fix(@angular-devkit/build-angular): clear context in Karma by default for single run executions

This works around angular#28271.

Author: dgp1130

packages/angular_devkit/build_angular/src/builders/karma/index.ts

@@ -146,6 +146,12 @@ export function execute(
         logger: context.logger,
       };
 
+      // Workaround https://github.com/angular/angular-cli/issues/28271, by clearing context by default
+      // for single run executions. Not clearing context for multi-run (watched) builds allows the
+      // Jasmine Spec Runner to be visible in the browser after test execution.
+      karmaOptions.client ??= {};
+      karmaOptions.client.clearContext ??= singleRun ?? false; // `singleRun` defaults to `false` per Karma docs.
+
       const parsedKarmaConfig = await karma.config.parseConfig(
         options.karmaConfig && path.resolve(context.workspaceRoot, options.karmaConfig),
         transforms.karmaOptions ? transforms.karmaOptions(karmaOptions) : karmaOptions,
@@ -208,9 +214,6 @@ function getBuiltInKarmaConfig(
       'karma-coverage',
       '@angular-devkit/build-angular/plugins/karma',
     ].map((p) => workspaceRootRequire(p)),
-    client: {
-      clearContext: false, // leave Jasmine Spec Runner output visible in browser
-    },
     jasmineHtmlReporter: {
       suppressAll: true, // removes the duplicated traces
     },

packages/schematics/angular/config/files/karma.conf.js.template

@@ -19,7 +19,6 @@ module.exports = function (config) {
         // for example, you can disable the random execution with `random: false`
         // or set a specific seed with `seed: 4321`
       },
-      clearContext: false // leave Jasmine Spec Runner output visible in browser
     },
     jasmineHtmlReporter: {
       suppressAll: true // removes the duplicated traces