rework web server so multiple clients can be server at a time

backend/execution_context.py

@@ -0,0 +1,82 @@
+from __future__ import annotations
+
+from contextlib import contextmanager
+from contextvars import ContextVar
+from typing import Any, Callable
+
+Callback = Callable[[str, Any], None]
+
+_callbacks_var: ContextVar[dict[str, Callback | None]] = ContextVar(
+    "argonode_execution_callbacks",
+    default={},
+)
+_node_id_var: ContextVar[str | None] = ContextVar("argonode_execution_node_id", default=None)
+
+
+@contextmanager
+def execution_callbacks(
+    *,
+    preview: Callback | None = None,
+    table: Callback | None = None,
+    mesh: Callback | None = None,
+    overlay: Callback | None = None,
+    value: Callback | None = None,
+    warning: Callback | None = None,
+):
+    token = _callbacks_var.set({
+        "preview": preview,
+        "table": table,
+        "mesh": mesh,
+        "overlay": overlay,
+        "value": value,
+        "warning": warning,
+    })
+    try:
+        yield
+    finally:
+        _callbacks_var.reset(token)
+
+
+@contextmanager
+def active_node(node_id: str):
+    token = _node_id_var.set(str(node_id))
+    try:
+        yield
+    finally:
+        _node_id_var.reset(token)
+
+
+def current_node_id() -> str | None:
+    return _node_id_var.get()
+
+
+def _emit(kind: str, payload: Any) -> None:
+    callbacks = _callbacks_var.get()
+    callback = callbacks.get(kind)
+    node_id = current_node_id()
+    if callback is not None and node_id:
+        callback(node_id, payload)
+
+
+def emit_preview(payload: Any) -> None:
+    _emit("preview", payload)
+
+
+def emit_table(rows: list) -> None:
+    _emit("table", rows)
+
+
+def emit_mesh(mesh: dict) -> None:
+    _emit("mesh", mesh)
+
+
+def emit_overlay(overlay: dict) -> None:
+    _emit("overlay", overlay)
+
+
+def emit_value(payload: Any) -> None:
+    _emit("value", payload)
+
+
+def emit_warning(message: str) -> None:
+    _emit("warning", message)