Oracle agent (and all sync subagent tasks) fails with JSON Parse
error in ACP environments because session.prompt() (blocking HTTP)
returns empty/incomplete responses.
Replace promptSyncWithModelSuggestionRetry with promptWithModelSuggestionRetry
(async, fire-and-forget) and add polling loop to wait for response
stability, matching the proven pattern from executeUnstableAgentTask.
Fixes#1681
