.NET: build AgentHooksOptions from a host declaration document #9330

Motivation

Microsoft.Agents.AI.AgentHooks wires Agent Hooks through AgentHooksOptions and AsAIAgentWithAgentHooks. Configuration lives in code. Agent Hooks 0.1.0-beta.2 adds a host declaration document (spec section 7.7, contract agent-hooks-declaration/1.0): one JSON file that states the host's configuration, its declared surface, and its interceptor bindings by kind. It can travel through enterprise managed settings, and the loader refuses anything the host's code cannot honour before any emission.

The .NET package should accept that document.

Proposal

• AgentHooksOptions.FromDeclaration, FromDeclarationPath, FromDeclarationJson and FromDeclarationNode, each taking an Action<HostRegistry> for binding kinds, built on InterceptionEmitter.FromDeclaration* in ResponsibleAI.AgentHooks.
• A host surface for Agent Framework (all eight points, terminate posture, buffered output, the capabilities the package supports) that the registry is built over; apps register kinds, resolvers and redactors, not a replacement surface.
• Options read the declaration's values; ResolvedDeclaration is the source of truth for anything the options do not mirror.

The existing code path keeps working. A document must state tool_seam_host_error: terminate, because the contract defaults to continue and the loader refuses a mismatch with the code's posture.

Scope

• dotnet/src/Microsoft.Agents.AI.AgentHooks (options, host surface, agent run state), xunit tests that run offline for the construction paths and the refusal classes, and ADR 0035 updated for the declaration path.
• Move the central ResponsibleAI.AgentHooks pin to 0.1.0-beta.2.

Notes

• Spec: https://github.com/responsibleai/agent-hooks/blob/main/spec/AGENT-HOOKS-0.1.md (section 7.7); implementer guide: https://github.com/responsibleai/agent-hooks/blob/main/docs/IMPLEMENTING.md.
• No conformance claim exists for the .NET package yet; a harness over the declaration path would be the natural first claim.