feat: auto-toggle Chromium app mode for small viewports

images/chromium-headful/Dockerfile

@@ -146,7 +146,7 @@ RUN --mount=type=cache,target=/tmp/cache/ffmpeg,sharing=locked,id=$CACHEIDPREFIX
     rm -rf /tmp/ffmpeg*
 EOT
 
-FROM ghcr.io/kernel/neko/base:3.0.8-v1.3.0 AS neko
+FROM ghcr.io/kernel/neko/base:3.0.8-v1.4.0 AS neko
 # ^--- now has event.SYSTEM_PONG with legacy support to keepalive
 FROM node:22-bullseye-slim AS node-22
 FROM docker.io/ubuntu:22.04

images/chromium-headful/xorg.conf

@@ -66,6 +66,10 @@ Section "Monitor"
   Modeline "960x720_60.00" 55.86 960 1008 1104 1248 720 721 724 746 -HSync +Vsync
   # 800x600 @ 60.00 Hz (GTF) hsync: 37.32 kHz; pclk: 38.22 MHz
   Modeline "800x600_60.00" 38.22 800 832 912 1024 600 601 604 622 -HSync +Vsync
+  # 768x1024 @ 60.00 Hz (GTF) hsync: 63.60 kHz; pclk: 65.13 MHz
+  Modeline "768x1024_60.00" 65.13 768 816 896 1024 1024 1025 1028 1060 -HSync +Vsync
+  # 390x844 @ 60.00 Hz (manual, non-CVT) pclk: 27.26 MHz (mobile: iPhone 14/15)
+  Modeline "390x844_60.00" 27.26 390 406 446 520 844 845 848 874 -HSync +Vsync
   # 2560x1440 @ 60.00 Hz (GTF) hsync: 89.52 kHz; pclk: 312.25 MHz
   Modeline "2560x1440_60.00" 312.25 2560 2752 3024 3488 1440 1443 1448 1493 -HSync +Vsync
   # 1024x768 @ 60.00 Hz (GTF) hsync: 47.70 kHz; pclk: 63.50 MHz
@@ -89,6 +93,10 @@ Section "Monitor"
   Modeline "960x720_30.00" 25.33 960 960 1056 1152 720 721 724 733 -HSync +Vsync
   # 800x600 @ 30.00 Hz (GTF) hsync: 18.33 kHz; pclk: 17.01 MHz
   Modeline "800x600_30.00" 17.01 800 792 864 928 600 601 604 611 -HSync +Vsync
+  # 768x1024 @ 30.00 Hz (GTF) hsync: 31.26 kHz; pclk: 30.01 MHz
+  Modeline "768x1024_30.00" 30.01 768 784 864 960 1024 1025 1028 1042 -HSync +Vsync
+  # 390x844 @ 30.00 Hz (manual, non-CVT) pclk: 12.57 MHz (mobile: iPhone 14/15)
+  Modeline "390x844_30.00" 12.57 390 406 446 488 844 845 848 859 -HSync +Vsync
   # 1920x1200 @ 30.00 Hz (GTF) hsync: 36.90 kHz; pclk: 96.00 MHz
   Modeline "1920x1200_30.00" 96.00 1920 2000 2200 2528 1200 1203 1209 1235 -HSync +Vsync
   # 1440x900 @ 30.00 Hz (GTF) hsync: 27.72 kHz; pclk: 52.80 MHz
@@ -120,6 +128,10 @@ Section "Monitor"
   Modeline "1200x800_25.00" 31.48 1200 1224 1352 1540 800 801 804 818 -HSync +Vsync
   # 800x1600 @ 24.92 Hz (CVT) hsync: 40.53 kHz; pclk: 41.50 MHz
   Modeline "800x1600_25.00"   41.50  800 832 912 1024  1600 1603 1613 1626 -Hsync +Vsync
+  # 768x1024 @ 25.00 Hz (GTF) hsync: 25.97 kHz; pclk: 24.52 MHz
+  Modeline "768x1024_25.00" 24.52 768 784 856 944 1024 1025 1028 1039 -HSync +Vsync
+  # 390x844 @ 25.00 Hz (manual, non-CVT) pclk: 11.14 MHz (mobile: iPhone 14/15)
+  Modeline "390x844_25.00" 11.14 390 406 446 520 844 845 848 857 -HSync +Vsync
 
