A synthesis subagent is invoked with the prompt "Write a cited summary of what the search and document analysis agents found." Its output is fluent but includes claims that appear in neither agent's results. What is the root cause?

Answer: A — The prompt never included the other agents' findings, and subagents don't inherit the coordinator's context

Subagents start with isolated context; they don't see the coordinator's history or other subagents' outputs. The coordinator must put the complete findings directly in the synthesis prompt. Without them, synthesis invents plausible content. Search tools (b) aren't its job, volume (c) isn't the issue since nothing was passed, and spawning synthesis in parallel (d) would give it even less to work with.