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extensions-registry

id: "extensions-registry" slug: "extensions-registry" title: "Extension registry — full text" description: "The full EXTENSIONS.md registry text: entry process, status rules, and the five registered extensions."​

Extensions are named, optional capability sets a writer declares in the top-level extensions array (see SPEC.md, "Extensions"). Core v1 parsing is never affected: a reader that doesn't know an extension ignores it.

Adding an entry​

Open a PR adding a section below. Each entry: name (lowercase, hyphenated, unique), status (draft → stable; deprecated retires it), purpose, the exact fields it reads/writes and where, and any conformance vectors (conformance/vectors/extensions.json). Status moves draft → stable when at least two independent implementations round-trip it. Exception: the two seed entries (images-inline, usage-metadata) entered the registry already stable — they predate the rule and are round-tripped across the ecosystem; the criterion governs entries that enter as draft.

Registry​

NameStatusEmitted byPurpose
images-inlinestablecurtis plugin, porter, curtis-web, curtis-cloud, curtis-ai-techImage payloads ride inside content
usage-metadatastableporter, curtis-web, curtis-ai-techPer-message cost/token/provider fields
tool-linkagedraftporter, curtis-ai-tech, curt-convert (same author — does not count toward stability)Tool-call requests and their results
agent-contextdraftcurtis plugin, porter, curtis-cloud, curtis-ai-techAgent/swarm provenance on conversations and messages
consensus-receiptdrafttractumSigned k-of-n consensus decision bound to the transcript evidence

Full per-consumer emit/accept data: capabilities.json.

images-inline — stable​

The convention this extension declares: images are not a separate field — a message whose content is a data URI (data:image/...;base64,...) or raw base64 carries an image inline. Declaring it tells other readers what to expect; it adds no fields and changes no behavior.

  • Fields: none beyond core — content carries the payload; kind: "image" is a common optional marker.
  • Readers never decode or transform content, and files never carry a byte-order mark (see SPEC.md, "File shape").

usage-metadata — stable​

Optional extra fields recording economics and provenance:

  • Message-level: tokens (object, e.g. { "input": 12, "output": 340 }), cost (number, writer's currency), provider (string).
  • Readers must preserve these verbatim on round-trip; they never affect validation.

tool-linkage — draft​

Links assistant tool calls to their tool-role results:

  • Assistant message: toolCalls (array of objects with id (string), name (string), arguments (writer's JSON value)).
  • Tool message: toolCallId (string) referencing the toolCalls[].id.
  • Round-trip is verbatim; readers must not reorder or drop entries.
  • Status draft. Second emitter added 2026-11-01 (curt-convert, same author as the reference) — stability still requires two independent implementations.

agent-context — draft​

Multi-agent provenance:

  • Conversation-level: agentId (string), skillIds (array of strings), swarmRole (string), leaderId (string).
  • Semantics are writer-defined; the extension guarantees only preservation.

consensus-receipt — draft​

A verifiable multi-agent consensus decision carried alongside the evidence it was drawn from. The conversation's messages ARE the evidence transcript; the decision rides in extension fields:

  • Conversation-level: consensusReceipt (object — the full signed receipt envelope: payload, algorithm, public_key, signature, payload_hash, signed_at, metadata) and consensusTranscripts (array of { "id": string, "sha256": string } — one entry per source transcript, where sha256 is the hex digest over that document's canonical JSON serialization).
  • The receipt's signed payload embeds its own copy of the consensusTranscripts refs. Verifiers recompute the hashes and compare — the decision is bound to this exact evidence or the artifact is invalid.
  • Writers SHOULD declare agent-context alongside this extension (the receipt's per-agent statements reference agents that agent-context provenance describes).
  • The extension guarantees only preservation. Signature and quorum verification semantics are writer-defined (tractum: Ed25519 or ML-DSA over canonical JSON, k-of-n quorum in payload.quorum).
  • Status draft: single implementation (tractum). Stable when a second independent implementation round-trips it.