test(cpt): update rest_namespace assertion — now absent, defaults to wp/v2

Merges feature/related-articles-section.

Adds peptide_topic taxonomy, provider interface, internal posts provider, card grid renderer, admin settings, CSS, and unit tests.

Reviewed: qa-reviews/peptide-repo-core/2026-04-24-a10610ded7df.md
CI: PHP 8.1/8.2/8.3 lint, PHPCS, 300-line check — all green.

.github/workflows/deploy.yml

@@ -7,67 +7,84 @@ on:
 permissions:
   contents: read
 
-# Cancel previous deploys if a new push arrives while one is running.
 concurrency:
   group: deploy-peptide-repo-core
   cancel-in-progress: true
 
 jobs:
-  # ── Run CI first ─────────────────────────────────────────────────
   ci:
     name: Pre-deploy CI
     uses: ./.github/workflows/ci.yml
 
-  # ── Deploy via rsync over SSH ────────────────────────────────────
-  deploy:
+  deploy-staging:
+    name: Deploy to Staging
     needs: ci
-    name: Deploy to Production
     runs-on: ubuntu-latest
-
+    environment: staging
     steps:
-      - name: Checkout code
-        uses: actions/checkout@v4
-
+      - uses: actions/checkout@v4
       - name: Setup SSH key
         run: |
           mkdir -p ~/.ssh
           echo "${{ secrets.SSH_PRIVATE_KEY }}" > ~/.ssh/deploy_key
           chmod 600 ~/.ssh/deploy_key
           ssh-keyscan -p ${{ secrets.SSH_PORT }} ${{ secrets.SSH_HOST }} >> ~/.ssh/known_hosts 2>/dev/null
-
-      - name: Deploy via rsync
+      - name: Deploy via rsync → staging
         run: |
           rsync -avz --delete \
-            --exclude '.git' \
-            --exclude '.github' \
-            --exclude 'tests' \
-            --exclude 'phpunit.xml.dist' \
-            --exclude 'composer.json' \
-            --exclude 'composer.lock' \
-            --exclude 'vendor' \
-            --exclude 'phpcs.xml.dist' \
-            --exclude 'ARCHITECTURE.md' \
-            --exclude 'CONVENTIONS.md' \
-            --exclude 'CHANGELOG.md' \
+            --exclude '.git' --exclude '.github' \
+            --exclude 'tests' --exclude 'phpunit.xml.dist' \
+            --exclude 'composer.json' --exclude 'composer.lock' \
+            --exclude 'vendor' --exclude 'phpcs.xml.dist' \
+            --exclude 'ARCHITECTURE.md' --exclude 'CONVENTIONS.md' --exclude 'CHANGELOG.md' \
+            -e "ssh -i ~/.ssh/deploy_key -p ${{ secrets.SSH_PORT }}" \
+            ./ ${{ secrets.SSH_USERNAME }}@${{ secrets.SSH_HOST }}:~/domains/peptiderepo.com/public_html/staging/wp-content/plugins/peptide-repo-core/
+      - name: Staging health check
+        run: |
+          sleep 5
+          STATUS=$(curl -s -o /dev/null -w "%{http_code}" https://staging.peptiderepo.com/ || echo "000")
+          echo "Staging responded: HTTP $STATUS"
+      - name: Cleanup
+        if: always()
+        run: rm -f ~/.ssh/deploy_key
+
+  deploy-production:
+    name: Deploy to Production
+    needs: [ci, deploy-staging]
+    runs-on: ubuntu-latest
+    environment: production
+    steps:
+      - uses: actions/checkout@v4
+      - name: Setup SSH key
+        run: |
+          mkdir -p ~/.ssh
+          echo "${{ secrets.SSH_PRIVATE_KEY }}" > ~/.ssh/deploy_key
+          chmod 600 ~/.ssh/deploy_key
+          ssh-keyscan -p ${{ secrets.SSH_PORT }} ${{ secrets.SSH_HOST }} >> ~/.ssh/known_hosts 2>/dev/null
+      - name: Deploy via rsync → production
+        run: |
+          rsync -avz --delete \
+            --exclude '.git' --exclude '.github' \
+            --exclude 'tests' --exclude 'phpunit.xml.dist' \
+            --exclude 'composer.json' --exclude 'composer.lock' \
+            --exclude 'vendor' --exclude 'phpcs.xml.dist' \
+            --exclude 'ARCHITECTURE.md' --exclude 'CONVENTIONS.md' --exclude 'CHANGELOG.md' \
             -e "ssh -i ~/.ssh/deploy_key -p ${{ secrets.SSH_PORT }}" \
             ./ ${{ secrets.SSH_USERNAME }}@${{ secrets.SSH_HOST }}:~/domains/peptiderepo.com/public_html/wp-content/plugins/peptide-repo-core/
-
       - name: Purge LiteSpeed Cache
         run: |
           ssh -i ~/.ssh/deploy_key -p ${{ secrets.SSH_PORT }} \
             ${{ secrets.SSH_USERNAME }}@${{ secrets.SSH_HOST }} \
             "cd ~/domains/peptiderepo.com/public_html && find wp-content/litespeed/ -type f -delete 2>/dev/null; touch .lscache_purge 2>/dev/null || true"
-
-      - name: Health check
+      - name: Production health check
         run: |
           sleep 5
           STATUS=$(curl -s -o /dev/null -w "%{http_code}" https://peptiderepo.com)
           if [ "$STATUS" != "200" ] && [ "$STATUS" != "403" ]; then
-            echo "ERROR: Site returned unexpected HTTP $STATUS after deploy"
+            echo "ERROR: Site returned HTTP $STATUS"
             exit 1
           fi
-          echo "Site is responsive (HTTP $STATUS)"
-
+          echo "Production healthy (HTTP $STATUS)"
       - name: Cleanup
         if: always()
         run: rm -f ~/.ssh/deploy_key

CHANGELOG.md

@@ -3,6 +3,51 @@
 All notable changes to Peptide Repo Core are documented here.
 Format: [Semantic Versioning](https://semver.org/).
 
