Guest https.get to an in-guest TLS server failed with ERR_AGENTOS_NODE_SYNC_RPC:
the client upgrade leaves the rustls handshake incomplete (looping would deadlock
the guest thread that must service the server-side upgrade), so the first write
hit WouldBlock from the loopback transport and surfaced as a fatal sync-RPC error.

- Buffer plaintext writes on loopback TLS sockets while the handshake is pending
  (bounded 4 MiB, warn at 80%, typed error on overflow); the TLS reader thread
  drives the handshake with a short poll timeout, flushes the buffer on
  completion, enforces TLS_HANDSHAKE_TIMEOUT, and honors deferred shutdown.
- Interrupt flags on the loopback transport let a direct write reclaim the
  stream mutex from the reader without waiting out its poll.
- Bridge: https.createServer now actually upgrades accepted sockets to TLS
  (options were previously discarded); client secureConnect defers to a
  macrotask without double-starting the read pump; first-read wake scheduling
  no longer requires bench metrics to be enabled; localAddress/localPort flow
  through connect.
- New net/tls_loopback_get bench op (guest+node lanes, explicit unsupported
  native/wasm reasons) and engine support for unsupported-lane rendering.
- Regression tests: loopback https round-trip; pending-write buffer cap.