diff --git a/.github/dependabot.yml b/.github/dependabot.yml
new file mode 100644
index 0000000000000..24e2573546f53
--- /dev/null
+++ b/.github/dependabot.yml
@@ -0,0 +1,213 @@
+# Configure Dependabot scanning.
+version: 2
+
+updates:
+  # Check for updates to GitHub Actions.
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    open-pull-requests-limit: 10
+    groups:
+      github-actions:
+        patterns:
+          - "*"
+
+  # Check for updates to Composer packages.
+  - package-ecosystem: "composer"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    open-pull-requests-limit: 10
+    ignore:
+      # These dependencies do not currently need to be managed with Dependabot.
+      - dependency-name: "squizlabs/php_codesniffer"
+      - dependency-name: "wp-coding-standards/wpcs"
+      - dependency-name: "phpcompatibility/php-compatibility"
+      - dependency-name: "yoast/phpunit-polyfills"
+    groups:
+      composer-packages:
+        patterns:
+          - "composer/ca-bundle"
+
+  # Monitor some npm dependencies for updates in groups.
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    open-pull-requests-limit: 20
+    ignore:
+      - dependency-name: "@wordpress/*"
+    groups:
+      ##
+      # Groups for updating devDependencies.
+      ##
+
+      # Dependencies related to Playwright testing (E2E, performance).
+      tests-playwright:
+        patterns:
+          - "*playwright*"
+      # Dependencies related to JavaScript testing with QUnit.
+      tests-qunit:
+        patterns:
+          - "*qunit*"
+          - "sinon*"
+      # Dependencies related to CSS and SASS building and manilupating.
+      dev-css-sass:
+        patterns:
+          - "autoprefixer"
+          # postcss and css related dependencies.
+          - "*css*"
+          - "*sass"
+      # Dependencies related to the Webpack build process.
+      dev-webpack:
+        patterns:
+          - "*webpack*"
+          - "react-refresh"
+          - "source-map-loader"
+      # Dependencies related to the local Docker development environment.
+      dev-docker:
+        patterns:
+          - "dotenv*"
+          - "wait-on"
+      # Dependencies that do not fall into a specific grouping.
+      dev-miscellaneous:
+        patterns:
+          - "chalk"
+          - "check-node-version"
+          - "ink-docstrap"
+          - "install-changed"
+          - "matchdep"
+          - "uuid"
+      # Dependencies related to JavaScript minification.
+      dev-uglify:
+        patterns:
+          - "*uglify*"
+      # All GruntJS related dependencies that do not relate to another group.
+      dev-grunt:
+        patterns:
+          - "*grunt*"
+
+      ##
+      # Groups for updating production dependencies.
+      ##
+
+      # Dependencies related to jQuery and its ecosystem.
+      external-jquery:
+        patterns:
+          - "jquery*"
+      # Dependencies related to React and its ecosystem.
+      external-react:
+        patterns:
+          - "react*"
+          - "!react-refresh"
+      # Dependencies used for bundling polyfill libraries into WordPress.
+      external-polyfills:
+        patterns:
+          - "core-js-url-browser"
+          - "element-closest"
+          - "formdata-polyfill"
+          - "imagesloaded"
+          - "objectFitPolyfill"
+          - "polyfill-library"
+          - "regenerator-runtime"
+          - "whatwg-fetch"
+          - "wicg-inert"
+      # Dependencies related to the Masonry library.
+      external-masonry:
+        patterns:
+          - "masonry-layout"
+      # Dependencies that do not fall into a specific grouping.
+      external-miscellaneous:
+        patterns:
+          - "backbone"
+          - "clipboard"
+          - "hoverintent"
+          - "json2php"
+          - "lodash"
+          - "moment"
+          - "underscore"
+
+  # Monitor npm dependencies within default themes.
+  - package-ecosystem: "npm"
+    directory: "/src/wp-content/themes/twentytwentyfive"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 20
+    groups:
+      twentytwentyfive-css:
+        patterns:
+          - "**browserslist*"
+          - "*css*"
+
+  - package-ecosystem: "npm"
+    directory: "/src/wp-content/themes/twentytwentytwo"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 20
+    groups:
+      twentytwentytwo-css:
+        patterns:
+          - "**browserslist*"
+          - "*css*"
+
+  - package-ecosystem: "npm"
+    directory: "/src/wp-content/themes/twentytwentyone"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 20
+    groups:
+      twentytwentyone-sass-css:
+        patterns:
+          - "**browserslist*"
+          - "autoprefixer"
+          - "*css*"
+          - "*sass*"
+          - "!*stylelint*"
+      twentytwentyone-eslint:
+        patterns:
+          - "**eslint*"
+      twentytwentyone-stylelint:
+        patterns:
+          - "**stylelint*"
+      twentytwentyone-miscellaneous:
+        patterns:
+          - "chokidar-cli"
+          - "minimist"
+          - "npm-run-all"
+
+  - package-ecosystem: "npm"
+    directory: "/src/wp-content/themes/twentytwenty"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 20
+    groups:
+      twentytwenty-css:
+        patterns:
+          - "**browserslist*"
+          - "autoprefixer"
+          - "*css*"
+      twentytwenty-stylelint:
+        patterns:
+          - "*stylelint*"
+      twentytwenty-miscellaneous:
+        patterns:
+          - "concurrently"
+          - "@wordpress/scripts"
+
+  - package-ecosystem: "npm"
+    directory: "/src/wp-content/themes/twentynineteen"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 20
+    groups:
+      twentynineteen-css-sass:
+        patterns:
+          - "**browserslist*"
+          - "autoprefixer"
+          - "*css*"
+          - "*sass*"
+      twentynineteen-miscellaneous:
+        patterns:
+          - "chokidar-cli"
+          - "npm-run-all"
diff --git a/.github/workflows/check-built-files.yml b/.github/workflows/check-built-files.yml
index 01a239c4eb3b0..72a1ad4e1a0a4 100644
--- a/.github/workflows/check-built-files.yml
+++ b/.github/workflows/check-built-files.yml
@@ -1,4 +1,4 @@
-# Checks for uncommitted changes to built files in pull requests.
+# Checks for uncommitted or unexpected changes to built files within pull requests.
 name: Check Built Files (PRs)
 
