What

Add unit tests for the QUIC protocol suite. Currently 18+ QUIC modules have zero unit test coverage.

Part of #953

Why

• QUIC is a user-facing protocol and core to the next-generation networking stack
• Zero coverage blocks v1.0 readiness (see Prepare network_system for v1.0 release #964)
• Other ecosystem libraries have 70%+ coverage — QUIC layer is a major gap

Where

Target modules (18+)

• connection, crypto, flow_control, stream_manager
• packet, frame, congestion_control, loss_recovery
• transport_parameters, version_negotiation
• quic_client, quic_server (core)
• handshake, retry, 0-RTT
• qlog, qpack (if present)

Run find sources -path '*quic*' -name '*.cpp' -not -path '*test*' to enumerate final list.

How

Technical Approach

1. Create tests/unit/quic/ directory mirroring source layout
2. For each source module, add GoogleTest-based unit test file
3. Mock or stub external I/O (UDP sockets, TLS) — focus on pure logic
4. Run under ASAN, TSAN, UBSAN

Acceptance Criteria

• Every identified QUIC module has at least one dedicated unit test file
• Line coverage for sources/**/quic/** >= 70% (codecov)
• All tests pass on Ubuntu/macOS/Windows CI
• ASAN/TSAN/UBSAN sanitizer builds pass
• No GTEST_SKIP markers (except for optional deps)