What

Add unit tests for UDP messaging (4) and integration (6) modules — 10 modules with zero coverage.

Part of #953

Why

• UDP messaging variants are used by real-time signalling paths — losses and reorderings must be exercised in tests
• Integration modules are the contract surface with sibling systems (container/logger/monitoring); silent breakage affects downstream consumers
• Smallest scope of the four Expand unit test coverage from 40% to 80% #953 sub-issues — strong candidate to establish the testing pattern reused by the others

Where

Target modules (10)

UDP messaging (4):

• messaging_udp_client
• messaging_udp_server
• secure_messaging_udp_client
• secure_messaging_udp_server

Integration (6):

• container_integration
• logger_integration
• monitoring_integration
• (enumerate remaining via find sources -path '*integration*' -name '*.cpp')

How

Technical Approach

1. UDP messaging: loopback transport + synthetic packet loss / reorder harness
2. Integration: stub sibling systems via their public Result interfaces
3. Establish shared test fixtures under tests/unit/support/ for reuse

Acceptance Criteria

• All 10 modules have dedicated unit test files
• UDP secure variants tested with a representative TLS/DTLS fixture
• Integration tests verify Result error propagation across module boundaries
• Coverage >= 75% for affected modules
• All sanitizer builds pass (ASAN, TSAN, UBSAN)
• Shared test support fixtures documented for reuse in Add unit tests for QUIC protocol suite (18+ modules) #982 and the other Expand unit test coverage from 40% to 80% #953 sub-issues