fix: address review feedback for icon path resolution

- Update constant reference to slackCLIAppIconPathEnv
- Stop falling through to manifest/icon.png when env var file is missing
- Add file existence check for manifest icon values
- Update tests for new behavior

Author: srtaalej

internal/config/dotenv.go

@@ -46,7 +46,7 @@ func (c *Config) LoadEnvironmentVariables() error {
 	}
 
 	// Load app icon path from environment variables
-	var appIconPath = strings.TrimSpace(c.os.Getenv(slackAppIconPathEnv))
+	var appIconPath = strings.TrimSpace(c.os.Getenv(slackCLIAppIconPathEnv))
 	if appIconPath != "" {
 		c.AppIconPathFlag = appIconPath
 	}

internal/pkg/apps/install.go

@@ -647,9 +647,12 @@ func resolveIconPath(ctx context.Context, clients *shared.ClientFactory, manifes
 		}
 		clients.IO.PrintDebug(ctx, "SLACK_CLI_APP_ICON_PATH file not found: %s", envIconPath)
 		_, _ = clients.IO.WriteOut().Write([]byte(style.SectionSecondaryf("Warning: icon path from SLACK_CLI_APP_ICON_PATH not found: %s", envIconPath)))
+		return ""
 	}
 	if manifestIcon != "" {
-		return manifestIcon
+		if _, err := os.Stat(manifestIcon); !os.IsNotExist(err) {
+			return manifestIcon
+		}
 	}
 	if _, err := os.Stat("icon.png"); !os.IsNotExist(err) {
 		return "icon.png"

internal/pkg/apps/install_test.go

@@ -1771,25 +1771,25 @@ func Test_resolveIconPath(t *testing.T) {
 			setupFiles: func(t *testing.T, dir string) {},
 			expected:   "",
 		},
-		"env var file not found falls back to manifest": {
+		"env var file not found returns empty": {
 			envIconPath:  "missing-icon.png",
 			manifestIcon: "manifest-icon.png",
 			setupFiles: func(t *testing.T, dir string) {
 				require.NoError(t, os.WriteFile(filepath.Join(dir, "manifest-icon.png"), []byte("img"), 0o644))
 			},
-			expected: "manifest-icon.png",
+			expected: "",
 		},
-		"env var file not found falls back to icon.png": {
-			envIconPath: "missing-icon.png",
+		"manifest icon file not found falls back to icon.png": {
+			manifestIcon: "missing-manifest-icon.png",
 			setupFiles: func(t *testing.T, dir string) {
 				require.NoError(t, os.WriteFile(filepath.Join(dir, "icon.png"), []byte("img"), 0o644))
 			},
 			expected: "icon.png",
 		},
-		"env var file not found and no fallback returns empty": {
-			envIconPath: "missing-icon.png",
-			setupFiles:  func(t *testing.T, dir string) {},
-			expected:    "",
+		"manifest icon file not found and no icon.png returns empty": {
+			manifestIcon: "missing-manifest-icon.png",
+			setupFiles:   func(t *testing.T, dir string) {},
+			expected:     "",
 		},
 	}
 	for name, tc := range tests {