What

Add unit tests for the facade (5) and adapter (17) layers. Currently 22 modules have zero coverage.

Part of #953

Why

• Facade layer is the primary public API — defects cascade to all consumers
• Adapters bridge protocol-specific behavior to the uniform facade interface
• Coverage is a prerequisite for API freeze in v1.0 (Prepare network_system for v1.0 release #964)

Where

Target modules

Facades (5): http, quic, tcp, udp, websocket facades under sources/facades/

Adapters (17):

• http: client adapter, server adapter
• quic: client adapter, server adapter
• tcp: client adapter, server adapter
• udp: client adapter, server adapter
• websocket: client adapter, server adapter
• (additional variants — enumerate via find sources -path '*adapter*' -name '*.cpp')

How

Technical Approach

1. Create tests/unit/facades/ and tests/unit/adapters/
2. Use gmock to stub the underlying transport
3. Verify the facade preserves contract: Result propagation, lifecycle, error translation
4. Test each adapter independently from its facade

Acceptance Criteria

• Each of the 22 modules has a dedicated test file
• Coverage for facade + adapter layers >= 75%
• All tests pass on Ubuntu/macOS/Windows CI
• Sanitizer builds pass (ASAN, TSAN, UBSAN)
• No contract regressions detected by facade tests