Add typed event payload modules for the streaming service.

surfsense_backend/app/services/streaming/events/text.py

@@ -0,0 +1,31 @@
+"""Text-block streaming events."""
+
+from __future__ import annotations
+
+from ..emitter import Emitter, attach_emitted_by
+from ..envelope import format_sse
+
+
+def format_text_start(text_id: str, *, emitter: Emitter | None = None) -> str:
+    return format_sse(
+        attach_emitted_by({"type": "text-start", "id": text_id}, emitter)
+    )
+
+
+def format_text_delta(
+    text_id: str,
+    delta: str,
+    *,
+    emitter: Emitter | None = None,
+) -> str:
+    return format_sse(
+        attach_emitted_by(
+            {"type": "text-delta", "id": text_id, "delta": delta}, emitter
+        )
+    )
+
+
+def format_text_end(text_id: str, *, emitter: Emitter | None = None) -> str:
+    return format_sse(
+        attach_emitted_by({"type": "text-end", "id": text_id}, emitter)
+    )