Suggest mode 6c: Capture and apply block-move suggestions (mechanism)

[adamsilverstein]

What

Adds the data-layer mechanism for block-move suggestions (#77434, task 6c). In Suggest mode a moved block stays at its new position but is tagged with metadata.suggestion = { type: 'pending-move', fromAnchorClientId, fromParentClientId, fromIndex }. Auto-save persists as a block-move op; Apply clears the marker; Reject runs moveBlockToPosition to revert.

Visual treatment lands in the next PR (#77979).

How

Move detection uses two signals:

1. Cross-parent: any block whose parent changed is a definite move.
2. Within-parent reorder: blocks not in the LCS of the parent's old vs new sibling order are reordered moves. The LCS step prevents tagging blocks whose index just shifted as a side-effect — moving B from index 1 to 3 in [A,B,C,D] tags only B.

Testing

• 141 unit tests pass. Lint clean.
• For full-stack testing instructions, see the foundations PR (#77967).

Stack

1. #77967 — Schema v2 bump (foundations)
2. #77968 — Capture block-remove (mechanism)
3. #77970 — Render block-remove preview (UI)
4. #77971 — Capture block-insert-after (mechanism)
5. #77973 — Render block-insert-after preview (UI)
6. #77978 — Capture block-move (mechanism)
7. #77979 — Render block-move preview (UI)

Refs #77434, #73411.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: adamsilverstein <adamsilverstein@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Size Change: +559 B (+0.01%)

Total Size: 8.59 MB

📦 View Changed

Filename	Size	Change
build/scripts/editor/index.min.js	479 kB	+559 B (+0.12%)

_{compressed-size-action}

[github-actions]

Flaky tests detected in 6f205be.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/25407196070
📝 Reported issues:

• [Flaky Test] should show correct homepage actions based on current homepage or posts page #77385 in /test/e2e/specs/site-editor/homepage-settings.spec.js