Assertion contracts and limits

Language: canon-expr/1. Source implementation; no release is claimed.

The concept guide explains compilation, acquisition and offline evaluation. These limits are read from the library constants; changing one requires compatibility review.

Budget	Maximum
Combined source bytes	65536
Tokens per expression	16384
Nesting	32
Expanded nodes	4096
Assertions	1024
Unique requests	4096
Bound values or evidence payload bytes	1048576

Typed documents

This is the exact ESS model embedded by the expression library. Semantic constraints are exercised by its conformance suite. Integer wire strings preserve i128 values through JSON; decimal coefficients use the same canonical strings.

domain: canon.expr
summary: Typed expression programs, catalog contracts, collected observations and pure evaluation reports.
naming:
  wire: expr
  display: Expression

types:
  # read from: docs/design/assertion-api.md (Scalar)
  - name: canon.expr.Scalar
    kind: enum
    variants: ["bool", "string", "integer", "decimal"]

  # read from: docs/design/assertion-api.md (Type)
  - name: canon.expr.Type
    kind: union
    tag: kind
    variants:
      scalar: canon.expr.Scalar
      list: canon.expr.Type
      map: canon.expr.Type
      record: Map<String, canon.expr.Type>
      optional: canon.expr.Type

  # read from: docs/design/assertion-api.md (Exact)
  - name: canon.expr.Exact
    kind: struct
    fields:
      - name: coefficient
        type: String
      - name: scale
        type: Integer

  # read from: docs/design/assertion-api.md (Value)
  - name: canon.expr.Value
    kind: union
    tag: kind
    variants:
      bool: Boolean
      string: String
      integer: String
      decimal: canon.expr.Exact
      list: List<canon.expr.Value>
      record: Map<String, canon.expr.Value>
      map: Map<String, canon.expr.Value>
      optional: Optional<canon.expr.Value>

  # read from: docs/design/assertion-api.md (Builtin)
  - name: canon.expr.Builtin
    kind: enum
    variants: ["length", "contains", "starts_with", "ends_with", "present"]

  # read from: docs/design/assertion-api.md (Provider)
  - name: canon.expr.Provider
    kind: struct
    fields:
      - name: provider
        type: String
      - name: operation
        type: String
      - name: digest
        type: String

  # read from: docs/design/assertion-api.md (Implementation)
  - name: canon.expr.Implementation
    kind: union
    tag: kind
    variants:
      observation: canon.expr.Provider
      recipe: String
      pure: canon.expr.Builtin

  # read from: docs/design/assertion-api.md (Parameter)
  - name: canon.expr.Parameter
    kind: struct
    fields:
      - name: name
        type: String
      - name: value_type
        type: canon.expr.Type
      - name: default
        type: Optional<canon.expr.Value>

  # read from: docs/design/assertion-api.md (Function)
  - name: canon.expr.Function
    kind: struct
    fields:
      - name: parameters
        type: List<canon.expr.Parameter>
      - name: returns
        type: canon.expr.Type
      - name: implementation
        type: canon.expr.Implementation

  # read from: docs/design/assertion-api.md (Catalog)
  - name: canon.expr.Catalog
    kind: struct
    fields:
      - name: format
        type: String
      - name: functions
        type: Map<String, canon.expr.Function>

  # read from: docs/design/assertion-api.md (Bindings)
  - name: canon.expr.Bindings
    kind: struct
    fields:
      - name: values
        type: Map<String, canon.expr.Value>
      - name: source_identity
        type: String
      - name: context_identity
        type: String

  # read from: docs/design/assertion-api.md (Request)
  - name: canon.expr.Request
    kind: struct
    fields:
      - name: id
        type: String
      - name: provider
        type: String
      - name: operation
        type: String
      - name: digest
        type: String
      - name: arguments
        type: Map<String, canon.expr.Value>
      - name: result_type
        type: canon.expr.Type

  # read from: docs/design/assertion-api.md (Outcome)
  - name: canon.expr.Outcome
    kind: union
    tag: kind
    variants:
      known: canon.expr.Value
      unavailable: String

  # read from: docs/design/assertion-api.md (Observation)
  - name: canon.expr.Observation
    kind: struct
    fields:
      - name: request_id
        type: String
      - name: plan_id
        type: String
      - name: observed_at
        type: Integer
      - name: valid_until
        type: Optional<Integer>
      - name: outcome
        type: canon.expr.Outcome

  # read from: docs/design/assertion-api.md (EvalContext)
  - name: canon.expr.EvalContext
    kind: struct
    fields:
      - name: now
        type: Integer
      - name: source_identity
        type: String
      - name: context_identity
        type: String

  # read from: docs/design/assertion-api.md (Truth)
  - name: canon.expr.Truth
    kind: enum
    variants: ["true", "false", "unknown"]

  # read from: docs/design/assertion-api.md (Evaluation)
  - name: canon.expr.Evaluation
    kind: struct
    fields:
      - name: expression
        type: String
      - name: truth
        type: canon.expr.Truth
      - name: reasons
        type: List<String>

  # read from: docs/design/assertion-api.md (Report)
  - name: canon.expr.Report
    kind: struct
    fields:
      - name: plan_id
        type: String
      - name: truth
        type: canon.expr.Truth
      - name: assertions
        type: List<canon.expr.Evaluation>

  # read from: docs/design/assertion-api.md (PlanDocument)
  - name: canon.expr.PlanDocument
    kind: struct
    fields:
      - name: id
        type: String
      - name: sources
        type: List<String>
      - name: catalog
        type: canon.expr.Catalog
      - name: bindings
        type: canon.expr.Bindings
      - name: context_types
        type: Map<String, canon.expr.Type>
      - name: requests
        type: List<canon.expr.Request>