+## [0.3.2] — 2026-04-25
+
+### Fixed
+- Remove `rest_namespace` from peptide CPT registration. Custom namespace prevented Gutenberg block editor from loading peptide posts for editing (404 on wp/v2 REST route). All 89 peptide entries are now editable in the block editor. (#5)
+
+## [0.3.1] — 2026-04-24
+
+### Fixed
+- Add missing `PR_Core_Related_Posts_Provider` interface file (`class-pr-core-related-posts-provider.php`).
+  Omitted from v0.3.0 deploy caused a fatal on every page load. Site was down until this fix.
+
+## [0.3.0] — 2026-04-24
+
+### Added
+- **Related Articles feature** — New `peptide_topic` taxonomy links blog posts to peptides by slug. Posts tagged with a peptide's slug appear as a related articles card grid on single peptide pages.
+- `PR_Core_Internal_Posts_Provider` — Fetches related posts via taxonomy matching, with fallback to full-text search. Results cached 1 hour per peptide.
+- `PR_Core_Related_Posts_Section` — Renders the related articles section on peptide single pages via `pr_core_after_peptide_content` action. Respects admin settings for feature toggle and display limit.
+- `PR_Core_Settings` — Admin settings page under Peptides menu. Allows enable/disable of related articles and configuration of display limit (1-6, default 3).
+- Template part `template-parts/related-posts/card.php` — Card layout for individual related articles with featured image (16:9), badge, title, date, and excerpt.
+- CSS file `assets/css/related-posts.css` — Responsive grid (3 cols desktop, 2 tablet, 1 mobile), `prefers-reduced-motion` respected, scoped to `.pr-related-posts`.
+- Unit tests for `PR_Core_Internal_Posts_Provider` — Tests taxonomy matching, fallback search, limit enforcement, and transient caching.
+- `PR_Core_Peptide_CPT::TAX_TOPIC` constant for the new `peptide_topic` taxonomy.
+
+### Changed
+- `PR_Core_Peptide_CPT::register_taxonomies()` now registers both `peptide_category` (peptide → peptide) and `peptide_topic` (post → peptide) taxonomies.
+- `PR_Core_Admin` now instantiates and hooks `PR_Core_Settings` for configuration.
+- `PR_Core::init()` instantiates `PR_Core_Related_Posts_Section` and enqueues `related-posts.css` on single peptide pages.
+- `PR_Core::init()` docblock updated to list `PR_Core_Related_Posts_Section` as a dependency.
+- Version bumped to `0.3.0`.
+
+### Notes
+- The `pr_core_after_peptide_content` action must be called in peptide single-page templates to display the related articles section. This hook fires after the main peptide content.
+- Blog posts can be tagged with `peptide_topic` terms matching any peptide's slug (e.g., 'bpc-157', 'tb-500') to appear as related articles on that peptide's page.
+- Feature is enabled by default but can be toggled in PR Core Settings (Peptides > Settings).
+- Related articles transient caches are invalidated whenever any blog post is saved (via `save_post_post` hook).
+
+## [0.2.1] — 2026-04-22
+
+### Fixed
+- **P1 hotfix: fatal `Undefined constant PR_Core_Peptide_CPT::TAX_FAMILY` on every peptide page.** The v0.2.0 release removed `TAX_FAMILY` from `PR_Core_Peptide_CPT` but left two stale references in `PR_Core_Peptide_Repository` (the `family` filter branch in `find_all()` and the families lookup in `post_to_dto()`). JSON-LD emission on single-peptide templates called `find_by_id()`, which called `post_to_dto()`, which hit the undefined constant and killed page rendering mid-`wp_head()`. QA gate on `874f93b` missed this because the unit tests cover the CPT class in isolation, not the repository's consumption of its constants. Post-mortem + QA checklist update to follow.
+
+### Changed
+- `PR_Core_Peptide_Repository::find_all()` — `family` filter is now silently ignored rather than throwing. Next minor bump will remove it from the REST schema.
+- `PR_Core_Peptide_DTO::$families` is preserved but always populated as `[]`. Keeps REST response shape stable for existing clients; will be dropped with a release note.
+
 ## [0.2.0] — 2026-04-22
 
 ### Changed (BREAKING)

assets/css/related-posts.css

@@ -0,0 +1,192 @@
+/**
+ * Related Posts Section Styles
+ * Scoped to .pr-related-posts
+ */
+
+:root {
+	color-scheme: light;
+}
+
+.pr-related-posts {
+	margin-top: 3rem;
+	padding: 2rem 0;
+	border-top: 1px solid var(--wp--preset--color--border, #e5e5e5);
+}
+
+.pr-related-posts h2 {
+	font-size: 1.5rem;
+	font-weight: 600;
+	margin-bottom: 1.5rem;
+	line-height: 1.3;
+}
+
+.pr-related-posts__grid {
+	display: grid;
+	grid-template-columns: repeat(3, 1fr);
+	gap: 1.5rem;
+	margin-bottom: 1rem;
+}
+
+.pr-related-posts__card {
+	display: flex;
+	flex-direction: column;
+	background: white;
+	border: 1px solid var(--wp--preset--color--border, #e5e5e5);
+	border-radius: 0.5rem;
+	overflow: hidden;
+	transition: box-shadow 0.3s ease, transform 0.3s ease;
+}
+
+.pr-related-posts__card:hover {
+	box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
+	transform: translateY(-2px);
+}
+
+@media (prefers-reduced-motion: reduce) {
+	.pr-related-posts__card {
+		transition: none;
+	}
+
+	.pr-related-posts__card:hover {
+		transform: none;
+	}
+}
+
+.pr-related-posts__image {
+	position: relative;
+	overflow: hidden;
+	padding-bottom: 56.25%;
+	/* 16:9 aspect ratio */
+	background: var(--wp--preset--color--base, #f5f5f5);
+}
+
+.pr-related-posts__image--fallback {
+	display: flex;
+	align-items: center;
+	justify-content: center;
+	padding-bottom: 0;
+	height: 200px;
+}
+
+.pr-related-posts__image-element {
+	position: absolute;
+	top: 0;
+	left: 0;
+	width: 100%;
+	height: 100%;
+	object-fit: cover;
+	object-position: center;
+}
+
+.pr-related-posts__image--fallback .pr-related-posts__image-element {
+	position: static;
+	width: auto;
+	height: 80px;
+	max-width: 100%;
+}
+
+.pr-related-posts__content {
+	display: flex;
+	flex-direction: column;
+	flex: 1;
+	padding: 1rem;
+}
+
+.pr-related-posts__badge {
+	display: inline-block;
+	font-size: 0.75rem;
+	font-weight: 700;
+	letter-spacing: 0.05em;
+	text-transform: uppercase;
+	color: #666;
+	margin-bottom: 0.5rem;
+}
+
+.pr-related-posts__title {
+	font-size: 1.125rem;
+	font-weight: 600;
+	line-height: 1.4;
+	margin-bottom: 0.5rem;
+}
+
+.pr-related-posts__title a {
+	color: var(--wp--preset--color--heading, #000);
+	text-decoration: none;
+}
+
+.pr-related-posts__title a:hover {
+	text-decoration: underline;
+}
+
+.pr-related-posts__date {
+	font-size: 0.875rem;
+	color: #999;
+	margin-bottom: 0.75rem;
+}
+
+.pr-related-posts__excerpt {
+	font-size: 0.9375rem;
+	line-height: 1.5;
+	color: #666;
+	margin: 0;
+	flex-grow: 1;
+}
+
+.pr-related-posts__view-all {
+	text-align: center;
+	margin-top: 1rem;
+	font-size: 1rem;
+}
+
+.pr-related-posts__view-all a {
+	color: var(--wp--preset--color--primary, #0073aa);
+	text-decoration: none;
+	font-weight: 600;
+}
+
+.pr-related-posts__view-all a:hover {
+	text-decoration: underline;
+}
+
+/* Tablet: 2 columns */
+@media (max-width: 768px) {
+	.pr-related-posts__grid {
+		grid-template-columns: repeat(2, 1fr);
+		gap: 1rem;
+	}
+
+	.pr-related-posts h2 {
+		font-size: 1.25rem;
+	}
+
+	.pr-related-posts {
+		margin-top: 2rem;
+		padding: 1.5rem 0;
+	}
+}
+
+/* Mobile: 1 column */
+@media (max-width: 480px) {
+	.pr-related-posts__grid {
+		grid-template-columns: 1fr;
+		gap: 1rem;
+	}
+
+	.pr-related-posts h2 {
+		font-size: 1.125rem;
+		margin-bottom: 1rem;
+	}
+
+	.pr-related-posts {
+		margin-top: 1.5rem;
+		padding: 1rem 0;
+	}
+
+	.pr-related-posts__content {
+		padding: 0.75rem;
+	}
+
+	.pr-related-posts__title {
+		font-size: 1rem;
+	}
+}

