From 1563aff9645a77af03fc1fba4c27c4261d77030c Mon Sep 17 00:00:00 2001
From: Yutaka Kurosaki <>
Date: Sat, 9 May 2026 10:25:08 +0900
Subject: [PATCH] Add implementation plan for Markdown media embed

Plan breaks the work into 9 TDD tasks: scaffold resolver, video
detection, audio detection, YouTube URL detection, YouTube timestamps,
Vimeo detection, listener+extension wiring, integration tests, full
test suite verification.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 .../plans/2026-05-09-media-embed.md           | 1040 +++++++++++++++++
 1 file changed, 1040 insertions(+)
 create mode 100644 docs/superpowers/plans/2026-05-09-media-embed.md

diff --git a/docs/superpowers/plans/2026-05-09-media-embed.md b/docs/superpowers/plans/2026-05-09-media-embed.md
new file mode 100644
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+++ b/docs/superpowers/plans/2026-05-09-media-embed.md
@@ -0,0 +1,1040 @@
+# Markdown Media Embed Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Extend the Markdown image syntax `![](url)` so that URLs pointing to local video/audio files, YouTube, or Vimeo render as `<video>`, `<audio>`, or `<iframe>` instead of `<img>`, while preserving the existing `html_input => 'strip'` safety policy.
+
+**Architecture:** Implement a CommonMark `ExtensionInterface` that registers a `DocumentParsedEvent` listener. The listener walks the AST, identifies `Image` nodes whose URLs match media patterns, and replaces them with `HtmlInline` nodes containing safe, escaped HTML. URL classification is delegated to a pure `MediaUrlResolver` class.
+
+**Tech Stack:** PHP 8.2 / Laravel 12 / `league/commonmark ^2.8` / PHPUnit (Laravel default).
+
+**Reference spec:** `docs/superpowers/specs/2026-05-09-media-embed-design.md`
+
+---
+
+## File Structure
+
+| File | Status | Responsibility |
+|---|---|---|
+| `src/app/Markdown/MediaUrlResolver.php` | Create | Pure URL classifier. Returns escaped HTML string or `null`. |
+| `src/app/Markdown/MediaEmbedListener.php` | Create | Glue layer. Walks AST, replaces matching `Image` nodes with `HtmlInline`. |
+| `src/app/Markdown/MediaEmbedExtension.php` | Create | CommonMark `ExtensionInterface`. Registers the listener. |
+| `src/app/Models/Document.php` | Modify | Add one line to `renderMarkdown()` to register the extension. |
+| `src/tests/Unit/Markdown/MediaUrlResolverTest.php` | Create | Exhaustive URL pattern tests against the resolver. |
+| `src/tests/Unit/Markdown/MediaEmbedExtensionTest.php` | Create | Integration tests through `Document::renderMarkdown()`. |
+
+All commands assume the project root `/Library/WebServer/Documents/knowledge-base`. Tests run inside the `php` container via `docker compose exec php`.
+
+---
+
+## Task 1: Scaffold `MediaUrlResolver` with fallback behavior
+
+**Files:**
+- Create: `src/app/Markdown/MediaUrlResolver.php`
+- Test: `src/tests/Unit/Markdown/MediaUrlResolverTest.php`
+
+- [ ] **Step 1: Write the failing test**
+
+Create `src/tests/Unit/Markdown/MediaUrlResolverTest.php`:
+
+```php
+<?php
+
+namespace Tests\Unit\Markdown;
+
+use App\Markdown\MediaUrlResolver;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Tests\TestCase;
+
+class MediaUrlResolverTest extends TestCase
+{
+    private MediaUrlResolver $resolver;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->resolver = new MediaUrlResolver();
+    }
+
+    #[DataProvider('nonMediaUrls')]
+    public function test_returns_null_for_non_media_urls(string $url): void
+    {
+        $this->assertNull($this->resolver->resolve($url));
+    }
+
+    public static function nonMediaUrls(): array
+    {
+        return [
+            'normal image' => ['/photo.jpg'],
+            'svg' => ['/icon.svg'],
+            'png' => ['/avatar.png'],
+            'no extension' => ['/foo'],
+            'empty string' => [''],
+            'javascript scheme' => ['javascript:alert(1)'],
+            'host-only' => ['http://'],
+            'youtu.be lookalike host' => ['https://example.com/youtu.be-fake/abc'],
+        ];
+    }
+}
+```
+
+- [ ] **Step 2: Run test to verify it fails**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: FAIL — `Class "App\Markdown\MediaUrlResolver" not found`.
