Draft: build microkernel-inspired core contracts

[jsoneaday]

Summary

• Document the microkernel-inspired core redesign and locked Module/Service/Actor/SideEffect terminology.
• Add Phase 1 Structure contracts for actor identity, capabilities, process supervision, job scheduling, SideEffects, and host secret attachment.
• Consolidate the existing agent registry contract name to AgentRegistryManaging and add AgentDirecting / AgentOrchestrationServing contracts.
• Add immutable AgentConfigurationReference support to agent records.
• Rename the Structure process contract folder to ProcessSupervision.

Scope

This is intentionally a draft. Runtime module/service implementations and caller migration are not included yet.

Validation

• New Structure core redesign contract tests pass.
• AgentRuntime tests pass.
• DBRepository tests pass.
• The full Structure suite builds; existing Keychain/temp-file tests remain environment-dependent.

Next

• Review the exact Phase 1 contracts.
• Continue with message-family and lifecycle boundaries after approval.