 on:
@@ -31,6 +31,7 @@ on:
       # Confirm any changes to relevant workflow files.
       - '.github/workflows/check-built-files.yml'
       - '.github/workflows/reusable-check-built-files.yml'
+      - '.github/workflows/reusable-compare-built-files-*.yml'
       # Changes to the default themes should be handled by the themes workflows.
       - '!src/wp-content/themes/twenty**'
 
@@ -46,9 +47,18 @@ concurrency:
 permissions: {}
 
 jobs:
+  # Checks built files for uncommitted changes.
   check-for-built-file-changes:
-    name: Check built files
-    if: ${{ github.repository == 'wordpress/wordpress-develop' }}
+    name: Check for uncommitted changes
+    if: ${{ github.repository == 'WordPress/wordpress-develop' || github.event_name == 'pull_request' }}
     uses: ./.github/workflows/reusable-check-built-files.yml
     permissions:
       contents: read
+
+  # Compares the build directory with the WordPress/WordPress repository.
+  compare-with-build-server:
+    name: Compare built files to WordPress/WordPress
+    uses: ./.github/workflows/reusable-compare-built-files-v1.yml
+    permissions:
+      contents: read
+    #if: ${{ github.repository == 'WordPress/wordpress-develop' || github.event_name == 'pull_request' }}
diff --git a/.github/workflows/pull-request-comments.yml b/.github/workflows/pull-request-comments.yml
index da30e2feb7f11..8744fe7be4444 100644
--- a/.github/workflows/pull-request-comments.yml
+++ b/.github/workflows/pull-request-comments.yml
@@ -5,7 +5,7 @@ on:
   pull_request_target:
     types: [ 'opened', 'synchronize', 'reopened', 'edited' ]
   workflow_run:
-    workflows: [ 'Test Build Processes' ]
+    workflows: [ 'Check Built Files (PRs)', 'Test Build Processes' ]
     types:
       - completed
 