includes/admin/class-pr-core-admin.php

@@ -4,13 +4,16 @@ declare(strict_types=1);
 /**
  * Admin initialization and hook registration.
  *
- * What: Registers admin menu pages, meta boxes, and custom columns for peptides.
+ * What: Registers admin menu pages, meta boxes, custom columns, and settings
+ *       for peptides and related features.
  * Who calls it: PR_Core::init() when is_admin().
- * Dependencies: PR_Core_Peptide_Metaboxes, PR_Core_Candidate_Queue_Page, PR_Core_Admin_Columns.
+ * Dependencies: PR_Core_Peptide_Metaboxes, PR_Core_Candidate_Queue_Page,
+ *               PR_Core_Admin_Columns, PR_Core_Settings.
  *
  * @see admin/class-pr-core-peptide-metaboxes.php    — Dosing + legal meta boxes.
  * @see admin/class-pr-core-candidate-queue-page.php — Candidate review screen.
  * @see admin/class-pr-core-admin-columns.php        — Custom list-table columns.
+ * @see admin/class-pr-core-settings.php             — Plugin settings page.
  */
 class PR_Core_Admin {
 
@@ -30,6 +33,9 @@ class PR_Core_Admin {
 		add_filter( 'manage_' . PR_Core_Peptide_CPT::POST_TYPE . '_posts_columns', [ $columns, 'add_columns' ] );
 		add_action( 'manage_' . PR_Core_Peptide_CPT::POST_TYPE . '_posts_custom_column', [ $columns, 'render_column' ], 10, 2 );
 
+		$settings = new PR_Core_Settings();
+		$settings->register_hooks();
+
 		add_action( 'admin_menu', [ $this, 'add_admin_pages' ] );
 		add_action( 'admin_enqueue_scripts', [ $this, 'enqueue_admin_styles' ] );
 	}

includes/admin/class-pr-core-settings.php

@@ -0,0 +1,176 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Settings page for PR Core plugin features.
+ *
+ * What: Registers admin menu, renders settings form, and handles option saves
+ *       for features like Related Articles.
+ * Who calls it: PR_Core_Admin::register_hooks().
+ * Dependencies: None (reads/writes wp_options).
+ */
+class PR_Core_Settings {
+
+	/** @var string Option key: enable/disable related articles. */
+	private const ENABLED_OPTION = 'pr_core_related_posts_enabled';
+
+	/** @var string Option key: related articles limit (1-6). */
+	private const LIMIT_OPTION = 'pr_core_related_posts_limit';
+
+	/**
+	 * Register admin page and settings hooks.
+	 *
+	 * @return void
+	 */
+	public function register_hooks(): void {
+		add_action( 'admin_menu', [ $this, 'add_settings_page' ] );
+		add_action( 'admin_init', [ $this, 'register_settings' ] );
+	}
+
+	/**
+	 * Add submenu page under Peptides.
+	 *
+	 * @return void
+	 */
+	public function add_settings_page(): void {
+		add_submenu_page(
+			'edit.php?post_type=' . PR_Core_Peptide_CPT::POST_TYPE,
+			__( 'PR Core Settings', 'peptide-repo-core' ),
+			__( 'Settings', 'peptide-repo-core' ),
+			'manage_options',
+			'pr-core-settings',
+			[ $this, 'render_page' ]
+		);
+	}
+
+	/**
+	 * Register settings fields.
+	 *
+	 * @return void
+	 */
+	public function register_settings(): void {
+		register_setting(
+			'pr_core_settings',
+			self::ENABLED_OPTION,
+			[
+				'type'              => 'boolean',
+				'default'           => true,
+				'sanitize_callback' => 'rest_sanitize_boolean',
+			]
+		);
+
+		register_setting(
+			'pr_core_settings',
+			self::LIMIT_OPTION,
+			[
+				'type'              => 'integer',
+				'default'           => 3,
+				'sanitize_callback' => [ $this, 'sanitize_limit' ],
+			]
+		);
+
+		add_settings_section(
+			'pr_core_related_articles',
+			__( 'Related Articles', 'peptide-repo-core' ),
+			[ $this, 'render_section' ],
+			'pr_core_settings'
+		);
+
+		add_settings_field(
+			self::ENABLED_OPTION,
+			__( 'Enable Related Articles', 'peptide-repo-core' ),
+			[ $this, 'render_enabled_field' ],
+			'pr_core_settings',
+			'pr_core_related_articles'
+		);
+
+		add_settings_field(
+			self::LIMIT_OPTION,
+			__( 'Number of Articles to Display', 'peptide-repo-core' ),
+			[ $this, 'render_limit_field' ],
+			'pr_core_settings',
+			'pr_core_related_articles'
+		);
+	}
+
+	/**
+	 * Render the settings page.
+	 *
+	 * @return void
+	 */
+	public function render_page(): void {
+		?>
+		<div class="wrap">
+			<h1><?php esc_html_e( 'Peptide Repo Core Settings', 'peptide-repo-core' ); ?></h1>
+			<form method="post" action="options.php">
+				<?php
+				settings_fields( 'pr_core_settings' );
+				do_settings_sections( 'pr_core_settings' );
+				submit_button();
+				?>
+			</form>
+		</div>
+		<?php
+	}
+
+	/**
+	 * Render section description.
+	 *
+	 * @return void
+	 */
+	public function render_section(): void {
+		echo '<p>' . esc_html__( 'Configure the Related Articles section that appears on peptide single pages.', 'peptide-repo-core' ) . '</p>';
+	}
+
+	/**
+	 * Render enabled toggle field.
+	 *
+	 * @return void
+	 */
+	public function render_enabled_field(): void {
+		$checked = (bool) get_option( self::ENABLED_OPTION, true );
+		?>
+		<input
+			type="checkbox"
+			name="<?php echo esc_attr( self::ENABLED_OPTION ); ?>"
+			value="1"
+			<?php checked( $checked, true ); ?>
+		/>
+		<label>
+			<?php esc_html_e( 'Display related articles on peptide pages', 'peptide-repo-core' ); ?>
+		</label>
+		<?php
+	}
+
+	/**
+	 * Render limit field.
+	 *
+	 * @return void
+	 */
+	public function render_limit_field(): void {
+		$limit = (int) get_option( self::LIMIT_OPTION, 3 );
+		?>
+		<input
+			type="number"
+			name="<?php echo esc_attr( self::LIMIT_OPTION ); ?>"
+			value="<?php echo esc_attr( (string) $limit ); ?>"
+			min="1"
+			max="6"
+		/>
+		<p class="description">
+			<?php esc_html_e( 'Number of articles to display (1-6). Default: 3.', 'peptide-repo-core' ); ?>
+		</p>
+		<?php
+	}
+
+	/**
+	 * Sanitize limit to 1-6 range.
+	 *
+	 * @param mixed $value Raw input.
+	 * @return int Sanitized value.
+	 */
+	public function sanitize_limit( $value ): int {
+		$limit = (int) $value;
+		return min( 6, max( 1, $limit ) );
+	}
+}

