perf: persist unfurl cache between deploys via UNFURL_CACHE_DIR

CACHE_DIR in unfurl-shortcode.js and manifest path in eleventy.config.js
now read UNFURL_CACHE_DIR env var (falls back to .cache/unfurl/ locally).
deploy.yml sets UNFURL_CACHE_DIR=/usr/local/git/.cache/unfurl — same
persistent runner volume used by OG_CACHE_DIR and sharp binary cache.

Without this, every deploy re-fetched all 283 interaction URLs from
scratch because .cache/ is gitignored and not preserved between builds.

.github/workflows/deploy.yml

@@ -128,6 +128,7 @@ jobs:
           GITEA_INTERNAL_URL: http://127.0.0.1:3000
           GITEA_ORG: giersig.eu
           OG_CACHE_DIR: /usr/local/git/.cache/og
+          UNFURL_CACHE_DIR: /usr/local/git/.cache/unfurl
 
       - name: Deploy via rsync
         run: |

eleventy.config.js

@@ -1854,7 +1854,9 @@ export default function (eleventyConfig) {
     // prefetchUrl() already caches responses on disk; re-calling it for known URLs
     // is pure overhead. Writing [...urls] (not [...seen, ...newUrls]) intentionally
     // prunes URLs from soft-deleted posts, preventing unbounded manifest growth.
-    const manifestPath = resolve(__dirname, ".cache", "unfurl-manifest.json");
+    const manifestPath = process.env.UNFURL_CACHE_DIR
+      ? resolve(process.env.UNFURL_CACHE_DIR, "manifest.json")
+      : resolve(__dirname, ".cache", "unfurl-manifest.json");
     let seen = new Set();
     try {
       seen = new Set(JSON.parse(readFileSync(manifestPath, "utf-8")));

lib/unfurl-shortcode.js

@@ -3,7 +3,7 @@ import { readFileSync, writeFileSync, mkdirSync, existsSync } from "fs";
 import { resolve } from "path";
 import { createHash } from "crypto";
 
-const CACHE_DIR = resolve(import.meta.dirname, "..", ".cache", "unfurl");
+const CACHE_DIR = process.env.UNFURL_CACHE_DIR || resolve(import.meta.dirname, "..", ".cache", "unfurl");
 const CACHE_DURATION_MS = 7 * 24 * 60 * 60 * 1000; // 1 week
 const FAILURE_CACHE_MS = 7 * 24 * 60 * 60 * 1000; // 1 week — YouTube/bot-blocked sites never succeed, no point retrying daily
 const USER_AGENT = "Mozilla/5.0 (compatible; Indiekit/1.0; +https://getindiekit.com)";