Concrete Message Schemas¶

Field	Value
Status	Draft
Related RFC	RFC 0001
Related drafts	Logical wire message model, JSON serialization, Error codes, Operations, Capabilities, Protocol Contexts, Content representation

This document maps each message kind in the logical wire model to a concrete logical body schema. It defines fields and their conditions independently of the selected JSON serialization, OSC carrier, and framing mechanism.

1. Notation and Shared Types¶

The notation below describes records and tagged alternatives. It resembles a typed data language but does not require JSON or any other serialization. Every listed field is required unless marked with ?. {} is an empty record, and a complete Message always carries a body, including when that body is empty.

ContentSnapshot {
  type: ContentType
  data: ContentData
}

NonEmptyText = one or more Unicode scalar values
Text = zero or more Unicode scalar values
DiagnosticText = zero or more Unicode scalar values
ScalarCount = integer from 0 through 9007199254740991

ControlFailure {
  code: ControlErrorCode
  message?: DiagnosticText
}

ContentType identifies one negotiated content representation. For the baseline text/plain representation, data is a logical text value. Each optional content type defines its own complete ContentData schema.

ControlErrorCode is the subset of the stable protocol-defined Error Codes marked as valid for a control response. OperationErrorCode is the subset marked as valid for protocol.error. A code appearing in a reporting path marked no violates that Message schema. message is an optional human-readable diagnostic and is not a machine- readable contract.

Request IDs, Operation IDs, Context IDs, and Block IDs retain the ownership, scope, uniqueness, and opacity rules of their semantic drafts. Their concrete JSON mapping is defined by JSON Serialization.

2. Envelope Field Matrix¶

version, kind, and body are required on every Message. The remaining envelope fields are permitted only as follows:

Message kind	`request_id`	`operation_id`	`context_id`
`capability.query`	required	absent	absent
`capability.response`	required	absent	absent
`context.open`	required	absent	absent
`context.open.response`	required	absent	success only
`context.close`	required	absent	required
`context.close.response`	required	absent	required
`block.append`	absent	required	required
`block.update`	absent	required	required
`block.extend`	absent	required	required
`block.replace_suffix`	absent	required	required
`block.seal`	absent	required	required
`protocol.error`	absent	required	required

An envelope field appearing where this table marks it absent makes the whole Message invalid. For context.open.response, context_id is required for an opened outcome and absent for an error outcome.

A correlated control response uses the same protocol version as its request. A protocol.error uses the same protocol version as its rejected Operation.

3. Capability Messages¶

The queried protocol version is the envelope’s version, so the query body is empty:

capability.query body {}

The response echoes the request ID and uses exactly one of these bodies:

capability.response body =
  | {
      outcome: supported
      optional_content_types: ContentType[]
    }
  | {
      outcome: unsupported
    }
  | {
      outcome: error
      error: ControlFailure
    }

supported confirms the complete baseline for the envelope’s version. Its list contains only optional content types and may be empty; baseline text/plain support is implied and is not listed. unsupported is the normal negative negotiation result. error reports a reliably correlated request failure and does not establish protocol support.

4. Context Messages¶

Opening a Context requires no parameters beyond the common envelope:

context.open body {}

context.open.response body =
  | {
      outcome: opened
    }
  | {
      outcome: error
      error: ControlFailure
    }

An opened response carries the newly allocated context_id in its envelope. An error response carries no Context ID and creates no Context.

Context closure addresses the Context through the envelope, so its request body is also empty:

context.close body {}

context.close.response body =
  | {
      outcome: closed
    }
  | {
      outcome: error
      error: ControlFailure
    }

Both closure messages carry the addressed context_id. A closed outcome means the ordered closure boundary has completed. An error outcome leaves an open Context unchanged.

5. Block Operation Messages¶

Append carries everything needed to create one complete Block:

block.append body {
  block_id: BlockId
  lifecycle: mutable | sealed
  content: ContentSnapshot
}

Update replaces the complete content value while retaining Block identity, lifecycle, and append position:

block.update body {
  block_id: BlockId
  content: ContentSnapshot
}

Extend adds a non-empty text/plain fragment to the current logical tail and names the exact content state on which it depends:

block.extend body {
  block_id: BlockId
  base_operation_id: OperationId
  fragment: NonEmptyText
}

The target Block must already use text/plain; Extend does not carry or change its Content Type. An empty fragment violates this body schema. A valid base field whose value does not equal the Block’s current content-state Operation ID is a semantic content_state_mismatch, not a structural failure.

ReplaceSuffix removes a non-empty suffix and replaces it with text that may be empty:

block.replace_suffix body {
  block_id: BlockId
  base_operation_id: OperationId
  retain: ScalarCount
  replacement: Text
}

retain counts Unicode scalar values from the beginning of the current text/plain content. The target Block must already use text/plain; ReplaceSuffix does not carry or change its Content Type. The body is structurally valid when retain is a ScalarCount; semantic evaluation additionally requires it to be less than the current scalar-value length. Otherwise, the Operation reports invalid_content_boundary.

Seal changes only the lifecycle of its target:

block.seal body {
  block_id: BlockId
}

The Context ID and Operation ID belong to the common envelope rather than these bodies. Successful Operations have no response.

6. Protocol Error Message¶

A rejected, reliably identified Block Operation produces:

protocol.error body {
  code: OperationErrorCode
  message?: DiagnosticText
}

The error echoes the rejected Operation’s context_id and operation_id in its envelope. Block identity is not repeated generically: when relevant, its value can appear in the human diagnostic, while machine behavior is selected by the stable error code and correlated Operation identity.

7. Validation¶

The receiver first validates the common envelope and then the body schema selected by version and kind. Tagged response alternatives are exclusive: fields belonging to another outcome are unknown fields and invalidate the complete Message.

Schema validity does not imply semantic validity. For example, a structurally valid block.update can still fail because its Block is unknown or sealed, and a structurally valid block.extend or block.replace_suffix can name a stale content state. Structural and semantic failures apply no requested Context or Block change. Correlation bookkeeping and error reporting follow the logical wire model, including non-reuse of a reliably identified failed Operation’s ID.

Baseline text/plain uses the Text schema above. Its display and native-text processing are defined in Plain Text Content; the schema does not normalize its data or reject the controls represented by visible labels.