includes/class-pr-core.php

@@ -6,11 +6,12 @@ declare(strict_types=1);
  *
  * What: Registers all hooks, runs migrations, boots subsystems.
  * Who calls it: peptide-repo-core.php on plugins_loaded.
- * Dependencies: PR_Core_Migration_Runner, PR_Core_Peptide_CPT, PR_Core_Admin,
- *               PR_Core_Disclaimer, PR_Core_Jsonld, PR_Core_Rest_Controller.
+ * Dependencies: PR_Core_Migration_Runner, PR_Core_Peptide_CPT, PR_Core_Topic_Taxonomy,
+ *              PR_Core_Admin, PR_Core_Disclaimer, PR_Core_Jsonld,
+ *              PR_Core_Rest_Controller, PR_Core_Related_Posts_Section.
  *
  * @see peptide-repo-core.php — Bootstrap that instantiates this class.
- * @see ARCHITECTURE.md       — Full data flow diagram.
+ * @see ARCHITECTURE.md    — Full data flow diagram.
  */
 class PR_Core {
 
@@ -30,6 +31,10 @@ class PR_Core {
 		$cpt = new PR_Core_Peptide_CPT();
 		$cpt->register_hooks();
 
+		// Register peptide_topic taxonomy (fires on init).
+		$topic_tax = new PR_Core_Topic_Taxonomy();
+		$topic_tax->register_hooks();
+
 		// One-shot rewrite flush on in-place version bumps. Runs at the very
 		// end of init (priority 999) so all CPTs/taxonomies — ours and
 		// anyone else's — are registered first. Handles updates deployed
@@ -49,6 +54,15 @@ class PR_Core {
 		$jsonld = new PR_Core_Jsonld();
 		$jsonld->register_hooks();
 
+		// Related Articles section (frontend).
+		$related_posts = new PR_Core_Related_Posts_Section(
+			new PR_Core_Internal_Posts_Provider()
+		);
+		$related_posts->register_hooks();
+
+		// Enqueue related-posts CSS on single peptide pages.
+		add_action( 'wp_enqueue_scripts', [ $this, 'enqueue_frontend_styles' ] );
+
 		// REST API.
 		$rest = new PR_Core_Rest_Controller();
 		$rest->register_hooks();
@@ -57,6 +71,24 @@ class PR_Core {
 		$this->register_public_filters();
 	}
 
+	/**
+	 * Enqueue frontend CSS on single peptide pages.
+	 *
+	 * @return void
+	 */
+	public function enqueue_frontend_styles(): void {
+		if ( ! is_singular( PR_Core_Peptide_CPT::POST_TYPE ) ) {
+			return;
+		}
+
+		wp_enqueue_style(
+			'pr-core-related-posts',
+			PR_CORE_PLUGIN_URL . 'assets/css/related-posts.css',
+			[],
+			PR_CORE_VERSION
+		);
+	}
+
 	/**
 	 * Register the public filter hooks that consumer plugins rely on.
 	 *
@@ -101,7 +133,7 @@ class PR_Core {
 	/**
 	 * Return disclaimer text for a given surface identifier.
 	 *
-	 * @param string $text    Existing text (empty string default).
+	 * @param string $text     Existing text (empty string default).
 	 * @param string $surface Surface identifier (dosing, legal, reconstitution, ai-answer).
 	 * @return string Disclaimer HTML.
 	 */
@@ -112,18 +144,18 @@ class PR_Core {
 	/**
 	 * Map evidence_strength enum value to human-readable label.
 	 *
-	 * @param string $label    Existing label (empty string default).
+	 * @param string $label     Existing label (empty string default).
 	 * @param string $strength Enum value.
 	 * @return string Localized label.
 	 */
 	public function filter_evidence_label( string $label, string $strength ): string {
 		$map = [
-			'preclinical'   => __( 'Preclinical', 'peptide-repo-core' ),
-			'case-series'   => __( 'Case Series', 'peptide-repo-core' ),
-			'observational' => __( 'Observational', 'peptide-repo-core' ),
-			'rct-small'     => __( 'Small RCT', 'peptide-repo-core' ),
-			'rct-large'     => __( 'Large RCT', 'peptide-repo-core' ),
-			'meta-analysis' => __( 'Meta-Analysis', 'peptide-repo-core' ),
+			'preclinical'    => __( 'Preclinical', 'peptide-repo-core' ),
+			'case-series'    => __( 'Case Series', 'peptide-repo-core' ),
+			'observational'  => __( 'Observational', 'peptide-repo-core' ),
+			'rct-small'      => __( 'Small RCT', 'peptide-repo-core' ),
+			'rct-large'      => __( 'Large RCT', 'peptide-repo-core' ),
+			'meta-analysis'  => __( 'Meta-Analysis', 'peptide-repo-core' ),
 		];
 
 		return $map[ $strength ] ?? $strength;

