Grid Multi-Body: Adapt Selection Models for Split Rows

Epic resolved. The Grid Multi-Body Selection abstraction natively supports cell, row, and column Peer State Adoption workflows without container pollution.

Input from Antigravity (Gemini 3.1 Pro):

✦ ## Handoff: Architectural Discovery on DevIndex Multi-Body Synchronization

A profound architectural discovery was made while debugging why smProps.selectedRows.includes(recordId) was failing during the E2E verification, while the cross-body row highlighting (.neo-selected) visually succeeded.

The App-Level State Collision (DevIndex Legacy)

We identified that the RowModel synchronization logic correctly propagates to peers via updateRows(); however, during testing, the Center body's selectedRows array was persistently empty. This paradoxical behavior (visuals passing, structural state failing) was caused by a legacy configuration in the DevIndex application itself.

The DevIndex application's Contributor.mjs data model retained an annotations: { selected: false } definition.

Inside RowModel.mjs, the toggle branch intercepts this logic before native DOM state mutation occurs:

if (me.hasAnnotations(record)) {
    // If the record uses an `annotations` field, `selectedRows` is explicitly bypassed. 
    me.updateAnnotations(record) 
} else {
    me.toggleRowSelection(recordId); // Mutates `selectedRows` array
}

Because the old annotations: {selected: false} was still active in the App Worker context, it bypassed the structural array completely! The reason all 3 bodies visibly highlighted the row was that modifying the record triggered the Store's recordChange event. A store event implicitly instructs the GridContainer to re-render that specific record across all active GridBody components, intrinsically applying the .neo-selected styling directly from the schema parser loop.

Fix Applied: Removed the legacy annotations field mapping in Contributor.mjs so the RowModel properly falls back to toggleRowSelection().

The Controller Defect in DevIndex

Activating the RowModel dynamically via the DevIndex demo UI (and subsequently our Neural Link script app.setProperties) currently only updates body.selectionModel:

// apps/devindex/view/home/MainContainerController.mjs
onSelectionModelChange(data) {
    this.getReference('grid').body.selectionModel = data.component.selectionModel;
}

Because it does not actively clone and re-assign the Selection Model config to bodyStart and bodyEnd, those locking columns remain abandoned on their default (or prior) selection models.

As an immediate consequence, getActivePeers() successfully retrieves instantiated sibling instances, but they might be CellModel instances instead of identically aligned RowModels! Because both models inherit updateRows() from BaseModel, it serendipitously accepts the DOM manipulation instructions; however, this is structurally fragile.

For the Next Agent (Wake-up Context)

1. Controller Parity: Proceed to update apps/devindex/view/home/MainContainerController.mjs to ensure dynamic Selection Model toggles reflect across all multi-body panes (bodyStart, body, bodyEnd).
2. Playwright Reset: Make sure Neural Link app.setProperties targets all active model layers in the test harness.
3. Verify Dev Server Caching: Rebuild or freshly serve the Dev Workspace so the deletion of the annotations field in Contributor.mjs correctly hits the browser without caching the obsolete App Worker chunk.

Session saved internally to the Memory Core. Waiting for the final validation passes.