Worklog for task "Build the core of the agents and dialogs service"

HTTP chat and minimal agent event reaction

Server contracts have been implemented upon which the central dialog service can be built:

• POST /api/chat supports standard JSON and streaming NDJSON;
• a unified ExecutionContext carries the execution id, response mode, abort signal, and event dispatch;
• start, sequential delta, successful completion, error, and cancellation are supported;
• explicit cancellation via DELETE, cancellation on disconnect/timeout/shutdown, and independence of parallel runs are provided;
• the Agent class and POST /api/agent with the message.received → Agent.react → message.publish chain have been implemented;
• actions are linked to the stimulus via stimulusId, and fragments of a single response share a common actionId;
• the reaction mock has already been replaced with a real call to the existing runChat/LLM.

Re-checks from the audit: HTTP chat 8/8 tests, agent reactions 2/2 tests.

This is the foundation of the dialog component, but so far without persistent conversation memory, event deduplication, and a general model of sites/visitors/dialogs.