When a cron job runs in isolated mode, the sessions_spawn tool now correctly
inherits the allowAgents permissions from the parent agent's config.
The fix adds a requesterAgentIdOverride parameter that flows through the
tool creation chain:
- resolveEffectiveToolPolicy() extracts the correct agentId from the session key
- This agentId is passed to sessions_spawn and agents_list tools
- The tools use this override instead of re-parsing the session key
This fixes#1767