+
+- [ ] **Step 3: Create the resolver skeleton**
+
+Create `src/app/Markdown/MediaUrlResolver.php`:
+
+```php
+<?php
+
+namespace App\Markdown;
+
+class MediaUrlResolver
+{
+    public function resolve(string $url): ?string
+    {
+        if ($url === '') {
+            return null;
+        }
+        return null;
+    }
+}
+```
+
+- [ ] **Step 4: Run test to verify it passes**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: PASS — all `nonMediaUrls` cases return null.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/app/Markdown/MediaUrlResolver.php src/tests/Unit/Markdown/MediaUrlResolverTest.php
+git commit -m "$(cat <<'EOF'
+Scaffold MediaUrlResolver with null fallback
+
+Initial skeleton returning null for any non-media URL. Subsequent commits
+add detection for video, audio, YouTube, and Vimeo.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+EOF
+)"
+```
+
+---
+
+## Task 2: Detect local video files
+
+**Files:**
+- Modify: `src/app/Markdown/MediaUrlResolver.php`
+- Modify: `src/tests/Unit/Markdown/MediaUrlResolverTest.php`
+
+- [ ] **Step 1: Add failing tests for video detection**
+
+Append to `MediaUrlResolverTest.php` (inside the class):
+
+```php
+    #[DataProvider('videoUrls')]
+    public function test_video_urls_produce_video_tag(string $url): void
+    {
+        $html = $this->resolver->resolve($url);
+        $this->assertNotNull($html);
+        $this->assertStringStartsWith('<video', $html);
+        $this->assertStringContainsString('controls', $html);
+        $this->assertStringContainsString('class="kb-video"', $html);
+    }
+
+    public static function videoUrls(): array
+    {
+        return [
+            'mp4' => ['/demo.mp4'],
+            'webm' => ['/demo.webm'],
+            'ogv' => ['/demo.ogv'],
+            'mov' => ['/demo.mov'],
+            'm4v' => ['/demo.m4v'],
+            'uppercase extension' => ['/demo.MP4'],
+            'with query string' => ['https://example.com/path/demo.mp4?token=abc'],
+            'absolute http' => ['https://example.com/demo.mp4'],
+        ];
+    }
+
+    public function test_video_url_is_html_escaped(): void
+    {
+        $html = $this->resolver->resolve('/path/with"quote.mp4');
+        $this->assertNotNull($html);
+        $this->assertStringNotContainsString('"quote.mp4"', $html);
+        $this->assertStringContainsString('&quot;', $html);
+    }
+```
+
+- [ ] **Step 2: Run tests to verify failure**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: FAIL — `videoUrls` cases assert `$html` not null but resolve() still returns null.
+
+- [ ] **Step 3: Implement video detection**
+
+Replace the body of `MediaUrlResolver.php` with:
+
+```php
+<?php
+
+namespace App\Markdown;
+
+class MediaUrlResolver
+{
+    private const VIDEO_EXT = ['mp4', 'webm', 'ogv', 'mov', 'm4v'];
+
+    public function resolve(string $url): ?string
+    {
+        if ($url === '') {
+            return null;
+        }
+        return $this->detectVideo($url);
+    }
+
+    private function detectVideo(string $url): ?string
+    {
+        if (!in_array($this->getPathExtension($url), self::VIDEO_EXT, true)) {
+            return null;
+        }
+        $safe = htmlspecialchars($url, ENT_QUOTES, 'UTF-8');
+        return "<video src=\"{$safe}\" controls class=\"kb-video\"></video>";
+    }
+
+    private function getPathExtension(string $url): string
+    {
+        $path = parse_url($url, PHP_URL_PATH);
+        if ($path === null || $path === false) {
+            return '';
+        }
+        return strtolower(pathinfo($path, PATHINFO_EXTENSION));
+    }
+}
+```
+
+- [ ] **Step 4: Run tests to verify pass**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: PASS — all video cases plus existing fallback cases.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/app/Markdown/MediaUrlResolver.php src/tests/Unit/Markdown/MediaUrlResolverTest.php
+git commit -m "$(cat <<'EOF'
+Detect local video URLs in MediaUrlResolver
+
+Recognizes mp4/webm/ogv/mov/m4v on URL path (case-insensitive, ignoring
+query strings) and emits <video controls class="kb-video">.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+EOF
+)"
+```
+
+---
+
+## Task 3: Detect local audio files
+
+**Files:**
+- Modify: `src/app/Markdown/MediaUrlResolver.php`
+- Modify: `src/tests/Unit/Markdown/MediaUrlResolverTest.php`
+
+- [ ] **Step 1: Add failing tests for audio detection**
+
+Append to `MediaUrlResolverTest.php`:
+
+```php
+    #[DataProvider('audioUrls')]
+    public function test_audio_urls_produce_audio_tag(string $url): void
+    {
+        $html = $this->resolver->resolve($url);
+        $this->assertNotNull($html);
+        $this->assertStringStartsWith('<audio', $html);
+        $this->assertStringContainsString('controls', $html);
+        $this->assertStringContainsString('class="kb-audio"', $html);
+    }
+
+    public static function audioUrls(): array
+    {
+        return [
+            'mp3' => ['/clip.mp3'],
+            'wav' => ['/clip.wav'],
+            'ogg' => ['/clip.ogg'],
+            'm4a' => ['/clip.m4a'],
+        ];
+    }
+```
+
+- [ ] **Step 2: Run tests to verify failure**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: FAIL — audio URLs return null.
