Add StreamingService and interrupt correlation for chat streams.

surfsense_backend/app/services/streaming/__init__.py

@@ -0,0 +1,20 @@
+"""Single-responsibility split of the streaming SSE protocol.
+
+Layout:
+* ``envelope/`` - SSE wire framing + ID generators
+* ``emitter/`` - identity of the agent that emitted an event + runtime registry
+* ``events/`` - one module per SSE event family
+* ``service.py`` - composition root used by the orchestrator
+* ``interrupt_correlation.py`` - id-aware lookup over LangGraph state
+
+Naming on the wire:
+* AI SDK protocol fields keep their existing camelCase
+  (``toolCallId``, ``messageId``, ``inputTextDelta``, ``langchainToolCallId``).
+* Every SurfSense-added field uses ``snake_case``, including the
+  top-level ``emitted_by`` envelope and all inner ``data`` payloads.
+
+Production keeps using ``app.services.new_streaming_service`` and
+``app.tasks.chat.stream_new_chat`` until the cutover phase.
+"""
+
+from __future__ import annotations