fix: Implement explicit no-flow w/FlowSignal

TODO.md

@@ -541,19 +541,19 @@ We need support for arbitrary objects, but still backed by the persistance seman
 - [ ] Implement Enum property, (also see <https://developer.blender.org/docs/release_notes/4.1/python_api/#enum-id-properties>)
 	- Use this to bridge the enum UI to actual StrEnum objects.
 	- This also maybe enables some very interesting use cases when it comes to ex. static verifiability of data provided to event callbacks.
-- [ ] Ensure certain options, namely `name` (as `ui_name`), `default`, `subtype`, (numeric) `min`, `max`, `step`, `precision`, (string) `maxlen`, `search`, and `search_options`, can be passed down via the `BLField()` constructor.
+- [x] Ensure certain options, namely `name` (as `ui_name`), `default`, `subtype`, (numeric) `min`, `max`, `step`, `precision`, (string) `maxlen`, `search`, and `search_options`, can be passed down via the `BLField()` constructor.
 	- [ ] Make a class method that parses the docstring.
 	- [ ] `description`: Use the docstring parser to extract the first description sentence of the attribute name from the subclass docstring, so we are both encouraged to document our nodes/sockets, and so we're not documenting twice.
 
 ### Niceness
 - [x] Rename the internal property to 'blfield__'.
-- [ ] Add a method that extracts the internal property name, for places where we need the Blender property name.
+- [x] Add a method that extracts the internal property name, for places where we need the Blender property name.
 	- **Key use case**: `draw.prop(self, self.field_name._bl_prop_name)`, which is also nice b/c no implicit string-based reference.
 	- The work done above with types makes this as fast and useful as internal props. Just make sure we validate that the type can be usefully accessed like this.
-- [ ] Add a field method (called w/instance) that updates min/max/etc. on the 'blfield__' prop, in a native property type compatible manner: https://developer.blender.org/docs/release_notes/3.0/python_api/#idproperty-ui-data-api
+- [x] Add a field method (called w/instance) that updates min/max/etc. on the 'blfield__' prop, in a native property type compatible manner: https://developer.blender.org/docs/release_notes/3.0/python_api/#idproperty-ui-data-api
     - Should also throw appropriate errors for invalid access from Python, while Blender handles access from the inside.
     - This allows us
-- [ ] Similarly, a field method that gets the 'blfield__' prop data as a dictionary.
+- [x] Similarly, a field method that gets the 'blfield__' prop data as a dictionary.
 
 ### Parallel Features
 - [x] Move serialization work to a `utils`.
@@ -569,3 +569,29 @@ We need support for arbitrary objects, but still backed by the persistance seman
     - Benefit: Any serializable object can be "simply used", at almost native speed (due to the aggressive read-cache).
     - Benefit: Better error properties for updating, access, setting, etc. .
 	- Benefit: Validate usage in a vastly greater amount of contexts.
+
+
+
+# Overnight Ideas
+- [ ] Fix file-load hiccups by persisting `_enum_cb_cache` and `_str_cb_cache`.
+
+- [x] Implement `FlowSignal`s as special return values for `@computes_output_socket`, instead of juggling `None`.
+	- `FlowSignal.FlowPending`: Data was asked for, and it's not yet available, but it's expected to become available.
+		- Semantically: "Just hold on for a hot second".
+		- Return: If in any socket data provided to cb, return the same signal insted of running the callback.
+		- Caches: Don't invalidate caches, since the user will expect their data to still persist.
+		- Net Effect: Absolutely nothing happens. Perhaps we can recolor the nodes, though.
+
+	- [ ] `FlowSignal.FlowLost`: Output socket requires data that simply isn't available.
+		- Generally, nodes don't return it
+		- Return: If in any socket data provided to cb, return the same signal insted of running the callback.
+		- Caches: Do invalidate caches, since the user will expect their data to still persist.
+		- Net Effect: Sometimes, stuff happens in the output method [BB
+		- Net Effect: `DataChanged` is an event that signifies Node data will reset along the flow.
+
+- [ ] Packing Imported Data in `Tidy3D Web Importer`, `Tidy3D File Importer`.
+	- Just `.to_hdf5_gz()` it into a `BytesIO`,  Base85
+
+- [ ] Remove Matplotlib Bottlenecks (~70ms -> ~5ms)
+	- Reuse `fig` per-`ManagedBLImage` (~25ms)
+	- Use `Agg` backend, plot with `fig.canvas.draw()`, and load image buffer directly as np.frombuffer(ax.figure.canvas.tostring_rgb(), dtype=np.uint8) (~40ms).

src/blender_maxwell/contracts/operator_types.py

@@ -15,3 +15,10 @@ class OperatorType(enum.StrEnum):
 	ManagePyDeps = enum.auto()
 
 	ConnectViewerNode = enum.auto()
+
+	# Socket: Tidy3DCloudTask
+	SocketCloudAuthenticate = enum.auto()
+	SocketReloadCloudFolderList = enum.auto()
+
+	# Node: Tidy3DWebImporter
+	NodeLoadCloudSim = enum.auto()

src/blender_maxwell/node_trees/maxwell_sim_nodes/contracts/__init__.py

@@ -37,6 +37,7 @@ from .flow_kinds import (
     ParamsFlow,
     ValueFlow,
 )
+from .flow_signals import FlowSignal
 from .icons import Icon
 from .mobj_types import ManagedObjType
 from .node_types import NodeType
@@ -93,4 +94,5 @@ __all__ = [
 	'LazyValueFuncFlow',
 	'ParamsFlow',
 	'ValueFlow',
+	'FlowSignal',
 ]

src/blender_maxwell/node_trees/maxwell_sim_nodes/contracts/flow_signals.py

@@ -0,0 +1,71 @@
+import enum
+import typing as typ
+
+
+_FLOW_SIGNAL_SET: set | None = None
+
+
+class FlowSignal(enum.StrEnum):
+	"""Special output socket return value, which indicates a piece of information about the state of the flow, instead of data.
+
+	Attributes:
+		FlowPending: The data that was requested is not available, but it is expected to become available soon.
+			- **Behavior**: When encountered downstream in `events` decorators for all `FlowKind`s, either `FlowSignal.FlowPending` should return instead of the method, or the decorated method should simply not run.
+			- **Caching**: Don't invalidate caches, since the user will expect their data to persist.
+			- **Net Effect**: All nodes that encounter FlowPending are forward-locked, possibly with an explanatory indicator. In terms of data, nothing happens - including no changes to the user's data.
+
+	"""
+
+	FlowPending = enum.auto()
+	NoFlow = enum.auto()
+
+	@classmethod
+	def all(cls) -> set[typ.Self]:
+		"""Query all flow signals, using a simple cache to ensure minimal overhead when used in ex. `draw()` functions.
+
+		Returns:
+			Set of FlowSignal enum items, for easy `O(1)` lookup
+		"""
+		global _FLOW_SIGNAL_SET  # noqa: PLW0603
+
+		if _FLOW_SIGNAL_SET is None:
+			_FLOW_SIGNAL_SET = set(FlowSignal)
+
+		return _FLOW_SIGNAL_SET
+
+	@classmethod
+	def check(cls, obj: typ.Any) -> set[typ.Self]:
+		"""Checks whether an arbitrary object is a `FlowSignal` with tiny overhead.
+
+		Notes:
+			Optimized by first performing an `isinstance` check against both `FlowSignal` and `str`.
+			Then, we can check membership in `cls.all()` with `O(1)`, since (by type narrowing like this) we've ensured that the object is hashable.
+
+		Returns:
+			Whether `obj` is a `FlowSignal`.
+
+		Examples:
+			A common pattern to ensure an object is **not** a `FlowSignal` is `not FlowSignal.check(obj)`.
+		"""
+		return isinstance(obj, FlowSignal | str) and obj in FlowSignal.all()
+
+	@classmethod
+	def check_single(cls, obj: typ.Any, single: typ.Self) -> set[typ.Self]:
+		"""Checks whether an arbitrary object is a particular `FlowSignal`, with tiny overhead.
+
+		Use this whenever it is important to make different decisions based on different `FlowSignal`s.
+
+		Notes:
+			Generally, you should use `cls.check()`.
+			It tends to only be important to know whether you're getting a proper object from the flow, or whether it's dumping a `FlowSignal` on you instead.
+
+			However, certain nodes might have a good reason to react differently .
+			One example is deciding whether to keep node-internal caches around in the absence of data: `FlowSignal.FlowPending` hints to keep it around (allowing the user to ex. change selections, etc.), while `FlowSignal.NoFlow` hints to get rid of it immediately (resetting the node entirely).
+
+		Returns:
+			Whether `obj` is a `FlowSignal`.
+
+		Examples:
+			A common pattern to ensure an object is **not** a `FlowSignal` is `not FlowSignal.check(obj)`.
+		"""
+		return isinstance(obj, FlowSignal | str) and obj == single

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/analysis/extract_data.py

@@ -5,6 +5,7 @@ import bpy
 import jax
 import jax.numpy as jnp
 import sympy.physics.units as spu
+import tidy3d as td
 
 from blender_maxwell.utils import bl_cache, logger
 from blender_maxwell.utils import extra_sympy_units as spux
@@ -15,9 +16,18 @@ from .. import base, events
 
 log = logger.get(__name__)
 
+TDMonitorData: typ.TypeAlias = td.components.data.monitor_data.MonitorData
+
 
 class ExtractDataNode(base.MaxwellSimNode):
-	"""Node for extracting data from particular objects.
+	"""Extract data from sockets for further analysis.
+
+	# Socket Sets
+	## Sim Data
+	Extracts monitors from a `MaxwelFDTDSimDataSocket`.
+
+	## Monitor Data
+	Extracts array attributes from a `MaxwelFDTDSimDataSocket`.
 