@@ -22,6 +22,7 @@ permissions: {}
 jobs:
   # Comments on a pull request when the author is a first time contributor.
   post-welcome-message:
+    name: Contributor welcome message
     runs-on: ubuntu-24.04
     permissions:
       issues: write
@@ -79,7 +80,7 @@ jobs:
 
   # Leaves a comment on a pull request with a link to test the changes in a WordPress Playground instance.
   playground-details:
-    name: Comment on a pull request with Playground details
+    name: Leave Playground testing details
     runs-on: ubuntu-24.04
     permissions:
       issues: write
@@ -87,6 +88,7 @@ jobs:
     if: >
       github.repository == 'WordPress/wordpress-develop' &&
       github.event.workflow_run.event == 'pull_request' &&
+      github.event.workflow_run.name == 'Test Build Processes' &&
       github.event.workflow_run.conclusion == 'success'
     steps:
       - name: Download artifact
@@ -180,6 +182,145 @@ jobs:
 
             github.rest.issues.createComment( commentInfo );
 
+  # Leaves a comment on a pull request noting differences between the PR and the build server.
+  build-server-comparison:
+    name: Note differences with the build server
+    runs-on: ubuntu-24.04
+    permissions:
+      issues: write
+      pull-requests: write
+    if: >
+      github.event.workflow_run.event == 'pull_request' &&
+      github.event.workflow_run.name == 'Check Built Files (PRs)' &&
+      github.event.workflow_run.conclusion == 'success'
+    steps:
+      - name: Download artifact
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
+        env:
+          RUN_ID: ${{ github.event.workflow_run.id }}
+        with:
+          script: |
+            const artifacts = await github.rest.actions.listWorkflowRunArtifacts( {
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               run_id: process.env.RUN_ID,
+            } );
+
+            const matchArtifact = artifacts.data.artifacts.filter( ( artifact ) => {
+              return artifact.name === 'build-server-comparison'
+            } )[0];
+
+            if ( ! matchArtifact ) {
+              core.setFailed( 'No artifact found!' );
+              return;
+            }
+
+            const download = await github.rest.actions.downloadArtifact( {
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               artifact_id: matchArtifact.id,
+               archive_format: 'zip',
+            } );
+
+            const fs = require( 'fs' );
+            fs.writeFileSync( '${{github.workspace}}/build-server-comparison.zip', Buffer.from( download.data ) )
+
+      - name: Unzip the artifact containing the comparison info
+        run: unzip build-server-comparison.zip
+
+      - name: Leave a comment with any differences noticed
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
+        with:
+          script: |
+            const fs = require( 'fs' );
+            const issue_number = Number( fs.readFileSync( './NR' ) );
+            const fileChanges = fs.readFileSync( './file-changes.txt', 'utf8' );
+            const diffContents = fs.readFileSync( './changes.diff', 'utf8' );
+            const MAX_DIFF_LENGTH = 50000; // GitHub has a 65,536 character limit for comments.
+
+            core.info( `Checking pull request #${issue_number}.` );
+
+            // Confirm that the pull request is still open before leaving a comment.
+            const pr = await github.rest.pulls.get({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: issue_number,
