Add WebMCP experiment

[webmyc]

What?

Adds an opt-in WebMCP experiment for the block editor, following #448. Fourteen tools let an agent browser read the current post, set its title, insert and edit blocks, move, duplicate and transform blocks, undo, save and publish. Changes happen through the editor's data stores and remain visible on the page.

Why?

WebMCP lets an agent work in the UI the person is looking at. The experiment does not mirror Abilities API tools; server-side abilities remain available through MCP.

How?

• Uses develop's Abstract_Feature, feature registry and loader. The bridge loads on post editor screens, offers a JavaScript registry and filter for additional page tools, and registers each tool separately with a default cap of 30.
• Registers built-in tools only when the current page has an initialized block editor, including when initialization finishes after DOM ready. Classic editor screens list and register no built-in tools.
• Updates, removals and moves check the editor's lock selectors. A move after the same block is a no-op; moving a block into itself or a descendant returns an error.
• The text shortcut supports blocks with a content attribute. Quote text is edited through its inner paragraphs; pullquote text uses its value attribute through the attribute tool.
• Save and publish await savePost(), check that saving has settled, and report didPostSaveRequestFail() as an error.
• Removes the unused eval files. CHANGELOG.md and CREDITS.md match develop; the changelog entry is below.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code, Codex
Model(s): Claude Fable 5.1, GPT-6
Used for: drafting the implementation, addressing review feedback, and adding regression tests. I reviewed and take responsibility for the result.

Testing Instructions

1. Run npm run build, then enable WebMCP under Settings, AI.
2. Open a post. In an agent browser, ask it to set the title and add a paragraph; both should change on the page.
3. Without an agent browser, call tools in the console:

   const tools = wpai.webmcp.getTools();
   await tools.find( t => t.name === 'editor-set-title' ).execute( { title: 'Hello' } );
   await tools.find( t => t.name === 'editor-insert-block' ).execute( { attributes: { content: 'A paragraph.' } } );

4. Run npm run test:php -- --filter WebMCP and npm run test:e2e -- tests/e2e/specs/experiments/webmcp.spec.js. The nine browser tests cover visible editing, structural tools, locked operations, self/descendant moves, quote attributes, failed saves/publishes, classic editor availability and non-editor screens.

Validation

• Build, TypeScript typecheck, JavaScript lint, PHPCS and PHPStan passed. JavaScript lint reports 33 warnings outside the changed files and zero errors; the changed JavaScript/TypeScript files lint without warnings.
• Full browser suite: 207 passed. Focused WebMCP suite: 9 passed.
• PHP suite and Composer strict test command: 1,777 tests, 5,003 assertions, 42 skipped.
• Multisite PHP suite: 1,777 tests, 5,014 assertions, 38 skipped.
• Local checks used Node 24.21.0, WordPress 7.1.2 and Docker wp-env. The local ~/wp-ai mount alias was removed using an ignored override, and pretty permalinks were restored before the full browser run.

Screenshots or screencast

No separate UI; the effect is the editor changing.

Changelog Entry

• New Experiment: WebMCP; lets an agent browser work in the block editor through document.modelContext, with tools that set the title, insert and edit blocks, save and publish, every change visible on the page as it happens.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.99%. Comparing base (ecc9ecd) to head (58ec101).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #1081      +/-   ##
=============================================
+ Coverage      81.95%   81.99%   +0.04%     
- Complexity      3350     3358       +8     
=============================================
  Files            135      136       +1     
  Lines          13026    13056      +30     
=============================================
+ Hits           10675    10705      +30     
  Misses          2351     2351              

Flag	Coverage Δ
unit	81.99% <100.00%> (+0.04%)	⬆️

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[jeffpaul]

@danieliser tagging you as you had some feedback on the prior iteration in #224.

[danieliser]

@zackkatz might have some feedback & insights here as well from his work on block-mcp and atomic editing for the block editor.

We use that for all agentic work outside a browser at this point. Any attempts to do it for WebMCP likely need similar exposures (though through the JS api of course).

[webmyc]

@danieliser thank you, that pointer was the useful kind. I read Block MCP's surface against what this PR had and three gaps were plain: no way to place a block inside a container, no structural operations beyond remove, and no discovery of what a position allows or what attributes a block type takes.

Pushed in ee48cf5, through the JS API as you said:

• editor-insert-block takes parentClientId and asks canInsertBlockType first, so a locked template, an allowed-blocks list or a parent restriction refuses the insert instead of being bypassed. That is the editor's own version of Block MCP's tier policy.
• editor-move-block, editor-duplicate-block, editor-transform-block (through the editor's transforms, so a paragraph becomes a heading the way the Transform menu does it).
• editor-get-block-types: what a position allows, or one block type's attribute schema.
• editor-undo: each tool call is one undo step, which is the in-editor counterpart of revision-backed undo.

Two things Block MCP solves that the editor gives for free, which is worth knowing when comparing the two: clientId is the stable ref for the session, and attribute changes re-render through the block's own save function, so there is no attrs and innerHTML drift to guard against.

What I did not carry over: atomic batches (one undo step per call seemed the honest unit inside an editor a person is watching) and path-based addressing (refs cover it once the outline is read). @zackkatz if either of those turned out to matter more than it looks from the outside, I would rather hear it now.

[github-actions]

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Co-authored-by: webmyc <urbankidro@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>
Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>
Co-authored-by: swissspidy <swissspidy@git.wordpress.org>
Co-authored-by: justlevine <justlevine@git.wordpress.org>
Co-authored-by: fellyph <fellyph@git.wordpress.org>
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[webmyc]

Thanks @dkotter, these are all fair. I'm working through them now: reverting the CHANGELOG and CREDITS edits, removing the evals files, fixing the quote blocks, the save check, locked blocks, the classic editor check and the two move cases, plus a rebase on develop. I'll reply on each thread when it's pushed.

[webmyc]

@dkotter I addressed all 11 review comments in 40e4313 and rebased onto develop; could you take another look?

GitHub CI is now green for this commit, including the PHP matrix and all three E2E shards; the full local browser suite also passed all 207 tests.

[webmyc]

@dkotter I addressed the six comments in f1a2157 and rebased onto develop. CI is green. Could you take another look?

[dkotter]

Thanks for all the work here! I think just a few more things and this will be good to go

[webmyc]

@dkotter the three are in da009a7, rebased onto develop, CI green. Thanks for the careful reviews.

[jeffpaul]

@swissspidy @gziolo @jorgefilipecosta would appreciate a parallel review from one of you on this one, will ideally ship in the 1.5.0 release either way though if you're swamped with work elsewhere (aka not the most urgent/important item)