[itlezy]

Summary

• preserve the logical source endpoint separately from the actual UDP destination, including buddy-relayed reasks
• keep reask scheduling pure and open the pending-reply gate only after local socket success
• keep failed or abandoned sends retryable without recording false remote timeouts or influencing TCP fallback
• reject duplicate pending completion and cover success, local failure, abandoned work, direct sends, and buddy sends

Validation

• cargo test -p emulebb-ed2k ed2k_client_udp --lib (116 passed)
• cargo test -p emulebb-ed2k --features packet-diagnostics (1,188 passed)
• cargo test -p emulebb-core --features packet-diagnostics (complete unit and integration matrix passed)
• cargo clippy --workspace --all-targets --locked -- -D warnings
• cargo fmt --check
• git diff --check