includes/core/class-pr-core-internal-posts-provider.php

@@ -0,0 +1,102 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Fetches posts related to a peptide via taxonomy and fallback text search.
+ *
+ * What: Implements PR_Core_Related_Posts_Provider by querying posts tagged
+ *       with the peptide's slug as a peptide_topic term. Falls back to
+ *       full-text search if no taxonomy matches found.
+ * Who calls it: PR_Core_Related_Posts_Section instantiates and calls this.
+ * Dependencies: PR_Core_Related_Posts_Provider interface, WP_Query,
+ *               peptide_topic taxonomy.
+ *
+ * @see includes/interfaces/interface-related-posts-provider.php
+ * @see includes/core/class-related-posts-section.php
+ */
+class PR_Core_Internal_Posts_Provider implements PR_Core_Related_Posts_Provider {
+
+	/**
+	 * Get posts related to a peptide.
+	 *
+	 * 1. Queries posts tagged with the peptide slug as a peptide_topic term.
+	 * 2. If 0 posts found, falls back to full-text search on post_title.
+	 * 3. Caches result as a transient (1 hour TTL).
+	 * 4. Never exceeds $limit posts.
+	 *
+	 * Side effects: Sets/updates transient cache for this peptide.
+	 *
+	 * @param int $peptide_id The peptide post ID.
+	 * @param int $limit      Maximum number of posts to return.
+	 * @return array<int, \WP_Post> Array of WP_Post objects (may be empty).
+	 */
+	public function get_posts( int $peptide_id, int $limit ): array {
+		$peptide = get_post( $peptide_id );
+		if ( ! $peptide || 'peptide' !== $peptide->post_type ) {
+			return [];
+		}
+
+		$cache_key = 'pr_core_related_' . $peptide_id;
+		$cached    = get_transient( $cache_key );
+		if ( is_array( $cached ) ) {
+			return array_slice( $cached, 0, $limit );
+		}
+
+		// Primary: query posts tagged with peptide's slug as peptide_topic.
+		$posts = $this->query_by_taxonomy( $peptide->post_name, $limit );
+
+		// Fallback: if empty, search by peptide title.
+		if ( empty( $posts ) ) {
+			$posts = $this->query_by_search( $peptide->post_title, $limit );
+		}
+
+		// Cache for 1 hour.
+		set_transient( $cache_key, $posts, HOUR_IN_SECONDS );
+
+		return $posts;
+	}
+
+	/**
+	 * Query posts tagged with a specific peptide_topic term.
+	 *
+	 * @param string $peptide_slug The peptide's post_name (slug).
+	 * @param int    $limit        Maximum posts to return.
+	 * @return array<int, \WP_Post>
+	 */
+	private function query_by_taxonomy( string $peptide_slug, int $limit ): array {
+		$query = new WP_Query( [
+			'post_type'      => 'post',
+			'posts_per_page' => $limit,
+			'orderby'        => 'date',
+			'order'          => 'DESC',
+			'tax_query'      => [
+				[
+					'taxonomy' => 'peptide_topic',
+					'field'    => 'slug',
+					'terms'    => $peptide_slug,
+				],
+			],
+		] );
+
+		return $query->posts ?: [];
+	}
+
+	/**
+	 * Fallback: query posts by full-text search on post_title.
+	 *
+	 * @param string $search_term The peptide's display title.
+	 * @param int    $limit       Maximum posts to return.
+	 * @return array<int, \WP_Post>
+	 */
+	private function query_by_search( string $search_term, int $limit ): array {
+		$query = new WP_Query( [
+			'post_type'      => 'post',
+			'posts_per_page' => $limit,
+			'orderby'        => 'date',
+			'order'          => 'DESC',
+			's'              => $search_term,
+		] );
+
+		return $query->posts ?: [];
+	}
+}

includes/core/class-pr-core-related-posts-provider.php

@@ -0,0 +1,24 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Contract for any provider that retrieves posts related to a peptide.
+ *
+ * What: Interface defining the get_posts() contract for related-post providers.
+ * Who calls it: PR_Core_Related_Posts_Section accepts any implementation.
+ * Dependencies: None.
+ *
+ * @see includes/core/class-pr-core-internal-posts-provider.php — default implementation.
+ * @see includes/core/class-pr-core-related-posts-section.php   — consumer.
+ */
+interface PR_Core_Related_Posts_Provider {
+
+	/**
+	 * Get posts related to a peptide.
+	 *
+	 * @param int $peptide_id The peptide post ID.
+	 * @param int $limit      Maximum number of posts to return.
+	 * @return array<int, \WP_Post> Array of WP_Post objects (may be empty).
+	 */
+	public function get_posts( int $peptide_id, int $limit ): array;
+}

includes/core/class-pr-core-related-posts-section.php

@@ -0,0 +1,126 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Renders the related articles section on peptide single pages.
+ *
+ * What: Hooks into pr_core_after_peptide_content and renders a card grid
+ *       of related posts fetched via PR_Core_Related_Posts_Provider.
+ * Who calls it: PR_Core::init() instantiates and registers hooks.
+ * Dependencies: PR_Core_Related_Posts_Provider interface, template-parts/related-posts/card.php.
+ *
+ * Settings read:
+ * - pr_core_related_posts_enabled (bool, default true)
+ * - pr_core_related_posts_limit (int, default 3, range 1-6)
+ */
+class PR_Core_Related_Posts_Section {
+
+	/** @var PR_Core_Related_Posts_Provider */
+	private $provider;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param PR_Core_Related_Posts_Provider $provider Provider instance.
+	 */
+	public function __construct( PR_Core_Related_Posts_Provider $provider ) {
+		$this->provider = $provider;
+	}
+
+	/**
+	 * Register the action hook.
+	 *
+	 * @return void
+	 */
+	public function register_hooks(): void {
+		add_action( 'pr_core_after_peptide_content', [ $this, 'render' ] );
+		add_action( 'save_post_post', [ $this, 'invalidate_caches' ] );
+	}
+
+	/**
+	 * Render the related posts section.
+	 *
+	 * Called via do_action( 'pr_core_after_peptide_content', $peptide_id ) in templates.
+	 * If feature disabled or no posts found, renders nothing.
+	 *
+	 * @param int $peptide_id The peptide post ID.
+	 * @return void
+	 */
+	public function render( int $peptide_id ): void {
+		$enabled = (bool) get_option( 'pr_core_related_posts_enabled', true );
+		if ( ! $enabled ) {
+			return;
+		}
+
+		$limit = (int) get_option( 'pr_core_related_posts_limit', 3 );
+		$limit = min( 6, max( 1, $limit ) );
+
+		$posts = $this->provider->get_posts( $peptide_id, $limit + 5 );
+		if ( empty( $posts ) ) {
+			return;
+		}
+
+		$peptide = get_post( $peptide_id );
+		?>
+		<section class="pr-related-posts" aria-label="<?php esc_attr_e( 'Related Articles', 'peptide-repo-core' ); ?>">
+			<h2><?php esc_html_e( 'Related Articles', 'peptide-repo-core' ); ?></h2>
+			<div class="pr-related-posts__grid">
+				<?php
+				$count = 0;
+				foreach ( $posts as $post ) {
+					if ( $count >= $limit ) {
+						break;
+					}
+					setup_postdata( $post );
+					get_template_part( 'template-parts/related-posts/card', null, [ 'post' => $post ] );
+					++$count;
+				}
+				wp_reset_postdata();
+				?>
+			</div>
+			<?php
+			if ( count( $posts ) > $limit && $peptide ) {
+				$term = get_term_by( 'slug', $peptide->post_name, 'peptide_topic' );
+				if ( $term ) {
+					$archive_url = get_term_link( $term );
+					if ( ! is_wp_error( $archive_url ) ) {
+						?>
+						<p class="pr-related-posts__view-all">
+							<a href="<?php echo esc_url( $archive_url ); ?>">
+								<?php
+								echo wp_kses_post(
+									sprintf(
+										__( 'View all %s articles &rarr;', 'peptide-repo-core' ),
+										esc_html( $peptide->post_title )
+									)
+								);
+								?>
+							</a>
+						</p>
+						<?php
+					}
+				}
+			}
+			?>
+		</section>
+		<?php
+	}
+
+	/**
+	 * Invalidate related posts transient caches when a post is saved.
+	 *
+	 * Hooks into save_post_post to clear any cached related-post queries
+	 * since the post corpus has changed.
+	 *
+	 * @return void
+	 */
+	public function invalidate_caches(): void {
+		global $wpdb;
+		$cache_keys = $wpdb->get_col(
+			"SELECT option_name FROM {$wpdb->options} WHERE option_name LIKE 'pr_core_related_%'"
+		);
+		foreach ( $cache_keys as $key ) {
+			delete_transient( str_replace( '_transient_', '', $key ) );
+		}
+	}
+}

includes/cpt/class-pr-core-peptide-cpt.php

@@ -2,9 +2,10 @@
 declare(strict_types=1);
 
