Capture/apply block-remove suggestions

[adamsilverstein]

What

Adds the data-layer mechanism for block-remove suggestions (#77434, task 6a). In Suggest mode a removeBlock dispatch no longer drops the block — the apply-and-tag flow re-inserts the subtree at its previous position and tags it with metadata.suggestion = { type: 'pending-remove' }. Auto-save persists the marker as a block-remove operation; Apply later runs the real removeBlock; Reject just clears the marker.

This PR ships the mechanism only — there is no visual treatment yet. Strikethrough/dim styling, summary, and diff variants land in the next PR (#77970).

Two commits

1. Capture block removals as pending-remove markers — interceptor extension: per-tick tree snapshot (parent + index + full subtree), removal detection, top-level-only re-insert, marker stamp.
2. Persist and apply block-remove suggestions — overlay reducer gets SET_STRUCTURAL_OP, auto-save's operationsForEntry emits the structural op, provider's applySuggestion branches on findStructuralOp and dispatches removeBlock, rejectSuggestion clears the marker.

Testing

• 124 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]

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[github-actions]

Size Change: +750 B (+0.01%)

Total Size: 7.52 MB

📦 View Changed

Filename	Size	Change
build/scripts/editor/index.min.js	485 kB	+750 B (+0.15%)

_{compressed-size-action}

[github-actions]

Flaky tests detected in 008eb74.
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/25406047322
📝 Reported issues:

• [Flaky Test] post title and content are editable and blocks can be inserted #77720 in /test/e2e/specs/editor/various/post-content-focus-mode.spec.js
• [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

[adamsilverstein]

Superseded by the fresh-stack restructure of Suggest mode (#73411).

The feature has been re-sliced from this 16-deep stack onto current trunk as a clean 2-PR stack:

• Suggest mode: core subsystem (intent modes, overlay capture, structural + attribute suggestions) #79713 — Suggest mode: core (intent modes, overlay capture, structural + attribute suggestions, REST/PHP, auto-save, sidebar, summary)
• Suggest mode: inline text and formatting suggestions via markers #79714 — Suggest mode: inline text suggestions (the <mark> marker layer)

The whole feature now sits behind a Suggestion Mode experiment (Settings → Experiments → Collaboration). Closing in favour of the new stack — details: #73411 (comment)