Fix stale call-site arguments after merge conflict resolution in messageStream.js

[Copilot]

Manual conflict resolution in commit b47995a ("Merge branch 'devel' into devel") adopted the new pollCancellationConfirmed(request, attempts = 0) signature but left one call site on the old two-argument form, breaking the stop/cancel data flow.

• stop() call site: updated to pass the request object instead of its destructured fields.

// before
pollCancellationConfirmed(request.sessionId, request.owner);

// after
void pollCancellationConfirmed(request);

With the old call, request.sessionId (a string) was bound to the request parameter and request.owner to attempts. Every internal access to request.runId / request.sessionId inside pollCancellationConfirmed then resolved to undefined, and the mismatched object reached releaseSessionRequest, so the entry in state.activeRequests was never cleared — leaving the UI stuck reporting a session as still running after Stop was clicked.

This aligns the stop() call with the other three call sites in the file, which already use the single-argument form.