altar

# Requirements Document

## Introduction

ALTAR (The Agent & Tool Arbitration Protocol) is a comprehensive, language-agnostic protocol designed to enable secure, observable, and stateful interoperability between autonomous agents, AI models, and traditional software systems. Building upon the foundation established by the `gemini_ex` Elixir client and the `snakepit` bidirectional tool bridge, ALTAR aims to become the industry standard for enterprise tool integration and agent orchestration.

The protocol addresses the critical need for a unified, transport-agnostic standard that allows different AI systems, programming languages, and runtime environments to seamlessly share tools and capabilities while maintaining security, observability, and state isolation.

## Requirements

### Requirement 1: Protocol Foundation and Compliance Levels

**User Story:** As a system architect, I want a transport-agnostic protocol specification with clear compliance levels so that I can implement ALTAR incrementally across different network layers and deployment scenarios.

#### Acceptance Criteria

1. WHEN defining the protocol THEN the specification SHALL be transport-agnostic, supporting TCP, WebSockets, gRPC, and message queues
2. WHEN implementing the protocol THEN it SHALL be language-agnostic with clear primitive type mappings for any modern programming language
3. WHEN designing the architecture THEN it SHALL follow a Host-Runtime model where the Host orchestrates communication between multiple Runtimes
4. WHEN establishing connections THEN the protocol SHALL support dynamic discovery and registration of Runtimes and their capabilities
5. WHEN handling communication THEN every message SHALL include correlation IDs and metadata for observability
6. WHEN defining compliance THEN the protocol SHALL specify Level 1 (core), Level 2 (enhanced), and Level 3 (enterprise) compliance profiles
7. WHEN implementing Level 1 THEN it SHALL include only Runtime Announce, Session Management, Tool Registration, and Synchronous Tool Invocation
8. WHEN implementing Level 2 THEN it SHALL add Streaming, Basic Security, and Observability features
9. WHEN implementing Level 3 THEN it SHALL add Advanced Security, Distributed Tracing, and Multi-Host Clustering

### Requirement 2: Core Entity Definitions

**User Story:** As a protocol implementer, I want clearly defined core entities so that I can build consistent implementations across different languages and platforms.

#### Acceptance Criteria

1. WHEN defining a Host THEN it SHALL be the central process implementing ALTAR protocol and orchestrating communication
2. WHEN defining a Runtime THEN it SHALL be any external process that connects to offer or consume tools
3. WHEN defining a Session THEN it SHALL provide stateful, isolated context with unique ID for tool registration and state management
4. WHEN defining Tool Definitions THEN they SHALL include declarative schemas with name, description, parameters, and metadata
5. WHEN defining Invocations THEN they SHALL have unique IDs for tracking and correlation across the system
6. WHEN defining Results THEN they SHALL support both synchronous responses and streaming chunks with structured error handling

### Requirement 3: Message Schema Specification

**User Story:** As a developer integrating ALTAR, I want standardized message schemas so that different implementations can communicate reliably.

#### Acceptance Criteria

1. WHEN a Runtime connects THEN it SHALL send an AnnounceRuntime message with runtime_id, language, version, and capabilities
2. WHEN registering tools THEN the Runtime SHALL send RegisterTools message with session_id and tool definitions array
3. WHEN invoking tools THEN the caller SHALL send ToolCall message with invocation_id, session_id, tool_name, parameters, and metadata
4. WHEN returning results THEN the Runtime SHALL send ToolResult message with invocation_id, status, payload, error_details, and runtime_metadata
5. WHEN streaming results THEN the Runtime SHALL send StreamChunk messages with invocation_id, chunk_id, payload, and is_final flag
6. WHEN managing sessions THEN the protocol SHALL support CreateSession and DestroySession messages with appropriate metadata and TTL handling

### Requirement 4: Enhanced Type System Definition

**User Story:** As a tool developer, I want a comprehensive, unambiguous type system so that I can define tool parameters that work across different programming languages with full schema validation.

