Evening session on EventPad. Fixed an edge case with pre-connected elements and got Automation slices working end-to-end.

TIL

1. Pre-Connected Elements Need Special Handling

Bug: Connect a screen to a command before the slice exists. Later, connect command → event (which infers the slice). Result: command and event are in the slice, but the screen isn’t.

Root cause: SliceInferred only included the two elements that triggered the inference. It didn’t check for existing connections.

Fix: When inferring an SC slice, check if the command has any existing ‘input’ connections and include those screens:

// On slice inference, also include pre-connected elements
const existingInputs = relations
  .filter(r => r.to === command.id && r.type === 'input')
  .map(r => elements.find(e => e.id === r.from));

Added a GWT scenario to prevent regression—these edge cases are easy to forget.

2. State View Slices Infer Both Directions

SV (State View) slices show “given these events, here’s the read model state.” Added slice inference for the updatedBy relation:

  • Event → ReadModel connection? Infer SV slice.
  • ReadModel → Event connection? Also infer SV slice.

Either direction works because the relationship is the same—events update the read model.

3. Element Ordering Has a Clear Hierarchy

Finally nailed down the visual stacking order for slices:

Top:    ⏹️ Screen / ⚙️ Processor
        🟦 Command
        🟩 ReadModel
Bottom: 🟧 Events

Events flow up, commands flow down. Always. sortSliceElements() auto-applies this on SliceInferred and SliceElementAdded.

4. AU Commands Should Be Picked, Not Created

Key insight for Automation slices: the command at the end of an AU flow should be an existing command from a State Change slice, not something you define inline.

AU flow: Event → Processor → (pick context ReadModel) → (pick Command)

Added a picker: true flag on actions that opens an element picker sheet instead of the create form. When you select an existing command, the slice completes.

// Action definition
{ label: 'Set Command', picker: true, elementType: 'command' }

// On selection
emit('SliceCompleted', { sliceId, commandId: picked.id });

Automations don’t create behavior—they orchestrate existing behavior. The model reflects this now.

5. Mockups Are the Source of Truth

The GWT scenarios in EVENT_MODEL.md keep growing, but the real source of truth is the live mockup. Every scenario I add gets validated there before going into the spec.

Spec follows implementation, not the other way around. At least at this stage.

Slices now handle pre-connected elements, SV infers correctly, and AU flows complete. The model is getting solid.