Async export parked on a guest-internal waker (no host call outstanding) traps as deadlock; wasmtime would stay pending

[lannbot]

An async-lifted export (wit-bindgen callback ABI) that parks on a guest-internal Waker — nothing host-side outstanding, woken later by a different export call — traps at the sync drive entry:

Trap: wasm trap: deadlock detected: event loop cannot make further progress
(export 'next': no thread is ready and no host call is outstanding)

This is the long-poll shape (next: async func() -> event woken by a later push). Under wasmtime call_concurrent/run_concurrent the export's future stays pending until the second call readies the task; the embedder is still able to act, so it is not a deadlock in the spec's sense — the guest task is WAITing on its wit-bindgen inter-task-wakeup stream, whose writer is guest code reachable through another export.

Minimal repro (wit-bindgen 0.60, async-spawn + inter-task-wakeup, jspi: false, runtime at 80ee6cb):

world guest {
  import note: func(what: string);
  export next: async func() -> u32;   // parks on a thread_local Waker until push()
  export push: async func(v: u32);    // pushes a value, wakes the waiter
}

const p = inst.exports.next();        // traps here (drive: deadlock)
await inst.exports.push(7);           // never reached

Guest: next is poll_fn(|cx| { pop queue or store cx.waker(); Pending }).await; push pushes and wake()s.

Expected: next() returns a pending Promise; push(7) resolves it with 7. Observed: trap on the next() call.

Context: found building polyvisor's kernel event path (a events.next long-poll export). Worked around by making the export non-parking and draining from the glue after each dispatched export call; recorded in polyvisor's design record as a polyengine divergence to revisit. Sibling of #289 (that one was a parked driver missing a host call registration; this one is "no host call at all is not a deadlock while the embedder holds exports").