 	Attributes:
 		extract_filter: Identifier for data to extract from the input.
@@ -45,31 +55,145 @@ class ExtractDataNode(base.MaxwellSimNode):
 		enum_cb=lambda self, _: self.search_extract_filters(),
 	)
 
-	# Sim Data
-	sim_data_monitor_nametype: dict[str, str] = bl_cache.BLField(
-		{}, use_prop_update=False
+	####################
+	# - Computed: Sim Data
+	####################
+	@property
+	def sim_data(self) -> td.SimulationData | None:
+		"""Computes the (cached) simulation data from the input socket.
+
+		Return:
+			Either the simulation data, if available, or None.
+		"""
+		sim_data = self._compute_input(
+			'Sim Data', kind=ct.FlowKind.Value, optional=True
 		)
+		if not ct.FlowSignal.check(sim_data):
+			log.critical('Sim Data was Not FlowSignal')
+			return sim_data
 
-	# Monitor Data
-	monitor_data_type: str = bl_cache.BLField('', use_prop_update=False)
-	monitor_data_components: list[str] = bl_cache.BLField([], use_prop_update=False)
+		log.critical('Sim Data was FlowSignal: %s', str(sim_data))
+		return None
+
+	@bl_cache.cached_bl_property()
+	def sim_data_monitor_nametype(self) -> dict[str, str] | None:
+		"""For simulation data, computes and and caches a map from name to "type".
+
+		Return:
+			The name to type of monitors in the simulation data.
+		"""
+		if self.sim_data is not None:
+			return {
+				monitor_name: monitor_data.type
+				for monitor_name, monitor_data in self.sim_data.monitor_data.items()
+			}
+
+		return None
 
 	####################
-	# - Computed Properties
+	# - Computed Properties: Monitor Data
 	####################
 	@property
-	def has_sim_data(self) -> bool:
-		return self.active_socket_set == 'Sim Data' and self.sim_data_monitor_nametype
+	def monitor_data(self) -> TDMonitorData | None:
+		"""Computes the (cached) monitor data from the input socket.
 
-	@property
-	def has_monitor_data(self) -> bool:
-		return self.active_socket_set == 'Monitor Data' and self.monitor_data_type
+		Return:
+			Either the monitor data, if available, or None.
+		"""
+		monitor_data = self._compute_input(
+			'Monitor Data', kind=ct.FlowKind.Value, optional=True
+		)
+		if not ct.FlowSignal.check(monitor_data):
+			return monitor_data
+
+		return None
+
+	@bl_cache.cached_bl_property()
+	def monitor_data_type(self) -> str | None:
+		"""For monitor data, computes and caches the monitor "type".
+
+		Notes:
+			Should be invalidated with (before) `self.monitor_data_components`.
+
+		Return:
+			The "type" of the monitor, if available, else None.
+		"""
+		if self.monitor_data is not None:
+			return self.monitor_data.type.removesuffix('Data')
+
+		return None
+
+	@bl_cache.cached_bl_property()
+	def monitor_data_components(self) -> list[str] | None:
+		r"""For monitor data, computes and caches the component sof the monitor.
+
+		The output depends entirely on the output of `self.monitor_data`.
+
+		- **Field(Time)**: Whichever `[E|H][x|y|z]` are not `None` on the monitor.
+		- **Permittivity**: Specifically `['xx', 'yy', 'zz']`.
+		- **Flux(Time)**: Only `['flux']`.
+		- **FieldProjection(...)**: All of $r$, $\theta$, $\phi$ for both `E` and `H`.
+		- **Diffraction**: Same as `FieldProjection`.
+
+		Notes:
+			Should be invalidated after with `self.monitor_data_type`.
+
+		Return:
+			The "type" of the monitor, if available, else None.
+		"""
+		if self.monitor_data is not None:
+			# Field/FieldTime
+			if self.monitor_data_type in ['Field', 'FieldTime']:
+				return [
+					field_component
+					for field_component in ['Ex', 'Ey', 'Ez', 'Hx', 'Hy', 'Hz']
+					if hasattr(self.monitor_data, field_component)
+				]
+
+			# Permittivity
+			if self.monitor_data_type == 'Permittivity':
+				return ['xx', 'yy', 'zz']
+
+			# Flux/FluxTime
+			if self.monitor_data_type in ['Flux', 'FluxTime']:
+				return ['flux']
+
+			# FieldProjection(Angle/Cartesian/KSpace)/Diffraction
+			if self.monitor_data_type in [
+				'FieldProjectionAngle',
+				'FieldProjectionCartesian',
+				'FieldProjectionKSpace',
+				'Diffraction',
+			]:
+				return [
+					'Er',
+					'Etheta',
+					'Ephi',
+					'Hr',
+					'Htheta',
+					'Hphi',
+				]
+
+		return None
 
 	####################
 	# - Extraction Filter Search
 	####################
 	def search_extract_filters(self) -> list[ct.BLEnumElement]:
-		if self.has_sim_data:
+		"""Compute valid values for `self.extract_filter`, for a dynamic `EnumProperty`.
+
+		Notes:
+			Should be reset (via `self.extract_filter`) with (after) `self.sim_data_monitor_nametype`, `self.monitor_data_components`, and (implicitly) `self.monitor_type`.
+
+			See `bl_cache.BLField` for more on dynamic `EnumProperty`.
+
+		Returns:
+			Valid `self.extract_filter` in a format compatible with dynamic `EnumProperty`.
+		"""
+		log.critical('Searching Extract Filters')
+		log.critical(self.sim_data_monitor_nametype)
+		log.critical(self.monitor_data_components)
+		if self.sim_data_monitor_nametype is not None:
 			return [
 				(monitor_name, monitor_name, monitor_type.removesuffix('Data'), '', i)
 				for i, (monitor_name, monitor_type) in enumerate(
@@ -77,9 +201,15 @@ class ExtractDataNode(base.MaxwellSimNode):
 				)
 			]
 
-		if self.has_monitor_data:
+		if self.monitor_data_components is not None:
 			return [
-				(component_name, component_name, f'ℂ {component_name[1]}-Pol', '', i)
+				(
+					component_name,
+					component_name,
+					f'ℂ {component_name[1]}-polarization of the {"electric" if component_name[0] == "E" else "magnetic"} field',
+					'',
+					i,
+				)
 				for i, component_name in enumerate(self.monitor_data_components)
 			]
 
@@ -89,156 +219,172 @@ class ExtractDataNode(base.MaxwellSimNode):
 	# - UI
 	####################
 	def draw_props(self, _: bpy.types.Context, col: bpy.types.UILayout) -> None:
+		"""Draw node properties in the node.
+
+		Parameters:
+			col: UI target for drawing.
+		"""
 		col.prop(self, self.blfields['extract_filter'], text='')
 
 	def draw_info(self, _: bpy.types.Context, col: bpy.types.UILayout) -> None:
-		if self.has_sim_data or self.has_monitor_data:
+		"""Draw dynamic information in the node, for user consideration.
+
+		Parameters:
+			col: UI target for drawing.
+		"""
+		has_sim_data = self.sim_data_monitor_nametype is not None
+		has_monitor_data = self.monitor_data_components is not None
+
+		if has_sim_data or has_monitor_data:
 			# Header
 			row = col.row()
 			row.alignment = 'CENTER'
-			if self.has_sim_data:
+			if has_sim_data:
 				row.label(text=f'{len(self.sim_data_monitor_nametype)} Monitors')
-			elif self.has_monitor_data:
+			elif has_monitor_data:
 				row.label(text=f'{self.monitor_data_type} Monitor Data')
 
 			# Monitor Data Contents
+			## TODO: More compact double-split
+			## TODO: Output shape data.
+			## TODO: Local ENUM_MANY tabs for visible column selection?
 			row = col.row()
 			box = row.box()
 			grid = box.grid_flow(row_major=True, columns=2, even_columns=True)
-			for name, desc in [
-				(name, desc) for idname, name, desc, *_ in self.search_extract_filters()
-			]:
-				grid.label(text=name)
-				grid.label(text=desc if desc else '')
+			for monitor_name, monitor_type in self.sim_data_monitor_nametype.items():
+				grid.label(text=monitor_name)
+				grid.label(text=monitor_type)
 
