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Renders an interactive UI artifact in the task feed: a versioned HTML/JS bundle loaded from a CDN inside a sandboxed iframe. Runtime reads/writes go through /api/app-runtime, gated by the configured tool’s allowlist. Display name “App Tool”. Off by default.

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When to use it (vs custom_interface vs python_code_tool vs generate_file)

generate_file with format: html produces a file, not a live feed widget. python_code_tool cannot “signal HTML” — its contract is markdown. For a task-feed scorecard the user can click, this is the tool.

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Authentication and enablement

Configured tool: each instance has a bundle + data-source binding + action allowlist. The LLM does not pick the bundle. Off by default; add and configure per agent.

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Inputs

  • configured_tool_id — injected by the worker from context (x-exclude-from-llm). Never pass a display name here.
  • params — bundle-specific payload forwarded as runtime.params. Shape comes from the configured tool’s input_schema override (e.g. {report_id: 59137}).

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Output

An artifact descriptor (CDN bundle URL, scoped session token, initial data). The frontend mounts the iframe; edits persist via App Runtime and show up as agent_action feed events.

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Limits and side effects

  • Iframe is sandboxed; runtime calls must match the binding allowlist.
  • Writes go through /api/app-runtime (and the db/http gateways behind it), not the worker.

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Expected errors

  • Missing configured_tool_id (not injected) — step cannot resolve the bundle.
  • configured_tool_id that is not a UUID — validation error.
  • Runtime action not on the allowlist — denied by the gateway.