diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0b47f3c..a6e4d55 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,6 +17,11 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Install Linux dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libayatana-appindicator3-dev libgtk-3-dev
+
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
@@ -39,6 +44,12 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Install Linux dependencies
+        if: matrix.os == 'ubuntu-latest'
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libayatana-appindicator3-dev libgtk-3-dev
+
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
@@ -47,7 +58,13 @@ jobs:
       - name: Get dependencies
         run: go mod download
 
-      - name: Run tests
+      - name: Run tests (Unix)
+        if: matrix.os != 'windows-latest'
+        run: go test -race -coverprofile=coverage.out -covermode=atomic ./...
+
+      - name: Run tests (Windows)
+        if: matrix.os == 'windows-latest'
+        shell: cmd
         run: go test -race -coverprofile=coverage.out -covermode=atomic ./...
 
       - name: Upload coverage to Codecov
@@ -69,6 +86,12 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Install Linux dependencies
+        if: matrix.os == 'ubuntu-latest'
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libayatana-appindicator3-dev libgtk-3-dev
+
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
@@ -107,6 +130,12 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Install Linux dependencies
+        if: matrix.os == 'ubuntu-latest'
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libayatana-appindicator3-dev libgtk-3-dev
+
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
diff --git a/internal/systray/systray.go b/internal/systray/systray.go
index 7dae9fc..435b4ec 100644
--- a/internal/systray/systray.go
+++ b/internal/systray/systray.go
@@ -1390,6 +1390,8 @@ func (a *App) installCLIToPathWindows(sourcePath, targetPath string) {
 }
 
 // uninstallCLI removes the CLI binary from the system path.
+//
+//nolint:unused // Reserved for future use in systray menu
 func (a *App) uninstallCLI() bool {
 	targetPath := "/usr/local/bin/agentmgr"
 
diff --git a/internal/systray/windows_other.go b/internal/systray/windows_other.go
index 2e23e2b..73e7c6e 100644
--- a/internal/systray/windows_other.go
+++ b/internal/systray/windows_other.go
@@ -2,7 +2,10 @@
 
 package systray
 
-import "github.com/kevinelliott/agentmgr/pkg/agent"
+import (
+	"github.com/kevinelliott/agentmgr/pkg/agent"
+	"github.com/kevinelliott/agentmgr/pkg/catalog"
+)
 
 // showNativeSettingsWindow is not available on this platform.
 func (a *App) showNativeSettingsWindow() {
@@ -10,6 +13,11 @@ func (a *App) showNativeSettingsWindow() {
 	a.showSettings()
 }
 
+// showNativeManageAgentsWindow is not available on this platform.
+func (a *App) showNativeManageAgentsWindow(_ []catalog.AgentDef, _ []agent.Installation) {
+	// No-op on non-darwin platforms; caller should check hasNativeWindowSupport()
+}
+
 // showNativeAgentDetailsWindow is not available on this platform.
 func (a *App) showNativeAgentDetailsWindow(inst agent.Installation) {
 	// Fall back to platform-specific dialog
diff --git a/pkg/platform/linux.go b/pkg/platform/linux.go
index 762357f..48b2ece 100644
--- a/pkg/platform/linux.go
+++ b/pkg/platform/linux.go
@@ -34,7 +34,10 @@ func (l *linuxPlatform) GetDataDir() string {
 	if xdgData := os.Getenv("XDG_DATA_HOME"); xdgData != "" {
 		return filepath.Join(xdgData, "agentmgr")
 	}
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return filepath.Join(os.TempDir(), ".local", "share", "agentmgr")
+	}
 	return filepath.Join(home, ".local", "share", "agentmgr")
 }
 
@@ -42,7 +45,10 @@ func (l *linuxPlatform) GetConfigDir() string {
 	if xdgConfig := os.Getenv("XDG_CONFIG_HOME"); xdgConfig != "" {
 		return filepath.Join(xdgConfig, "agentmgr")
 	}
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return filepath.Join(os.TempDir(), ".config", "agentmgr")
+	}
 	return filepath.Join(home, ".config", "agentmgr")
 }
 
@@ -50,7 +56,10 @@ func (l *linuxPlatform) GetCacheDir() string {
 	if xdgCache := os.Getenv("XDG_CACHE_HOME"); xdgCache != "" {
 		return filepath.Join(xdgCache, "agentmgr")
 	}
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return filepath.Join(os.TempDir(), ".cache", "agentmgr")
+	}
 	return filepath.Join(home, ".cache", "agentmgr")
 }
 
@@ -76,16 +85,17 @@ func (l *linuxPlatform) EnableAutoStart(ctx context.Context) error {
 }
 
 func (l *linuxPlatform) DisableAutoStart(ctx context.Context) error {
-	// Try both methods
-	l.disableSystemdAutoStart(ctx)
-	l.disableXDGAutoStart()
+	// Try both methods - errors are intentionally ignored as this is best-effort cleanup
+	_ = l.disableSystemdAutoStart(ctx) //nolint:errcheck
+	_ = l.disableXDGAutoStart()        //nolint:errcheck
 	return nil
 }
 
 func (l *linuxPlatform) IsAutoStartEnabled(ctx context.Context) (bool, error) {
 	// Check systemd
 	if l.hasSystemd() {
-		if enabled, _ := l.isSystemdEnabled(ctx); enabled {
+		enabled, err := l.isSystemdEnabled(ctx)
+		if err == nil && enabled {
 			return true, nil
 		}
 	}
@@ -150,7 +160,10 @@ func (l *linuxPlatform) getSystemdUserDir() string {
 	if xdgConfig := os.Getenv("XDG_CONFIG_HOME"); xdgConfig != "" {
 		return filepath.Join(xdgConfig, "systemd", "user")
 	}
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return filepath.Join(os.TempDir(), ".config", "systemd", "user")
+	}
 	return filepath.Join(home, ".config", "systemd", "user")
 }
 
@@ -194,7 +207,10 @@ func (l *linuxPlatform) getXDGAutostartDir() string {
 	if xdgConfig := os.Getenv("XDG_CONFIG_HOME"); xdgConfig != "" {
 		return filepath.Join(xdgConfig, "autostart")
 	}
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return filepath.Join(os.TempDir(), ".config", "autostart")
+	}
 	return filepath.Join(home, ".config", "autostart")
 }
 
@@ -253,6 +269,7 @@ func (l *linuxPlatform) ShowNotification(title, message string) error {
 	}
 	// Try zenity
 	if _, err := exec.LookPath("zenity"); err == nil {
+		// #nosec G204 -- title and message are from controlled internal sources
 		return exec.Command("zenity", "--notification", "--text="+title+"\n"+message).Run()
 	}
 	return fmt.Errorf("no notification system available")
@@ -273,6 +290,7 @@ func (l *linuxPlatform) ShowChangelogDialog(agentName, fromVer, toVer, changelog
 func (l *linuxPlatform) showZenityDialog(agentName, fromVer, toVer, changelog string) DialogResult {
 	text := fmt.Sprintf("%s\n\n%s → %s\n\n%s", agentName, fromVer, toVer, changelog)
 
+	// #nosec G204 -- arguments are from controlled catalog sources, not user input
 	cmd := exec.Command("zenity", "--question",
 		"--title=Update Available",
 		"--text="+text,