{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://bpa.local/schemas/browser-protocol/v2",
  "title": "BPA Browser Protocol v2 Message",
  "oneOf": [
    { "$ref": "#/$defs/sessionHello" },
    { "$ref": "#/$defs/sessionWelcome" },
    { "$ref": "#/$defs/sessionResume" },
    { "$ref": "#/$defs/capabilityReport" },
    { "$ref": "#/$defs/pageObservation" },
    { "$ref": "#/$defs/pageProbeRequest" },
    { "$ref": "#/$defs/pageProbeResult" },
    { "$ref": "#/$defs/command" },
    { "$ref": "#/$defs/commandAck" },
    { "$ref": "#/$defs/commandResult" },
    { "$ref": "#/$defs/resultAck" },
    { "$ref": "#/$defs/cancelRequest" },
    { "$ref": "#/$defs/cancelAck" },
    { "$ref": "#/$defs/cancelEffective" },
    { "$ref": "#/$defs/heartbeat" },
    { "$ref": "#/$defs/sessionError" },
    { "$ref": "#/$defs/evidenceBegin" },
    { "$ref": "#/$defs/evidenceChunk" },
    { "$ref": "#/$defs/evidenceComplete" },
    { "$ref": "#/$defs/evidenceAck" }
  ],
  "$defs": {
    "id": {
      "type": "string",
      "minLength": 1,
      "maxLength": 200,
      "pattern": "^[A-Za-z0-9][A-Za-z0-9._:-]*$"
    },
    "digest": {
      "type": "string",
      "pattern": "^sha256:[a-f0-9]{64}$"
    },
    "timestamp": {
      "type": "string",
      "format": "date-time"
    },
    "baseProperties": {
      "type": "object",
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 0 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "type": "string" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": { "type": "object" }
      }
    },
    "envelopeRequired": {
      "type": "array",
      "prefixItems": [
        { "const": "protocol" },
        { "const": "version" },
        { "const": "message_id" },
        { "const": "session_id" },
        { "const": "seq" },
        { "const": "sent_at" },
        { "const": "type" },
        { "const": "trace_id" },
        { "const": "payload" }
      ]
    },
    "capability": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "node_id",
        "versions",
        "risk_level",
        "permissions",
        "routes"
      ],
      "properties": {
        "node_id": { "$ref": "#/$defs/id" },
        "versions": {
          "type": "array",
          "minItems": 1,
          "uniqueItems": true,
          "items": { "$ref": "#/$defs/id" }
        },
        "risk_level": { "enum": ["R0", "R1", "R2", "R3", "R4"] },
        "permissions": {
          "type": "array",
          "uniqueItems": true,
          "items": { "$ref": "#/$defs/id" }
        },
        "routes": {
          "type": "array",
          "minItems": 1,
          "items": {
            "type": "object",
            "additionalProperties": false,
            "required": [
              "origin",
              "pathname_prefixes",
              "observer_capability_id"
            ],
            "properties": {
              "origin": { "type": "string", "format": "uri" },
              "pathname_prefixes": {
                "type": "array",
                "minItems": 1,
                "uniqueItems": true,
                "items": {
                  "type": "string",
                  "minLength": 1,
                  "maxLength": 2048,
                  "pattern": "^/"
                }
              },
              "observer_capability_id": { "$ref": "#/$defs/id" }
            }
          }
        },
        "adapter_id": { "$ref": "#/$defs/id" },
        "adapter_version": { "$ref": "#/$defs/id" }
      }
    },
    "tabRef": {
      "type": "object",
      "additionalProperties": false,
      "required": ["browser_instance_id", "tab_id", "origin"],
      "properties": {
        "browser_instance_id": { "$ref": "#/$defs/id" },
        "tab_id": { "type": "integer", "minimum": 0 },
        "window_id": { "type": "integer", "minimum": 0 },
        "origin": { "type": "string", "format": "uri" }
      }
    },
    "permissionGrant": {
      "$ref": "https://bpa.local/schemas/permission/v1"
    },
    "coreSigningKey": {
      "type": "object",
      "additionalProperties": false,
      "required": ["key_id", "algorithm", "public_key_spki_base64"],
      "properties": {
        "key_id": { "$ref": "#/$defs/id" },
        "algorithm": { "const": "Ed25519" },
        "public_key_spki_base64": {
          "type": "string",
          "minLength": 40,
          "maxLength": 128,
          "pattern": "^[A-Za-z0-9+/]+={0,2}$"
        }
      }
    },
    "resultStatus": {
      "enum": ["succeeded", "rejected", "failed", "timed_out", "cancelled", "uncertain"]
    },
    "browserFeatures": {
      "type": "array",
      "minItems": 3,
      "uniqueItems": true,
      "items": {
        "enum": [
          "page_observation_v2",
          "exact_tab_binding_v2",
          "active_page_probe_v1"
        ]
      },
      "allOf": [
        { "contains": { "const": "page_observation_v2" } },
        { "contains": { "const": "exact_tab_binding_v2" } },
        { "contains": { "const": "active_page_probe_v1" } }
      ]
    },
    "messageBase": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 0 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "type": "string" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": { "type": "object" }
      }
    },
    "sessionHello": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "const": "new" },
        "seq": { "const": 0 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "session.hello" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "browser_instance_id",
            "extension_id",
            "extension_version",
