What

Expand unit test coverage for protocols/http2/http2_server.cpp from current 38.3% line / 19.4% branch to >=70% line / >=50% branch.

Part of #953.

Why

• File is 554 LOC. Server-side HTTP/2 logic has more complex branch combinations than client.
• Predecessor narrow test expansion (test: expand coverage for src/protocols/http2/http2_server.cpp #992) covered request handling happy path; missing error paths and concurrent stream scenarios.
• v1.0 readiness gate requires >=80% line coverage ecosystem-wide (see Prepare network_system for v1.0 release #964).

Where

• Source: protocols/http2/http2_server.cpp (554 LOC)
• Tests: tests/unit/protocols/http2/

How

Approach

1. Audit existing http2_server tests for uncovered branches.
2. Add tests for error paths: malformed client requests, GOAWAY initiation, RST_STREAM emission, stream ID exhaustion.
3. Add tests for boundary cases: max concurrent streams, server push, header table updates, settings frame interleaving.
4. Add tests for protocol violations: invalid pseudo-headers, header compression errors, flow-control violations.
5. Re-run coverage workflow to verify thresholds met.

Acceptance Criteria

• protocols/http2/http2_server.cpp line coverage >= 70%
• protocols/http2/http2_server.cpp branch coverage >= 50%
• All new tests pass on Ubuntu/macOS/Windows CI
• All sanitizer builds (ASAN, TSAN, UBSAN) pass
• Coverage workflow re-measurement attached as a comment on this issue