+
+- [ ] **Step 3: Implement audio detection**
+
+In `MediaUrlResolver.php`, add the audio constant and method, and update `resolve()`:
+
+```php
+    private const AUDIO_EXT = ['mp3', 'wav', 'ogg', 'm4a'];
+
+    public function resolve(string $url): ?string
+    {
+        if ($url === '') {
+            return null;
+        }
+        return $this->detectVideo($url)
+            ?? $this->detectAudio($url);
+    }
+
+    private function detectAudio(string $url): ?string
+    {
+        if (!in_array($this->getPathExtension($url), self::AUDIO_EXT, true)) {
+            return null;
+        }
+        $safe = htmlspecialchars($url, ENT_QUOTES, 'UTF-8');
+        return "<audio src=\"{$safe}\" controls class=\"kb-audio\"></audio>";
+    }
+```
+
+- [ ] **Step 4: Run tests to verify pass**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: PASS.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/app/Markdown/MediaUrlResolver.php src/tests/Unit/Markdown/MediaUrlResolverTest.php
+git commit -m "$(cat <<'EOF'
+Detect local audio URLs in MediaUrlResolver
+
+Recognizes mp3/wav/ogg/m4a and emits <audio controls class="kb-audio">.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+EOF
+)"
+```
+
+---
+
+## Task 4: Detect YouTube URLs (no timestamps yet)
+
+**Files:**
+- Modify: `src/app/Markdown/MediaUrlResolver.php`
+- Modify: `src/tests/Unit/Markdown/MediaUrlResolverTest.php`
+
+- [ ] **Step 1: Add failing tests for YouTube URLs**
+
+Append to `MediaUrlResolverTest.php`:
+
+```php
+    #[DataProvider('youtubeUrls')]
+    public function test_youtube_urls_produce_iframe(string $url): void
+    {
+        $html = $this->resolver->resolve($url);
+        $this->assertNotNull($html);
+        $this->assertStringStartsWith('<iframe', $html);
+        $this->assertStringContainsString('youtube-nocookie.com/embed/dQw4w9WgXcQ', $html);
+        $this->assertStringContainsString('class="kb-embed kb-embed-youtube"', $html);
+        $this->assertStringContainsString('loading="lazy"', $html);
+        $this->assertStringContainsString('allowfullscreen', $html);
+    }
+
+    public static function youtubeUrls(): array
+    {
+        return [
+            'short youtu.be' => ['https://youtu.be/dQw4w9WgXcQ'],
+            'watch v=' => ['https://www.youtube.com/watch?v=dQw4w9WgXcQ'],
+            'shorts' => ['https://www.youtube.com/shorts/dQw4w9WgXcQ'],
+            'embed' => ['https://www.youtube.com/embed/dQw4w9WgXcQ'],
+            'mobile' => ['https://m.youtube.com/watch?v=dQw4w9WgXcQ'],
+            'no www watch' => ['https://youtube.com/watch?v=dQw4w9WgXcQ'],
+        ];
+    }
+
+    #[DataProvider('invalidYoutubeUrls')]
+    public function test_invalid_youtube_urls_return_null(string $url): void
+    {
+        $this->assertNull($this->resolver->resolve($url));
+    }
+
+    public static function invalidYoutubeUrls(): array
+    {
+        return [
+            'too short id' => ['https://youtu.be/short'],
+            'host mismatch' => ['https://example.com/watch?v=dQw4w9WgXcQ'],
+            'XSS attempt in id' => ['https://youtu.be/abc"><script>'],
+        ];
+    }
+```
+
+- [ ] **Step 2: Run tests to verify failure**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: FAIL — YouTube URLs return null.