 	####################
 	# - Events
 	####################
 	@events.on_value_changed(
+		# Trigger
 		socket_name={'Sim Data', 'Monitor Data'},
 		prop_name='active_socket_set',
-		input_sockets={'Sim Data', 'Monitor Data'},
-		input_sockets_optional={'Sim Data': True, 'Monitor Data': True},
 		run_on_init=True,
 	)
-	def on_sim_data_changed(self, input_sockets: dict):
-		if input_sockets['Sim Data'] is not None:
-			# Sim Data Monitors: Set Name -> Type
-			self.sim_data_monitor_nametype = {
-				monitor_name: monitor_data.type
-				for monitor_name, monitor_data in input_sockets[
-					'Sim Data'
-				].monitor_data.items()
-			}
-		elif self.sim_data_monitor_nametype:
-			self.sim_data_monitor_nametype = {}
-
-		if input_sockets['Monitor Data'] is not None:
-			# Monitor Data Type
-			self.monitor_data_type = input_sockets['Monitor Data'].type.removesuffix(
-				'Data'
-			)
-
-			# Field/FieldTime
-			if self.monitor_data_type in ['Field', 'FieldTime']:
-				self.monitor_data_components = [
-					field_component
-					for field_component in ['Ex', 'Ey', 'Ez', 'Hx', 'Hy', 'Hz']
-					if hasattr(input_sockets['Monitor Data'], field_component)
-				]
-
-			# Permittivity
-			if self.monitor_data_type == 'Permittivity':
-				self.monitor_data_components = ['xx', 'yy', 'zz']
-
-			# Flux/FluxTime
-			if self.monitor_data_type in ['Flux', 'FluxTime']:
-				self.monitor_data_components = ['flux']
-
-			# FieldProjection(Angle/Cartesian/KSpace)/Diffraction
-			if self.monitor_data_type in [
-				'FieldProjectionAngle',
-				'FieldProjectionCartesian',
-				'FieldProjectionKSpace',
-				'Diffraction',
-			]:
-				self.monitor_data_components = [
-					'Er',
-					'Etheta',
-					'Ephi',
-					'Hr',
-					'Htheta',
-					'Hphi',
-				]
-		else:
-			if self.monitor_data_type:
-				self.monitor_data_type = ''
-			if self.monitor_data_components:
-				self.monitor_data_components = []
-
-		# Invalidate Computed Property Caches
+	def on_input_sockets_changed(self) -> None:
+		"""Invalidate the cached properties for sim data / monitor data, and reset the extraction filter."""
+		self.sim_data_monitor_nametype = bl_cache.Signal.InvalidateCache
+		self.monitor_data_type = bl_cache.Signal.InvalidateCache
+		self.monitor_data_components = bl_cache.Signal.InvalidateCache
 		self.extract_filter = bl_cache.Signal.ResetEnumItems
 
 	####################
 	# - Output: Sim Data -> Monitor Data
 	####################
 	@events.computes_output_socket(
+		# Trigger
 		'Monitor Data',
 		kind=ct.FlowKind.Value,
+		# Loaded
 		props={'extract_filter'},
 		input_sockets={'Sim Data'},
 	)
-	def compute_monitor_data(self, props: dict, input_sockets: dict):
-		if input_sockets['Sim Data'] is not None and props['extract_filter'] != 'NONE':
+	def compute_monitor_data(
+		self, props: dict, input_sockets: dict
+	) -> TDMonitorData | ct.FlowSignal:
+		"""Compute `Monitor Data` by querying an attribute of `Sim Data`.
+
+		Notes:
+			The attribute to query is read directly from `self.extract_filter`.
+			This is also the mechanism that protects from trying to reference an invalid attribute.
+
+		Returns:
+			Monitor data, if available, else `ct.FlowSignal.FlowPending`.
+		"""
+		sim_data = input_sockets['Sim Data']
+		has_sim_data = not ct.FlowSignal.check(sim_data)
+
+		if has_sim_data and props['extract_filter'] != 'NONE':
 			return input_sockets['Sim Data'].monitor_data[props['extract_filter']]
 
-		return None
+		# Propagate NoFlow
+		if ct.FlowSignal.check_single(sim_data, ct.FlowSignal.NoFlow):
+			return ct.FlowSignal.NoFlow
+
+		return ct.FlowSignal.FlowPending
 
 	####################
 	# - Output: Monitor Data -> Data
 	####################
 	@events.computes_output_socket(
+		# Trigger
 		'Data',
 		kind=ct.FlowKind.Array,
+		# Loaded
 		props={'extract_filter'},
 		input_sockets={'Monitor Data'},
 		input_socket_kinds={'Monitor Data': ct.FlowKind.Value},
 	)
-	def compute_data(self, props: dict, input_sockets: dict) -> jax.Array | None:
-		if (
-			input_sockets['Monitor Data'] is not None
-			and props['extract_filter'] != 'NONE'
-		):
+	def compute_data(
+		self, props: dict, input_sockets: dict
+	) -> jax.Array | ct.FlowSignal:
+		"""Compute `Data:Array` by querying an array-like attribute of `Monitor Data`, then constructing an `ct.ArrayFlow`.
+
+		Uses the internal `xarray` data returned by Tidy3D.
+
+		Notes:
+			The attribute to query is read directly from `self.extract_filter`.
+			This is also the mechanism that protects from trying to reference an invalid attribute.
+
+			Used as the first part of the `LazyFuncValue` chain used for further array manipulations with Math nodes.
+
+		Returns:
+			The data array, if available, else `ct.FlowSignal.FlowPending`.
+		"""
+		has_monitor_data = not ct.FlowSignal.check(input_sockets['Monitor Data'])
+
+		if has_monitor_data and props['extract_filter'] != 'NONE':
 			xarray_data = getattr(
 				input_sockets['Monitor Data'], props['extract_filter']
 			)
-			return jnp.array(xarray_data.data)
-			## TODO: Let the array itself have its output unit too!
+			return ct.ArrayFlow(values=jnp.array(xarray_data.data), unit=None)
+			## TODO: Try np.array instead, as it removes a copy, while still (I believe) being JIT-compatible.
 
-		return None
+		return ct.FlowSignal.FlowPending
 
 	@events.computes_output_socket(
+		# Trigger
 		'Data',
 		kind=ct.FlowKind.LazyValueFunc,
+		# Loaded
 		output_sockets={'Data'},
 		output_socket_kinds={'Data': ct.FlowKind.Array},
 	)
 	def compute_extracted_data_lazy(
 		self, output_sockets: dict
 	) -> ct.LazyValueFuncFlow | None:
-		if output_sockets['Data'] is not None:
+		"""Declare `Data:LazyValueFunc` by creating a simple function that directly wraps `Data:Array`.
+
+		Returns:
+			The composable function array, if available, else `ct.FlowSignal.FlowPending`.
+		"""
+		has_output_data = not ct.FlowSignal.check(output_sockets['Data'])
+
+		if has_output_data:
 			return ct.LazyValueFuncFlow(
-				func=lambda: output_sockets['Data'], supports_jax=True
+				func=lambda: output_sockets['Data'].values, supports_jax=True
 			)
 
-		return None
+		return ct.FlowSignal.FlowPending
 
 	####################
 	# - Auxiliary: Monitor Data -> Data
 	####################
 	@events.computes_output_socket(
+		'Data',
+		kind=ct.FlowKind.Params,
+	)
+	def compute_data_params(self) -> ct.ParamsFlow:
+		return ct.ParamsFlow()
+
+	@events.computes_output_socket(
+		# Trigger
 		'Data',
 		kind=ct.FlowKind.Info,
+		# Loaded
 		props={'monitor_data_type', 'extract_filter'},
 		input_sockets={'Monitor Data'},
 		input_socket_kinds={'Monitor Data': ct.FlowKind.Value},
@@ -247,14 +393,18 @@ class ExtractDataNode(base.MaxwellSimNode):
 	def compute_extracted_data_info(
 		self, props: dict, input_sockets: dict
 	) -> ct.InfoFlow:
+		"""Declare `Data:Info` by manually selecting appropriate axes, units, etc. for each monitor type.
+
+		Returns:
+			Information describing the `Data:LazyValueFunc`, if available, else `ct.FlowSignal.FlowPending`.
+		"""
+		has_monitor_data = not ct.FlowSignal.check(input_sockets['Monitor Data'])
+
 		# Retrieve XArray
-		if (
-			input_sockets['Monitor Data'] is not None
-			and props['extract_filter'] != 'NONE'
-		):
+		if has_monitor_data and props['extract_filter'] != 'NONE':
 			xarr = getattr(input_sockets['Monitor Data'], props['extract_filter'])
 		else:
-			return ct.InfoFlow()
+			return ct.FlowSignal.FlowPending
 
 		info_output_names = {
 			'output_names': [props['extract_filter']],

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/analysis/math/filter_math.py

@@ -48,8 +48,12 @@ class FilterMathNode(base.MaxwellSimNode):
 	)
 
 	@property
-	def _info(self) -> ct.InfoFlow:
-		return self._compute_input('Data', kind=ct.FlowKind.Info)
+	def data_info(self) -> ct.InfoFlow | None:
+		info = self._compute_input('Data', kind=ct.FlowKind.Info)
+		if not ct.FlowSignal.check(info):
+			return info
+
+		return None
 
 	####################
 	# - Operation Search
@@ -71,16 +75,18 @@ class FilterMathNode(base.MaxwellSimNode):
 	# - Dim Search
 	####################
 	def search_dims(self) -> list[ct.BLEnumElement]:
-		if (info := self._info).dim_names:
+		if self.data_info is not None:
 			dims = [
 				(dim_name, dim_name, dim_name, '', i)
-				for i, dim_name in enumerate(info.dim_names)
+				for i, dim_name in enumerate(self.data_info.dim_names)
 			]
 
