{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Pi Extension Protocol",
  "type": "object",
  "required": ["id", "version", "type", "payload"],
  "properties": {
    "id": { "type": "string", "description": "Correlation id for request/response" },
    "version": { "type": "string", "enum": ["1.0"] },
    "type": {
      "type": "string",
      "enum": [
        "register",
        "tool_call",
        "tool_result",
        "slash_command",
        "slash_result",
        "event_hook",
        "host_call",
        "host_result",
        "log",
        "error"
      ]
    },
    "payload": { "type": "object" }
  },
  "allOf": [
    {
      "if": { "properties": { "type": { "const": "register" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/register" } } }
    },
    {
      "if": { "properties": { "type": { "const": "tool_call" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/tool_call" } } }
    },
    {
      "if": { "properties": { "type": { "const": "tool_result" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/tool_result" } } }
    },
    {
      "if": { "properties": { "type": { "const": "slash_command" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/slash_command" } } }
    },
    {
      "if": { "properties": { "type": { "const": "slash_result" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/slash_result" } } }
    },
    {
      "if": { "properties": { "type": { "const": "event_hook" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/event_hook" } } }
    },
    {
      "if": { "properties": { "type": { "const": "host_call" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/host_call" } } }
    },
    {
      "if": { "properties": { "type": { "const": "host_result" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/host_result" } } }
    },
    {
      "if": { "properties": { "type": { "const": "log" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/log" } } }
    },
    {
      "if": { "properties": { "type": { "const": "error" } } },
      "then": { "properties": { "payload": { "$ref": "#/$defs/error" } } }
    }
  ],
  "$defs": {
    "register": {
      "type": "object",
      "required": ["name", "version", "api_version"],
      "properties": {
        "name": { "type": "string" },
        "version": { "type": "string" },
        "api_version": { "type": "string" },
        "capabilities": { "type": "array", "items": { "type": "string" } },
        "capability_manifest": { "$ref": "#/$defs/capability_manifest" },
        "tools": { "type": "array", "items": { "type": "object" } },
        "slash_commands": { "type": "array", "items": { "type": "object" } },
        "event_hooks": { "type": "array", "items": { "type": "string" } }
      }
    },
    "capability_manifest": {
      "type": "object",
      "required": ["schema", "capabilities"],
      "properties": {
        "schema": { "type": "string", "enum": ["pi.ext.cap.v1"] },
        "capabilities": {
          "type": "array",
          "items": { "$ref": "#/$defs/capability_requirement" }
        }
      }
    },
    "capability_requirement": {
      "type": "object",
      "required": ["capability"],
      "properties": {
        "capability": { "type": "string" },
        "methods": { "type": "array", "items": { "type": "string" } },
        "scope": { "$ref": "#/$defs/capability_scope" }
      }
    },
    "capability_scope": {
      "type": "object",
      "properties": {
        "paths": { "type": "array", "items": { "type": "string" } },
        "hosts": { "type": "array", "items": { "type": "string" } },
        "env": { "type": "array", "items": { "type": "string" } }
      }
    },
    "tool_call": {
      "type": "object",
      "required": ["call_id", "name", "input"],
      "properties": {
        "call_id": { "type": "string" },
        "name": { "type": "string" },
        "input": { "type": "object" },
        "context": { "type": "object" }
      }
    },
    "tool_result": {
      "type": "object",
      "required": ["call_id", "output", "is_error"],
      "properties": {
        "call_id": { "type": "string" },
        "output": { "type": "object" },
        "is_error": { "type": "boolean" }
      }
    },
    "host_call": {
      "type": "object",
      "required": ["call_id", "capability", "method", "params"],
      "properties": {
        "call_id": { "type": "string" },
        "capability": { "type": "string", "description": "Capability key to evaluate and audit (must match core-derived requirement)" },
