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ai-python-custom-loop

Use when building custom agent loops. Modify tool dispatch, history management, hooks, control flow.

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vercel-labs/seal
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July 17, 2026 at 17:25
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name
ai-python-custom-loop
description
Use when building custom agent loops. Modify tool dispatch, history management, hooks, control flow.
metadata
{"sdk-version":"0.2.1"}
# ai-python-custom-loop Keep the default shape unless you must change control flow: ```python class MyAgent(ai.Agent): async def loop(self, context: ai.Context): while context.keep_running(): async with ( ai.stream(context=context) as stream, ai.ToolRunner() as runner, ): async for event in ai.util.merge(stream, runner.events()): yield event if isinstance(event, ai.events.ToolEnd): runner.schedule(context.resolve(event.tool_call)) context.add(stream.message) context.add(runner.get_tool_message()) ``` Rules: - Call `context.keep_running()` at the top of each turn. - Use `ai.stream(context=context)` so model, messages, tools, output type, and params stay together. - Yield events from the loop. `Agent.run` hides replay events from callers. - On `ToolEnd`, use `context.resolve(event.tool_call)`. It handles validation, approval gates, and cached replay results. - Do not call `tool.fn` directly unless you also handle validation, approvals, and cached results. - Schedule resolved calls with `ToolRunner.schedule(...)`. - `ToolRunner.schedule(...)` also accepts a zero-arg async callable that returns `ai.events.ToolCallResult`. - If you make a result yourself, use `runner.add_result(ai.tool_result(...))`. - Add `stream.message`, then `runner.get_tool_message()`. `context.add(...)` skips replay messages. - Every tool call must get one tool result. - For hooks, let `context.resolve(...)` build the gated call. Use `ai-python-serverless-execution` for request boundaries. - For durable calls, keep this shape and wrap only model or tool I/O. Use `ai-python-durable-execution`.
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