Hide the console window of zmx children spawned by the Windows shell

Tools/windows/Tests/WindowsShell.Tests.ps1

@@ -599,6 +599,17 @@ Assert-Contract ($codespaceDialogSource -match 'WM_CTLCOLORLISTBOX' -and $codesp
 Assert-Contract ($codespaceDialogSource -match 'IsDialogMessageW') `
   "the codespace sheet must remain keyboard navigable"
 
+$zmxSessionSource = Get-Content -LiteralPath (Join-Path $shellRoot "src\ZmxSession.zig") -Raw
+$terminalSurfaceSource = Get-Content -LiteralPath (Join-Path $shellRoot "src\TerminalSurface.zig") -Raw
+$workspaceTeardownSource = Get-Content -LiteralPath (Join-Path $shellRoot "src\WorkspaceTeardown.zig") -Raw
+Assert-Contract ($zmxSessionSource -match '(?s)pub fn child\(.*?\.create_no_window = true;') `
+  "zmx children must be created without a console window"
+Assert-Contract ($terminalSurfaceSource -notmatch 'std\.process\.Child\.init\(' -and
+  $workspaceTeardownSource -notmatch 'std\.process\.Child\.init\(' -and
+  [regex]::Matches($terminalSurfaceSource, 'ZmxSession\.child\(').Count -eq 2 -and
+  [regex]::Matches($workspaceTeardownSource, 'ZmxSession\.child\(').Count -eq 1) `
+  "zmx attach, resize, and kill must spawn through ZmxSession.child so the GUI shell never opens a console window"
+
 $zig = Resolve-TestZig
 Invoke-Native "Accessibility contract executable tests" {
   Push-Location $shellRoot

graphcode-windows/src/TerminalSurface.zig

@@ -1564,11 +1564,7 @@ pub const Workspace = struct {
                 &session_buffer,
             )).len;
         }
-        var child = std.process.Child.init(attach_args[0..attach_len], self.allocator);
-        child.cwd = self.cwd;
-        child.stdin_behavior = .Pipe;
-        child.stdout_behavior = .Pipe;
-        child.stderr_behavior = .Ignore;
+        var child = ZmxSession.child(self.allocator, attach_args[0..attach_len], self.cwd, .attach);
         try child.spawn();
         if (child.stdin) |stdin| {
             var mode: c.DWORD = c.PIPE_NOWAIT;
@@ -1704,12 +1700,7 @@ pub const Workspace = struct {
                 self.setInputError("terminal PTY resize tracking allocation failed");
                 return;
             };
-            var child = std.process.Child.init(command, self.allocator);
-            child.cwd = self.cwd;
-            child.stdin_behavior = .Ignore;
-            child.stdout_behavior = .Ignore;
-            child.stderr_behavior = .Ignore;
-            child.create_no_window = true;
+            var child = ZmxSession.child(self.allocator, command, self.cwd, .control);
             child.spawn() catch {
                 self.allocator.free(session);
                 slot.attempted_resize_size = size;

graphcode-windows/src/WorkspaceTeardown.zig

@@ -342,10 +342,7 @@ pub const Live = struct {
         defer allocator.free(zmx);
         const argv = killArgv(allocator, zmx, ids) catch return 0;
         defer freeKillArgv(allocator, argv);
-        var child = std.process.Child.init(argv, allocator);
-        child.stdin_behavior = .Ignore;
-        child.stdout_behavior = .Ignore;
-        child.stderr_behavior = .Ignore;
+        var child = ZmxSession.child(allocator, argv, null, .control);
         _ = child.spawnAndWait() catch return 0;
         return ids.len;
     }

graphcode-windows/src/ZmxSession.zig

@@ -12,6 +12,50 @@ pub fn allocName(allocator: std.mem.Allocator, session: []const u8) ![]u8 {
     return std.fmt.allocPrint(allocator, prefix ++ "{s}", .{session});
 }
 
+pub const ChildStdio = enum {
+    /// `zmx attach`: the shell writes terminal input and reads terminal output.
+    attach,
+    /// One-shot control commands such as `resize` and `kill`.
+    control,
+};
+
+/// zmx.exe is a console-subsystem program. Spawned from the GUI shell without
+/// CREATE_NO_WINDOW, Windows allocates it a new console, which the default
+/// terminal host shows as a visible window that steals foreground.
+pub fn child(
+    allocator: std.mem.Allocator,
+    argv: []const []const u8,
+    cwd: ?[]const u8,
+    stdio: ChildStdio,
+) std.process.Child {
+    var result = std.process.Child.init(argv, allocator);
+    result.cwd = cwd;
+    result.stdin_behavior = if (stdio == .attach) .Pipe else .Ignore;
+    result.stdout_behavior = if (stdio == .attach) .Pipe else .Ignore;
+    result.stderr_behavior = .Ignore;
+    result.create_no_window = true;
+    return result;
+}
+
+test "zmx children keep their stdio contract and never open a console window" {
+    const attach_argv = [_][]const u8{ "zmx.exe", "attach", "graphcode-alpha", "--size", "80x24" };
+    const attach = child(std.testing.allocator, &attach_argv, "C:\\GraphCode\\bin", .attach);
+    try std.testing.expectEqual(std.process.Child.StdIo.Pipe, attach.stdin_behavior);
+    try std.testing.expectEqual(std.process.Child.StdIo.Pipe, attach.stdout_behavior);
+    try std.testing.expectEqual(std.process.Child.StdIo.Ignore, attach.stderr_behavior);
+    try std.testing.expectEqualStrings("C:\\GraphCode\\bin", attach.cwd.?);
+    try std.testing.expectEqual(attach_argv.len, attach.argv.len);
+    try std.testing.expectEqual(true, attach.create_no_window);
+
+    const kill_argv = [_][]const u8{ "zmx.exe", "kill", "graphcode-alpha" };
+    const control = child(std.testing.allocator, &kill_argv, null, .control);
+    try std.testing.expectEqual(std.process.Child.StdIo.Ignore, control.stdin_behavior);
+    try std.testing.expectEqual(std.process.Child.StdIo.Ignore, control.stdout_behavior);
+    try std.testing.expectEqual(std.process.Child.StdIo.Ignore, control.stderr_behavior);
+    try std.testing.expect(control.cwd == null);
+    try std.testing.expectEqual(true, control.create_no_window);
+}
+
 test "canonical zmx session names add the ownership prefix exactly once" {
     var storage: [64]u8 = undefined;
     try std.testing.expectEqualStrings("graphcode-alpha", try nameBuffer("alpha", &storage));