            "bridge_build_id",
            "supported_protocols",
            "features",
            "last_acked_command_seq"
          ],
          "properties": {
            "browser_instance_id": { "$ref": "#/$defs/id" },
            "extension_id": { "$ref": "#/$defs/id" },
            "extension_version": { "$ref": "#/$defs/id" },
            "bridge_build_id": { "$ref": "#/$defs/id" },
            "supported_protocols": {
              "type": "array",
              "minItems": 1,
              "uniqueItems": true,
              "items": { "const": "bpa.browser/2" }
            },
            "features": { "$ref": "#/$defs/browserFeatures" },
            "last_acked_command_seq": { "type": "integer", "minimum": 0 },
            "resume_token": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "sessionWelcome": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "session.welcome" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "selected_protocol",
            "heartbeat_ms",
            "resume_token",
            "resume_token_expires_at",
            "max_message_bytes",
            "core_signing_key"
          ],
          "properties": {
            "selected_protocol": { "const": "bpa.browser/2" },
            "heartbeat_ms": { "type": "integer", "minimum": 1000, "maximum": 120000 },
            "resume_token": { "$ref": "#/$defs/id" },
            "resume_token_expires_at": { "$ref": "#/$defs/timestamp" },
            "core_signing_key": { "$ref": "#/$defs/coreSigningKey" },
            "max_message_bytes": { "const": 524288 }
          }
        }
      }
    },
    "sessionResume": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "session.resume" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["accepted", "replay_from_command_seq"],
          "properties": {
            "accepted": { "type": "boolean" },
            "replay_from_command_seq": { "type": "integer", "minimum": 0 },
            "reason_code": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "capabilityReport": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "capability.report" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["capabilities", "manifest_digest", "features"],
          "properties": {
            "capabilities": {
              "type": "array",
              "maxItems": 500,
              "items": { "$ref": "#/$defs/capability" }
            },
            "manifest_digest": { "$ref": "#/$defs/digest" },
            "features": { "$ref": "#/$defs/browserFeatures" }
          }
        }
      }
    },
    "pageObservation": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "page.observation" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "tab_ref",
            "pathname",
            "content_script_ready",
            "authentication",
            "observation_state",
            "page_epoch",
            "observation_revision",
            "observer_capability_id",
            "observed_at"
          ],
          "properties": {
            "tab_ref": { "$ref": "#/$defs/tabRef" },
            "pathname": {
              "type": "string",
              "minLength": 1,
              "maxLength": 2048,
              "pattern": "^/"
            },
            "content_script_ready": { "type": "boolean" },
            "authentication": {
              "oneOf": [
                {
                  "type": "object",
                  "additionalProperties": false,
                  "required": ["state"],
                  "properties": {
                    "state": { "enum": ["unknown", "anonymous"] }
                  }
                },
                {
                  "type": "object",
                  "additionalProperties": false,
                  "required": ["state", "context_ref"],
                  "properties": {
                    "state": { "enum": ["authenticated", "membership"] },
                    "context_ref": { "$ref": "#/$defs/id" }
                  }
                }
              ]
            },
            "observation_state": {
              "enum": [
                "content_script_missing",
                "loading",
                "probing",
                "auth_required",
                "challenge",
                "ready",
                "departed",
                "stale"
              ]
            },
            "page_epoch": { "$ref": "#/$defs/id" },
            "observation_revision": { "type": "integer", "minimum": 1 },
            "observer_capability_id": { "$ref": "#/$defs/id" },
            "observed_at": { "$ref": "#/$defs/timestamp" },
            "reason_code": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "pageProbeRequest": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "page.probe.request" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["request_id", "tab_ref", "deadline"],
          "properties": {
            "request_id": { "$ref": "#/$defs/id" },
            "tab_ref": { "$ref": "#/$defs/tabRef" },
            "deadline": { "$ref": "#/$defs/timestamp" }
          }
        }
      }
    },
    "pageProbeResult": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "page.probe.result" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "request_id",
            "tab_ref",
            "accepted",
            "observation_revision"
          ],
          "properties": {
            "request_id": { "$ref": "#/$defs/id" },
            "tab_ref": { "$ref": "#/$defs/tabRef" },
            "accepted": { "type": "boolean" },
