test(features): remove unsafe test assertions

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/background-agent/compaction-aware-message-resolver.test.ts

@@ -49,7 +49,7 @@ describe("isCompactionAgent", () => {
 
     test("returns false for null", () => {
       // when
-      const result = isCompactionAgent(null as unknown as string)
+      const result = isCompactionAgent(testCoerce<string>(null))
 
       // then
       expect(result).toBe(false)