 /**
- * Registers the peptide custom post type and associated taxonomy.
+ * Registers the peptide custom post type and associated taxonomies.
  *
  * What: Defines the peptide CPT with REST support, archive, and monograph meta fields.
+ *       Also registers the peptide_category taxonomy (for peptide categorization).
  * Who calls it: PR_Core::init() on plugins_loaded.
  * Dependencies: None.
  *
@@ -183,7 +184,8 @@ class PR_Core_Peptide_CPT {
 			'show_in_nav_menus'  => true,
 			'show_in_rest'       => true,
 			'rest_base'          => 'peptides',
-			'rest_namespace'     => 'pr-core/v1',
+			// 'rest_namespace' omitted — custom namespaces break Gutenberg
+			// (it fetches wp/v2 hardcoded). WordPress defaults to wp/v2. (#5)
 			'menu_position'      => 25,
 			'menu_icon'          => 'dashicons-database',
 			'capability_type'    => 'post',
@@ -201,35 +203,36 @@ class PR_Core_Peptide_CPT {
 	 * Register the `peptide_category` taxonomy.
 	 *
 	 * Guarded with `taxonomy_exists()` for the same reason CPT registration
-	 * is guarded. The 8 existing terms + term_relationships stay intact —
+	 * is guarded. The 8 existing category terms + term_relationships stay intact —
 	 * they key on taxonomy name `peptide_category` in wp_term_taxonomy,
 	 * which is exactly what we register here.
 	 *
 	 * v0.2.0: `pr_peptide_family` taxonomy removed — never populated, never
 	 * surfaced in UI.
 	 *
+	 * v0.3.0: `peptide_topic` taxonomy moved to PR_Core_Topic_Taxonomy class.
+	 *
 	 * Side effects: registers taxonomy with WordPress.
 	 *
 	 * @return void
 	 */
 	public static function register_taxonomies(): void {
-		if ( taxonomy_exists( self::TAX_CATEGORY ) ) {
-			return;
+		// Register peptide_category taxonomy.
+		if ( ! taxonomy_exists( self::TAX_CATEGORY ) ) {
+			register_taxonomy( self::TAX_CATEGORY, self::POST_TYPE, [
+				'labels'             => [
+					'name'          => __( 'Peptide Categories', 'peptide-repo-core' ),
+					'singular_name' => __( 'Peptide Category', 'peptide-repo-core' ),
+				],
+				'public'             => true,
+				'publicly_queryable' => true,
+				'show_in_rest'       => true,
+				'show_ui'            => true,
+				'show_admin_column'  => true,
+				'hierarchical'       => true,
+				'rewrite'            => [ 'slug' => 'peptide-category', 'with_front' => false ],
+			] );
 		}
-
-		register_taxonomy( self::TAX_CATEGORY, self::POST_TYPE, [
-			'labels'             => [
-				'name'          => __( 'Peptide Categories', 'peptide-repo-core' ),
-				'singular_name' => __( 'Peptide Category', 'peptide-repo-core' ),
-			],
-			'public'             => true,
-			'publicly_queryable' => true,
-			'show_in_rest'       => true,
-			'show_ui'            => true,
-			'show_admin_column'  => true,
-			'hierarchical'       => true,
-			'rewrite'            => [ 'slug' => 'peptide-category', 'with_front' => false ],
-		] );
 	}
 
 	/**

includes/cpt/class-pr-core-topic-taxonomy.php

@@ -0,0 +1,62 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Registers the peptide_topic taxonomy for linking blog posts to peptides.
+ *
+ * What: Defines the `peptide_topic` taxonomy attached to the post CPT.
+ *       Non-hierarchical, uses peptide slugs as terms (e.g., 'bpc-157', 'tb-500').
+ *       Enables the Related Articles feature for blog posts tagged with a peptide topic.
+ * Who calls it: PR_Core::init() on plugins_loaded.
+ * Dependencies: None.
+ *
+ * Ownership: As of v0.3.0, PR Core owns `peptide_topic` taxonomy.
+ * Registration is guarded by `taxonomy_exists()` so deploy order does not matter.
+ *
+ * @see ARCHITECTURE.md — Taxonomy specification.
+ * @see CONVENTIONS.md — Taxonomy ownership rule.
+ */
+class PR_Core_Topic_Taxonomy {
+
+	/** @var string Taxonomy: topic (links blog posts to peptides by slug). */
+	public const TAX_TOPIC = 'peptide_topic';
+
+	/**
+	 * Register WordPress hooks for taxonomy registration.
+	 *
+	 * @return void
+	 */
+	public function register_hooks(): void {
+		add_action( 'init', [ __CLASS__, 'register_topic_taxonomy' ] );
+	}
+
+	/**
+	 * Register the `peptide_topic` taxonomy.
+	 *
+	 * Guarded with `taxonomy_exists()`: if another plugin has already
+	 * registered the `peptide_topic` taxonomy, this call no-ops.
+	 *
+	 * Side effects: registers taxonomy with WordPress.
+	 *
+	 * @return void
+	 */
+	public static function register_topic_taxonomy(): void {
+		if ( taxonomy_exists( self::TAX_TOPIC ) ) {
+			return;
+		}
+
+		register_taxonomy( self::TAX_TOPIC, 'post', [
+			'labels'             => [
+				'name'          => __( 'Peptide Topics', 'peptide-repo-core' ),
+				'singular_name' => __( 'Peptide Topic', 'peptide-repo-core' ),
+			],
+			'public'             => true,
+			'publicly_queryable' => true,
+			'show_in_rest'       => true,
+			'show_ui'            => true,
+			'show_admin_column'  => true,
+			'hierarchical'       => false,
+			'rewrite'            => [ 'slug' => 'peptide-topic', 'with_front' => false ],
+		] );
+	}
+}

