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Run setup is how you choose what input a workflow run starts with — before any step executes. In Workflow Studio, open Workflow configuration → Trigger.
Run setup is separate from the canvas graph. Saving Run setup defaults does not auto-save step wiring on the canvas.

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Three layers (do not confuse)

LayerWhereWhat
Graph step configCanvas nodesAuthored prompt, tool_args, Lua script, etc.
Input schemaPublished workflow versionField definitions for {{input.*}} (no values)
Run setupWorkflow configuration → TriggerStart values for this run (and optional saved defaults)
At run start, Studio sends trigger_payload + trigger_steps to the runtime. Steps resolve templates like {{input.topic}} from that data.

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Shared input (trigger_payload)

Most workflows only need Shared input — workflow-wide values referenced as {{input.*}} in step templates.
If you have not published an input schema, Studio offers optional fields message, topic, and data. Use Define input schema at publish (under Shared input) to open version history on the publish form and add required fields.
When you have published an input schema, those fields drive Run setup validation and appear in template intellisense. Example fields after you publish an input schema:
  • topic → {{input.topic}}
  • message → {{input.message}}

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Per-step overrides (trigger_steps)

Optional. Use when a specific entry step needs different start values than the shared payload. Per-step forms use each step’s catalog / MCP input schema when available. If the canvas already defines a value (for example prompt on an Agent Call), Run setup treats that field as satisfied — you only need an override when you want different start data than the graph. 
{
  "trigger_payload": { "topic": "digest" },
  "trigger_steps": {
    "uuid-of-root-step": { "prompt": "override for this step only" }
  }
}
Per-step keys map to run.input._steps.<stepId>.* at runtime (engine overlay on canvas defaults).

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Start steps

Pick which steps receive starting input:
  • Entry steps — graph roots; run automatically at t=0.
  • Optional steps (no_auto_start) — only run if you select them in Run setup.

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Save defaults

Click Save defaults to persist the current Run setup on the workflow version (run_setup_json):
  • trigger_step_ids
  • trigger_payload
  • trigger_steps
Defaults reload when you reopen the workflow. Publish copies the current Run setup snapshot to the new published version. Expand Start params preview at the bottom of the Trigger tab to see the JSON Studio will send (trigger_payload and trigger_steps). Studio Run / Dry-run always uses in-session values (no use_run_setup_defaults flag).

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API and external triggers

API / PAT starts use saved defaults only when you pass: 
{
  "command": "start",
  "params": {
    "use_run_setup_defaults": true,
    "trigger_payload": { "topic": "weekly" }
  }
}
Caller params win on key conflicts. Without the flag, only trigger_payload / trigger_steps in the request apply. Inbound webhooks and cron follow the same rule — saved Run setup merges only when subscription/trigger extras (webhooks) or config (cron) sets use_run_setup_defaults: true. See External triggers.