+            });
+
+            if ( pr.data.state !== 'open' ) {
+              core.info( 'The pull request has been closed. No comment will be left.' );
+              return;
+            }
+
+            // Comments are only added after the first successful build. Check for the presence of a comment and bail early.
+            const commentInfo = {
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number,
+            };
+
+            const comments = ( await github.rest.issues.listComments( commentInfo ) ).data;
+
+            for ( const currentComment of comments ) {
+              if ( currentComment.user.type === 'Bot' && currentComment.body.includes( 'Build Server Comparison' ) ) {
+                commentInfo.comment_id = currentComment.id;
+                break;
+              }
+            };
+
+            commentInfo.body = "## Build Server Comparison\n\n";
+
+            // Post or update the comment.
+            if ( fileChanges.trim() === '' ) {
+              commentInfo.body += 'The contents of the `build` directory after running `npm run build` matches the contents of the WordPress/WordPress repository. No differences were found.';
+            } else {
+              commentInfo.body += `The contents of the \`build\` directory after running \`npm run build\` has been compared with the contents of the WordPress/WordPress repository.
+
+            **Review these differences carefully for any unexpected results.**
+
+            ### List of Modified Files
+
+            \`\`\`
+            ${ fileChanges }
+            \`\`\`
+
+            ### Full Diff File
+            `;
+
+              if ( diffContents.length > MAX_DIFF_LENGTH ) {
+                const cutoff = diffContents.lastIndexOf( '\n', MAX_DIFF_LENGTH );
+                const truncated = diffContents.substring( 0, cutoff );
+
+                commentInfo.body += `<details>
+              <summary>Click to expand (truncated)</summary>
+
+              \`\`\`diff
+              ${ truncated }
+              \`\`\`
+
+              ⚠️ The diff was too large to display in full.
+
+              </details>`;
+              } else {
+                commentInfo.body += `<details>
+              <summary>Click to expand</summary>
+
+              \`\`\`diff
+              ${ diffContents }
+              \`\`\`
+
+              </details>`;
+              }
+
+              commentInfo.body += `\n\n[Download the complete .diff file from the workflow run](https://github.com/${ context.repo.owner }/${ context.repo.repo }/actions/runs/${ context.payload.workflow_run.id }).`;
+            }
+
+            if ( commentInfo.comment_id ) {
+              github.rest.issues.updateComment( commentInfo );
+            } else {
+              github.rest.issues.createComment( commentInfo );
+            }
+
   # Manages comments reminding contributors to include a Trac ticket link when opening a pull request.
   trac-ticket-check:
     name: Manage Trac ticket reminders for pull requests
diff --git a/.github/workflows/reusable-check-built-files.yml b/.github/workflows/reusable-check-built-files.yml
index 11d97639a30fc..30bb3ed5021b4 100644
--- a/.github/workflows/reusable-check-built-files.yml
+++ b/.github/workflows/reusable-check-built-files.yml
@@ -1,7 +1,7 @@
 ##
 # A reusable workflow that checks for uncommitted changes to built files in pull requests.
 ##
-name: Check Built Files (PRs)
+name: Check for Changes to Versioned Files (reusable)
 
