Decisions

The architecture decision records behind MCP Hangar: the choice, the alternatives, and the consequences. A superseded record stays, so the reasoning that led to the current design can still be read.

NumberDecisionStatus
ADR-001Command Query Responsibility Segregation (CQRS)Accepted
ADR-002Event SourcingSuperseded
ADR-003Saga PatternAccepted
ADR-004Preemptive Implementation of SEP-1766 (Digest Pinning) and SEP-1763 (Interceptor Framework)Acceptedpartly superseded
ADR-005SEP-1763 Interceptor Framework ComplianceSuperseded
ADR-006Runtime Enforcement StrategySuperseded
ADR-007Langfuse Integration for LLM ObservabilityAccepted
ADR-008Task Governance is Relay-OnlyAcceptedpartly superseded
ADR-009Independent Release TopologyAcceptedpartly superseded
ADR-010Retire the Agent + Hangar Cloud Product TierAccepted
ADR-011Single Source of Truth for Cross-Repo FactsAccepted
ADR-012Interceptor SEP-Pin Tracking PolicyAccepted
ADR-013Egress Policy Enforcement Model (MCPEgressPolicy)Accepted
ADR-014Tasks are Relayed With GovernanceAccepted
ADR-015The Tasks Wire is VendoredAccepted
ADR-016Approval Resolution Has One Authorized Chokepoint, and Core Knows No VendorsAccepted
ADR-017Pending Approvals Use io.mcp-hangar/approval, and Carry No Requested SchemaAccepted
ADR-018Event Sourcing, Actually WiredAccepted
ADR-019One Storage Decision, and Two Backends That Are Never MixedAccepted
ADR-020More Than One GatewayAccepted
ADR-021A Remote Upstream in the Configuration File Stays Outside the SSRF PolicyAccepted
ADR-022The Management Surface Is Whatever the Caller Is Allowed to CallAccepted
ADR-023The MCP Registry Entry Describes a Package, Not a ServiceAccepted
ADR-024A Human Approval Hold Belongs on a Tool Call, Not on a FetchAccepted
ADR-025A Header Selector Must Not Match a Header Nobody ValidatedAccepted
ADR-026Stdio Is an Authenticated Transport, and the Config Names Its PrincipalAccepted
ADR-027egress Is a Trust Mode, Not a Preset of the Front DoorProposed
ADR-028On a Front Door, the Tool-Access Policy Is the Invoke Gate for Upstream ToolsProposed
ADR-029One Enrichment Boundary and a Bounded Decision Vocabulary for TracesProposed

29 decision records. They are written inmcp-hangar/docs, where new ones are proposed.