Cron jobs create AIAgent without passing session_db, so messages from
cron runs (and their delegate_task subagents) are never written to the
SQLite session store. This means session_search cannot find any cron
conversation history — the same class of bug fixed for the gateway in
8aa531c (PR #105).
Initialize SessionDB in run_job() and pass it to AIAgent, following the
identical pattern used in gateway/run.py.
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