   # 2560x1440 @ 10.00 Hz (GTF) hsync: 14.65 kHz; pclk: 48.76 MHz
   Modeline "2560x1440_10.00" 48.76 2560 2568 2816 3104 1440 1441 1444 1465 -HSync +Vsync
@@ -143,7 +155,7 @@ Section "Screen"
   SubSection "Display"
     Viewport 0 0
     Depth 24
-    Modes "2560x1440_60.00" "1920x1080_60.00" "1920x1200_60.00" "1440x900_60.00" "1280x720_60.00" "1200x800_60.00" "1152x648_60.00" "1024x768_60.00" "1024x576_60.00" "960x720_60.00" "800x600_60.00" "2560x1440_30.00" "1920x1080_30.00" "1920x1200_30.00" "1440x900_30.00" "1368x768_30.00" "1280x720_30.00" "1200x800_30.00" "1152x648_30.00" "1024x768_30.00" "1024x576_30.00" "960x720_30.00" "800x600_30.00" "800x1600_30.00" "3840x2160_25.00" "2560x1440_25.00" "1920x1080_25.00" "1920x1200_25.00" "1600x900_25.00" "1440x900_25.00" "1368x768_25.00" "1200x800_25.00" "1024x768_25.00" "800x1600_25.00" "2560x1440_10.00" "1920x1080_10.00" "1920x1200_10.00" "1440x900_10.00" "1200x800_10.00" "1024x768_10.00"
+    Modes "2560x1440_60.00" "1920x1080_60.00" "1920x1200_60.00" "1440x900_60.00" "1280x720_60.00" "1200x800_60.00" "1152x648_60.00" "1024x768_60.00" "1024x576_60.00" "960x720_60.00" "800x600_60.00" "768x1024_60.00" "390x844_60" "2560x1440_30.00" "1920x1080_30.00" "1920x1200_30.00" "1440x900_30.00" "1368x768_30.00" "1280x720_30.00" "1200x800_30.00" "1152x648_30.00" "1024x768_30.00" "1024x576_30.00" "960x720_30.00" "800x600_30.00" "800x1600_30.00" "768x1024_30.00" "390x844_30" "3840x2160_25.00" "2560x1440_25.00" "1920x1080_25.00" "1920x1200_25.00" "1600x900_25.00" "1440x900_25.00" "1368x768_25.00" "1200x800_25.00" "1024x768_25.00" "800x1600_25.00" "768x1024_25.00" "390x844_25" "2560x1440_10.00" "1920x1080_10.00" "1920x1200_10.00" "1440x900_10.00" "1200x800_10.00" "1024x768_10.00"
   EndSubSection
 EndSection
 

server/.gitignore

@@ -28,6 +28,7 @@ go.work
 
 .tmp/
 bin/
+chromium-launcher
 recordings/
 
 # downconverted openapi spec

server/cmd/api/api/chromium.go

@@ -21,6 +21,15 @@ import (
 
 var nameRegex = regexp.MustCompile(`^[A-Za-z0-9._-]{1,255}$`)
 
+const (
+	// chromiumFlagsPath is the runtime flags file read by the chromium-launcher at startup.
+	chromiumFlagsPath = "/chromium/flags"
+
+	// appModeURL is the URL loaded in --app mode for small viewports. Keep in
+	// sync with "NewTabPageLocation" in shared/chromium-policies/managed/policy.json.
+	appModeURL = "https://start.duckduckgo.com"
+)
+
 // UploadExtensionsAndRestart handles multipart upload of one or more extension zips, extracts
 // them under /home/kernel/extensions/<name>, writes /chromium/flags to enable them, restarts
 // Chromium via supervisord, and waits (via UpstreamManager) until DevTools is ready.
@@ -291,14 +300,12 @@ func (s *ApiService) UploadExtensionsAndRestart(ctx context.Context, request oap
 }
 
 // mergeAndWriteChromiumFlags reads existing flags, merges them with new flags,
-// and writes the result back to /chromium/flags. Returns the merged tokens or an error.
+// and writes the result back to chromiumFlagsPath. Returns the merged tokens or an error.
 func (s *ApiService) mergeAndWriteChromiumFlags(ctx context.Context, newTokens []string) ([]string, error) {
 	log := logger.FromContext(ctx)
 
