feat: auto-derive youtubeVideoId from URL in reply-context

Adds a `youtubeId` filter that extracts the video ID from any YouTube
URL (youtube.com?v= and youtu.be/ formats). reply-context.njk now
computes youtubeVideoId automatically from the interaction URL fields,
so YouTube embeds work without needing youtubeVideoId in post frontmatter.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

_includes/components/reply-context.njk

@@ -8,6 +8,7 @@
 {% set likedUrl = likeOf or like_of %}
 {% set repostedUrl = repostOf or repost_of %}
 {% set bookmarkedUrl = bookmarkOf or bookmark_of %}
+{% set youtubeVideoId = youtubeVideoId or (repostedUrl | youtubeId) or (likedUrl | youtubeId) or (bookmarkedUrl | youtubeId) or (replyTo | youtubeId) %}
 
 {% if replyTo or likedUrl or repostedUrl or bookmarkedUrl %}
 <aside class="reply-context mb-6" aria-label="Reply context">

eleventy.config.js

@@ -966,6 +966,16 @@ export default function (eleventyConfig) {
     });
   });
 
+  eleventyConfig.addFilter("youtubeId", (url) => {
+    if (!url || typeof url !== "string") return null;
+    try {
+      const u = new URL(url);
+      if (u.hostname === "youtu.be") return u.pathname.slice(1).split("?")[0] || null;
+      if (u.hostname.endsWith("youtube.com")) return u.searchParams.get("v") || null;
+    } catch {}
+    return null;
+  });
+
   eleventyConfig.addFilter("stripTrailingSlash", (url) => {
     if (!url || typeof url !== "string") return url || "";
     return url.endsWith("/") ? url.slice(0, -1) : url;