fix: Coerce node and edge types before syncing updates

[philippjfr]

Description

I fixed a server-side serialization error when node_types or edge_types are assigned after construction. The constructor converts NodeType and EdgeType descriptors to JSON dicts, but on a later update Panel synced the raw value to the frontend before the _normalize_specs watcher replaced it, so a descriptor's schema class reached bokeh and the patch failed with SerializationError: can't serialize <class 'param.parameterized.ParameterizedMetaclass'>. panel-flowdash hits this whenever lazily loaded components rebuild the canvas's node types.

• _process_param_change now coerces node_types and edge_types with _coerce_spec_map, so only JSON descriptors are synced regardless of watcher order.
• _normalize_specs now accepts multiple events. It watches both parameters in args mode, so flow.param.update(node_types=..., edge_types=...) raised TypeError: _normalize_specs() takes 2 positional arguments but 3 were given.

import panel as pn
import param
import panel_reactflow as pr

pn.extension()


class Config(param.Parameterized):
    x = param.Integer(default=1)


flow = pr.ReactFlow(sizing_mode="stretch_both", min_height=400)
button = pn.widgets.Button(name="Set node types")
button.on_click(lambda _: flow.param.update(node_types={"a": pr.NodeType(type="a", schema=Config)}))

pn.Column(button, flow).servable()

Serve this and click the button. Before, the server logs SerializationError: can't serialize <class 'param.parameterized.ParameterizedMetaclass'>; after, the update is applied without error.

I added test_updated_node_types_reach_model_as_descriptors and test_node_and_edge_types_updated_together, both of which fail on main and pass with this change. The non-UI test suite and pre-commit pass, as do the panel-flowdash unit and UI suites against this branch.

AI Disclosure

Tool & Model: Kilo Code + Claude Opus 5.5
Usage: Traced the serialization error from panel-flowdash, implemented the fix and tests, and drafted this description; I reviewed the diff and ran the listed checks.

• I have tested all AI-generated content in my PR.
• I take responsibility for all AI-generated content in my PR.

Checklist

• Tests added and are passing
• Added documentation