fix(windows): prevent Center() from stealing focus when StartHidden:true (#5249)

* fix(windows): prevent Center() from stealing focus when StartHidden is true

When StartHidden:true is set, the Center() method's SetWindowPos call
would activate the window and steal focus from the foreground application.
Adding SWP_NOACTIVATE to the flags prevents this behavior.

Fixes #4882

* test(4882): make Center() focus test a real regression guard

The previous test only OR'd together locally-redefined SWP_* constants and
never referenced Center(), so it passed even if form.go reverted to
SWP_NOSIZE only (per PR review). Replace it with an AST-based assertion that
parses form.go and verifies Center()'s SetWindowPos call still includes
SWP_NOACTIVATE. Runs on any OS (winc is Windows-only), and fails if the flag
is dropped.

---------

Co-authored-by: Wails Documentation Agent <agent@wails.local>
Co-authored-by: taliesin-ai <bot@taliesin.ai>

Author: 3 people

v2/internal/frontend/desktop/windows/winc/form.go

@@ -168,7 +168,7 @@ func (fm *Form) Center() {
 	winHeight := winRect.Bottom - winRect.Top
 	windowX := screenMiddleW - (winWidth / 2)
 	windowY := screenMiddleH - (winHeight / 2)
-	w32.SetWindowPos(fm.hwnd, w32.HWND_TOP, int(windowX), int(windowY), int(winWidth), int(winHeight), w32.SWP_NOSIZE)
+	w32.SetWindowPos(fm.hwnd, w32.HWND_TOP, int(windowX), int(windowY), int(winWidth), int(winHeight), w32.SWP_NOSIZE|w32.SWP_NOACTIVATE)
 }
 
 func (fm *Form) Fullscreen() {

v2/test/4882/center_noactivate_test.go

@@ -0,0 +1,87 @@
+package test
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"path/filepath"
+	"testing"
+)
+
+// formSource is the winc Form implementation that defines Center().
+const formSource = "../../internal/frontend/desktop/windows/winc/form.go"
+
+// TestCenterSetsNoActivate is the regression guard for #4882: launching an app
+// with StartHidden:true must not steal focus from the foreground window.
+// Form.Center() prevents that by passing SWP_NOACTIVATE to SetWindowPos.
+//
+// winc is Windows-only (build-tagged), so instead of linking it we assert
+// against the source of Center() directly: this fails if the flag is ever
+// dropped from that call, which is the exact regression that reintroduces the
+// bug. (The previous version of this test only OR'd together local copies of
+// the constants and would pass even if form.go reverted — see PR review.)
+func TestCenterSetsNoActivate(t *testing.T) {
+	fset := token.NewFileSet()
+	file, err := parser.ParseFile(fset, filepath.FromSlash(formSource), nil, 0)
+	if err != nil {
+		t.Fatalf("parsing %s: %v", formSource, err)
+	}
+
+	var center *ast.FuncDecl
+	for _, decl := range file.Decls {
+		fn, ok := decl.(*ast.FuncDecl)
+		if ok && fn.Recv != nil && fn.Name.Name == "Center" {
+			center = fn
+			break
+		}
+	}
+	if center == nil {
+		t.Fatalf("could not find Center() in %s", formSource)
+	}
+
+	var foundSetWindowPos, foundNoActivate bool
+	ast.Inspect(center, func(n ast.Node) bool {
+		call, ok := n.(*ast.CallExpr)
+		if !ok {
+			return true
+		}
+		sel, ok := call.Fun.(*ast.SelectorExpr)
+		if !ok || sel.Sel.Name != "SetWindowPos" {
+			return true
+		}
+		foundSetWindowPos = true
+		for _, arg := range call.Args {
+			if exprReferences(arg, "SWP_NOACTIVATE") {
+				foundNoActivate = true
+			}
+		}
+		return true
+	})
+
+	if !foundSetWindowPos {
+		t.Fatal("Center() no longer calls SetWindowPos; update this regression guard")
+	}
+	if !foundNoActivate {
+		t.Error("Center()'s SetWindowPos call is missing SWP_NOACTIVATE — this reintroduces the StartHidden focus-steal bug (#4882)")
+	}
+}
+
+// exprReferences reports whether expr references an identifier with the given
+// name, e.g. the w32.SWP_NOACTIVATE term inside a bitwise-or of flags.
+func exprReferences(expr ast.Expr, name string) bool {
+	found := false
+	ast.Inspect(expr, func(n ast.Node) bool {
+		switch v := n.(type) {
+		case *ast.SelectorExpr:
+			if v.Sel.Name == name {
+				found = true
+			}
+		case *ast.Ident:
+			if v.Name == name {
+				found = true
+			}
+		}
+		return !found
+	})
+	return found
+}