-	const flagsPath = "/chromium/flags"
-
-	// Read existing runtime flags from /chromium/flags (if any)
-	existingTokens, err := chromiumflags.ReadOptionalFlagFile(flagsPath)
+	// Read existing runtime flags (if any)
+	existingTokens, err := chromiumflags.ReadOptionalFlagFile(chromiumFlagsPath)
 	if err != nil {
 		log.Error("failed to read existing flags", "error", err)
 		return nil, fmt.Errorf("failed to read existing flags: %w", err)
@@ -309,22 +316,27 @@ func (s *ApiService) mergeAndWriteChromiumFlags(ctx context.Context, newTokens [
 	// Merge existing flags with new flags using token-aware API
 	mergedTokens := chromiumflags.MergeFlags(existingTokens, newTokens)
 
-	// Ensure the chromium directory exists
-	if err := os.MkdirAll("/chromium", 0o755); err != nil {
-		log.Error("failed to create chromium dir", "error", err)
-		return nil, fmt.Errorf("failed to create chromium dir: %w", err)
-	}
-
-	// Write flags file with merged flags
-	if err := chromiumflags.WriteFlagFile(flagsPath, mergedTokens); err != nil {
+	if err := writeChromiumFlags(mergedTokens); err != nil {
 		log.Error("failed to write flags", "error", err)
-		return nil, fmt.Errorf("failed to write flags: %w", err)
+		return nil, err
 	}
 
 	log.Info("flags written", "merged", mergedTokens)
 	return mergedTokens, nil
 }
 
+// writeChromiumFlags ensures the /chromium directory exists and writes tokens
+// to chromiumFlagsPath. Shared by mergeAndWriteChromiumFlags and ensureAppMode.
+func writeChromiumFlags(tokens []string) error {
+	if err := os.MkdirAll("/chromium", 0o755); err != nil {
+		return fmt.Errorf("failed to create chromium dir: %w", err)
+	}
+	if err := chromiumflags.WriteFlagFile(chromiumFlagsPath, tokens); err != nil {
+		return fmt.Errorf("failed to write flags file: %w", err)
+	}
+	return nil
+}
+
 // restartChromiumAndWait restarts Chromium via supervisorctl and waits for DevTools to be ready.
 // Returns an error if the restart fails or times out.
 func (s *ApiService) restartChromiumAndWait(ctx context.Context, operation string) error {

server/cmd/api/api/display.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	nekooapi "github.com/m1k1o/neko/server/lib/oapi"
+	"github.com/onkernel/kernel-images/server/lib/chromiumflags"
 	"github.com/onkernel/kernel-images/server/lib/logger"
 	oapi "github.com/onkernel/kernel-images/server/lib/oapi"
 )
@@ -88,6 +89,21 @@ func (s *ApiService) PatchDisplay(ctx context.Context, req oapi.PatchDisplayRequ
 		restartChrome = *req.Body.RestartChromium
 	}
 
