PROMPT 08 Integration Tests

# Implementation Prompt 08: Integration Tests and Final Verification

**Goal:** Create comprehensive integration tests that verify the complete system working together, including the critical test scenarios from PRE_IMPLEMENTATION_CHECKLIST.md.

**Test Strategy:** Full integration tests with real components. All tests green, no warnings.

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## Context: What You're Building

You're implementing the final integration tests that verify:
1. **Full request/response cycle** with all components
2. **Concurrent busy retries** don't interfere
3. **Transport down** clears all state correctly
4. **Oversized frames** are rejected properly
5. **Stop during retry** prevents double replies
6. **All failure paths** work correctly

These tests validate the entire system working together, not just individual units.

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## Required Reading: Critical Test Scenarios

From PRE_IMPLEMENTATION_CHECKLIST.md, these are the MUST-PASS scenarios:

### Test 1: Concurrent Busy Retries

**Scenario:** Two requests hit `:busy` simultaneously