Self-awareness

Use repl_execute for every host.* call. The host object exists only in the persistent JavaScript control REPL; Python and R data kernels do not receive it.

Inspect available capabilities

const caps = await host.capabilities()

The current project-native result contains 20 known boolean keys:

• mcp gates connector calls through host.mcp(server, method, args?).
• compute gates the host.compute namespace.
• agents gates the host.agents namespace.
• skills gates the host.skills namespace.
• artifacts gates managed-file discovery through host.artifacts(options?) and exact path resolution through host.artifactPath(versionId).
• lineage gates the read-only host.lineage namespace.
• frames gates the read-only host.frames namespace.
• sessions gates Main-only, read-only Session diagnostics through host.sessions.list(options?) and exact lookup through host.sessions.inspect(sessionId) in the current Project.
• llm gates one-shot, tool-less inference through host.llm(request, options?).
• currentModel gates exact current-model lookup through host.currentModel(). It returns the calling Session's exact current model id and fails when the live backend cannot establish one.
• listModels gates configured Host LLM model discovery through host.listModels(). It returns the frozen, stable-sorted configured model ids for the current Host LLM Provider and framework. It never refreshes over the network or merges ids across Providers.
• viewImage gates transient image attachment through host.viewImage(source, options?). Sources may be an Artifact or Upload Version in the current Project, or a path relative to the current execution workspace. For a generated file, pass the same relative path used to save it.
• delegate, children, collect, stopChild, and resolveMessage are Main/root-only delegated work operations.
• sendFrameMessage and messageReceipt are available to Main/root and Delegate agents when their trusted route is provisioned.
• submitOutput is available only to an authenticated Delegate Attempt with an admitted output schema.

Newer runtimes may return additive boolean keys. Do not assume their meaning until their matching Skill documents them. Older runtimes can omit known keys.

Interpret every key narrowly:

• true means the current session capability authorizes the namespace and the application has its handler configured. It does not mean a resource exists, approval is unnecessary, or a call will succeed.
• false means the capability name is known but unavailable to this caller.
• A missing key means this runtime does not know that capability. Test with === true.

const caps = await host.capabilities()
if (caps.compute === true) {
  const availableHosts = await host.compute.listHosts()
}

if (caps.llm === true) {
  const result = await host.llm('Summarize the current findings.')
}

if (caps.currentModel === true) {
  const sessionModel = await host.currentModel()
}

if (caps.listModels === true) {
  const hostLlmModels = await host.listModels()
}

if (caps.sessions === true) {
  const recentSessions = await host.sessions.list({ limit: 20 })
}

if (caps.viewImage === true) {
  await host.viewImage({ path: 'results/plot.png' }, { maxSize: 1200 })
}

if (caps.sendFrameMessage === true) {
  await host.sendFrameMessage('parent', 'The analysis is ready.')
}

Do not infer capabilities by reflecting over host, and do not treat this result as a resource, credential, permission, or readiness inventory. Call it again when current availability matters; each call returns a fresh frozen projection.

host.help() documents registered topics only. A not_found result identifies missing Help documentation: not_found does not override host.capabilities() or prove that a method is absent.

Discover managed Project files

When caps.artifacts === true, use await host.artifacts(options) to list generated Artifacts and user Uploads across the current Project. Optional camelCase fields are versionId, frameId, filename, exact, search, contentType, after, before, cursor, and limit (default 20, maximum 100). versionId is exclusive; exact requires filename; search and filename cannot be combined. contentType accepts an exact MIME type or a top-level prefix such as text/. Bare dates are UTC midnight, after is inclusive, and before is exclusive.

const page = await host.artifacts({ search: 'report', limit: 20 })
const localPath = page.artifacts[0]
  ? await host.artifactPath(page.artifacts[0].latestVersionId)
  : undefined

frameId matches only the exact producer Frame of a generated Artifact's latest Version. It does not expand to a root's descendants or the whole Session, and Uploads without trusted Frame provenance are excluded while this filter is present. There is no Session or Project override and no all-Projects scope. count is the total number of matches before cursor pagination; the current page size is artifacts.length. nextCursor is absent on the last page.

{
  count, projectId, truncated, nextCursor,
  artifacts: [{
    id, filename, contentType, sizeBytes, latestVersionId, checksum,
    projectId, sessionId, rootFrameId, agentFrameId, isUserUpload,
    createdAt, latestVersionCreatedAt
  }]
}

Result and Artifact fields use camelCase. contentType, checksum, rootFrameId, and agentFrameId are always present and may be null. Results contain metadata and immutable Version identity, never content; use host.artifactPath(versionId) to resolve a checksum-validated, Session-scoped read-only local copy of an exact generated Artifact Version or Upload Version, then use the existing file workflow. Version ID collisions, missing Versions, cross-Project ownership, and checksum mismatches fail closed.