+
+- [ ] **Step 3: Implement YouTube detection (no timestamps)**
+
+In `MediaUrlResolver.php`, update `resolve()` and add YouTube methods:
+
+```php
+    public function resolve(string $url): ?string
+    {
+        if ($url === '') {
+            return null;
+        }
+        return $this->detectVideo($url)
+            ?? $this->detectAudio($url)
+            ?? $this->detectYouTube($url);
+    }
+
+    private function detectYouTube(string $url): ?string
+    {
+        $patterns = [
+            '#^https?://youtu\.be/([A-Za-z0-9_-]{11})(?:[/?#]|$)#',
+            '#^https?://(?:www\.|m\.)?youtube\.com/watch\?(?:[^#]*&)?v=([A-Za-z0-9_-]{11})(?:[&#]|$)#',
+            '#^https?://(?:www\.|m\.)?youtube\.com/shorts/([A-Za-z0-9_-]{11})(?:[/?#]|$)#',
+            '#^https?://(?:www\.|m\.)?youtube\.com/embed/([A-Za-z0-9_-]{11})(?:[/?#]|$)#',
+        ];
+        $videoId = null;
+        foreach ($patterns as $p) {
+            if (preg_match($p, $url, $m)) {
+                $videoId = $m[1];
+                break;
+            }
+        }
+        if ($videoId === null) {
+            return null;
+        }
+        $src = "https://www.youtube-nocookie.com/embed/{$videoId}";
+        return $this->iframeHtml($src, 'youtube');
+    }
+
+    private function iframeHtml(string $src, string $provider): string
+    {
+        $safe = htmlspecialchars($src, ENT_QUOTES, 'UTF-8');
+        return '<iframe src="' . $safe . '" '
+            . 'width="560" height="315" '
+            . 'loading="lazy" '
+            . 'referrerpolicy="strict-origin-when-cross-origin" '
+            . 'allow="autoplay; encrypted-media; picture-in-picture" '
+            . 'allowfullscreen frameborder="0" '
+            . 'class="kb-embed kb-embed-' . $provider . '"></iframe>';
+    }
+```
+
+- [ ] **Step 4: Run tests to verify pass**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: PASS.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/app/Markdown/MediaUrlResolver.php src/tests/Unit/Markdown/MediaUrlResolverTest.php
+git commit -m "$(cat <<'EOF'
+Detect YouTube URLs and emit privacy-enhanced iframe
+
+Recognizes youtu.be, watch?v=, shorts, embed, and mobile variants.
+Emits an iframe pointing to youtube-nocookie.com with lazy loading,
+strict-origin referrer policy, and allowfullscreen.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+EOF
+)"
+```
+
+---
+
+## Task 5: YouTube timestamp normalization
+
+**Files:**
+- Modify: `src/app/Markdown/MediaUrlResolver.php`
+- Modify: `src/tests/Unit/Markdown/MediaUrlResolverTest.php`
+
+- [ ] **Step 1: Add failing tests for YouTube timestamps**
+
+Append to `MediaUrlResolverTest.php`:
+
+```php
+    #[DataProvider('youtubeTimestampUrls')]
+    public function test_youtube_timestamp_normalizes_to_start(string $url, int $expectedStart): void
+    {
+        $html = $this->resolver->resolve($url);
+        $this->assertNotNull($html);
+        $this->assertStringContainsString("?start={$expectedStart}", $html);
+    }
+
+    public static function youtubeTimestampUrls(): array
+    {
+        return [
+            't=30s' => ['https://youtu.be/dQw4w9WgXcQ?t=30s', 30],
+            't=30 (no suffix)' => ['https://www.youtube.com/watch?v=dQw4w9WgXcQ&t=30', 30],
+            't=1m20s' => ['https://youtu.be/dQw4w9WgXcQ?t=1m20s', 80],
+            't=1h2m3s' => ['https://youtu.be/dQw4w9WgXcQ?t=1h2m3s', 3723],
+            'start=45' => ['https://www.youtube.com/watch?v=dQw4w9WgXcQ&start=45', 45],
+        ];
+    }
+```
+
+- [ ] **Step 2: Run tests to verify failure**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: FAIL — `?start=N` not present in iframe src.