 			# Squeeze: Dimension Must Have Length=1
 			## We must also correct the "NUMBER" of the enum.
 			if self.operation == 'SQUEEZE':
-				filtered_dims = [dim for dim in dims if info.dim_lens[dim[0]] == 1]
+				filtered_dims = [
+					dim for dim in dims if self.data_info.dim_lens[dim[0]] == 1
+				]
 				return [(*dim[:-1], i) for i, dim in enumerate(filtered_dims)]
 
 			return dims
@@ -91,42 +97,43 @@ class FilterMathNode(base.MaxwellSimNode):
 	####################
 	def draw_props(self, _: bpy.types.Context, layout: bpy.types.UILayout) -> None:
 		layout.prop(self, self.blfields['operation'], text='')
-		if self._info.dim_names:
+		if self.data_info is not None and self.data_info.dim_names:
 			layout.prop(self, self.blfields['dim'], text='')
 
 	####################
 	# - Events
 	####################
-	@events.on_value_changed(
-		prop_name='active_socket_set',
-		run_on_init=True,
-	)
-	def on_socket_set_changed(self):
-		self.operation = bl_cache.Signal.ResetEnumItems
-
 	@events.on_value_changed(
 		socket_name='Data',
 		prop_name='active_socket_set',
-		props={'active_socket_set'},
+		run_on_init=True,
 		input_sockets={'Data'},
-		input_socket_kinds={'Data': ct.FlowKind.Info},
-		# run_on_init=True,
 	)
-	def on_any_change(self, props: dict, input_sockets: dict):
+	def on_any_change(self, input_sockets: dict):
+		if all(
+			not ct.FlowSignal.check_single(
+				input_socket_value, ct.FlowSignal.FlowPending
+			)
+			for input_socket_value in input_sockets.values()
+		):
+			self.operation = bl_cache.Signal.ResetEnumItems
 			self.dim = bl_cache.Signal.ResetEnumItems
 
 	@events.on_value_changed(
 		socket_name='Data',
 		prop_name='dim',
+		## run_on_init: Implicitly triggered.
 		props={'active_socket_set', 'dim'},
 		input_sockets={'Data'},
 		input_socket_kinds={'Data': ct.FlowKind.Info},
-		# run_on_init=True,
 	)
 	def on_dim_change(self, props: dict, input_sockets: dict):
+		if input_sockets['Data'] == ct.FlowSignal.FlowPending:
+			return
+
 		# Add/Remove Input Socket "Value"
 		if (
-			input_sockets['Data'] != ct.InfoFlow()
+			not ct.Flowsignal.check(input_sockets['Data'])
 			and props['active_socket_set'] == 'By Dim Value'
 			and props['dim'] != 'NONE'
 		):
@@ -144,7 +151,7 @@ class FilterMathNode(base.MaxwellSimNode):
 			):
 				self.loose_input_sockets = {
 					'Value': wanted_socket_def(),
-				}
+				}  ## TODO: Can we do the boilerplate in base.py?
 		elif self.loose_input_sockets:
 			self.loose_input_sockets = {}
 
@@ -163,13 +170,16 @@ class FilterMathNode(base.MaxwellSimNode):
 		lazy_value_func = input_sockets['Data'][ct.FlowKind.LazyValueFunc]
 		info = input_sockets['Data'][ct.FlowKind.Info]
 
+		# Check Flow
+		if (
+			any(ct.FlowSignal.check(inp) for inp in [info, lazy_value_func])
+			or props['operation'] == 'NONE'
+		):
+			return ct.FlowSignal.FlowPending
+
 		# Compute Bound/Free Parameters
 		func_args = [int] if props['active_socket_set'] == 'By Dim Value' else []
-		if props['dim'] != 'NONE':
 		axis = info.dim_names.index(props['dim'])
-		else:
-			msg = 'Dimension cannot be empty'
-			raise ValueError(msg)
 
 		# Select Function
 		filter_func: typ.Callable[[jax.Array], jax.Array] = {
@@ -201,6 +211,10 @@ class FilterMathNode(base.MaxwellSimNode):
 		lazy_value_func = output_sockets['Data'][ct.FlowKind.LazyValueFunc]
 		params = output_sockets['Data'][ct.FlowKind.Params]
 
+		# Check Flow
+		if any(ct.FlowSignal.check(inp) for inp in [lazy_value_func, params]):
+			return ct.FlowSignal.FlowPending
+
 		# Compute Array
 		return ct.ArrayFlow(
 			values=lazy_value_func.func_jax(*params.func_args, **params.func_kwargs),
@@ -221,15 +235,14 @@ class FilterMathNode(base.MaxwellSimNode):
 		# Retrieve Inputs
 		info = input_sockets['Data']
 
-		# Compute Bound/Free Parameters
-		## Empty Dimension -> Empty InfoFlow
-		if input_sockets['Data'] != ct.InfoFlow() and props['dim'] != 'NONE':
-			axis = info.dim_names.index(props['dim'])
-		else:
-			return ct.InfoFlow()
+		# Check Flow
+		if ct.FlowSignal.check(info) or props['dim'] == 'NONE':
+			return ct.FlowSignal.FlowPending
 
 		# Compute Information
 		## Compute Info w/By-Operation Change to Dimensions
+		axis = info.dim_names.index(props['dim'])
+
 		if (props['active_socket_set'], props['operation']) in [
 			('By Dim', 'SQUEEZE'),
 			('By Dim Value', 'FIX'),
@@ -246,8 +259,8 @@ class FilterMathNode(base.MaxwellSimNode):
 				output_units=info.output_units,
 			)
 
-		# Fallback to Empty InfoFlow
-		return ct.InfoFlow()
+		msg = f'Active socket set {props["active_socket_set"]} and operation {props["operation"]} don\'t have an InfoFlow defined'
+		raise RuntimeError(msg)
 
 	@events.computes_output_socket(
 		'Data',
@@ -264,6 +277,9 @@ class FilterMathNode(base.MaxwellSimNode):
 		info = input_sockets['Data'][ct.FlowKind.Info]
 		params = input_sockets['Data'][ct.FlowKind.Params]
 
+		if any(ct.FlowSignal.check(inp) for inp in [info, params]):
+			return ct.FlowSignal.FlowPending
+
 		# Compute Composed Parameters
 		## -> Only operations that add parameters.
 		## -> A dimension must be selected.
@@ -274,7 +290,7 @@ class FilterMathNode(base.MaxwellSimNode):
 				('By Dim Value', 'FIX'),
 			]
 			and props['dim'] != 'NONE'
-			and input_sockets['Value'] is not None
+			and not ct.FlowSignal.check(input_sockets['Value'])
 		):
 			# Compute IDX Corresponding to Coordinate Value
 			## -> Each dimension declares a unit-aware real number at each index.

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/analysis/math/map_math.py

@@ -54,9 +54,8 @@ class MapMathNode(base.MaxwellSimNode):
 	)
 
 	def search_operations(self) -> list[ct.BLEnumElement]:
-		items = []
 		if self.active_socket_set == 'By Element':
-			items += [
+			items = [
 				# General
 				('REAL', 'ℝ(v)', 'real(v) (by el)'),
 				('IMAG', 'Im(v)', 'imag(v) (by el)'),
@@ -73,11 +72,11 @@ class MapMathNode(base.MaxwellSimNode):
 				('ATAN', 'atan v', 'atan(v) (by el)'),
 			]
 		elif self.active_socket_set in 'By Vector':
-			items += [
+			items = [
 				('NORM_2', '||v||₂', 'norm(v, 2) (by Vec)'),
 			]
 		elif self.active_socket_set == 'By Matrix':
-			items += [
+			items = [
 				# Matrix -> Number
 				('DET', 'det V', 'det(V) (by Mat)'),
 				('COND', 'κ(V)', 'cond(V) (by Mat)'),
@@ -96,7 +95,10 @@ class MapMathNode(base.MaxwellSimNode):
 				('SVD', 'svd V', 'svd(V) -> U·Σ·V† (by Mat)'),
 			]
 		elif self.active_socket_set == 'Expr':
-			items += [('EXPR_EL', 'By Element', 'Expression-defined (by el)')]
+			items = [('EXPR_EL', 'By Element', 'Expression-defined (by el)')]
+		else:
+			msg = f'Active socket set {self.active_socket_set} is unknown'
+			raise RuntimeError(msg)
 
 		return [(*item, '', i) for i, item in enumerate(items)]
 
@@ -127,6 +129,14 @@ class MapMathNode(base.MaxwellSimNode):
 		input_sockets_optional={'Mapper': True},
 	)
 	def compute_data(self, props: dict, input_sockets: dict):
+		if (
+			ct.FlowSignal.check(input_sockets['Data']) or props['operation'] == 'NONE'
+		) or (
+			props['active_socket_set'] == 'Expr'
+			and ct.FlowSignal.check(input_sockets['Mapper'])
+		):
+			return ct.FlowSignal.FlowPending
+
 		mapping_func: typ.Callable[[jax.Array], jax.Array] = {
 			'By Element': {
 				'REAL': lambda data: jnp.real(data),
@@ -186,11 +196,17 @@ class MapMathNode(base.MaxwellSimNode):
 	def compute_array(self, output_sockets: dict) -> ct.ArrayFlow:
 		lazy_value_func = output_sockets['Data'][ct.FlowKind.LazyValueFunc]
 		params = output_sockets['Data'][ct.FlowKind.Params]
+
+		if all(not ct.FlowSignal.check(inp) for inp in [lazy_value_func, params]):
 			return ct.ArrayFlow(
-			values=lazy_value_func.func_jax(*params.func_args, **params.func_kwargs),
-			unit=None,  ## TODO: Unit Propagation
+				values=lazy_value_func.func_jax(
+					*params.func_args, **params.func_kwargs
+				),
+				unit=None,
 			)
 
