Added workflow connectors

[JPPhoto]

Summary

Adds persisted editor-only workflow connectors to the node editor.

This is a frontend feature/fix that introduces a lightweight connector node for visual edge routing, with editor persistence, connector-aware validation/type propagation, and frontend flattening before execution so runtime never sees connector nodes or edges. It also adds workflow UI support for creating/removing connectors, improves connector deletion splice-through behavior, and allows unresolved connectors to accept compatible downstream targets so target-first wiring works correctly.

Also included:

• non-DOM test coverage for connector topology, reducer behavior, validation, candidate resolution, graph flattening, and workflow validation
• cleanup of the connector deletion path to use the real generic node-removal flow
• a small package.json script update to Vitest's worker settings (--maxWorkers=50%) for build/test scripts

Related Issues / Discussions

QA Instructions

So much to do:

1. Open the Workflow Editor and confirm workflows still render after reload.
2. Right-click empty workflow canvas and confirm Add Connector appears.
3. Add a connector, move/select it, and drag connections from/to it.
4. For fun: double-click an existing edge and confirm a connector is inserted.
5. Verify target-first wiring:
   • connect a compatible target field to an unresolved connector
   • then connect a compatible upstream source and confirm it is accepted
   • try an incompatible upstream source and confirm it is rejected
6. Verify deletion splice-through:
   • 1 -> 1 connector delete reconnects source to target
   • 1 -> N reconnects all valid downstream targets
   • 1 -> 0 removes the connector without creating edges
   • invalid splice-through cases disable Delete Connector
7. Save/reload a workflow with connectors and confirm they persist.
8. Execute the workflow and confirm connectors do not appear in the runtime graph/execution views.

Merge Plan

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

[lstein]

What would be really neat is to be able to minimize the portions of the graph that are on either side of the connector, converting them into "black boxes". Later, the same UI could be used to define subroutine-like things.

[JPPhoto]

What would be really neat is to be able to minimize the portions of the graph that are on either side of the connector, converting them into "black boxes". Later, the same UI could be used to define subroutine-like things.

Since this would essentially collapse all inputs, I could see it working for visual clarity but hard to use for subroutines. Though as you know, subroutines are on my personal radar.

[Pfannkuchensack]

The things from package.json and vite.config.mts are right ?

[JPPhoto]

@Pfannkuchensack I believe all of your issues were addressed.

1. On invokeai/frontend/web/src/features/nodes/components/flow/Flow.tsx:
   The window-level context menu interception was too broad and could suppress other context menus inside the workflow surface. I changed it so the workflow menu only activates for connector targets and the React Flow pane, instead of swallowing every contextmenu event inside the wrapper.

2. On invokeai/frontend/web/src/features/nodes/components/flow/Flow.tsx:
   I removed the ref-driven render dependency and switched the workflow menu to reactive state. I also memoized connector splice validation so getConnectorDeletionSpliceConnections() is no longer recomputed from the render path on every open-menu render.

3. On invokeai/frontend/web/src/features/nodes/store/util/connectorTopology.ts:
   I cleaned up the repeated lookup logic by hoisting the connector input edge id and output edge id set outside the loop and using clearer membership checks.

4. On invokeai/frontend/web/package.json and invokeai/frontend/web/vite.config.mts:
   Those changes were accidentally committed but we should definitely consider them as they speed testing time considerably!

All tests pass.

[Pfannkuchensack]

Works good.