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Track B (milestone 5 / §16 hardening): - tests/hostile_network.rs: in-process UDP relay/shim between a test client and a real dosh-server that can drop, reorder, and duplicate datagrams, and rebind its upstream socket mid-session. Asserts: session survives loss/reorder, duplicated/replayed Input is applied at most once, stale packets after resume are ignored (not fatal), and a client source-address change preserves the session. - tests/parser_robustness.rs: deterministic randomized tests throwing garbage at every reachable public parser (packet decode, from_body for all protocol/native structs, authorized_keys, known_hosts, host-key line, ssh-ed25519 blob, bootstrap, attach ticket); asserts none panic. - fuzz/: standalone cargo-fuzz crate (own [workspace], non-default member) with libfuzzer-sys harnesses for packet decode, from_body, authorized_keys, known_hosts, handshake structs+verifiers, and attach tickets. README documents the run command. - .github/workflows/ci.yml: add fuzz-smoke job (nightly + cargo-fuzz, short -max_total_time per target, tolerant if tooling unavailable); existing fmt/test/build/bench steps unchanged. cargo fmt --check and cargo test are green. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>