[Nemu-x]

Bounds REALITY's pre-authentication work while preserving long-lived fallback traffic. RealityConfig.HandshakeTimeout defaults to 15 seconds and is lifted after successful authentication/handshake or fallback selection. Pending client and target sockets close on timeout or context cancellation, and mirror connections forward deadline calls.

Also addresses the related audit findings:

• Stop the final unmetered fallback read exactly at AfterBytes.
• Omit AuthKey and short ID from debug logs.
• Cache the parsed X25519 private key and reuse the 17 KiB target buffers. The asynchronous target reader retains ownership of its buffer until it exits.
• Run application VerifyPeerCertificate and VerifyConnection callbacks after JLS authentication; rejection still fails the handshake.

Validation:

• Linux Go 1.26.9: full go test -race -count=1 -timeout 10m ./... passed.
• Linux Go 1.20: full go test -count=1 -timeout 10m ./... passed.
• Regression tests cover silent clients, cancellation, fallback surviving beyond the handshake timeout, mirror deadlines, threshold accounting, key rotation/cloning, log redaction and rejecting JLS verifier callbacks.
• Sequential Linux X25519 microbenchmark, three runs: uncached 46.7–47.3 us / 320 B / 7 allocations; cached 23.0–24.3 us / 128 B / 3 allocations. This measures the key-agreement operation, not end-to-end VPN throughput.

No protocol format or module-path changes. No release tags are created.