The 'Parallel Task Execution' rule encourages agents to spawn subagents,
but defines no completion contract. Observed failure mode: subagents
followed the rule, spawned their own children, and returned 'waiting
for background agents' as their final answer. All children completed
successfully, but their results were orphaned because a parent whose
turn has ended cannot receive completion notifications - leaving
zombie 'running' tasks and lost work.
Adds three rules that apply at every delegation depth:
1. Your final message IS the deliverable (never end with 'waiting')
2. If you delegate, you own collection (no fire-and-forget)
3. Decompose only when work cannot fit in one context
