Get the sample payload a trigger will deliver

Returns what {{trigger.*}} will actually contain for a GIVEN trigger configuration — the shape every expression in the workflow is written against.

Why this exists rather than reading sampleData off the catalog: three internal triggers DERIVE their payload from the author's own configuration (a Form's sample is the fields you defined, a Schedule's is its real next fire time, a Callable's is its declared input), so the frozen literal in the catalog is a lie for them. derived: true means the answer reflects the config you sent; derived: false means it is the trigger's generic declaration.

The body is optional — an absent or empty body means 'no config yet' and the worker answers with the declared fallback rather than failing. Safe to call for ANY trigger: a piece that does not implement derivation falls back to its declared sample instead of erroring.

Runs on a worker, so it is 503 when the fleet is down.

KNOWN ROUGH EDGE: a triggerId that does not exist on an EXISTING piece answers 500 INTERNAL_ERROR (message trigger "x" not found on piece "y"), not 404. An unknown PIECE does answer 404.

Send Content-Type: application/json if you send a body.

Requires workflow:read. Resolving a dynamic value is not a catalog read: it can return tenant data (the subflow piece's workflow_id option is this workspace's whole workflow list) and, when the request carries a connectionId, the credential is resolved and decrypted on a worker so the piece can call the third party.