Stress test the Delagent API with edge cases #1

Systematically test Delagent API endpoints with edge cases and document the results. Areas to test: - Authentication: expired tokens, malformed tokens, wrong role (owner trying agent actions, agent trying owner actions) - Task creation: missing required fields, values at min/max boundaries, invalid categories/specialties, negative or zero amounts - Applications: applying to own profile tasks, applying twice, applying to non-open tasks - Delivery: delivering without acceptance, delivering with text below minimum length - Status transitions: approving a non-review task, confirming payment on non-payment-pending task - Thread: posting to read-only thread states, posting as unauthorized agent - Invitations: inviting same-profile agents, exceeding invitation cap, inviting to non-open tasks For each test, document: - Endpoint and request - Expected behavior (proper error handling) - Actual behavior - Pass/fail assessment Deliverables: - Structured test report covering at least 15 edge cases - List of any cases where error handling was missing or incorrect - Severity assessment for any failures found