+	// App mode: Chromium's --app flag removes the tab bar and toolbar chrome,
+	// allowing the window to resize below the normal ~500px minimum width
+	// and ~200px minimum height.
+	// We automatically toggle this based on the requested viewport dimensions.
+	const appModeWidthThreshold = 500
+	const appModeHeightThreshold = 200
+	needsAppMode := width < appModeWidthThreshold || height < appModeHeightThreshold
+	if toggled, err := s.ensureAppMode(ctx, needsAppMode); err != nil {
+		log.Error("failed to toggle app mode", "error", err)
+		// Non-fatal: continue with the resize even if app mode toggle fails.
+	} else if toggled {
+		// App mode changed — force a chromium restart so it picks up the new flags.
+		restartChrome = true
+	}
+
 	// Route to appropriate resolution change handler
 	if displayMode == "xorg" {
 		if s.isNekoEnabled() {
@@ -390,3 +406,55 @@ func (s *ApiService) setResolutionViaNeko(ctx context.Context, width, height, re
 	log.Info("successfully changed resolution via Neko API", "width", width, "height", height, "refresh_rate", refreshRate)
 	return nil
 }
+
+// ensureAppMode adds or removes the --app flag from the Chromium runtime flags
+// file. When enabling, any existing --app flag is removed first so the URL is
+// always exactly appModeURL (defined in chromium.go). It returns (true, nil)
+// when the flag state was changed (meaning Chromium needs a restart), or
+// (false, nil) when no change was needed.
+func (s *ApiService) ensureAppMode(ctx context.Context, enable bool) (toggled bool, err error) {
+	log := logger.FromContext(ctx)
+	const appPrefix = "--app"
+	wantFlag := appPrefix + "=" + appModeURL
+
+	existing, err := chromiumflags.ReadOptionalFlagFile(chromiumFlagsPath)
+	if err != nil {
+		return false, fmt.Errorf("failed to read flags file: %w", err)
+	}
+
+	// Always strip any --app/--app=... flags so we can compare cleanly.
+	stripped := chromiumflags.RemoveFlagsByPrefix(existing, appPrefix)
+
+	if enable {
+		updated := append(stripped, wantFlag)
+		// If the exact flag was already present and nothing else changed, no-op.
+		if chromiumflags.HasFlagWithPrefix(existing, appPrefix) && len(updated) == len(existing) {
+			// Check the existing flag is the exact one we want.
+			for _, tok := range existing {
+				if tok == wantFlag {
+					log.Info("app mode already enabled with correct URL, no change needed")
+					return false, nil
+				}
+			}
+		}
+		log.Info("enabling app mode for small viewport", "flag", wantFlag)
+		if err := writeChromiumFlags(updated); err != nil {
+			return false, err
+		}
+		log.Info("app mode toggled", "enabled", true, "flags", updated)
+		return true, nil
+	}
+
+	// Disabling: if nothing was stripped, already disabled.
+	if len(stripped) == len(existing) {
+		log.Info("app mode already disabled, no change needed")
+		return false, nil
+	}
+
+	log.Info("disabling app mode for normal viewport")
+	if err := writeChromiumFlags(stripped); err != nil {
+		return false, err
+	}
+	log.Info("app mode toggled", "enabled", false, "flags", stripped)
+	return true, nil
+}

server/cmd/chromium-launcher/main.go

@@ -116,6 +116,7 @@ func main() {
 	}
 }
 
+
 // execLookPath helps satisfy syscall.Exec's requirement to pass an absolute path.
 func execLookPath(file string) (string, error) {
 	if strings.ContainsRune(file, os.PathSeparator) {

server/cmd/chromium-launcher/main_test.go

@@ -34,3 +34,4 @@ func TestExecLookPath(t *testing.T) {
 		t.Fatalf("execLookPath PATH search failed: p=%q err=%v", p, err)
 	}
 }
+

server/go.mod

@@ -101,4 +101,4 @@ require (
 	modernc.org/sqlite v1.23.1 // indirect
 )
 
-replace github.com/m1k1o/neko/server => github.com/onkernel/neko/server v0.0.0-20251008185748-46e2fc7d3866
+replace github.com/m1k1o/neko/server => github.com/onkernel/neko/server v0.0.0-20260213021128-abe9ac59a634

server/go.sum

@@ -133,8 +133,8 @@ github.com/oasdiff/yaml v0.0.0-20250309154309-f31be36b4037 h1:G7ERwszslrBzRxj//J
 github.com/oasdiff/yaml v0.0.0-20250309154309-f31be36b4037/go.mod h1:2bpvgLBZEtENV5scfDFEtB/5+1M4hkQhDQrccEJ/qGw=
 github.com/oasdiff/yaml3 v0.0.0-20250309153720-d2182401db90 h1:bQx3WeLcUWy+RletIKwUIt4x3t8n2SxavmoclizMb8c=
 github.com/oasdiff/yaml3 v0.0.0-20250309153720-d2182401db90/go.mod h1:y5+oSEHCPT/DGrS++Wc/479ERge0zTFxaF8PbGKcg2o=
-github.com/onkernel/neko/server v0.0.0-20251008185748-46e2fc7d3866 h1:Cix/sgZLCsavpiTFxDLPbUOXob50IekCg5mgh+i4D4Q=
-github.com/onkernel/neko/server v0.0.0-20251008185748-46e2fc7d3866/go.mod h1:0+zactiySvtKwfe5JFjyNrSuQLA+EEPZl5bcfcZf1RM=
+github.com/onkernel/neko/server v0.0.0-20260213021128-abe9ac59a634 h1:Q8v6O/VRVLKcEHMSGC0ItDmLFShKLny/0bBggC/1jjk=
+github.com/onkernel/neko/server v0.0.0-20260213021128-abe9ac59a634/go.mod h1:0+zactiySvtKwfe5JFjyNrSuQLA+EEPZl5bcfcZf1RM=
 github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8Oi/yOhh5U=
 github.com/opencontainers/go-digest v1.0.0/go.mod h1:0JzlMkj0TRzQZfJkVvzbP0HBR3IKzErnv2BNG4W4MAM=
 github.com/opencontainers/image-spec v1.1.1 h1:y0fUlFfIZhPF1W537XOLg0/fcx6zcHCJwooC2xJA040=

