The spawn tool accepts empty strings as valid task arguments, which
causes a subagent to run with no meaningful work. The subagent's
completion message is then routed back to the originating channel
(e.g. Signal, Discord), where the main agent processes it and may
hallucinate an unrelated response that gets sent to users.
Validate that the task parameter is non-empty after trimming whitespace.
Related: #545
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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