test(http2/hpack): expand coverage for hpack.cpp (#1044)

* test(http2/hpack): add extra coverage suite for issue #1031

Adds tests/unit/hpack_extra_coverage_test.cpp closing remaining gaps after
hpack_test.cpp and hpack_coverage_test.cpp:

- Static table boundary entries (index 61, name-only lookup ordering,
  mismatched-value fall-through)
- Dynamic table get() past entry_count, growing max_size without eviction,
  full-match preference over name-only match
- Encoder static-name-mismatched-value path forcing literal-with-indexing
  via static name reference
- Decoder happy paths for literal-without-indexing (0x00) new-name and
  indexed-name forms, never-indexed (0x10) prefix, and multi-header blocks
- Multi-byte integer decoding under the 64-bit overflow threshold
- Huffman stub encoded_size and byte-for-byte round-trip contract lock
- Encoder/decoder pair convergence for static-only emissions and mixed
  static/dynamic flows

Each decoder-path test builds wire bytes by hand against RFC 7541 §6 so
the decoder is the unit under test, not the encoder upstream of it.

* docs(changelog): note hpack extra coverage tests for #1031

Author: kcenon

CHANGELOG.md

@@ -40,6 +40,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Add `message_validator_extended_test` for extended message validation edge cases
   - Add `sliding_histogram_test` for `sliding_histogram` statistics and percentile calculations
   - Update Codecov configuration to track unit and integration coverage separately
+- Expand HPACK (`src/protocols/http2/hpack.cpp`) unit coverage with `hpack_extra_coverage_test` — closes static-table boundary lookups, decoder happy paths for literal-without-indexing / never-indexed prefixes, multi-byte integer non-overflow path, huffman stub contract, and mixed static/dynamic round-trips ([#1031](https://github.com/kcenon/network_system/issues/1031))
 
 ### Added
 

docs/CHANGELOG.md

@@ -35,6 +35,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Internal (1): `websocket_socket`
   - Registered all 11 test targets in `tests/CMakeLists.txt`
   - Part of the #953 coverage expansion effort targeting 48% to 80% unit test coverage
+- **Additional HPACK coverage tests (#1031)**
+  - Added `tests/unit/hpack_extra_coverage_test.cpp` complementing `hpack_test.cpp` (Issue #976) and `hpack_coverage_test.cpp` (Issue #1009)
+  - Closes static-table boundary lookups (index 61, name-only ordering, mismatched-value fall-through), dynamic-table get-past-end and grow-without-eviction paths, encoder static-name-mismatched-value forcing literal-with-indexing path, decoder happy paths for literal-without-indexing (`0x00`) new-name and indexed-name forms plus never-indexed (`0x10`) prefix, multi-byte integer decoding under the 64-bit overflow threshold, huffman stub `encoded_size` and byte-for-byte round-trip contract, and encoder/decoder pair convergence for static-only emissions
+  - Registered `network_hpack_extra_coverage_test` in `tests/CMakeLists.txt`
+  - Part of the #953 coverage expansion effort, targeting `src/protocols/http2/hpack.cpp` line >= 70% / branch >= 60%
 - **Modernized Doxygen Documentation with doxygen-awesome-css (#927)**
   - Vendored doxygen-awesome-css theme with dark mode toggle, code copy buttons, and responsive sidebar
   - Added custom header (`docs/header.html`) and branding CSS (`docs/custom.css`)

tests/CMakeLists.txt

@@ -4838,6 +4838,12 @@ add_network_test(network_hpack_module_test unit/hpack_test.cpp)
 # integer-length boundary round-trips (Issue #1009)
 add_network_test(network_hpack_coverage_test unit/hpack_coverage_test.cpp)
 
+# HPACK additional coverage: static-table boundary entries, decoder happy paths
+# for literal-without-indexing / never-indexed prefixes, multi-byte integer
+# non-overflow path, huffman stub contract, mixed static/dynamic round-trips
+# (Issue #1031)
+add_network_test(network_hpack_extra_coverage_test unit/hpack_extra_coverage_test.cpp)
+
 add_network_test(network_http2_client_module_test unit/http2_client_test.cpp)
 add_network_test(network_http2_server_module_test unit/http2_server_test.cpp)