+		return ct.FlowSignal.FlowPending
+
 	####################
 	# - Compute Auxiliary: Info / Params
 	####################
@@ -205,11 +221,16 @@ class MapMathNode(base.MaxwellSimNode):
 		info = input_sockets['Data']
 
 		# Complex -> Real
-		if props['active_socket_set'] == 'By Element' and props['operation'] in [
+		if (
+			props['active_socket_set'] == 'By Element'
+			and props['operation']
+			in [
 				'REAL',
 				'IMAG',
 				'ABS',
-		]:
+			]
+			and not ct.FlowSignal.check(info)
+		):
 			return ct.InfoFlow(
 				dim_names=info.dim_names,
 				dim_idx=info.dim_idx,
@@ -232,7 +253,7 @@ class MapMathNode(base.MaxwellSimNode):
 		input_sockets={'Data'},
 		input_socket_kinds={'Data': ct.FlowKind.Params},
 	)
-	def compute_data_params(self, input_sockets: dict) -> ct.ParamsFlow:
+	def compute_data_params(self, input_sockets: dict) -> ct.ParamsFlow | ct.FlowSignal:
 		return input_sockets['Data']
 
 

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/analysis/viz.py

@@ -218,11 +218,11 @@ class VizNode(base.MaxwellSimNode):
 	## - Mode Searcher
 	#####################
 	@property
-	def _info(self) -> ct.InfoFlow:
+	def data_info(self) -> ct.InfoFlow:
 		return self._compute_input('Data', kind=ct.FlowKind.Info)
 
 	def search_modes(self) -> list[ct.BLEnumElement]:
-		info = self._info
+		if not ct.FlowSignal.check(self.data_info):
 			return [
 				(
 					viz_mode,
@@ -231,13 +231,16 @@ class VizNode(base.MaxwellSimNode):
 					VizMode.to_icon(viz_mode),
 					i,
 				)
-			for i, viz_mode in enumerate(VizMode.valid_modes_for(info))
+				for i, viz_mode in enumerate(VizMode.valid_modes_for(self.data_info))
 			]
 
+		return []
+
 	#####################
 	## - Target Searcher
 	#####################
 	def search_targets(self) -> list[ct.BLEnumElement]:
+		if self.viz_mode != 'NONE':
 			return [
 				(
 					viz_target,
@@ -246,8 +249,11 @@ class VizNode(base.MaxwellSimNode):
 					VizTarget.to_icon(viz_target),
 					i,
 				)
-			for i, viz_target in enumerate(VizTarget.valid_targets_for(self.viz_mode))
+				for i, viz_target in enumerate(
+					VizTarget.valid_targets_for(self.viz_mode)
+				)
 			]
+		return []
 
 	#####################
 	## - UI
@@ -264,17 +270,20 @@ class VizNode(base.MaxwellSimNode):
 	@events.on_value_changed(
 		socket_name='Data',
 		input_sockets={'Data'},
+		run_on_init=True,
 		input_socket_kinds={'Data': ct.FlowKind.Info},
 		input_sockets_optional={'Data': True},
-		run_on_init=True,
 	)
-	def on_socket_set_changed(self, input_sockets: dict):
+	def on_any_changed(self, input_sockets: dict):
+		if not ct.FlowSignal.check_single(
+			input_sockets['Data'], ct.FlowSignal.FlowPending
+		):
 			self.viz_mode = bl_cache.Signal.ResetEnumItems
 			self.viz_target = bl_cache.Signal.ResetEnumItems
 
 	@events.on_value_changed(
 		prop_name='viz_mode',
-		# run_on_init=True,
+		## run_on_init: Implicitly triggered.
 	)
 	def on_viz_mode_changed(self):
 		self.viz_target = bl_cache.Signal.ResetEnumItems
@@ -287,7 +296,6 @@ class VizNode(base.MaxwellSimNode):
 		props={'viz_mode', 'viz_target', 'colormap'},
 		input_sockets={'Data'},
 		input_socket_kinds={'Data': {ct.FlowKind.Array, ct.FlowKind.Info}},
-		input_sockets_optional={'Data': True},
 		stop_propagation=True,
 	)
 	def on_show_plot(
@@ -296,12 +304,19 @@ class VizNode(base.MaxwellSimNode):
 		input_sockets: dict,
 		props: dict,
 	):
+		# Retrieve Inputs
 		array_flow = input_sockets['Data'][ct.FlowKind.Array]
 		info = input_sockets['Data'][ct.FlowKind.Info]
 
-		if input_sockets['Data'] is None:
+		# Check Flow
+		if (
+			any(ct.FlowSignal.check(inp) for inp in [array_flow, info])
+			or props['viz_mode'] == 'NONE'
+			or props['viz_target'] == 'NONE'
+		):
 			return
 
+		# Viz Target
 		if props['viz_target'] == VizTarget.Plot2D:
 			managed_objs['plot'].mpl_plot_to_image(
 				lambda ax: VizMode.to_plotter(props['viz_mode'])(

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/base.py

@@ -597,7 +597,7 @@ class MaxwellSimNode(bpy.types.Node):
 			)
 
 		if optional:
-			return None
+			return ct.FlowSignal.NoFlow
 
 		msg = f'Input socket "{input_socket_name}" on "{self.bl_idname}" is not an active input socket'
 		raise ValueError(msg)
@@ -645,14 +645,8 @@ class MaxwellSimNode(bpy.types.Node):
 			return output_socket_methods[0](self)
 
 		# Auxiliary Fallbacks
-		if kind == ct.FlowKind.Info:
-			return ct.InfoFlow()
-
-		if kind == ct.FlowKind.Params:
-			return ct.ParamsFlow()
-
-		if optional:
-			return None
+		if optional or kind in [ct.FlowKind.Info, ct.FlowKind.Params]:
+			return ct.FlowSignal.NoFlow
 
 		msg = f'No output method for ({output_socket_name}, {kind})'
 		raise ValueError(msg)
@@ -777,6 +771,12 @@ class MaxwellSimNode(bpy.types.Node):
 			# Invalidate Input Socket Cache
 			if input_socket_name is not None:
 				if socket_kinds is None:
+					log.critical(
+						'[%s] Invalidating: (%s, %s)',
+						self.sim_node_name,
+						input_socket_name,
+						str(socket_kinds),
+					)
 					self._compute_input.invalidate(
 						input_socket_name=input_socket_name,
 						kind=...,
@@ -784,6 +784,12 @@ class MaxwellSimNode(bpy.types.Node):
 					)
 				else:
 					for socket_kind in socket_kinds:
+						log.critical(
+							'[%s] Invalidating: (%s, %s)',
+							self.sim_node_name,
+							input_socket_name,
+							str(socket_kind),
+						)
 						self._compute_input.invalidate(
 							input_socket_name=input_socket_name,
 							kind=socket_kind,
@@ -838,6 +844,15 @@ class MaxwellSimNode(bpy.types.Node):
 		)
 		for event_method in triggered_event_methods:
 			stop_propagation |= event_method.stop_propagation
+			log.critical(
+				'$[%s] [%s %s %s %s] Running: (%s)',
+				self.sim_node_name,
+				event,
+				socket_name,
+				socket_kinds,
+				prop_name,
+				event_method.callback_info,
+			)
 			event_method(self)
 
 		# Propagate Event to All Sockets in "Trigger Direction"

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/events.py

@@ -270,6 +270,8 @@ def event_decorator(
 			)
 
 			# Call Method
+			## If there is a FlowPending, then the method would fail.
+			## Therefore, propagate FlowPending if found.
 			return method(
 				node,
 				**method_kw_args,

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/inputs/web_importers/tidy_3d_web_importer.py

@@ -1,9 +1,12 @@
 import typing as typ
 from pathlib import Path
 
-from blender_maxwell.utils import logger
+import bpy
+import tidy3d as td
+
+from blender_maxwell.services import tdcloud
+from blender_maxwell.utils import bl_cache, logger
 
-from ......services import tdcloud
 from .... import contracts as ct
 from .... import sockets
 from ... import base, events
@@ -11,6 +14,40 @@ from ... import base, events
 log = logger.get(__name__)
 
 
+class LoadCloudSim(bpy.types.Operator):
+	bl_idname = ct.OperatorType.NodeLoadCloudSim
+	bl_label = '(Re)Load Sim'
+	bl_description = '(Re)Load simulation data associated with the attached cloud task'
+
+	@classmethod
+	def poll(cls, context):
+		return (
+			# Node Type
+			hasattr(context, 'node')
+			and hasattr(context.node, 'node_type')
+			and context.node.node_type == ct.NodeType.Tidy3DWebImporter
+			# Cloud Status
+			and tdcloud.IS_ONLINE
+			and tdcloud.IS_AUTHENTICATED
+		)
+
+	def execute(self, context):
+		node = context.node
+
+		# Try Loading Simulation Data
+		node.sim_data = bl_cache.Signal.InvalidateCache
+		sim_data = node.sim_data
+		if sim_data is None:
+			self.report(
+				{'ERROR'},
+				'Sim Data could not be loaded. Check your network connection.',
+			)
+		else:
+			self.report({'INFO'}, 'Sim Data loaded.')
+
+		return {'FINISHED'}
+
+
 def _sim_data_cache_path(task_id: str) -> Path:
 	"""Compute an appropriate location for caching simulations downloaded from the internet, unique to each task ID.
 
