Default dashboard thumbnails to PNG

PNG screenshots are now the default for dashboard previews,
with SVG available by setting WEBTERM_SCREENSHOT_MODE=svg.
Documentation and tests updated accordingly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

README.md

@@ -13,7 +13,7 @@ https://github.com/user-attachments/assets/62c52183-83a3-4fb5-97b1-ed001de4f53a
 - Typeahead find for quickly finding and launching sessions with minimal friction
 - Web terminal with reconnect support
 - Ghostty WebAssembly terminal engine for fast rendering from [`ghostty-web`](https://github.com/rcarmo/ghostty-web)
-- Session dashboard with live SVG (or optional PNG) screenshots from [`go-te`](https://github.com/rcarmo/go-te)
+- Session dashboard with live PNG (or optional SVG) screenshots from [`go-te`](https://github.com/rcarmo/go-te)
 - Docker watch mode (`webterm-command` / `webterm-theme` labels)
 - Docker compose manifest ingestion
 - CPU sparkline tiles for compose services
@@ -97,7 +97,7 @@ go run ./cmd/webterm -- --compose-manifest ./docker-compose.yaml
 - `WEBTERM_DOCKER_USERNAME`: user for Docker exec sessions
 - `WEBTERM_DOCKER_AUTO_COMMAND`: override auto command (`/bin/bash` default)
 - `WEBTERM_SCREENSHOT_FORCE_REDRAW`: force redraw before screenshots (`true/1/yes/on`)
-- `WEBTERM_SCREENSHOT_MODE`: screenshot format for dashboard thumbnails (`svg` default, set `png` to enable PNG)
+- `WEBTERM_SCREENSHOT_MODE`: screenshot format for dashboard thumbnails (`png` default, set `svg` to use SVG)
 - `DOCKER_HOST`: Docker daemon endpoint override
 
 ## Development (Makefile-first)

docs/ARCHITECTURE.md

@@ -35,7 +35,7 @@ webterm/server.go (LocalServer)
    - live WS stream (`stdout`)
    - replay buffer (reconnect support)
    - terminal-state tracker (`go-te`) for screenshots
-4. Dashboard pulls `/screenshot.svg` (default) or `/screenshot.png` when `WEBTERM_SCREENSHOT_MODE=png`, and listens on `/events` for activity.
+4. Dashboard pulls `/screenshot.png` (default) or `/screenshot.svg` when `WEBTERM_SCREENSHOT_MODE=svg`, and listens on `/events` for activity.
 
 ## Static assets
 

webterm/server.go

@@ -240,8 +240,8 @@ func NewLocalServer(config Config, options ServerOptions) *LocalServer {
 		fontSize = DefaultFontSize
 	}
 	screenshotMode := strings.ToLower(strings.TrimSpace(os.Getenv(ScreenshotModeEnv)))
-	if screenshotMode != "png" {
-		screenshotMode = "svg"
+	if screenshotMode != "svg" {
+		screenshotMode = "png"
 	}
 	apps := append([]App{}, config.Apps...)
 	for _, app := range options.LandingApps {

webterm/server_test.go

@@ -456,7 +456,6 @@ func TestScreenshotAndETag(t *testing.T) {
 }
 
 func TestScreenshotPNGAndETag(t *testing.T) {
-	t.Setenv(ScreenshotModeEnv, "png")
 	server, httpServer, _ := newServerForTests(t, false)
 	if _, err := server.sessionManager.NewSession("shell", "sid", "shell", 80, 24); err != nil {
 		t.Fatalf("NewSession error = %v", err)
@@ -534,13 +533,13 @@ func TestDashboardIncludesContextMenuSanitizedDownload(t *testing.T) {
 	if !strings.Contains(text, "contextmenu") || !strings.Contains(text, "sanitize_font_urls=1&download=1") {
 		t.Fatalf("expected contextmenu sanitized download wiring in dashboard page")
 	}
-	if !strings.Contains(text, "screenshot.svg") {
-		t.Fatalf("expected dashboard to request svg screenshots by default")
+	if !strings.Contains(text, "screenshot.png") {
+		t.Fatalf("expected dashboard to request png screenshots by default")
 	}
 }
 
-func TestDashboardUsesPNGWhenEnabled(t *testing.T) {
-	t.Setenv(ScreenshotModeEnv, "png")
+func TestDashboardUsesSVGWhenConfigured(t *testing.T) {
+	t.Setenv(ScreenshotModeEnv, "svg")
 	_, httpServer, _ := newServerForTests(t, true)
 	resp, err := http.Get(httpServer.URL + "/")
 	if err != nil {
@@ -549,8 +548,8 @@ func TestDashboardUsesPNGWhenEnabled(t *testing.T) {
 	body, _ := io.ReadAll(resp.Body)
 	_ = resp.Body.Close()
 	text := string(body)
-	if !strings.Contains(text, "screenshot.png") {
-		t.Fatalf("expected dashboard to request png screenshots when enabled")
+	if !strings.Contains(text, "screenshot.svg") {
+		t.Fatalf("expected dashboard to request svg screenshots when configured")
 	}
 	if !strings.Contains(text, "sanitize_font_urls=1&download=1") || !strings.Contains(text, "screenshot.svg") {
 		t.Fatalf("expected contextmenu downloads to use svg screenshots")