You are building a multi-agent research system using the Claude Agent SDK.

Option C identifies the architectural contradiction. A specialized subagent’s role prompt says what work it should perform, but granting it every tool simultaneously signals that unrelated actions are available and potentially legitimate. The synthesis agent can therefore interpret web search as a permissible way to fill gaps, while the report generator may invoke document-analysis tools even though those responsibilities belong elsewhere. Anthropic’s Agent SDK documentation describes subagents as focused workers with tailored instructions and explicitly supports restricting each subagent to specific tools; it notes that tool restrictions reduce unintended actions. There is no documented universal threshold at which choosing among 18 tools becomes unreliable, so option B invents a “four or five tools” limit. Context consumption in option A may affect efficiency, but it does not directly explain the role-specific cross-calling pattern. Option D is also incorrect because the observed behavior occurs after delegation, inside agents that already possess the tools. The remedy is least-capability configuration: give the web agent search tools, the document agent document tools, the synthesis agent only the inputs and utilities required to combine findings, and the report agent formatting or file-output tools. Aligning role, description, and tool allowlist removes the conflicting affordances.

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