lift: branch on the driver's exit verdict, not a re-derived done() (0.6.6 regression)

[lannbot]

An async-typed lifted export's driver exits on one of two verdicts:
done() held (task.return seen, no wasm call or hop in flight) or
idle (#292 / #310). Since #310 the lift RE-EVALUATED driveDone() in
its .then continuation to decide between finishHostEntry and
backgroundCompletion. That predicate is time-varying: one microtask
after an EXIT-done, another driver of the same store (the settlement
pump servicing a settled host call) can resume a background activation
that transiently hop-parks, so midWasmCall()/hopParked() read true
and the lift took backgroundCompletion() — which resolves on
Task.onFinished, i.e. never for a callback-ABI task whose spawned
futures are immortal. Regression from 0.6.5, whose continuation was
pending.then(finishHostEntry) unconditionally.

Observed in polyvisor: lifecycle.boot (spawns the engine driver,
event pump and accept loop, then task.returns) never resolved on a
reload once a store sync task added enough host-call traffic for the
pump to win the race. Trace: EXIT-done ... done=true followed by
-> backgroundCompletion threads=1 resolvedSeen=true.

Fix: drive/driveLoop/driveAsync return their exit verdict
(DriveExit = "done" | "idle") and the lift branches on that. The
verdict is a fact about the loop that ran; re-deriving it later asks a
different question. driveStoreAsync discards the verdict (the pumps
have no completion to route).

Test: runtime/tests/lift_done_verdict_test.ts — a callback-ABI lift
with an immortal second thread task.returns and exits done; a foreign
thread hop-parks in the microtask window before the continuation.
Red on main ("expected resolved, got pending"), green with the fix.

Consumer evidence: polymorph-components/polyvisor, deno task e2e on 0.6.6 fails drive-connect/drive-round-trip (boot never resolves on reload); forcing trapOnIdle: true or latching the verdict makes all 16 scenarios pass. Traces: POLYENGINE_DRIVE_TRACE + a log at the lift's exit sites.

Not in this PR (to file separately): backgroundCompletion resolves on Task.onFinished (last thread unregisters) rather than on the task's resolve callback, so a task with long-lived spawned futures that idles before task.return never answers the host even after it returns.

Automerge armed.