@@ -34,68 +71,89 @@ class Tidy3DWebImporterNode(base.MaxwellSimNode):
 		),
 	}
 
-	####################
-	# - Event Methods
-	####################
-	@events.computes_output_socket(
-		'FDTD Sim Data',
-		input_sockets={'Cloud Task'},
+	sim_data_loaded: bool = bl_cache.BLField(False)
+
+	@bl_cache.cached_bl_property()
+	def sim_data(self) -> td.SimulationData | None:
+		cloud_task = self._compute_input(
+			'Cloud Task', kind=ct.FlowKind.Value, optional=True
 		)
-	def compute_sim_data(self, input_sockets: dict) -> str:
-		## TODO: REMOVE TEST
-		log.info('Loading SimulationData File')
-		import sys
-
-		for module_name, module in sys.modules.copy().items():
-			if module_name == '__mp_main__':
-				print('Problematic Module Entry', module_name)
-				print(module)
-				# print('MODULE REPR', module)
-				continue
-		# return td.SimulationData.from_file(
-		# fname='/home/sofus/src/blender_maxwell/dev/sim_demo.hdf5'
-		# )
-
-		# Validate Task Availability
-		if (cloud_task := input_sockets['Cloud Task']) is None:
-			msg = f'"{self.bl_label}" CloudTask doesn\'t exist'
-			raise RuntimeError(msg)
-
-		# Validate Task Existence
-		if not isinstance(cloud_task, tdcloud.CloudTask):
-			msg = f'"{self.bl_label}" CloudTask input "{cloud_task}" has wrong "should_exists", as it isn\'t an instance of tdcloud.CloudTask'
-			raise TypeError(msg)
-
-		# Validate Task Status
-		if cloud_task.status != 'success':
-			msg = f'"{self.bl_label}" CloudTask is "{cloud_task.status}", not "success"'
-			raise RuntimeError(msg)
-
-		# Download and Return SimData
-		return tdcloud.TidyCloudTasks.download_task_sim_data(
-			cloud_task, _sim_data_cache_path(cloud_task.task_id)
-		)
-
-	@events.on_value_changed(
-		socket_name='Cloud Task', run_on_init=True, input_sockets={'Cloud Task'}
-	)
-	def on_cloud_task_changed(self, input_sockets: dict):
 		if (
-			(cloud_task := input_sockets['Cloud Task']) is not None
+			# Check Flow
+			not ct.FlowSignal.check(cloud_task)
+			# Check Task
+			and cloud_task is not None
 			and isinstance(cloud_task, tdcloud.CloudTask)
 			and cloud_task.status == 'success'
 		):
-			self.loose_output_sockets = {
-				'FDTD Sim Data': sockets.MaxwellFDTDSimDataSocketDef(),
-			}
+			sim_data = tdcloud.TidyCloudTasks.download_task_sim_data(
+				cloud_task, _sim_data_cache_path(cloud_task.task_id)
+			)
+			self.sim_data_loaded = True
+			return sim_data
+
+		return None
+
+	####################
+	# - UI
+	####################
+	def draw_operators(self, context, layout):
+		if self.sim_data_loaded:
+			layout.operator(ct.OperatorType.NodeLoadCloudSim, text='Reload Sim')
 		else:
+			layout.operator(ct.OperatorType.NodeLoadCloudSim, text='Load Sim')
+
+	####################
+	# - Events
+	####################
+	@events.on_value_changed(socket_name='Cloud Task')
+	def on_cloud_task_changed(self):
+		self.inputs['Cloud Task'].on_cloud_updated()
+		## TODO: Must we babysit sockets like this?
+
+	@events.on_value_changed(
+		prop_name='sim_data_loaded', run_on_init=True, props={'sim_data_loaded'}
+	)
+	def on_cloud_task_changed(self, props: dict):
+		if props['sim_data_loaded']:
+			if not self.loose_output_sockets:
+				self.loose_output_sockets = {
+					'Sim Data': sockets.MaxwellFDTDSimDataSocketDef(),
+				}
+		elif self.loose_output_sockets:
 			self.loose_output_sockets = {}
 
+	####################
+	# - Output
+	####################
+	@events.computes_output_socket(
+		'Sim Data',
+		props={'sim_data_loaded'},
+		input_sockets={'Cloud Task'},
+	)
+	def compute_sim_data(self, props: dict, input_sockets: dict) -> str:
+		if props['sim_data_loaded']:
+			cloud_task = input_sockets['Cloud Task']
+			if (
+				# Check Flow
+				not ct.FlowSignal.check(cloud_task)
+				# Check Task
+				and cloud_task is not None
+				and isinstance(cloud_task, tdcloud.CloudTask)
+				and cloud_task.status == 'success'
+			):
+				return self.sim_data
+
+			return ct.FlowSignal.FlowPending
+
+		return ct.FlowSignal.FlowPending
+
 
 ####################
 # - Blender Registration
 ####################
 BL_REGISTER = [
+	LoadCloudSim,
 	Tidy3DWebImporterNode,
 ]
 BL_NODES = {

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/outputs/web_exporters/tidy3d_web_exporter.py

@@ -209,7 +209,7 @@ class Tidy3DWebExporterNode(base.MaxwellSimNode):
 		else:
 			self.cache_est_cost = -1.0
 			self.loose_output_sockets = {}
-			self.inputs['Cloud Task'].sync_prepare_new_task()
+			self.inputs['Cloud Task'].on_prepare_new_task()
 			self.inputs['Cloud Task'].locked = False
 
 		self.on_prop_changed('tracked_task_id', context)
@@ -249,7 +249,7 @@ class Tidy3DWebExporterNode(base.MaxwellSimNode):
 		# Declare to Cloud Task that it Exists Now
 		## This will change the UI to not allow free-text input.
 		## If the socket is linked, this errors.
-		self.inputs['Cloud Task'].sync_created_new_task(cloud_task)
+		self.inputs['Cloud Task'].on_new_task_created(cloud_task)
 
 		# Track the Newly Uploaded Task ID
 		self.tracked_task_id = cloud_task.task_id

src/blender_maxwell/node_trees/maxwell_sim_nodes/sockets/base.py

@@ -548,7 +548,7 @@ class MaxwellSimSocket(bpy.types.NodeSocket):
 		Returns:
 			An empty `ct.InfoFlow`.
 		"""
-		return ct.InfoFlow()
+		return ct.FlowSignal.NoFlow
 
 	# Param
 	@property
@@ -561,7 +561,7 @@ class MaxwellSimSocket(bpy.types.NodeSocket):
 		Returns:
 			An empty `ct.ParamsFlow`.
 		"""
-		return ct.ParamsFlow()
+		return ct.FlowSignal.NoFlow
 
 	####################
 	# - FlowKind: Auxiliary
@@ -577,8 +577,7 @@ class MaxwellSimSocket(bpy.types.NodeSocket):
 		Raises:
 			NotImplementedError: When used without being overridden.
 		"""
-		msg = f'Socket {self.bl_label} {self.socket_type}): Tried to get "ct.FlowKind.Value", but socket does not define it'
-		raise NotImplementedError(msg)
+		return ct.FlowSignal.NoFlow
 
 	@value.setter
 	def value(self, value: ct.ValueFlow) -> None:
@@ -604,8 +603,7 @@ class MaxwellSimSocket(bpy.types.NodeSocket):
 		Raises:
 			NotImplementedError: When used without being overridden.
 		"""
-		msg = f'Socket {self.bl_label} {self.socket_type}): Tried to get "ct.FlowKind.Array", but socket does not define it'
-		raise NotImplementedError(msg)
+		return ct.FlowSignal.NoFlow
 
 	@array.setter
 	def array(self, value: ct.ArrayFlow) -> None:
@@ -631,8 +629,7 @@ class MaxwellSimSocket(bpy.types.NodeSocket):
 		Raises:
 			NotImplementedError: When used without being overridden.
 		"""
-		msg = f'Socket {self.bl_label} {self.socket_type}): Tried to get "ct.FlowKind.LazyValueFunc", but socket does not define it'
-		raise NotImplementedError(msg)
+		return ct.FlowSignal.NoFlow
 
 	@lazy_value_func.setter
 	def lazy_value_func(self, lazy_value_func: ct.LazyValueFuncFlow) -> None:
@@ -658,8 +655,7 @@ class MaxwellSimSocket(bpy.types.NodeSocket):
 		Raises:
 			NotImplementedError: When used without being overridden.
 		"""
-		msg = f'Socket {self.bl_label} {self.socket_type}): Tried to get "ct.FlowKind.LazyArrayRange", but socket does not define it'
-		raise NotImplementedError(msg)
+		return ct.FlowSignal.NoFlow
 