The public result is a fresh frozen projection. It does not expose fuzzy scores, storage keys, markers, or a content-read API.

Read immutable Version lineage

When caps.lineage === true, start with await host.lineage.graph(versionId, options) to inspect the dependency graph without reading Artifact content. options accepts only direction ('up' by default or 'down'), maxDepth (default 5, maximum 20), and maxNodes (default 100, maximum 500). Graphs use stable BFS order; an Upload is an upstream leaf and may be a downstream root. A truncated result includes a reason and frontierVersionIds for a narrower follow-up query.

const caps = await host.capabilities()
if (caps.lineage === true) {
  const graph = await host.lineage.graph(versionId)
  const generated = graph.nodes.find((node) => !node.isUserUpload)
  const provenance = generated ? await host.lineage.get(generated.versionId) : undefined
}

Use await host.lineage.get(versionId) only for a generated Artifact Version after graph discovery. It returns the existing immutable core provenance projection: reproduction code when available, producer and environment status/evidence, and typed input Version evidence. Upload Versions are rejected by get; obtain their metadata with host.artifacts({ versionId }).

Both calls are fresh, frozen reads scoped only by the session-bound control token to the current Project, including Versions created in another Session of that Project. They never accept Project or Session scope fields, create extraction work, or return content, messages, full execution outputs, reviews, paths, storage keys, Bearer tokens, or internal routes. Missing or ambiguous identities, cross-Project edges, and corrupt evidence fail closed. There is no indexed property, clear(), client cache, Python/R host, or lineage API outside the JavaScript control REPL.

Discover Agent Frames

When caps.frames === true, use await host.frames.list(options) for a metadata-only catalog across Sessions in the token-owned current Project. It never searches message bodies. Optional camelCase fields are search, sessionId, rootsOnly (default true), kind, archived (exclude/include/only, default exclude), after, before, cursor, and limit (default 20, maximum 100). Metadata search fuzzily matches Session title, agentName, and delegateName.

Use await host.frames.get(frameId, options) with an exact full Frame ID to read one visible conversation path. sessionId may narrow or disambiguate within the current Project. branchId selects a specific Branch; without it, the Frame's active Branch is used. The latest 40 messages are returned chronologically by default, with a maximum of 100. Pass before with the returned previousCursor to page backward through older messages.

The result contains frozen Project, Session, Frame, Branch, visible transcript, and sanitized runtime segment projections. Messages follow the selected Branch graph rather than stored array order. The response never returns private reasoning, tool activities and raw inputs/outputs, terminal output, image bytes, local paths, storage and provider identifiers, internal event/stream identifiers, cost, or synthesized summaries. Missing, ambiguous, wrong-Session, invalid-Branch, and stale-cursor reads fail explicitly without enabling cross-Project discovery.

Diagnose Project Sessions

When caps.sessions === true, use await host.sessions.list(options) to inspect durable Session metadata and bounded live runtime evidence across the token-owned current Project. This capability is available only to Main through its session-bound control route. Optional camelCase fields are archived (exclude/include/only, default exclude), search, cursor, and limit (default 20, maximum 100). Search fuzzily matches Session title and exact Session identity. Results are ordered by most recent update and return totalCount, frozen Session projections, and nextCursor when another page exists.

Use await host.sessions.inspect(sessionId) for one exact Session in the current Project. Both operations report durable identity, title, status, timestamps, archive/run metadata, current runtime attachment and pending-work flags, and the latest bounded runtime observation when available. Live runtime fields are current evidence only: a detached Session or an omitted observation does not rewrite or infer historical state. Missing or unreadable Sessions fail explicitly, and an incomplete Project catalog fails closed rather than returning a partial list.

activeConversation contains only frameId, branchId, and messageCount navigation metadata. It never returns messages, transcripts, private reasoning, tool payloads, terminal output, or synthesized diagnosis. Use host.frames.get(frameId, { sessionId, branchId }) when transcript detail is required. There is no Project override, mutation, recovery, cancellation, or message-send API in host.sessions; all returned projections are fresh and frozen.

Continue with the owning Skill

• Load the matching mcp-* Skill before using a connector through host.mcp.
• Load remote-compute-ssh for the host.compute API and workflow.
• Load customize for Specialist and Skill authoring workflows.

Maintain this contract

When a new host introspection surface ships, add its public capability key and update this Skill in the same feature change. Document only behavior that has shipped; do not predeclare future APIs as false.