+
+- [ ] **Step 3: Implement timestamp extraction**
+
+In `MediaUrlResolver.php`, modify `detectYouTube()` and add helper methods:
+
+```php
+    private function detectYouTube(string $url): ?string
+    {
+        $patterns = [
+            '#^https?://youtu\.be/([A-Za-z0-9_-]{11})(?:[/?#]|$)#',
+            '#^https?://(?:www\.|m\.)?youtube\.com/watch\?(?:[^#]*&)?v=([A-Za-z0-9_-]{11})(?:[&#]|$)#',
+            '#^https?://(?:www\.|m\.)?youtube\.com/shorts/([A-Za-z0-9_-]{11})(?:[/?#]|$)#',
+            '#^https?://(?:www\.|m\.)?youtube\.com/embed/([A-Za-z0-9_-]{11})(?:[/?#]|$)#',
+        ];
+        $videoId = null;
+        foreach ($patterns as $p) {
+            if (preg_match($p, $url, $m)) {
+                $videoId = $m[1];
+                break;
+            }
+        }
+        if ($videoId === null) {
+            return null;
+        }
+        $src = "https://www.youtube-nocookie.com/embed/{$videoId}";
+        $start = $this->extractYouTubeStart($url);
+        if ($start !== null) {
+            $src .= "?start={$start}";
+        }
+        return $this->iframeHtml($src, 'youtube');
+    }
+
+    private function extractYouTubeStart(string $url): ?int
+    {
+        if (preg_match('/[?&]t=([^&#]+)/', $url, $m)) {
+            $seconds = $this->parseTimestamp($m[1]);
+            if ($seconds !== null) {
+                return $seconds;
+            }
+        }
+        if (preg_match('/[?&]start=(\d+)/', $url, $m)) {
+            return (int) $m[1];
+        }
+        return null;
+    }
+
+    private function parseTimestamp(string $t): ?int
+    {
+        if (ctype_digit($t)) {
+            return (int) $t;
+        }
+        $total = 0;
+        $matched = false;
+        if (preg_match('/(\d+)h/', $t, $m)) {
+            $total += (int) $m[1] * 3600;
+            $matched = true;
+        }
+        if (preg_match('/(\d+)m/', $t, $m)) {
+            $total += (int) $m[1] * 60;
+            $matched = true;
+        }
+        if (preg_match('/(\d+)s/', $t, $m)) {
+            $total += (int) $m[1];
+            $matched = true;
+        }
+        return $matched ? $total : null;
+    }
+```
+
+- [ ] **Step 4: Run tests to verify pass**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: PASS.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/app/Markdown/MediaUrlResolver.php src/tests/Unit/Markdown/MediaUrlResolverTest.php
+git commit -m "$(cat <<'EOF'
+Normalize YouTube timestamp parameters to ?start=N
+
+Accepts ?t=30s, ?t=30, ?t=1m20s, ?t=1h2m3s, and ?start=N. Converts to
+seconds and emits as ?start=N on the embed URL. ?t= takes priority over
+?start= when both are present.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+EOF
+)"
+```
+
+---
+
+## Task 6: Detect Vimeo URLs
+
+**Files:**
+- Modify: `src/app/Markdown/MediaUrlResolver.php`
+- Modify: `src/tests/Unit/Markdown/MediaUrlResolverTest.php`
+
+- [ ] **Step 1: Add failing tests for Vimeo URLs**
+
+Append to `MediaUrlResolverTest.php`:
+
+```php
+    #[DataProvider('vimeoUrls')]
+    public function test_vimeo_urls_produce_iframe(string $url): void
+    {
+        $html = $this->resolver->resolve($url);
+        $this->assertNotNull($html);
+        $this->assertStringStartsWith('<iframe', $html);
+        $this->assertStringContainsString('player.vimeo.com/video/123456789', $html);
+        $this->assertStringContainsString('dnt=1', $html);
+        $this->assertStringContainsString('class="kb-embed kb-embed-vimeo"', $html);
+    }
+
+    public static function vimeoUrls(): array
+    {
+        return [
+            'vimeo.com' => ['https://vimeo.com/123456789'],
+            'www.vimeo.com' => ['https://www.vimeo.com/123456789'],
+            'player.vimeo.com' => ['https://player.vimeo.com/video/123456789'],
+        ];
+    }
+
+    #[DataProvider('vimeoTimestampUrls')]
+    public function test_vimeo_timestamp_preserved_as_hash(string $url): void
+    {
+        $html = $this->resolver->resolve($url);
+        $this->assertNotNull($html);
+        $this->assertStringContainsString('#t=30s', $html);
+    }
+
+    public static function vimeoTimestampUrls(): array
+    {
+        return [
+            'hash form' => ['https://vimeo.com/123456789#t=30s'],
+            'query form' => ['https://vimeo.com/123456789?t=30s'],
+        ];
+    }
+
+    public function test_vimeo_invalid_id_returns_null(): void
+    {
+        $this->assertNull($this->resolver->resolve('https://vimeo.com/notanumber'));
+    }
+```
+
+- [ ] **Step 2: Run tests to verify failure**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: FAIL — Vimeo URLs return null.