includes/interfaces/interface-related-posts-provider.php

@@ -0,0 +1,21 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Interface for fetching related posts for a peptide.
+ *
+ * What: Defines the contract for retrieving posts related to a given peptide.
+ * Who calls it: PR_Core_Related_Posts_Section uses implementations to fetch related articles.
+ * Dependencies: None.
+ */
+interface PR_Core_Related_Posts_Provider {
+
+	/**
+	 * Get posts related to a peptide.
+	 *
+	 * @param int $peptide_id The peptide post ID.
+	 * @param int $limit      Maximum number of posts to return.
+	 * @return array<int, \WP_Post> Array of WP_Post objects (may be empty).
+	 */
+	public function get_posts( int $peptide_id, int $limit ): array;
+}

includes/repositories/class-pr-core-peptide-repository.php

@@ -92,14 +92,10 @@ class PR_Core_Peptide_Repository {
 			] ];
 		}
 
-		if ( ! empty( $filters['family'] ) ) {
-			$args['tax_query']   = $args['tax_query'] ?? [];
-			$args['tax_query'][] = [
-				'taxonomy' => PR_Core_Peptide_CPT::TAX_FAMILY,
-				'field'    => 'slug',
-				'terms'    => sanitize_text_field( $filters['family'] ),
-			];
-		}
+		// v0.2.0: `family` filter silently ignored — `pr_peptide_family` taxonomy
+		// was removed with the CPT consolidation. Callers passing `family` get
+		// all-category results rather than a fatal. Remove this key from the
+		// REST schema in a future minor bump.
 
 		if ( ! empty( $filters['evidence_strength'] ) ) {
 			$args['meta_query'] = [ [
@@ -135,7 +131,10 @@ class PR_Core_Peptide_Repository {
 		$aliases     = json_decode( $aliases_raw ?: '[]', true ) ?: [];
 
 		$categories = wp_get_post_terms( $post->ID, PR_Core_Peptide_CPT::TAX_CATEGORY, [ 'fields' => 'names' ] );
-		$families   = wp_get_post_terms( $post->ID, PR_Core_Peptide_CPT::TAX_FAMILY, [ 'fields' => 'names' ] );
+		// v0.2.0: `pr_peptide_family` taxonomy removed. DTO `families` field
+		// preserved as empty array to keep the REST response shape stable for
+		// clients; will be dropped in a future minor bump with a release note.
+		$families   = [];
 
 		return new PR_Core_Peptide_DTO( [
 			'id'                       => $post->ID,
@@ -156,7 +155,7 @@ class PR_Core_Peptide_Repository {
 			'last_editorial_review_at' => get_post_meta( $post->ID, 'last_editorial_review_at', true ) ?: '',
 			'medical_editor_id'        => (int) get_post_meta( $post->ID, 'medical_editor_id', true ),
 			'categories'               => is_array( $categories ) ? $categories : [],
-			'families'                 => is_array( $families ) ? $families : [],
+			'families'                 => $families,
 		] );
 	}
 }

peptide-repo-core.php

@@ -3,7 +3,7 @@
  * Plugin Name: Peptide Repo Core
  * Plugin URI:  https://peptiderepo.com
  * Description: Canonical peptide schema — shared data layer for the peptiderepo.com ecosystem. Provides the peptide CPT, dosing rows, legal status cells, AI candidate queue, disclaimer component, and JSON-LD output.
- * Version:     0.2.0
+ * Version:     0.3.2
  * Author:      peptiderepo
  * Author URI:  https://peptiderepo.com
  * License:     GPL-2.0-or-later
@@ -22,7 +22,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 
 /* ── Constants ────────────────────────────────────────────────────────── */
 
-define( 'PR_CORE_VERSION', '0.2.0' );
+define( 'PR_CORE_VERSION', '0.3.2' );
 define( 'PR_CORE_PLUGIN_FILE', __FILE__ );
 define( 'PR_CORE_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
 define( 'PR_CORE_PLUGIN_URL', plugin_dir_url( __FILE__ ) );

template-parts/related-posts/card.php

@@ -0,0 +1,67 @@
+<?php
+/**
+ * Related posts card template part.
+ *
+ * Variables:
+ * - $post: WP_Post object with thumbnail, title, excerpt, date.
+ *
+ * @package peptide-repo-core
+ */
+
+if ( ! isset( $args['post'] ) ) {
+	return;
+}
+
+$post = $args['post'];
+?>
+<article class="pr-related-posts__card">
+	<?php
+	if ( has_post_thumbnail( $post ) ) {
+		?>
+		<div class="pr-related-posts__image">
+			<?php
+			echo wp_kses_post(
+				get_the_post_thumbnail(
+					$post,
+					'post-thumbnail',
+					[
+						'class'    => 'pr-related-posts__image-element',
+						'loading'  => 'lazy',
+						'decoding' => 'async',
+					]
+				)
+			);
+			?>
+		</div>
+		<?php
+	} else {
+		?>
+		<div class="pr-related-posts__image pr-related-posts__image--fallback">
+			<img src="<?php echo esc_url( get_site_icon_url( 512 ) ); ?>" alt="<?php esc_attr_e( 'Site logo', 'peptide-repo-core' ); ?>" class="pr-related-posts__image-element" loading="lazy" decoding="async" />
+		</div>
+		<?php
+	}
+	?>
+	<div class="pr-related-posts__content">
+		<span class="pr-related-posts__badge"><?php esc_html_e( 'Article', 'peptide-repo-core' ); ?></span>
+		<h3 class="pr-related-posts__title">
+			<a href="<?php echo esc_url( get_permalink( $post ) ); ?>">
+				<?php echo esc_html( $post->post_title ); ?>
+			</a>
+		</h3>
+		<time class="pr-related-posts__date" datetime="<?php echo esc_attr( mysql2date( 'c', $post->post_date ) ); ?>">
+			<?php echo esc_html( mysql2date( get_option( 'date_format' ), $post->post_date ) ); ?>
+		</time>
+		<?php
+		if ( $post->post_excerpt ) {
+			$excerpt = wp_strip_all_tags( $post->post_excerpt );
+			$excerpt = wp_kses_post( wp_trim_words( $excerpt, 20 ) );
+			?>
+			<p class="pr-related-posts__excerpt">
+				<?php echo wp_kses_post( $excerpt ); ?>
+			</p>
+			<?php
+		}
+		?>
+	</div>
+</article>

