Behaviour for task modules that describe a named sub-agent "skill".

Each task module describes a sub-agent that is registered on the parent agent's Sagents.Middleware.SubAgent and invoked via the built-in task tool. The sub-agent runs in an isolated context with its own middleware/tool stack, performs task-specific work, and reports back to the parent.

Task modules are typically compiled into Sagents.SubAgent.Compiled entries by host applications, which combine the task's instructions/0 with Sagents.SubAgent.task_subagent_boilerplate/0 to form the child agent's system prompt.

Callbacks

• task_name/0 — short, kebab-case identifier exposed to the parent LLM as the subagent_type enum value (e.g. "search-web").
• description/0 — one-line blurb surfaced in the task tool's auto- generated menu. Always in the parent's context.
• use_instructions/0 — optional. Detailed "how to invoke this" guide for the parent LLM. Lazy-loaded via get_task_instructions only when the parent decides it wants to use this task. Describes prerequisites (what inputs/source data must exist), what to pass in the instructions arg, and what outputs the task produces. If not implemented, the host should treat this as "no lazy-loaded docs" — the task is invoked using only description/0 as parent- visible guidance.
• instructions/0 — the task's internal working prompt. Baked into the child sub-agent's system prompt at invocation. Never shown to the parent. Should focus on the substantive procedure — the universal boilerplate (no user questions, complete-or-fail, etc.) is supplied by Sagents.SubAgent.task_subagent_boilerplate/0.
• display_text/0 — optional. Human-facing status string shown in the host UI while this task is running. If not implemented, the middleware falls back to a generic "Running task" label (see Sagents.Middleware.SubAgent); host compilers may instead derive a humanized form of task_name/0.
• model_override/0 — optional. If defined and returns a non-nil value, the host should use the returned model (e.g. a configured chat-model struct) for this task's sub-agent instead of the default model supplied at compile time. Useful for narrow, bounded tasks where a cheaper/faster model is sufficient (e.g. summarization, classification). Returning nil — or not implementing this callback at all — means "use the host's default."

Host compilers should guard optional callbacks with function_exported?/3 before calling them, and supply the documented fallback when absent.