#### Acceptance Criteria

1. WHEN defining primitive types THEN the system SHALL support string (UTF-8), integer (64-bit signed), float (64-bit IEEE 754), boolean, and binary types
2. WHEN defining complex types THEN the system SHALL support array[T] where T can be any ALTAR type including objects
3. WHEN defining object types THEN the system SHALL support object[Schema] with recursive property definitions
4. WHEN defining parameters THEN each SHALL have name, type, description, required, and optional constraint fields
5. WHEN validating parameters THEN the system SHALL enforce type constraints, required field validation, and recursive schema validation
6. WHEN serializing data THEN the type system SHALL provide clear mapping rules for JSON, Protocol Buffers, and other serialization formats

### Requirement 5: Session Management and State Isolation

**User Story:** As a system administrator, I want robust session management so that I can isolate different user contexts and manage resource lifecycles effectively.

#### Acceptance Criteria

1. WHEN creating sessions THEN the system SHALL generate unique session IDs and support client-suggested IDs with Host override capability
2. WHEN managing session lifecycle THEN the system SHALL support configurable TTL with automatic cleanup of expired sessions
3. WHEN isolating state THEN each session SHALL maintain separate tool registrations and execution contexts
4. WHEN destroying sessions THEN the system SHALL properly clean up all associated resources and notify connected Runtimes
5. WHEN handling session metadata THEN the system SHALL support arbitrary key-value metadata for session context

### Requirement 6: Secure Tool Discovery and Contract Management

**User Story:** As a Runtime developer, I want secure tool discovery with Host-managed contracts so that I can fulfill tool implementations without compromising security.

#### Acceptance Criteria

1. WHEN a Runtime starts THEN it SHALL automatically discover available tools through reflection or configuration
2. WHEN fulfilling tools THEN the Runtime SHALL send FulfillTools messages indicating which Host-defined contracts it can implement
3. WHEN managing contracts THEN the Host SHALL maintain trusted Tool Manifests defining expected tool schemas and security requirements
4. WHEN validating tools THEN the Host SHALL use its own trusted schemas for parameter validation, not Runtime-provided schemas
5. WHEN namespacing tools THEN all tool names SHALL be prefixed with runtime_id to prevent collisions (e.g., "python-worker-1/calculate_metrics")
6. WHEN querying tools THEN the Host SHALL provide discovery endpoints for listing available tools per session with their fulfilling runtimes

### Requirement 7: Enhanced Invocation and Execution Flow

**User Story:** As an AI agent, I want reliable tool invocation with comprehensive error handling so that I can execute tools across different Runtimes and receive consistent results.

#### Acceptance Criteria

1. WHEN invoking tools THEN the system SHALL support both synchronous and asynchronous execution patterns
2. WHEN executing tools THEN each invocation SHALL have a unique correlation ID for tracking and debugging
3. WHEN invoking a tool THEN the client SHALL generate a unique `invocation_id` that the Host can use for idempotency
4. WHEN handling parameters THEN the system SHALL validate parameters against Host-managed tool contracts before execution
5. WHEN returning results THEN the system SHALL support structured success payloads and detailed error information
6. WHEN streaming results THEN the system SHALL maintain chunk ordering and provide clear stream termination signals
7. WHEN handling streaming errors THEN StreamChunk messages SHALL include optional error_details field for in-band error reporting
8. WHEN streaming errors occur THEN error chunks SHALL have is_final set to true and payload should be ignored

### Requirement 8: Error Handling and Resilience

**User Story:** As a system operator, I want comprehensive error handling so that I can diagnose and recover from failures effectively.

#### Acceptance Criteria

1. WHEN tools fail THEN the system SHALL return structured error messages with error codes, descriptions, and context
2. WHEN Runtimes disconnect THEN the Host SHALL handle graceful degradation and cleanup of associated sessions
3. WHEN validation fails THEN the system SHALL provide detailed validation error messages with field-level feedback
4. WHEN timeouts occur THEN the system SHALL support configurable timeout handling with appropriate error responses
5. WHEN handling partial failures THEN streaming operations SHALL support error chunks and recovery mechanisms

### Requirement 9: Observability and Telemetry

**User Story:** As a DevOps engineer, I want built-in observability so that I can monitor, trace, and debug ALTAR protocol interactions.

