[rahamohebbi]

Summary

Adds the pieces a product needs to call an actor for text without taking the actor down when Ollama is absent.

• ITextGenerator, OllamaTextGenerator, and ChainedTextGenerator return a result on network or model failure.
• CompletionAgent answers a CompletionRequest and uses the request's fallback text when generation fails.
• AddAgctorHostedRuntime() initializes the in-memory runtime when the host starts.
• AddAgctor() registers IAgentRegistry, which AgentFactory already required.

Actor model

• New behavior uses actors / messages rather than shared mutable workflow state (or explains why not)

CompletionAgent only speaks through message envelopes. Generators are dependencies of that actor, not a shared workflow.

Tests

• Unit tests updated (AgctorSDK.Core.Tests)
• Integration tests updated when the change crosses process or HTTP/MCP boundaries
• dotnet build Agctor.sln and the relevant dotnet test projects pass locally

CompletionAgentTests covers direct replies, fallback text, and runtime request-response. Core unit tests: 201 passed. Core integration tests that do not need Ollama: 14 passed, 1 skipped.

Docs and attribution

• README / XML comments updated if a public API changed
• CHANGELOG.md Unreleased section updated for user-visible changes
• No secrets, local config, or build artifacts included