Initial commit: wireframe packet capture/analysis tool

Terminal packet capture and analysis tool built to learn the C++
memory model (byte layout, alignment, endianness, std::span over
unowned buffers) via a real capture pipeline.

- Hand-rolled L2-L4 decoders (Ethernet, IPv4, IPv6 with extension
  header walking, TCP, UDP) over std::span, no struct-casting
- L7 dissector interface with DNS, HTTP, and TLS SNI implementations
- pcapng read/write for Wireshark-compatible capture files
- Bounded capture queue: drop-on-backpressure for live capture,
  blocking push for faithful file replay
- Kernel-level BPF filtering (-f) and a separate display-only search
  (-g / interactive) that doesn't touch what's captured
- Replay mode (-r) reads a saved pcapng file back through the same
  pipeline as live capture, no root or live device needed
- pcap_stats() surfaces kernel/interface drops invisible to the
  capture queue's own counter
- Three frontends sharing one CaptureSession setup path: CLI, TUI
  (FTXUI, primary), GUI (Dear ImGui + SDL3, secondary)
- 89 unit tests (doctest) plus 9 libFuzzer harnesses covering every
  hand-rolled parser; fuzzing found and fixed a real OOM in the
  pcapng reader (unbounded allocation from an untrusted length field)

1 files changed, 44 insertions, 0 deletions

diff --git a/include/wireframe/net/ethernet.hpp b/include/wireframe/net/ethernet.hpp
new file mode 100644
index 0000000..2da4cc8
--- /dev/null
+++ b/include/wireframe/net/ethernet.hpp
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <algorithm>
+#include <array>
+#include <cstdint>
+#include <optional>
+#include <span>
+
+#include "wireframe/byteio.hpp"
+
+namespace wireframe::net {
+
+inline constexpr std::size_t kEthernetHeaderLen = 14;
+inline constexpr std::uint16_t kEthertypeIPv4 = 0x0800;
+inline constexpr std::uint16_t kEthertypeIPv6 = 0x86DD;
+inline constexpr std::uint16_t kEthertypeArp = 0x0806;
+
+struct MacAddress {
+    std::array<unsigned char, 6> bytes;
+};
+
+struct EthernetHeader {
+    MacAddress dst;
+    MacAddress src;
+    std::uint16_t ethertype;
+};
+
+struct EthernetFrame {
+    EthernetHeader header;
+    std::span<const unsigned char> payload;
+};
+
+inline std::optional<EthernetFrame> parse_ethernet(std::span<const unsigned char> bytes) {
+    if (bytes.size() < kEthernetHeaderLen) return std::nullopt;
+
+    EthernetHeader header{};
+    std::copy_n(bytes.begin(), 6, header.dst.bytes.begin());
+    std::copy_n(bytes.begin() + 6, 6, header.src.bytes.begin());
+    header.ethertype = read_be16(bytes, 12);
+
+    return EthernetFrame{header, bytes.subspan(kEthernetHeaderLen)};
+}
+
+}  // namespace wireframe::net