 on:
   workflow_call:
@@ -9,7 +9,7 @@ on:
 permissions: {}
 
 jobs:
-  # Checks a PR for uncommitted changes to built files.
+  # Checks a PR for uncommitted changes to versioned files.
   #
   # When changes are detected, the patch is stored as an artifact for processing by the Commit Built File Changes
   # workflow.
@@ -29,8 +29,8 @@ jobs:
   # - Displays the result of git diff for debugging purposes.
   # - Saves the diff to a patch file.
   # - Uploads the patch file as an artifact.
-  update-built-files:
-    name: Check and update built files
+  check-versioned-files:
+    name: Check for changes
     runs-on: ubuntu-24.04
     timeout-minutes: 10
     permissions:
diff --git a/.github/workflows/reusable-compare-built-files-v1.yml b/.github/workflows/reusable-compare-built-files-v1.yml
new file mode 100644
index 0000000000000..59fa79dc5e111
--- /dev/null
+++ b/.github/workflows/reusable-compare-built-files-v1.yml
@@ -0,0 +1,110 @@
+##
+# A reusable workflow that compares the results of the build script with the most recent commit to WordPress/WordPress.
+##
+name: Compare Built Files (reusable)
+
+on:
+  workflow_call:
+
+# Disable permissions for all available scopes by default.
+# Any needed permissions should be configured at the job level.
+permissions: {}
+
+jobs:
+  # Runs the PHP coding standards checks.
+  #
+  # Violations are reported inline with annotations.
+  #
+  # Performs the following steps:
+  # - Checks out the repository.
+  # - Sets up Node.js.
+  # - Sets up PHP.
+  # - Installs Composer dependencies.
+  # - Logs debug information about the GitHub Action runner.
+  # - Installs npm dependencies.
+  # - Builds WordPress to run from the build directory.
+  # - Ensures version-controlled files are not modified or deleted.
+  # - Checks out the WordPress/WordPress repository.
+  # - Creates a directory for text files to be uploaded as an artifact.
+  # - Stores a list of files that differ in the build directory from WordPress/WordPress.
+  # - Stores a diff file comparing the build directory to WordPress/WordPress.
+  # - Saves the pull request number to a text file.
+  # - Uploads the generated files as an artifact.
+  compare-built-files:
+    name: Compare built files to WordPress/WordPress
+    runs-on: ubuntu-24.04
+    permissions:
+      contents: read
+    timeout-minutes: 10
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          show-progress: ${{ runner.debug == '1' && 'true' || 'false' }}
+          persist-credentials: false
+
+      - name: Set up Node.js
+        uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6.3.0
+        with:
+          node-version-file: '.nvmrc'
+          cache: npm
+
+      - name: Set up PHP
+        uses: shivammathur/setup-php@accd6127cb78bee3e8082180cb391013d204ef9f # v2.37.0
+        with:
+          php-version: '8.4'
+          coverage: none
+
+      # Since Composer dependencies are installed using `composer update` and no lock file is in version control,
+      # passing a custom cache suffix ensures that the cache is flushed at least once per week.
+      - name: Install Composer dependencies
+        uses: ramsey/composer-install@65e4f84970763564f46a70b8a54b90d033b3bdda # v4.0.0
+        with:
+          custom-cache-suffix: $(/bin/date -u --date='last Mon' "+%F")
+
+      - name: Log debug information
+        run: |
+          npm --version
+          node --version
+          git --version
+
+      - name: Install npm Dependencies
+        run: npm ci
+
+      - name: Build WordPress to run from build directory
+        run: npm run build
+
+      - name: Ensure version-controlled files are not modified or deleted
+        run: git diff --exit-code
+
+      - name: Checkout WordPress/WordPress
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          repository: 'WordPress/WordPress'
+          ref: ${{ github.base_ref == 'trunk' && 'master' || format( '{0}-branch', github.base_ref ) }}
+          path: ${{ github.workspace }}/build-server
+          show-progress: ${{ runner.debug == '1' && 'true' || 'false' }}
+          persist-credentials: false
+
+      - name: Create directory for artifacts
+        run: mkdir artifacts
+
+      - name: Create a list of files that have changed
+        run: diff -rq ${{ github.workspace }}/build ${{ github.workspace }}/build-server | sed "s|${{ github.workspace }}/||g" > artifacts/file-changes.txt
+
+      - name: Create a list of files that have changed
+        run: diff -r ${{ github.workspace }}/build ${{ github.workspace }}/build-server | sed "s|${{ github.workspace }}/||g" > artifacts/changes.diff
+
+      - name: Save PR number
+        run: echo "${EVENT_NUMBER}" > ./artifacts/NR
+        env:
+          EVENT_NUMBER: ${{ github.event.number }}
+
+      # Uploads the associated text files as an artifact.
+      - name: Upload comparison results as an artifact
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
+        if: ${{ github.repository == 'WordPress/wordpress-develop' && github.event_name == 'pull_request' }}
+        with:
+          name: build-server-comparison
+          path: artifacts/
diff --git a/composer.json b/composer.json
index ee5c5d0c0aa03..e72f63119c3ac 100644
--- a/composer.json
+++ b/composer.json
@@ -23,7 +23,7 @@
 		"squizlabs/php_codesniffer": "3.13.5",
 		"wp-coding-standards/wpcs": "~3.3.0",
 		"phpcompatibility/phpcompatibility-wp": "~2.1.3",
-		"phpstan/phpstan": "2.1.39",
+		"phpstan/phpstan": "2.1.45",
 		"yoast/phpunit-polyfills": "^1.1.0"
 	},
 	"config": {