tests/test-internal-posts-provider.php

@@ -0,0 +1,168 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Unit tests for PR_Core_Internal_Posts_Provider.
+ *
+ * Tests the provider's taxonomy-based and fallback search behavior,
+ * caching, and limit enforcement. Uses mocked WP_Query.
+ */
+class PR_Core_Internal_Posts_Provider_Test {
+
+	/**
+	 * Test: returns empty array when peptide ID is invalid.
+	 */
+	public function test_returns_empty_when_peptide_not_found() {
+		$provider = new PR_Core_Internal_Posts_Provider();
+		$result   = $provider->get_posts( 99999, 3 );
+
+		assert( [] === $result, 'Expected empty array for invalid peptide ID' );
+	}
+
+	/**
+	 * Test: returns posts matching peptide_topic taxonomy.
+	 */
+	public function test_returns_taxonomy_matched_posts() {
+		$provider = new PR_Core_Internal_Posts_Provider();
+
+		// Create a peptide post.
+		$peptide_id = wp_insert_post( [
+			'post_type'   => 'peptide',
+			'post_title'  => 'BPC-157',
+			'post_name'   => 'bpc-157',
+			'post_status' => 'publish',
+		] );
+
+		// Create and tag a blog post with peptide_topic = 'bpc-157'.
+		$post_id = wp_insert_post( [
+			'post_type'   => 'post',
+			'post_title'  => 'BPC-157 Research',
+			'post_status' => 'publish',
+		] );
+		wp_set_post_terms( $post_id, 'bpc-157', 'peptide_topic' );
+
+		$result = $provider->get_posts( $peptide_id, 3 );
+
+		assert( ! empty( $result ), 'Expected at least one post' );
+		assert( 1 === count( $result ), 'Expected exactly one post' );
+		assert( $post_id === $result[0]->ID, 'Expected post ID to match' );
+
+		// Cleanup.
+		wp_delete_post( $peptide_id, true );
+		wp_delete_post( $post_id, true );
+	}
+
+	/**
+	 * Test: falls back to text search when taxonomy returns nothing.
+	 */
+	public function test_falls_back_to_search_when_no_taxonomy_matches() {
+		$provider = new PR_Core_Internal_Posts_Provider();
+
+		// Create a peptide post with no matching term.
+		$peptide_id = wp_insert_post( [
+			'post_type'   => 'peptide',
+			'post_title'  => 'Semaglutide',
+			'post_name'   => 'semaglutide-unique',
+			'post_status' => 'publish',
+		] );
+
+		// Create a blog post with "Semaglutide" in title (no peptide_topic tag).
+		$post_id = wp_insert_post( [
+			'post_type'   => 'post',
+			'post_title'  => 'Semaglutide Dosing Guide',
+			'post_status' => 'publish',
+		] );
+
+		$result = $provider->get_posts( $peptide_id, 3 );
+
+		assert( ! empty( $result ), 'Expected fallback search to return posts' );
+		assert( $post_id === $result[0]->ID, 'Expected fallback search to find title match' );
+
+		// Cleanup.
+		wp_delete_post( $peptide_id, true );
+		wp_delete_post( $post_id, true );
+	}
+
+	/**
+	 * Test: never returns more posts than $limit.
+	 */
+	public function test_respects_limit_constraint() {
+		$provider = new PR_Core_Internal_Posts_Provider();
+
+		// Create peptide.
+		$peptide_id = wp_insert_post( [
+			'post_type'   => 'peptide',
+			'post_title'  => 'TB-500',
+			'post_name'   => 'tb-500',
+			'post_status' => 'publish',
+		] );
+
+		// Create 5 tagged posts.
+		for ( $i = 0; $i < 5; ++$i ) {
+			$post_id = wp_insert_post( [
+				'post_type'   => 'post',
+				'post_title'  => 'TB-500 Article ' . $i,
+				'post_status' => 'publish',
+			] );
+			wp_set_post_terms( $post_id, 'tb-500', 'peptide_topic' );
+		}
+
+		$result = $provider->get_posts( $peptide_id, 3 );
+
+		assert( 3 === count( $result ), 'Expected exactly 3 posts for limit=3' );
+
+		// Cleanup.
+		wp_delete_post( $peptide_id, true );
+	}
+
+	/**
+	 * Test: returns cached transient on second call.
+	 */
+	public function test_returns_cached_transient_on_second_call() {
+		$provider = new PR_Core_Internal_Posts_Provider();
+
+		// Create peptide.
+		$peptide_id = wp_insert_post( [
+			'post_type'   => 'peptide',
+			'post_title'  => 'AOD-9604',
+			'post_name'   => 'aod-9604',
+			'post_status' => 'publish',
+		] );
+
+		// First call: query and cache.
+		$result_1 = $provider->get_posts( $peptide_id, 3 );
+
+		// Verify transient was set.
+		$cache_key = 'pr_core_related_' . $peptide_id;
+		$cached    = get_transient( $cache_key );
+		assert( ! empty( $cached ), 'Expected transient to be set' );
+
+		// Second call: should return cached data.
+		$result_2 = $provider->get_posts( $peptide_id, 3 );
+
+		// Results should match.
+		if ( ! empty( $result_1 ) ) {
+			assert( count( $result_1 ) === count( $result_2 ), 'Expected cached results to match' );
+		}
+
+		// Cleanup.
+		wp_delete_post( $peptide_id, true );
+		delete_transient( $cache_key );
+	}
+}
+
+// Run tests if executed directly in PHPUnit context (tests/bootstrap.php will autoload).
+if ( function_exists( 'assert_options' ) ) {
+	assert_options( ASSERT_ACTIVE, 1 );
+	assert_options( ASSERT_WARNING, 0 );
+	assert_options( ASSERT_BAIL, 1 );
+
+	$test = new PR_Core_Internal_Posts_Provider_Test();
+	$test->test_returns_empty_when_peptide_not_found();
+	$test->test_returns_taxonomy_matched_posts();
+	$test->test_falls_back_to_search_when_no_taxonomy_matches();
+	$test->test_respects_limit_constraint();
+	$test->test_returns_cached_transient_on_second_call();
+
+	echo "All tests passed!\n";
+}

tests/unit/test-peptide-cpt.php

@@ -10,7 +10,7 @@
  *   - TAX_FAMILY constant is removed.
  *   - register_peptide_post_type() guard: no-op when post_type_exists returns true.
  *   - register_peptide_post_type() payload: args match the harmonized contract
- *     (thumbnail in supports, rewrite slug peptides, pr-core/v1 REST namespace).
+ *     (thumbnail in supports, rewrite slug peptides, rest_namespace absent — Gutenberg requires wp/v2).
  *   - register_taxonomies() guard: no-op when taxonomy_exists returns true.
  *   - register_taxonomies() only registers peptide_category; pr_peptide_family is gone.
  *
@@ -65,7 +65,7 @@ pr_assert_equals( true, $args['public'] ?? null, 'public = true' );
 pr_assert_equals( true, $args['publicly_queryable'] ?? null, 'publicly_queryable = true' );
 pr_assert_equals( true, $args['show_in_rest'] ?? null, 'show_in_rest = true' );
 pr_assert_equals( 'peptides', $args['rest_base'] ?? null, 'rest_base = "peptides"' );
-pr_assert_equals( 'pr-core/v1', $args['rest_namespace'] ?? null, 'rest_namespace = "pr-core/v1"' );
+pr_assert( ! array_key_exists( 'rest_namespace', $args ), 'rest_namespace absent — defaults to wp/v2 (Gutenberg requirement)' );
 pr_assert_equals( 'post', $args['capability_type'] ?? null, 'capability_type = "post"' );
 pr_assert_equals( true, $args['map_meta_cap'] ?? null, 'map_meta_cap = true' );
 pr_assert_equals( false, $args['hierarchical'] ?? null, 'hierarchical = false' );