ADR-0012: Runtime Run resource and observable execution

Decision

Interactive and programmatic agent executions are represented by durable Runtime Run resources. Agentstration.Runtime.Abstractions owns the provider-neutral Run model and ports, Agentstration.Runtime.Core owns lifecycle and execution orchestration, Agentstration.Runtime.Contracts owns public HTTP contracts, and Agentstration.Runtime.Storage.Sqlite persists Runs and their ordered events.

A Run references an exact managed agent resource generation. Runtime resolves a ready deployment and executes it through IRuntimeRegistry; it never constructs a concrete agent. Creation is asynchronous, observation uses Server-Sent Events, cancellation is explicit, and retry creates a new Run. Direct interactive Runs do not create Work Items.

Consequences

Web, API, Work, and future Flow entry points can converge on the same Runtime Run lifecycle. The local default gains an independent runtime-plane.db. SSE is initially backed by persisted event polling, which supports reconnection through Last-Event-ID without introducing WebSockets or an external broker. Provider-specific streaming, detailed token metrics, tool-call interception, and authorization-based trace redaction remain adapter-level extensions.