#### Acceptance Criteria

1. WHEN processing messages THEN the system SHALL emit telemetry events with timestamps, correlation IDs, and performance metrics
2. WHEN executing tools THEN the system SHALL track execution time, resource usage, and success/failure rates
3. WHEN handling sessions THEN the system SHALL provide session lifecycle events and resource utilization metrics
4. WHEN tracing requests THEN the system SHALL support distributed tracing with span propagation across Runtime boundaries
5. WHEN logging events THEN the system SHALL provide structured logging with consistent field names and formats

### Requirement 10: Security and Authorization Framework

**User Story:** As a security engineer, I want extensible security mechanisms so that I can implement appropriate authentication and authorization for enterprise deployments.

#### Acceptance Criteria

1. WHEN Runtimes connect THEN the system SHALL support pluggable authentication mechanisms (API keys, certificates, OAuth)
2. WHEN authorizing tool calls THEN the system SHALL provide hooks for session-based and tool-based authorization
3. WHEN handling sensitive data THEN the system SHALL support encryption of message payloads and parameter values
4. WHEN auditing access THEN the system SHALL log all authentication attempts and authorization decisions
5. WHEN sandboxing execution THEN the system SHALL provide extension points for resource limits and execution constraints
6. WHEN defining a session's security context THEN the `SecurityContext` message SHALL include `principal_id`, `tenant_id`, and `claims` fields

### Requirement 11: Integration with Existing Systems

**User Story:** As a developer migrating from existing tool systems, I want compatibility layers so that I can integrate ALTAR with current implementations like Google's GenAI SDK and MCP.

#### Acceptance Criteria

1. WHEN integrating with GenAI SDK THEN the system SHALL provide adapters for Google's FunctionDeclaration and Tool formats
2. WHEN supporting MCP THEN the system SHALL offer compatibility layers for Model Context Protocol message formats
3. WHEN bridging existing tools THEN the system SHALL support automatic conversion from common tool definition formats
4. WHEN maintaining compatibility THEN the system SHALL provide versioning mechanisms for protocol evolution
5. WHEN migrating systems THEN the system SHALL support gradual adoption patterns with hybrid deployments

### Requirement 12: Developer Experience and Dynamic Registration

**User Story:** As a developer, I want flexible development workflows so that I can rapidly iterate on tools during development while maintaining security in production.

#### Acceptance Criteria

1. WHEN developing tools THEN the Host SHALL support optional "Development Mode" allowing dynamic tool registration
2. WHEN in Development Mode THEN the Host SHALL accept RegisterTools messages with full ToolContract definitions for rapid iteration
3. WHEN in Production Mode THEN the Host SHALL only accept FulfillTools messages against pre-defined manifests for security
4. WHEN switching modes THEN the Host SHALL clearly log the security implications and current mode status
5. WHEN discovering contracts THEN Runtimes SHALL be able to query available contracts via GetAvailableContracts RPC
6. WHEN bootstrapping THEN Runtimes SHALL discover available contracts before sending FulfillTools messages
7. WHEN defining capabilities THEN the protocol SHALL specify well-known capability strings (streaming, altar_level_2, binary_payloads)

### Requirement 13: Enhanced Protocol Refinements

**User Story:** As a protocol implementer, I want unambiguous message definitions so that I can build robust, interoperable implementations.

#### Acceptance Criteria

1. WHEN handling null values THEN the Value type SHALL include explicit null_value field to avoid ambiguity
2. WHEN tracing requests THEN ToolCall messages SHALL include top-level correlation_id field for end-to-end distributed tracing
3. WHEN propagating context THEN correlation_id SHALL be passed through all subsequent ToolCall and ToolResult messages
4. WHEN announcing capabilities THEN Runtimes SHALL use standardized capability strings defined in the protocol specification
5. WHEN handling binary data THEN the protocol SHALL support efficient binary payload transmission without base64 encoding

### Requirement 14: Performance and Scalability

**User Story:** As a platform engineer, I want high-performance protocol implementation so that I can support enterprise-scale deployments with thousands of concurrent tool invocations.

#### Acceptance Criteria

1. WHEN handling concurrent requests THEN the system SHALL support thousands of simultaneous tool invocations per Host
2. WHEN managing connections THEN the system SHALL efficiently handle hundreds of connected Runtimes
3. WHEN processing messages THEN the system SHALL minimize serialization overhead and memory allocation
4. WHEN scaling horizontally THEN the system SHALL support Host clustering and load distribution
5. WHEN optimizing performance THEN the system SHALL provide connection pooling and message batching capabilities