOGIN_SHELL_ENV_NAMES = [
   "WAYLAND_DISPLAY",
 ] as const;
 const WINDOWS_PROFILE_ENV_NAMES = ["PATH", "FNM_DIR", "FNM_MULTISHELL_PATH"] as const;
+const LOCALE_ENV_NAMES = ["LANG", "LC_ALL", "LC_CTYPE"] as const;
+const FALLBACK_LC_CTYPE = "en_US.UTF-8";
 const WINDOWS_SHELL_CANDIDATES = ["pwsh.exe", "powershell.exe"] as const;
 const LOGIN_SHELL_TIMEOUT = Duration.seconds(5);
 const LAUNCHCTL_TIMEOUT = Duration.seconds(2);
@@ -472,6 +477,29 @@ const installPosixEnvironment = Effect.fn("desktop.shellEnvironment.installPosix
       }
     }
 
+    // Locale variables form one precedence group: LC_ALL can override an inherited
+    // LANG or LC_CTYPE, so only hydrate the group when the process has none of them.
+    if (
+      config.platform === "darwin" &&
+      LOCALE_ENV_NAMES.every((name) => Option.isNone(trimNonEmpty(config.env[name])))
+    ) {
+      for (const name of LOCALE_ENV_NAMES) {
+        const value = trimNonEmpty(shellEnvironment[name]);
+        if (Option.isSome(value)) {
+          config.env[name] = value.value;
+        }
+      }
+
+      // GUI launches inherit no locale from launchd, so spawned agents land in the C
+      // locale and pbcopy decodes their UTF-8 output as MacRoman. Older supported
+      // macOS releases do not provide C.UTF-8, so set only LC_CTYPE to a UTF-8 locale
+      // available on those releases. Leaving LANG unset keeps C-stable collation and
+      // formatting, so output parsing is unaffected.
+      if (LOCALE_ENV_NAMES.every((name) => Option.isNone(trimNonEmpty(config.env[name])))) {
+        config.env.LC_CTYPE = FALLBACK_LC_CTYPE;
+      }
+    }
+
     if (
       config.platform === "linux" &&
       Option.isNone(trimNonEmpty(config.env.DBUS_SESSION_BUS_ADDRESS))