Here is an isolated HTML page and its JavaScript. Map the user-visible promises, state transitions, external dependencies, and recovery paths. Add reversible fault-injection seams or test adapters only in this test copy. Inject a small, prioritized set of failures - network timeout, malformed or delayed response, storage full, permission denial, duplicate delivery, and retry after partial success - and run the resulting AI Tests. For each fault, preserve the before-and-after state, user-visible outcome, console and network evidence, invariant checked, blast radius, cleanup, and whether the result is observed, blocked, or not assessed. Do not target production systems or real customer data.