Runtime semantics (3)

The three kinds that describe runtime behavior outside features themselves. Two of them carry Layer 2.

rule — rul_ (carries Layer 2)

Engine-executable expression — typically a validation predicate.

{
  "id": "rul_name_not_empty_a1b2",
  "kind": "rule",
  "name": "habit_name_not_empty",
  "expression": "length(state.draftHabitName) > 0",
  "errorMessage": "Habit name cannot be empty",
  "behavior": {
    "enforced_at": [
      { "kind": "ui_disabled", "ui_view": "ui_habits_screen_a1b2",
        "binding": "submitButton" },
      { "kind": "pre_call", "feature": "feat_create_habit_h14a",
        "on_failure": "abort" }
    ]
  }
}

The expression is the rule’s predicate (RFC-002 syntax). The behavior.enforced_at array binds the rule to specific UI sites and call points. See RFC-002 — Rule expression grammar.

ui_view — ui_ (carries Layer 2)

A screen — or, in v0.3, a multi-screen view tree.

{
  "id": "ui_habits_screen_a1b2",
  "kind": "ui_view",
  "name": "Habits screen",
  "viewType": "list",
  "behavior": {
    "rootScreen": "list",
    "screens": {
      "list": {
        "sections": [
          { "kind": "heading", "level": 1, "text": "My habits" },
          { "kind": "list", "source": "state.habits",
            "itemTemplate": [
              { "kind": "text", "body": "{{ item.name }}" }
            ] },
          { "kind": "button", "label": "Add habit",
            "dispatch": "navigate_to_add", "variant": "primary" }
        ]
      },
      "add": {
        "sections": [
          { "kind": "heading", "level": 2, "text": "New habit" },
          { "kind": "input", "name": "habitName", "bind": "state.draftHabitName" },
          { "kind": "button", "label": "Create",
            "dispatch": "feat_create_habit_h14a", "variant": "primary" }
        ]
      }
    }
  }
}

viewType is one of list / form / detail / dashboard / wizard / custom. It seeds Pattern C’s template selection when Layer 2 is empty.

Multi-screen views compile to a top-level $Switch keyed by a state slot. See Codegen → SenLang bridge.

integration — int_

External service descriptor — protocol, base URL, auth method.

{
  "id": "int_habits_api_c3d4",
  "kind": "integration",
  "name": "Habits REST API",
  "protocol": "http",
  "baseUrl": "https://api.example.com",
  "auth": "bearer"
}

protocol is one of http / webhook / sms / email / graphql / grpc / mcp / sse / websocket / database.

No Layer 2 — integrations are descriptive. Features bind to them via depends_on edges:

{
  "type": "depends_on",
  "from": "feat_load_habits_e5f6",
  "to":   "int_habits_api_c3d4"
}

The codegen bridge uses the integration to resolve relative endpoint URLs in feature.behavior.steps[*].endpoint.

See also

• Spec → Layer 2 schemas — rule.behavior and ui_view.behavior.
• RFC-002 — Rule expression grammar — expression field syntax.
• RFC-003 — Events on ui_view — section dispatch semantics.