 	@lazy_array_range.setter
 	def lazy_array_range(self, value: ct.LazyArrayRangeFlow) -> None:
@@ -892,6 +888,7 @@ class MaxwellSimSocket(bpy.types.NodeSocket):
 		# Info Drawing
 		if self.use_info_draw:
 			info = self.compute_data(kind=ct.FlowKind.Info)
+			if not ct.FlowSignal.check(info):
 				self.draw_info(info, col)
 
 	def draw_output(
@@ -920,6 +917,7 @@ class MaxwellSimSocket(bpy.types.NodeSocket):
 		# Draw FlowKind.Info related Information
 		if self.use_info_draw:
 			info = self.compute_data(kind=ct.FlowKind.Info)
+			if not ct.FlowSignal.check(info):
 				self.draw_info(info, col)
 
 	####################

src/blender_maxwell/node_trees/maxwell_sim_nodes/sockets/basic/data.py

@@ -34,10 +34,6 @@ class DataBLSocket(base.MaxwellSimSocket):
 			must_match={'format': self.format},
 		)
 
-	@property
-	def value(self):
-		return None
-
 	####################
 	# - UI
 	####################

src/blender_maxwell/node_trees/maxwell_sim_nodes/sockets/maxwell/fdtd_sim.py

@@ -7,10 +7,6 @@ class MaxwellFDTDSimBLSocket(base.MaxwellSimSocket):
 	socket_type = ct.SocketType.MaxwellFDTDSim
 	bl_label = 'Maxwell FDTD Simulation'
 
-	@property
-	def value(self) -> None:
-		return None
-
 
 ####################
 # - Socket Configuration

src/blender_maxwell/node_trees/maxwell_sim_nodes/sockets/maxwell/fdtd_sim_data.py

@@ -6,10 +6,6 @@ class MaxwellFDTDSimDataBLSocket(base.MaxwellSimSocket):
 	socket_type = ct.SocketType.MaxwellFDTDSimData
 	bl_label = 'Maxwell FDTD Simulation'
 
-	@property
-	def value(self):
-		return None
-
 
 ####################
 # - Socket Configuration

src/blender_maxwell/node_trees/maxwell_sim_nodes/sockets/tidy3d/cloud_task.py

@@ -1,6 +1,10 @@
+import enum
+
 import bpy
 
-from .....services import tdcloud
+from blender_maxwell.services import tdcloud
+from blender_maxwell.utils import bl_cache
+
 from ... import contracts as ct
 from .. import base
 
@@ -9,30 +13,32 @@ from .. import base
 # - Operators
 ####################
 class ReloadFolderList(bpy.types.Operator):
-	bl_idname = 'blender_maxwell.sockets__reload_folder_list'
+	bl_idname = ct.OperatorType.SocketReloadCloudFolderList
 	bl_label = 'Reload Tidy3D Folder List'
 	bl_description = 'Reload the the cached Tidy3D folder list'
 
 	@classmethod
 	def poll(cls, context):
 		return (
-			tdcloud.IS_AUTHENTICATED
+			tdcloud.IS_ONLINE
+			and tdcloud.IS_AUTHENTICATED
 			and hasattr(context, 'socket')
 			and hasattr(context.socket, 'socket_type')
 			and context.socket.socket_type == ct.SocketType.Tidy3DCloudTask
 		)
 
 	def execute(self, context):
-		socket = context.socket
+		bl_socket = context.socket
 
 		tdcloud.TidyCloudFolders.update_folders()
-		tdcloud.TidyCloudTasks.update_tasks(socket.existing_folder_id)
+		tdcloud.TidyCloudTasks.update_tasks(bl_socket.existing_folder_id)
+		bl_socket.on_cloud_updated()
 
 		return {'FINISHED'}
 
 
 class Authenticate(bpy.types.Operator):
-	bl_idname = 'blender_maxwell.sockets__authenticate'
+	bl_idname = ct.OperatorType.SocketCloudAuthenticate
 	bl_label = 'Authenticate Tidy3D'
 	bl_description = 'Authenticate the Tidy3D Web API from a Cloud Task socket'
 
@@ -51,6 +57,7 @@ class Authenticate(bpy.types.Operator):
 		if not tdcloud.check_authentication():
 			tdcloud.authenticate_with_api_key(bl_socket.api_key)
 			bl_socket.api_key = ''
+			bl_socket.on_cloud_updated()
 
 		return {'FINISHED'}
 
@@ -59,6 +66,16 @@ class Authenticate(bpy.types.Operator):
 # - Socket
 ####################
 class Tidy3DCloudTaskBLSocket(base.MaxwellSimSocket):
+	"""Interact with Tidy3D Cloud Tasks.
+
+	Attributes:
+		api_key: API key for the Tidy3D cloud.
+		should_exist: Whether or not the cloud task should already exist.
+		existing_folder_id: ID of an existing folder on the Tidy3D cloud.
+		existing_task_id: ID of an existing task on the Tidy3D cloud.
+		new_task_name: Name of a new task to submit to the Tidy3D cloud.
+	"""
+
 	socket_type = ct.SocketType.Tidy3DCloudTask
 	bl_label = 'Tidy3D Cloud Task'
 
@@ -67,81 +84,90 @@ class Tidy3DCloudTaskBLSocket(base.MaxwellSimSocket):
 	####################
 	# - Properties
 	####################
-	# Authentication
-	api_key: bpy.props.StringProperty(
-		name='API Key',
-		description='API Key for the Tidy3D Cloud',
-		default='',
-		options={'SKIP_SAVE'},
-		subtype='PASSWORD',
+	api_key: str = bl_cache.BLField('', prop_ui=True, str_secret=True)
+	should_exist: bool = bl_cache.BLField(False)
+
+	existing_folder_id: enum.Enum = bl_cache.BLField(
+		prop_ui=True, enum_cb=lambda self, _: self.search_cloud_folders()
+	)
+	existing_task_id: enum.Enum = bl_cache.BLField(
+		prop_ui=True, enum_cb=lambda self, _: self.search_cloud_tasks()
 	)
 
-	# Task Existance Presumption
-	should_exist: bpy.props.BoolProperty(
-		name='Cloud Task Should Exist',
-		description='Whether or not the cloud task should already exist',
-		default=False,
+	new_task_name: str = bl_cache.BLField('', prop_ui=True)
+
+	@property
+	def capabilities(self) -> ct.CapabilitiesFlow:
+		return ct.CapabilitiesFlow(
+			socket_type=self.socket_type,
+			active_kind=self.active_kind,
+			must_match={'should_exist': self.should_exist},
 		)
 
-	# Identifiers
-	existing_folder_id: bpy.props.EnumProperty(
-		name='Folder of Cloud Tasks',
-		description='An existing folder on the Tidy3D Cloud',
-		items=lambda self, _: self.retrieve_folders(),
-		update=(lambda self, context: self.on_prop_changed('existing_folder_id', context)),
-	)
-	existing_task_id: bpy.props.EnumProperty(
-		name='Existing Cloud Task',
-		description='An existing task on the Tidy3D Cloud, within the given folder',
-		items=lambda self, _: self.retrieve_tasks(),
-		update=(lambda self, context: self.on_prop_changed('existing_task_id', context)),
+	@property
+	def value(
+		self,
+	) -> tuple[tdcloud.CloudTaskName, tdcloud.CloudFolder] | tdcloud.CloudTask | None:
+		if tdcloud.IS_AUTHENTICATED:
+			# Retrieve Folder
+			cloud_folder = tdcloud.TidyCloudFolders.folders().get(
+				self.existing_folder_id
 			)
+			if cloud_folder is None:
+				msg = f"Selected folder {cloud_folder} doesn't exist (it was probably deleted elsewhere)"
+				raise RuntimeError(msg)
 
-	# (Potential) New Task
-	new_task_name: bpy.props.StringProperty(
-		name='New Cloud Task Name',
-		description='Name of a new task to submit to the Tidy3D Cloud',
-		default='',
-		update=(lambda self, context: self.on_prop_changed('new_task_name', context)),
+			# Doesn't Exist: Return Construction Information
+			if not self.should_exist:
+				return (self.new_task_name, cloud_folder)
+
+			# No Task Selected: Return None
+			if self.existing_task_id == 'NONE':
+				return None
+
+			# Retrieve Cloud Task
+			cloud_task = tdcloud.TidyCloudTasks.tasks(cloud_folder).get(
+				self.existing_task_id
 			)
+			if cloud_task is None:
+				msg = f"Selected task {cloud_task} doesn't exist (it was probably deleted elsewhere)"
+				raise RuntimeError(msg)
+
+			return cloud_task
+
+		return None
 
