fix(og): batch spawning to prevent OOM during watcher rebuilds

Full OG regeneration (2,350 images) OOM-kills when the Eleventy watcher
is running (~1.8 GB RSS), leaving only ~1.2 GB headroom in the 3 GB
container. WASM native memory from Satori/Resvg grows beyond what GC
can reclaim within a single process.

Solution: spawn og-cli in batches of 100 images. Each invocation exits
after its batch, fully releasing all WASM native memory. Exit code 2
signals "more work remains" and the spawner re-loops. Peak memory per
batch stays under ~500 MB regardless of total image count.

Also seed newManifest from existing manifest so unscanned entries survive
batch writes.

Confab-Link: http://localhost:8080/sessions/edb1b7b0-da66-4486-bd9c-d1cfa7553b88

eleventy.config.js

@@ -1114,25 +1114,46 @@ export default function (eleventyConfig) {
     return digests;
   });
 
-  // Generate OpenGraph images for posts without photos
-  // Runs on every build (including watcher rebuilds) — manifest caching makes it fast
-  // for incremental: only new posts without an OG image get generated (~200ms each)
+  // Generate OpenGraph images for posts without photos.
+  // Uses batch spawning: each invocation generates up to BATCH_SIZE images then exits,
+  // fully releasing WASM native memory (Satori Yoga + Resvg Rust) between batches.
+  // Exit code 2 = batch complete, more work remains → re-spawn.
+  // Manifest caching makes incremental builds fast (only new posts get generated).
   eleventyConfig.on("eleventy.before", () => {
     const contentDir = resolve(__dirname, "content");
     const cacheDir = resolve(__dirname, ".cache");
     const siteName = process.env.SITE_NAME || "My IndieWeb Blog";
+    const BATCH_SIZE = 100;
+    let totalGenerated = 0;
+    let batch = 0;
     try {
-      execFileSync(process.execPath, [
-        "--max-old-space-size=512",
-        "--expose-gc",
-        resolve(__dirname, "lib", "og-cli.js"),
-        contentDir,
-        cacheDir,
-        siteName,
-      ], {
-        stdio: "inherit",
-        env: { ...process.env, NODE_OPTIONS: "" },
-      });
+      // eslint-disable-next-line no-constant-condition
+      while (true) {
+        batch++;
+        try {
+          execFileSync(process.execPath, [
+            "--max-old-space-size=512",
+            "--expose-gc",
+            resolve(__dirname, "lib", "og-cli.js"),
+            contentDir,
+            cacheDir,
+            siteName,
+            String(BATCH_SIZE),
+          ], {
+            stdio: "inherit",
+            env: { ...process.env, NODE_OPTIONS: "" },
+          });
+          // Exit code 0 = all done
+          break;
+        } catch (err) {
+          if (err.status === 2) {
+            // Exit code 2 = batch complete, more images remain
+            totalGenerated += BATCH_SIZE;
+            continue;
+          }
+          throw err;
+        }
+      }
 
       // Sync new OG images to output directory.
       // During incremental builds, .cache/og is in watchIgnores so Eleventy's

lib/og-cli.js

@@ -4,16 +4,27 @@
  * CLI entry point for OG image generation.
  * Runs as a separate process to isolate memory from Eleventy.
  *
- * Usage: node lib/og-cli.js <contentDir> <cacheDir> <siteName>
+ * Usage: node lib/og-cli.js <contentDir> <cacheDir> <siteName> [batchSize]
+ *
+ * batchSize: Max images to generate per invocation (0 = unlimited).
+ *            When set, exits after generating that many images so the caller
+ *            can re-spawn (releasing all WASM native memory between batches).
+ *            Exit code 2 = batch complete, more work remains.
  */
 
 import { generateOgImages } from "./og.js";
 
-const [contentDir, cacheDir, siteName] = process.argv.slice(2);
+const [contentDir, cacheDir, siteName, batchSizeStr] = process.argv.slice(2);
 
 if (!contentDir || !cacheDir || !siteName) {
-  console.error("[og] Usage: node og-cli.js <contentDir> <cacheDir> <siteName>");
+  console.error("[og] Usage: node og-cli.js <contentDir> <cacheDir> <siteName> [batchSize]");
   process.exit(1);
 }
 
-await generateOgImages(contentDir, cacheDir, siteName);
+const batchSize = parseInt(batchSizeStr, 10) || 0;
+const result = await generateOgImages(contentDir, cacheDir, siteName, batchSize);
+
+// Exit code 2 signals "batch complete, more images remain"
+if (result?.hasMore) {
+  process.exit(2);
+}

lib/og.js

@@ -278,8 +278,10 @@ function scanContentFiles(contentDir) {
  * @param {string} contentDir - Path to content/ directory
  * @param {string} cacheDir - Path to .cache/ directory
  * @param {string} siteName - Site name for the card
+ * @param {number} batchSize - Max images to generate (0 = unlimited)
+ * @returns {{ hasMore: boolean }} Whether more images need generation
  */
-export async function generateOgImages(contentDir, cacheDir, siteName) {
+export async function generateOgImages(contentDir, cacheDir, siteName, batchSize = 0) {
   const ogDir = join(cacheDir, "og");
   mkdirSync(ogDir, { recursive: true });
 
@@ -296,7 +298,8 @@ export async function generateOgImages(contentDir, cacheDir, siteName) {
 
   let generated = 0;
   let skipped = 0;
-  const newManifest = {};
+  // Seed with existing manifest so unscanned entries survive batch writes
+  const newManifest = { ...manifest };
   const SAVE_INTERVAL = 10;
   // GC every 5 images to keep WASM native memory bounded.
   // Satori (Yoga WASM) + Resvg (Rust WASM) allocate ~50-100 MB native memory
@@ -352,14 +355,25 @@ export async function generateOgImages(contentDir, cacheDir, siteName) {
       const rss = process.memoryUsage().rss;
       if (rss > peakRss) peakRss = rss;
     }
+
+    // Batch limit: stop after N images so the caller can re-spawn
+    // (fully releasing WASM native memory between batches)
+    if (batchSize > 0 && generated >= batchSize) {
+      break;
+    }
   }
 
+  const hasMore = batchSize > 0 && generated >= batchSize;
+
   if (hasGC) global.gc();
   writeFileSync(manifestPath, JSON.stringify(newManifest, null, 2));
   const mem = process.memoryUsage();
   if (mem.rss > peakRss) peakRss = mem.rss;
   console.log(
     `[og] Generated ${generated} images, skipped ${skipped} (cached or have photos)` +
+    (hasMore ? ` [batch, more remain]` : ``) +
     ` | RSS: ${(mem.rss / 1024 / 1024).toFixed(0)} MB, peak: ${(peakRss / 1024 / 1024).toFixed(0)} MB, heap: ${(mem.heapUsed / 1024 / 1024).toFixed(0)} MB`,
   );
+
+  return { hasMore };
 }