            "observation_revision": { "type": "integer", "minimum": 1 },
            "reason_code": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "command": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "command.dispatch" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "command_seq",
            "run_id",
            "workflow_id",
            "workflow_version",
            "node_execution_id",
            "command_id",
            "idempotency_key",
            "fencing_token",
            "attempt",
            "node",
            "input",
            "permission_grant",
            "deadline",
            "tab_ref",
            "page_epoch",
            "observation_revision"
          ],
          "properties": {
            "command_seq": { "type": "integer", "minimum": 1 },
            "run_id": { "$ref": "#/$defs/id" },
            "workflow_id": { "$ref": "#/$defs/id" },
            "workflow_version": { "$ref": "#/$defs/id" },
            "node_execution_id": { "$ref": "#/$defs/id" },
            "command_id": { "$ref": "#/$defs/id" },
            "idempotency_key": { "$ref": "#/$defs/id" },
            "fencing_token": { "type": "integer", "minimum": 1 },
            "attempt": { "type": "integer", "minimum": 1, "maximum": 10 },
            "node": {
              "type": "object",
              "additionalProperties": false,
              "required": ["id", "version"],
              "properties": {
                "id": { "$ref": "#/$defs/id" },
                "version": { "$ref": "#/$defs/id" }
              }
            },
            "input": {},
            "permission_grant": { "$ref": "#/$defs/permissionGrant" },
            "deadline": { "$ref": "#/$defs/timestamp" },
            "timing_policy": {
              "$ref": "https://bpa.local/schemas/timing-policy/v1"
            },
            "tab_ref": { "$ref": "#/$defs/tabRef" },
            "page_epoch": { "$ref": "#/$defs/id" },
            "observation_revision": { "type": "integer", "minimum": 1 },
            "authentication_context_ref": { "$ref": "#/$defs/id" },
            "approval_token_ref": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "commandAck": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "command.ack" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["command_seq", "command_id", "node_execution_id", "accepted", "fencing_token"],
          "properties": {
            "command_seq": { "type": "integer", "minimum": 1 },
            "command_id": { "$ref": "#/$defs/id" },
            "node_execution_id": { "$ref": "#/$defs/id" },
            "accepted": { "type": "boolean" },
            "fencing_token": { "type": "integer", "minimum": 1 },
            "reason_code": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "commandResult": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "command.result" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "command_seq",
            "command_id",
            "node_execution_id",
            "idempotency_key",
            "fencing_token",
            "status"
          ],
          "properties": {
            "command_seq": { "type": "integer", "minimum": 1 },
            "command_id": { "$ref": "#/$defs/id" },
            "node_execution_id": { "$ref": "#/$defs/id" },
            "idempotency_key": { "$ref": "#/$defs/id" },
            "fencing_token": { "type": "integer", "minimum": 1 },
            "status": { "$ref": "#/$defs/resultStatus" },
            "output": {},
            "error": {
              "type": "object",
              "additionalProperties": false,
              "required": ["code", "message"],
              "properties": {
                "code": { "$ref": "#/$defs/id" },
                "message": { "type": "string", "maxLength": 4000 },
                "retryable": { "type": "boolean" }
              }
            },
            "evidence_refs": {
              "type": "array",
              "uniqueItems": true,
              "items": { "$ref": "#/$defs/id" }
            },
            "page_epoch": { "$ref": "#/$defs/id" },
            "risk_signals": {
              "type": "array",
              "maxItems": 20,
              "items": {
                "$ref": "https://bpa.local/schemas/risk-signal/v1"
              }
            },
            "timing_observation": {
              "type": "object",
              "additionalProperties": false,
              "required": ["rate_limit_wait_ms"],
              "properties": {
                "rate_limit_wait_ms": {
                  "type": "integer",
                  "minimum": 0,
                  "maximum": 120000
                },
                "readiness_wait_ms": {
                  "type": "integer",
                  "minimum": 0,
                  "maximum": 120000
                },
                "stable_for_ms": {
                  "type": "integer",
                  "minimum": 0,
                  "maximum": 10000
                }
              }
            }
          }
        }
      }
    },
    "resultAck": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "result.ack" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["command_id", "node_execution_id", "accepted"],
          "properties": {
            "command_id": { "$ref": "#/$defs/id" },
            "node_execution_id": { "$ref": "#/$defs/id" },
            "accepted": { "type": "boolean" },
            "reason_code": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "cancelRequest": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "cancel.request" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["command_id", "node_execution_id", "fencing_token", "reason_code"],
