Maple agent tracing: Genkit

Goal

One conversation = one Maple Agent Session, one turn per flow run, with the transcript, every model call (model, tokens) and every tool call (name, args, result, failures).

Span tree per flow run:

supportChat            genkit:metadata:subtype=flow, genkit:isRoot=true  -> invoke_agent
└── generate           genkit:type=util (one nested generate per tool-loop step, left unmapped)
    ├── googleai/gemini-2.5-flash   subtype=model  -> chat
    ├── getWeather                  subtype=tool   -> execute_tool
    └── generate
        └── googleai/gemini-2.5-flash   subtype=model  -> chat

Beta agents (ai.defineAgent() / defineCustomAgent / definePromptAgent from genkit/beta): root span has subtype agent and genkit:metadata:agent:sessionId (Genkit's session id), which the processor uses as the conversation id. Under it: runTurn-<n> (flowStep), render (promptTemplate), generate, model, tool spans. One trace per chat.send().