fix: resolve all test failures and Cubic review issues

- Fix unstable-agent-babysitter: add promptAsync to test mock
- Fix claude-code-mcp-loader: isolate tests from user home configs
- Fix npm-dist-tags: encode packageName for scoped packages
- Fix agent-builder: clone source to prevent shared object mutation
- Fix add-plugin-to-opencode-config: handle JSONC with leading comments
- Fix auth-plugins/add-provider-config: error on parse failures
- Fix bun-install: clear timeout on completion
- Fix git-diff-stats: include untracked files in diff summary

src/agents/agent-builder.ts

@@ -19,7 +19,7 @@ export function buildAgent(
   browserProvider?: BrowserAutomationProvider,
   disabledSkills?: Set<string>
 ): AgentConfig {
-  const base = isFactory(source) ? source(model) : source
+  const base = isFactory(source) ? source(model) : { ...source }
   const categoryConfigs: Record<string, CategoryConfig> = categories
     ? { ...DEFAULT_CATEGORIES, ...categories }
     : DEFAULT_CATEGORIES