feat(go): implement reflection API v2 over WebSocket

[apascal07]

Implements the V2 Reflection API in Genkit Go, matching the JS implementation in js/core/src/reflection-v2.ts. Where V1 is a polling HTTP server running inside the runtime, V2 is a WebSocket client: the CLI manager runs the server and runtimes connect to it and handle JSON-RPC 2.0 requests.

Activated when GENKIT_REFLECTION_V2_SERVER is set to the manager's WebSocket URL; otherwise genkit.Init falls back to V1.

Protocol methods implemented

Method	Direction	Type	Notes
register	Runtime → Manager	Notification	Sent on connect with runtime ID, pid, genkit version, protocol version.
configure	Manager → Runtime	Notification	Sets the telemetry server URL.
listActions	Manager → Runtime	Request	Returns all registered + resolvable actions wrapped in an actions map.
listValues	Manager → Runtime	Request	Returns registered values (note: type filtering is parsed for compatibility but not yet supported by the Go registry).
runAction	Manager → Runtime	Request	Executes an action. Emits runActionState for early trace-ID delivery, and streamChunk notifications when stream: true. Errors are mapped to a JS-compatible Status shape with {code, message, details: {traceId, stack}}.
cancelAction	Manager → Runtime	Request	Cancels an in-flight action by trace ID.
sendInputStreamChunk / endInputStream	Manager → Runtime	Notification	No-op with debug log — bidirectional input streaming is not yet implemented on either side.

[gemini-code-assist]

Code Review

This pull request introduces the Genkit Reflection Protocol V2, transitioning from an HTTP polling model to a bidirectional WebSocket-based communication system between the Genkit CLI and runtimes. The changes include a new protocol specification, a refactored abstract BaseRuntimeManager architecture in the CLI tools, and new client implementations in both Go and JavaScript. Additionally, the tools server has been updated to support bidirectional streaming and input streaming for bidirectional actions. I have no feedback to provide.