          "properties": {
            "command_id": { "$ref": "#/$defs/id" },
            "node_execution_id": { "$ref": "#/$defs/id" },
            "fencing_token": { "type": "integer", "minimum": 1 },
            "reason_code": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "cancelAck": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "cancel.ack" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "command_id",
            "node_execution_id",
            "fencing_token",
            "acknowledged"
          ],
          "properties": {
            "command_id": { "$ref": "#/$defs/id" },
            "node_execution_id": { "$ref": "#/$defs/id" },
            "fencing_token": { "type": "integer", "minimum": 1 },
            "acknowledged": { "type": "boolean" },
            "action_started": { "type": "boolean" },
            "reason_code": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "cancelEffective": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "cancel.effective" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "command_id",
            "node_execution_id",
            "fencing_token",
            "status"
          ],
          "properties": {
            "command_id": { "$ref": "#/$defs/id" },
            "node_execution_id": { "$ref": "#/$defs/id" },
            "fencing_token": { "type": "integer", "minimum": 1 },
            "status": { "enum": ["cancelled", "uncertain"] },
            "safe_stop": { "type": "boolean" }
          }
        }
      }
    },
    "heartbeat": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "enum": ["heartbeat.ping", "heartbeat.pong"] },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["nonce"],
          "properties": {
            "nonce": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "sessionError": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 0 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "session.error" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["code", "message", "fatal"],
          "properties": {
            "code": { "$ref": "#/$defs/id" },
            "message": { "type": "string", "minLength": 1, "maxLength": 4000 },
            "fatal": { "type": "boolean" },
            "related_message_id": { "$ref": "#/$defs/id" }
          }
        }
      }
    },
    "evidenceBegin": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "evidence.begin" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": [
            "evidence_id",
            "run_id",
            "node_execution_id",
            "kind",
            "media_type",
            "size",
            "digest",
            "chunk_size",
            "chunk_count"
          ],
          "properties": {
            "evidence_id": { "$ref": "#/$defs/id" },
            "run_id": { "$ref": "#/$defs/id" },
            "node_execution_id": { "$ref": "#/$defs/id" },
            "kind": { "enum": ["dom_summary", "screenshot", "file", "verification", "error"] },
            "media_type": { "type": "string", "minLength": 1, "maxLength": 200 },
            "size": { "type": "integer", "minimum": 0, "maximum": 1073741824 },
            "digest": { "$ref": "#/$defs/digest" },
            "chunk_size": { "const": 262144 },
            "chunk_count": { "type": "integer", "minimum": 0, "maximum": 4096 }
          }
        }
      }
    },
    "evidenceChunk": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "evidence.chunk" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["evidence_id", "index", "data_base64", "chunk_digest"],
          "properties": {
            "evidence_id": { "$ref": "#/$defs/id" },
            "index": { "type": "integer", "minimum": 0, "maximum": 4095 },
            "data_base64": { "type": "string", "maxLength": 349528 },
            "chunk_digest": { "$ref": "#/$defs/digest" }
          }
        }
      }
    },
    "evidenceComplete": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "evidence.complete" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["evidence_id", "digest", "chunk_count"],
          "properties": {
            "evidence_id": { "$ref": "#/$defs/id" },
            "digest": { "$ref": "#/$defs/digest" },
            "chunk_count": { "type": "integer", "minimum": 0, "maximum": 4096 }
          }
        }
      }
    },
    "evidenceAck": {
      "type": "object",
      "additionalProperties": false,
      "required": [
        "protocol",
        "version",
        "message_id",
        "session_id",
        "seq",
        "sent_at",
        "type",
        "trace_id",
        "payload"
      ],
      "properties": {
        "protocol": { "const": "bpa.browser/2" },
        "version": { "const": "2.0.0" },
        "message_id": { "$ref": "#/$defs/id" },
        "session_id": { "$ref": "#/$defs/id" },
        "seq": { "type": "integer", "minimum": 1 },
        "sent_at": { "$ref": "#/$defs/timestamp" },
        "type": { "const": "evidence.ack" },
        "trace_id": { "$ref": "#/$defs/id" },
        "payload": {
          "type": "object",
          "additionalProperties": false,
          "required": ["evidence_id", "accepted"],
          "properties": {
            "evidence_id": { "$ref": "#/$defs/id" },
            "accepted": { "type": "boolean" },
            "next_chunk_index": { "type": "integer", "minimum": 0, "maximum": 4096 },
            "reason_code": { "$ref": "#/$defs/id" }
          }
        }
      }
    }
  }
}