Fetch a stored prompt or artifact by id as JSON-LD: the two records sim_prompt and sim_reroll store besides a model. An artifact (@type Artifact) is an LLM reply that was not stored as a model — a report, code, or model JSON that failed validation — returned whole as content (the store caps an artifact at 262144 bytes), with contentKind. A prompt (@type Prompt) is what was asked: text, system, llmProvider, llmModel and requestTemplate (the version of the fixed instruction and settings sim_prompt wrapped them in). A prompt with no requestTemplate was stored before sim_prompt's description said a stored prompt and its results are readable by anyone with an id, so its text and system are withheld, and so is the content of an artifact it produced: withheld names the fields left out, and note says why. parent is the id it was run against (a prompt) or produced by (an artifact), and lineage is the derivation record for it (wasDerivedFrom, activity, ancestry nearest first, wasAttributedTo, generatedAtTime), absent when none was recorded. A model id, or an id of another stored kind, is refused naming what it is and the tool or route that reads it. Public: no sign-in and no compute tokens; writes nothing. GET /api/artifacts/{id} serves the same document.