        "method": { "type": "string", "description": "Connector method name (e.g., tool, exec, http, session, ui)" },
        "params": { "type": "object" },
        "timeout_ms": { "type": "integer", "minimum": 0 },
        "cancel_token": { "type": "string" },
        "context": { "type": "object" }
      }
    },
    "host_result": {
      "type": "object",
      "required": ["call_id", "output", "is_error"],
      "properties": {
        "call_id": { "type": "string" },
        "output": { "type": "object" },
        "is_error": { "type": "boolean" },
        "error": { "$ref": "#/$defs/host_call_error" },
        "chunk": { "$ref": "#/$defs/host_stream_chunk" }
      },
      "allOf": [
        {
          "if": { "properties": { "is_error": { "const": true } } },
          "then": { "required": ["error"] }
        },
        {
          "if": { "properties": { "is_error": { "const": false } } },
          "then": { "not": { "required": ["error"] } }
        }
      ]
    },
    "host_call_error_code": {
      "type": "string",
      "enum": ["timeout", "denied", "io", "invalid_request", "internal"]
    },
    "host_call_error": {
      "type": "object",
      "required": ["code", "message"],
      "properties": {
        "code": { "$ref": "#/$defs/host_call_error_code" },
        "message": { "type": "string" },
        "details": { "type": "object" },
        "retryable": { "type": "boolean" }
      }
    },
    "host_stream_backpressure": {
      "type": "object",
      "properties": {
        "credits": { "type": "integer", "minimum": 0 },
        "delay_ms": { "type": "integer", "minimum": 0 }
      }
    },
    "host_stream_chunk": {
      "type": "object",
      "required": ["index", "is_last"],
      "properties": {
        "index": { "type": "integer", "minimum": 0 },
        "is_last": { "type": "boolean" },
        "backpressure": { "$ref": "#/$defs/host_stream_backpressure" }
      }
    },
    "slash_command": {
      "type": "object",
      "required": ["name"],
      "properties": {
        "name": { "type": "string" },
        "args": { "type": "array", "items": { "type": "string" } },
        "input": { "type": "object" }
      }
    },
    "slash_result": {
      "type": "object",
      "required": ["output", "is_error"],
      "properties": {
        "output": { "type": "object" },
        "is_error": { "type": "boolean" }
      }
    },
    "event_hook": {
      "type": "object",
      "required": ["event"],
      "properties": {
        "event": { "type": "string" },
        "data": { "type": "object" }
      }
    },
    "log": {
      "type": "object",
      "required": ["schema", "ts", "level", "event", "message", "correlation"],
      "properties": {
        "schema": { "type": "string", "enum": ["pi.ext.log.v1"] },
        "ts": { "type": "string", "format": "date-time" },
        "level": { "type": "string", "enum": ["debug", "info", "warn", "error"] },
        "event": { "type": "string" },
        "message": { "type": "string" },
        "correlation": { "$ref": "#/$defs/log_correlation" },
        "source": { "$ref": "#/$defs/log_source" },
        "data": { "type": "object" }
      }
    },
    "log_correlation": {
      "type": "object",
      "required": ["extension_id", "scenario_id"],
      "properties": {
        "extension_id": { "type": "string" },
        "scenario_id": { "type": "string" },
        "session_id": { "type": "string" },
        "run_id": { "type": "string" },
        "artifact_id": { "type": "string" },
        "tool_call_id": { "type": "string" },
        "slash_command_id": { "type": "string" },
        "event_id": { "type": "string" },
        "host_call_id": { "type": "string" },
        "rpc_id": { "type": "string" },
        "trace_id": { "type": "string" },
        "span_id": { "type": "string" }
      }
    },
    "log_source": {
      "type": "object",
      "required": ["component"],
      "properties": {
        "component": {
          "type": "string",
          "enum": ["capture", "harness", "runtime", "extension"]
        },
        "host": { "type": "string" },
        "pid": { "type": "integer", "minimum": 0 }
      }
    },
    "error": {
      "type": "object",
      "required": ["code", "message"],
      "properties": {
        "code": { "type": "string" },
        "message": { "type": "string" },
        "details": { "type": "object" }
      }
    }
  }
}