+
+- [ ] **Step 3: Implement Vimeo detection**
+
+In `MediaUrlResolver.php`, update `resolve()` and add Vimeo methods:
+
+```php
+    public function resolve(string $url): ?string
+    {
+        if ($url === '') {
+            return null;
+        }
+        return $this->detectVideo($url)
+            ?? $this->detectAudio($url)
+            ?? $this->detectYouTube($url)
+            ?? $this->detectVimeo($url);
+    }
+
+    private function detectVimeo(string $url): ?string
+    {
+        if (!preg_match('#^https?://(?:www\.|player\.)?vimeo\.com/(?:video/)?(\d+)#', $url, $m)) {
+            return null;
+        }
+        $videoId = $m[1];
+        $src = "https://player.vimeo.com/video/{$videoId}?dnt=1";
+        $hash = $this->extractVimeoHash($url);
+        if ($hash !== null) {
+            $src .= '#' . $hash;
+        }
+        return $this->iframeHtml($src, 'vimeo');
+    }
+
+    private function extractVimeoHash(string $url): ?string
+    {
+        if (preg_match('/#(t=[^&]+)/', $url, $m)) {
+            return $m[1];
+        }
+        if (preg_match('/[?&](t=[^&#]+)/', $url, $m)) {
+            return $m[1];
+        }
+        return null;
+    }
+```
+
+- [ ] **Step 4: Run tests to verify pass**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: PASS.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/app/Markdown/MediaUrlResolver.php src/tests/Unit/Markdown/MediaUrlResolverTest.php
+git commit -m "$(cat <<'EOF'
+Detect Vimeo URLs and emit iframe with dnt=1
+
+Recognizes vimeo.com/{id} and player.vimeo.com/video/{id}. Preserves
+timestamps from #t=30s and ?t=30s as #t=30s on the embed URL (Vimeo
+convention).
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+EOF
+)"
+```
+
+---
+
+## Task 7: Wire up extension and listener; integrate with `Document::renderMarkdown()`
+
+**Files:**
+- Create: `src/app/Markdown/MediaEmbedListener.php`
+- Create: `src/app/Markdown/MediaEmbedExtension.php`
+- Create: `src/tests/Unit/Markdown/MediaEmbedExtensionTest.php`
+- Modify: `src/app/Models/Document.php`
+
+- [ ] **Step 1: Write the failing integration test**
+
+Create `src/tests/Unit/Markdown/MediaEmbedExtensionTest.php`:
+
+```php
+<?php
+
+namespace Tests\Unit\Markdown;
+
+use App\Models\Document;
+use Tests\TestCase;
+
+class MediaEmbedExtensionTest extends TestCase
+{
+    public function test_normal_image_still_renders_as_img(): void
+    {
+        $html = Document::renderMarkdown('![alt](/photo.png)');
+        $this->assertStringContainsString('<img', $html);
+        $this->assertStringContainsString('src="/photo.png"', $html);
+    }
+
+    public function test_video_url_renders_as_video_tag(): void
+    {
+        $html = Document::renderMarkdown('![](/demo.mp4)');
+        $this->assertStringContainsString('<video', $html);
+        $this->assertStringContainsString('src="/demo.mp4"', $html);
+        $this->assertStringNotContainsString('<img', $html);
+    }
+
+    public function test_youtube_url_renders_as_iframe(): void
+    {
+        $html = Document::renderMarkdown('![](https://youtu.be/dQw4w9WgXcQ)');
+        $this->assertStringContainsString('<iframe', $html);
+        $this->assertStringContainsString('youtube-nocookie.com', $html);
+    }
+
+    public function test_vimeo_url_renders_as_iframe(): void
+    {
+        $html = Document::renderMarkdown('![](https://vimeo.com/123456789)');
+        $this->assertStringContainsString('<iframe', $html);
+        $this->assertStringContainsString('player.vimeo.com', $html);
+    }
+}
+```
+
+- [ ] **Step 2: Run tests to verify failure**
+
+```bash
+docker compose exec php php artisan test --filter=MediaEmbedExtensionTest
+```
+
+Expected: FAIL — `![](/demo.mp4)` still renders as `<img>` because the extension is not registered.