 	####################
-	# - Property Methods
+	# - Searchers
 	####################
-	def sync_existing_folder_id(self, context):
-		folder_task_ids = self.retrieve_tasks()
-
-		self.existing_task_id = folder_task_ids[0][0]
-		## There's guaranteed to at least be one element, even if it's "NONE".
-
-		self.on_prop_changed('existing_folder_id', context)
-
-	def retrieve_folders(self) -> list[tuple]:
-		folders = tdcloud.TidyCloudFolders.folders()
-		if not folders:
-			return [('NONE', 'None', 'No folders')]
-
+	def search_cloud_folders(self) -> list[ct.BLEnumElement]:
+		if tdcloud.IS_AUTHENTICATED:
 			return [
 				(
 					cloud_folder.folder_id,
 					cloud_folder.folder_name,
-				f"Folder 'cloud_folder.folder_name' with ID {folder_id}",
+					f'Folder {cloud_folder.folder_name} (ID={folder_id})',
+					'',
+					i,
+				)
+				for i, (folder_id, cloud_folder) in enumerate(
+					tdcloud.TidyCloudFolders.folders().items()
 				)
-			for folder_id, cloud_folder in folders.items()
 			]
 
-	def retrieve_tasks(self) -> list[tuple]:
-		if (
-			cloud_folder := tdcloud.TidyCloudFolders.folders().get(
-				self.existing_folder_id
-			)
-		) is None:
-			return [('NONE', 'None', "Folder doesn't exist")]
+		return []
 
+	def search_cloud_tasks(self) -> list[ct.BLEnumElement]:
+		if self.existing_folder_id == 'NONE' or not tdcloud.IS_AUTHENTICATED:
+			return []
+
+		# Get Cloud Folder
+		cloud_folder = tdcloud.TidyCloudFolders.folders().get(self.existing_folder_id)
+		if cloud_folder is None:
+			return []
+
+		# Get Cloud Tasks
 		tasks = tdcloud.TidyCloudTasks.tasks(cloud_folder)
-		if not tasks:
-			return [('NONE', 'None', 'No tasks in folder')]
-
 		return [
 			(
 				## Task ID
@@ -158,9 +184,9 @@ class Tidy3DCloudTaskBLSocket(base.MaxwellSimSocket):
 				## Task Description
 				f'Task Status: {task.status}',
 				## Status Icon
-				_icon
+				icon
 				if (
-					_icon := {
+					icon := {
 						'draft': 'SEQUENCE_COLOR_08',
 						'initialized': 'SHADING_SOLID',
 						'queued': 'SEQUENCE_COLOR_03',
@@ -185,52 +211,28 @@ class Tidy3DCloudTaskBLSocket(base.MaxwellSimSocket):
 		]
 
 	####################
-	# - Task Sync Methods
+	# - Node-Initiated Updates
 	####################
-	def sync_created_new_task(self, cloud_task):
-		"""Called whenever the task specified in `new_task_name` has been actually created.
-
-		This changes the socket somewhat: Folder/task IDs are set, and the socket is switched to presume that the task exists.
-
-		If the socket is linked, then an error is raised.
-		"""
-		# Propagate along Link
-		if self.is_linked:
-			msg = 'Cannot sync newly created task to linked Cloud Task socket.'
-			raise ValueError(msg)
-			## TODO: A little aggressive. Is there a good use case?
-
-		# Synchronize w/New Task Information
+	def on_new_task_created(self, cloud_task: tdcloud.CloudTask) -> None:
 		self.existing_folder_id = cloud_task.folder_id
 		self.existing_task_id = cloud_task.task_id
 		self.should_exist = True
 
-	def sync_prepare_new_task(self):
-		"""Called to switch the socket to no longer presume that the task it specifies exists (yet).
-
-		If the socket is linked, then an error is raised.
-		"""
-		# Propagate along Link
-		if self.is_linked:
-			msg = 'Cannot sync newly created task to linked Cloud Task socket.'
-			raise ValueError(msg)
-			## TODO: A little aggressive. Is there a good use case?
-
-		# Synchronize w/New Task Information
+	def on_prepare_new_task(self):
 		self.should_exist = False
 
+	def on_cloud_updated(self):
+		self.existing_folder_id = bl_cache.Signal.ResetEnumItems
+		self.existing_task_id = bl_cache.Signal.ResetEnumItems
+
 	####################
-	# - Socket UI
+	# - UI
 	####################
 	def draw_label_row(self, row: bpy.types.UILayout, text: str):
 		row.label(text=text)
 
 		auth_icon = 'LOCKVIEW_ON' if tdcloud.IS_AUTHENTICATED else 'LOCKVIEW_OFF'
-		row.operator(
-			Authenticate.bl_idname,
-			text='',
-			icon=auth_icon,
-		)
+		row.label(text='', icon=auth_icon)
 
 	def draw_prelock(
 		self,
@@ -245,11 +247,11 @@ class Tidy3DCloudTaskBLSocket(base.MaxwellSimSocket):
 			row.label(text='Tidy3D API Key')
 
 			row = col.row()
-			row.prop(self, 'api_key', text='')
+			row.prop(self, self.blfields['api_key'], text='')
 
 			row = col.row()
 			row.operator(
-				Authenticate.bl_idname,
+				ct.OperatorType.SocketCloudAuthenticate,
 				text='Connect',
 			)
 
@@ -260,9 +262,9 @@ class Tidy3DCloudTaskBLSocket(base.MaxwellSimSocket):
 		# Cloud Folder Selector
 		row = col.row()
 		row.label(icon='FILE_FOLDER')
-		row.prop(self, 'existing_folder_id', text='')
+		row.prop(self, self.blfields['existing_folder_id'], text='')
 		row.operator(
-			ReloadFolderList.bl_idname,
+			ct.OperatorType.SocketReloadCloudFolderList,
 			text='',
 			icon='FILE_REFRESH',
 		)
@@ -272,47 +274,14 @@ class Tidy3DCloudTaskBLSocket(base.MaxwellSimSocket):
 		if not self.should_exist:
 			row = col.row()
 			row.label(icon='NETWORK_DRIVE')
-			row.prop(self, 'new_task_name', text='')
+			row.prop(self, self.blfields['new_task_name'], text='')
 
 			col.separator(factor=1.0)
 
 			box = col.box()
 			row = box.row()
 
-		row.prop(self, 'existing_task_id', text='')
-
-	@property
-	def value(
-		self,
-	) -> tuple[tdcloud.CloudTaskName, tdcloud.CloudFolder] | tdcloud.CloudTask | None:
-		# Retrieve Folder
-		## Authentication is presumed OK
-		if (
-			cloud_folder := tdcloud.TidyCloudFolders.folders().get(
-				self.existing_folder_id
-			)
-		) is None:
-			msg = "Selected folder doesn't exist (it was probably deleted elsewhere)"
-			raise RuntimeError(msg)
-
-		# No Tasks in Folder
-		## The UI should set to "NONE" when there are no tasks in a folder
-		if self.existing_task_id == 'NONE':
-			return None
-
-		# Retrieve Task
-		if self.should_exist:
-			if (
-				cloud_task := tdcloud.TidyCloudTasks.tasks(cloud_folder).get(
-					self.existing_task_id
-				)
-			) is None:
-				msg = "Selected task doesn't exist (it was probably deleted elsewhere)"
-				raise RuntimeError(msg)
-
-			return cloud_task
-
-		return (self.new_task_name, cloud_folder)
+		row.prop(self, self.blfields['existing_task_id'], text='')
 
 
 ####################

src/blender_maxwell/services/tdcloud.py

@@ -268,7 +268,7 @@ class TidyCloudTasks:
 
 		# Get Sim Data (from file and/or download)
 		if path_sim.is_file():
-			log.info('Loading Cloud Task "%s" from "%s"', cloud_task.cloud_id, path_sim)
+			log.info('Loading Cloud Task "%s" from "%s"', cloud_task.task_id, path_sim)
 			sim_data = td.SimulationData.from_file(str(path_sim))
 		else:
 			log.info(
@@ -420,7 +420,7 @@ class TidyCloudTasks:
 
 		# Repopulate All Caches
 		## By deleting the folder ID, all tasks within will be reloaded
-		del cls.cache_folder_tasks[folder_id]
+		cls.cache_folder_tasks.pop(folder_id, None)
 
 		return dict(cls.tasks(cloud_folder).items())
 

src/blender_maxwell/utils/bl_cache.py

@@ -375,6 +375,7 @@ class CachedBLProperty:
 			return
 
 		if value == Signal.InvalidateCache:
+			log.critical('![%s] Invalidating %s', str(bl_instance), str(self))
 			self._invalidate_cache(bl_instance)
 			return
 
@@ -447,7 +448,7 @@ class CachedBLProperty:
 ####################
 # - Property Decorators
 ####################
-def cached_bl_property(persist: bool = ...):
+def cached_bl_property(persist: bool = False):
 	"""Decorator creating a descriptor that caches a computed attribute of a Blender node/socket.
 
 	Many such `bl_instance`s rely on fast access to computed, cached properties, for example to ensure that `draw()` remains effectively non-blocking.
@@ -545,6 +546,7 @@ class BLField:
 		self._str_cb = str_cb
 		self._enum_cb = enum_cb
 
+		## HUGE TODO: Persist these
 		self._str_cb_cache = {}
 		self._enum_cb_cache = {}
 
@@ -575,6 +577,7 @@ class BLField:
 		Thus, whenever the user wants the items in the enum to update, they must manually set the descriptor attribute to the value `Signal.ResetEnumItems`.
 		"""
 		if self._enum_cb_cache.get(_self.instance_id) is None:
+			log.critical('REGEN ENUM')
 			# Retrieve Dynamic Enum Items
 			enum_items = self._enum_cb(_self, context)