What?

Closes #76774

Places the caret at the end of a block (instead of the start) when selecting a block from the List View panel via keyboard activation (Enter/Space).

Why?

When selecting a block via List View, the caret was placed at the start of the block. This meant pressing Enter would create a new block before the selected block, which is unexpected. Users expect a new block to be created after the selected block.

How?

Uses event.detail to distinguish between mouse clicks and keyboard activation (Enter/Space) in the List View's selectEditorBlock handler (block.js):

• Keyboard activation (event.detail === 0): Passes -1 as the focusPosition, which tells useFocusFirstElement to place the caret at the end of the block and transfer focus to the canvas. This matches standard tree grid semantics — pressing Enter on a list item activates it, moving focus into the canvas for editing.
• Mouse clicks (event.detail >= 1): Passes null as the focusPosition, which prevents useFocusFirstElement from transferring focus to the canvas. This keeps focus in the List View so that subsequent keyboard operations (arrow navigation, copy/paste) continue to work as expected.

Why the distinction is necessary

The useFocusFirstElement hook has [initialPosition, clientId] as its effect dependencies. Previously, selectBlock was called with the default initialPosition of 0 (caret at start). When clicking the same block again, the value stayed 0 → 0 — no dependency change, so the effect didn't re-run, and focus stayed in the List View. This was coincidental but correct behavior.

Simply changing to -1 (caret at end) would cause 0 → -1 — a dependency change — which would make the effect re-run and steal focus from the List View on every mouse click. By passing null for mouse clicks, we explicitly opt out of the focus transfer (since useFocusFirstElement returns early for null/undefined), while still getting the desired "focus canvas at end of block" behavior for keyboard activation.

Testing Instructions

Mouse click (focus stays in List View)

1. Open a post with multiple Paragraph blocks.
2. Open the List View panel.
3. Click a Paragraph in List View.
4. Verify focus stays in the List View (not the canvas).
5. Use arrow keys to navigate between items — this should work normally.
6. Use Ctrl/Cmd+C to copy a block — this should work normally.

Keyboard activation (focus moves to canvas)

1. Open a post with two Paragraph blocks containing text.
2. Open the List View panel (Alt+Shift+O / Ctrl+Shift+O).
3. Use arrow keys to navigate to the first Paragraph.
4. Press Enter to activate the block.
5. Verify the canvas is now focused with the caret at the end of the block text.
6. Press Enter to create a new block.
7. Verify the new block appears after the selected block (not before it).

Use of AI Tools

This PR was authored with the assistance of Claude Code (Claude Opus 4.6).