+
+- [ ] **Step 3: Create the listener**
+
+Create `src/app/Markdown/MediaEmbedListener.php`:
+
+```php
+<?php
+
+namespace App\Markdown;
+
+use League\CommonMark\Event\DocumentParsedEvent;
+use League\CommonMark\Extension\CommonMark\Node\Inline\Image;
+use League\CommonMark\Node\Inline\HtmlInline;
+
+class MediaEmbedListener
+{
+    public function __construct(private readonly MediaUrlResolver $resolver)
+    {
+    }
+
+    public function handle(DocumentParsedEvent $event): void
+    {
+        $imagesToReplace = [];
+        foreach ($event->getDocument()->iterator() as $node) {
+            if ($node instanceof Image) {
+                $imagesToReplace[] = $node;
+            }
+        }
+
+        foreach ($imagesToReplace as $image) {
+            $html = $this->resolver->resolve($image->getUrl());
+            if ($html !== null) {
+                $image->replaceWith(new HtmlInline($html));
+            }
+        }
+    }
+}
+```
+
+- [ ] **Step 4: Create the extension**
+
+Create `src/app/Markdown/MediaEmbedExtension.php`:
+
+```php
+<?php
+
+namespace App\Markdown;
+
+use League\CommonMark\Environment\EnvironmentBuilderInterface;
+use League\CommonMark\Event\DocumentParsedEvent;
+use League\CommonMark\Extension\ExtensionInterface;
+
+class MediaEmbedExtension implements ExtensionInterface
+{
+    public function register(EnvironmentBuilderInterface $environment): void
+    {
+        $listener = new MediaEmbedListener(new MediaUrlResolver());
+        $environment->addEventListener(DocumentParsedEvent::class, [$listener, 'handle']);
+    }
+}
+```
+
+- [ ] **Step 5: Register the extension in `Document::renderMarkdown`**
+
+Edit `src/app/Models/Document.php`. Locate `renderMarkdown()` (around line 122) and add the extension registration:
+
+```php
+    public static function renderMarkdown(string $markdown): string
+    {
+        $converter = new CommonMarkConverter([
+            'html_input' => 'strip',
+            'allow_unsafe_links' => false,
+        ]);
+
+        $converter->getEnvironment()->addExtension(new GithubFlavoredMarkdownExtension());
+        $converter->getEnvironment()->addExtension(new \App\Markdown\MediaEmbedExtension());
+
+        return $converter->convert($markdown)->getContent();
+    }
+```
+
+- [ ] **Step 6: Run tests to verify pass**
+
+```bash
+docker compose exec php php artisan test --filter=MediaEmbedExtensionTest
+```
+
+Expected: PASS — all four cases.
+
+- [ ] **Step 7: Run the resolver tests to confirm no regression**
+
+```bash
+docker compose exec php php artisan test --filter=MediaUrlResolverTest
+```
+
+Expected: PASS.