server/lib/chromiumflags/chromiumflags.go

@@ -224,6 +224,31 @@ func MergeExtensionPath(args []string, extPath string) []string {
 	return result
 }
 
+// RemoveFlagsByPrefix returns a new slice with any tokens that match the given
+// prefix removed. For example, prefix "--app" removes "--app", "--app=about:blank", etc.
+// It does NOT match longer flag names that merely share the prefix
+// (e.g. "--app" will not match "--application-name").
+func RemoveFlagsByPrefix(tokens []string, prefix string) []string {
+	out := make([]string, 0, len(tokens))
+	for _, tok := range tokens {
+		if tok == prefix || strings.HasPrefix(tok, prefix+"=") {
+			continue
+		}
+		out = append(out, tok)
+	}
+	return out
+}
+
+// HasFlagWithPrefix returns true if any token equals prefix or starts with prefix + "=".
+func HasFlagWithPrefix(tokens []string, prefix string) bool {
+	for _, tok := range tokens {
+		if tok == prefix || strings.HasPrefix(tok, prefix+"=") {
+			return true
+		}
+	}
+	return false
+}
+
 // WriteFlagFile writes the provided tokens to the given path as JSON in the
 // form: { "flags": ["--foo", "--bar=1"] } with file mode 0644.
 // The function creates or truncates the file.

server/lib/chromiumflags/chromiumflags_test.go

@@ -7,6 +7,8 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestParseFlags(t *testing.T) {
@@ -214,6 +216,62 @@ func TestWriteFlagFileAndReadBack(t *testing.T) {
 
 // TestWriteFlagFileFromString removed: callers should use WriteFlagFile with tokens.
 
+func TestRemoveFlagsByPrefix(t *testing.T) {
+	tests := []struct {
+		name   string
+		tokens []string
+		prefix string
+		want   []string
+	}{
+		{
+			name:   "remove exact match",
+			tokens: []string{"--foo", "--app", "--bar"},
+			prefix: "--app",
+			want:   []string{"--foo", "--bar"},
+		},
+		{
+			name:   "remove prefix=value match",
+			tokens: []string{"--foo", "--app=about:blank", "--bar"},
+			prefix: "--app",
+			want:   []string{"--foo", "--bar"},
+		},
+		{
+			name:   "does not remove longer flag names",
+			tokens: []string{"--foo", "--application-name=test", "--app=about:blank"},
+			prefix: "--app",
+			want:   []string{"--foo", "--application-name=test"},
+		},
+		{
+			name:   "nothing to remove",
+			tokens: []string{"--foo", "--bar"},
+			prefix: "--app",
+			want:   []string{"--foo", "--bar"},
+		},
+		{
+			name:   "empty input",
+			tokens: []string{},
+			prefix: "--app",
+			want:   []string{},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := RemoveFlagsByPrefix(tt.tokens, tt.prefix)
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("RemoveFlagsByPrefix() = %#v, want %#v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestHasFlagWithPrefix(t *testing.T) {
+	assert.True(t, HasFlagWithPrefix([]string{"--app=about:blank", "--foo"}, "--app"))
+	assert.True(t, HasFlagWithPrefix([]string{"--foo", "--app"}, "--app"))
+	assert.False(t, HasFlagWithPrefix([]string{"--application-name=test"}, "--app"))
+	assert.False(t, HasFlagWithPrefix([]string{"--foo", "--bar"}, "--app"))
+	assert.False(t, HasFlagWithPrefix([]string{}, "--app"))
+}
+
 func TestMergeFlags(t *testing.T) {
 	tests := []struct {
 		name         string