Codex code-review round 5: agent()/parallel()/pipeline() returned HOST Promise
objects into the script realm — Object.getPrototypeOf(agent('x')) reached host
Promise.prototype, contradicting the realm contract (correctness containment,
not the accepted sandbox stance). The rejection channel had the same leak one
hop away: a caught hook failure was a host WorkflowError (host Error.prototype
chain), and phase()/log() threw host errors synchronously.
All three surfaces are realm-built now:
- hook promises: the realm's own Promise.resolve (bound at context setup)
assimilates the host promise, so the script-visible promise carries realm
prototypes; the realm promise gets the same no-op rejection consumer as the
host one (a script may drop it).
- hook failures: rejections and phase/log sync throws are translated at the
boundary into realm-built clones (name/code/message/fatal via an in-realm
factory); non-WorkflowError host failures become generic realm Errors
carrying their describeThrown rendering.
- the combinators recognize FATAL clones structurally
(isFatalWorkflowErrorClone: proxy-guarded descriptor reads), preserving the
fatal-vs-null discipline across the boundary; a script forging the shape
kills only its own run. drive() maps any post-cancel failure to 'cancelled'
by run state (a CANCELLED clone deliberately fails the host instanceof).
Tests: realm-promise identity for all three hooks + host Promise.prototype
pollution unreachable; clone shape (instanceof realm Error, name/code/fatal/
message) with prototype-chain mutation staying realm-side; a rejecting
provider result crossing as a generic clone; phase/log sync-throw clones;
combinator catch branches (string throw, proxy throw, shape-miss forgery →
null; forged fatal → kills own run); existing fatal-propagation, cancellation,
and unhandled-rejection tests as canaries.
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