+
+- [ ] **Step 8: Commit**
+
+```bash
+git add src/app/Markdown/MediaEmbedListener.php src/app/Markdown/MediaEmbedExtension.php src/app/Models/Document.php src/tests/Unit/Markdown/MediaEmbedExtensionTest.php
+git commit -m "$(cat <<'EOF'
+Wire MediaEmbedExtension into Document::renderMarkdown
+
+The extension registers a DocumentParsedEvent listener that walks the
+AST, finds Image nodes whose URLs match media patterns (via
+MediaUrlResolver), and replaces them with HtmlInline nodes containing
+the appropriate <video>/<audio>/<iframe> markup.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+EOF
+)"
+```
+
+---
+
+## Task 8: Integration tests for mixed content and edge cases
+
+**Files:**
+- Modify: `src/tests/Unit/Markdown/MediaEmbedExtensionTest.php`
+
+- [ ] **Step 1: Add tests for mixed content scenarios**
+
+Append to `MediaEmbedExtensionTest.php`:
+
+```php
+    public function test_image_and_video_coexist_in_same_document(): void
+    {
+        $md = "![photo](/photo.png)\n\n![](/demo.mp4)";
+        $html = Document::renderMarkdown($md);
+        $this->assertStringContainsString('<img', $html);
+        $this->assertStringContainsString('<video', $html);
+    }
+
+    public function test_multiple_media_in_same_paragraph(): void
+    {
+        $html = Document::renderMarkdown('![](/a.mp4) and ![](/b.mp4)');
+        $this->assertSame(2, substr_count($html, '<video'));
+    }
+
+    public function test_video_inside_list_item(): void
+    {
+        $html = Document::renderMarkdown("- ![](/demo.mp4)");
+        $this->assertStringContainsString('<li>', $html);
+        $this->assertStringContainsString('<video', $html);
+    }
+
+    public function test_wiki_link_unaffected_alongside_media(): void
+    {
+        $html = Document::renderMarkdown("![](/demo.mp4)\n\n[[Other Doc]]");
+        $this->assertStringContainsString('<video', $html);
+        $this->assertStringContainsString('[[Other Doc]]', $html);
+    }
+
+    public function test_youtube_with_timestamp_in_document(): void
+    {
+        $html = Document::renderMarkdown('![](https://www.youtube.com/watch?v=dQw4w9WgXcQ&t=30s)');
+        $this->assertStringContainsString('?start=30', $html);
+    }
+
+    public function test_audio_url_renders_as_audio_tag(): void
+    {
+        $html = Document::renderMarkdown('![](/clip.mp3)');
+        $this->assertStringContainsString('<audio', $html);
+        $this->assertStringContainsString('src="/clip.mp3"', $html);
+    }
+```
+
+Note on the wiki link test: `Document::renderMarkdown` produces raw HTML; `[[Other Doc]]` is converted to anchors only by `Document::processLinks()`, which is called separately. The test asserts that the raw `[[...]]` text passes through `renderMarkdown` unmodified — that is the contract being verified.
+
+- [ ] **Step 2: Run tests**
+
+```bash
+docker compose exec php php artisan test --filter=MediaEmbedExtensionTest
+```
+
+Expected: PASS — all six new cases plus the four from Task 7.
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add src/tests/Unit/Markdown/MediaEmbedExtensionTest.php
+git commit -m "$(cat <<'EOF'
+Add integration tests for mixed media in Markdown rendering
+
+Covers image+video coexistence, multiple videos in one paragraph,
+videos inside list items, wiki link non-interference, YouTube
+timestamps end-to-end, and audio rendering through renderMarkdown.
+
+Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+EOF
+)"
+```
+
+---
+
+## Task 9: Full test suite verification
+
+**Files:**
+- None (verification only)
+
+- [ ] **Step 1: Run full test suite**
+
+```bash
+docker compose exec php composer test
+```
+
+Expected: All tests pass. The new tests are additive and should not affect existing Profile/Auth/etc. tests.
+
+- [ ] **Step 2: If anything failed, investigate and fix**
+
+If a previously-passing test now fails, the most likely cause is a regression in `Document::renderMarkdown()` from the extension change. Investigate with:
+
+```bash
+docker compose exec php php artisan test --filter=<failing-test-name> -v
+```
+
+Common potential issues:
+- An existing seeded `Document` containing Markdown that newly matches a media pattern (e.g. `![](/foo.mov)`) renders differently. This is the intended new behavior; update the test fixture if it asserts the old `<img>` form.
+- Namespace import collision in `Document.php`. Ensure `use App\Markdown\MediaEmbedExtension;` is added at the top of the file (or use the fully-qualified name as shown in Task 7).
+
+- [ ] **Step 3: If clean, no commit needed**
+
+If all tests pass, no further commit is required. The work is complete.
+
+If a fix was needed, commit it:
+
+```bash
+git add <changed-files>
+git commit -m "Fix regression introduced by MediaEmbedExtension"
+```
+
+---
+
+## Out of Scope (future tasks, not part of this plan)
+
+- `docs:rerender` Artisan command to re-render existing `Document::rendered_html` rows after deployment
+- CSS rules for `.kb-video`, `.kb-audio`, `.kb-embed-*` (likely added when designing public-facing layout)
+- Updating `CLAUDE.md` to describe the new media-embed convention
+- VTT subtitles / `<track>` elements
+- Additional providers (Twitch, SoundCloud, Spotify)