Bound renderer memory use and configure worker heap ceiling

renderer/render.mjs

@@ -19,6 +19,25 @@ export async function renderSnapshot(
   const server = createServer(async (req, res) => {
     try {
       const url = new URL(req.url, "http://localhost");
+      if (url.pathname === "/terrain.json") {
+        res.setHeader("Content-Type", "application/json");
+        // Avoid Playwright's recursive protocol serialization of millions of
+        // block records. Keep serialization buffers bounded and honor backpressure.
+        const send = async (chunk) => {
+          if (res.destroyed) throw new Error("Terrain connection closed");
+          await new Promise((resolve, reject) => {
+            res.write(chunk, (error) => error ? reject(error) : resolve());
+          });
+        };
+        const { blocks, ...metadata } = snapshot;
+        await send(JSON.stringify(metadata).slice(0, -1) + ',"blocks":[');
+        for (let i = 0; i < blocks.length; i += 2048) {
+          if (signal?.aborted) throw new Error("Rendering cancelled");
+          await send((i ? "," : "") + JSON.stringify(blocks.slice(i, i + 2048)).slice(1, -1));
+        }
+        res.end("]}");
+        return;
+      }
       let path =
         url.pathname === "/three.js"
           ? "node_modules/three/build/three.module.js"
@@ -44,6 +63,7 @@ export async function renderSnapshot(
       );
       res.end(await readFile(path));
     } catch {
+      if (res.headersSent) { res.destroy(); return; }
       res.writeHead(404);
       res.end();
     }
@@ -59,7 +79,11 @@ export async function renderSnapshot(
     page.on("pageerror", (err) => console.error("Renderer:", err.message));
     await page.goto(`http://127.0.0.1:${server.address().port}`);
     await page.waitForFunction(() => window.rendererReady);
-    const stats = await page.evaluate((s) => window.buildTerrain(s), snapshot);
+    const stats = await page.evaluate(async () => {
+      const response = await fetch("/terrain.json");
+      if (!response.ok) throw new Error("Unable to load terrain snapshot");
+      return window.buildTerrain(await response.json());
+    });
     for (const p of viewpoints) {
       if (signal?.aborted) throw new Error("Rendering cancelled");
       await mkdir(`${output}/${p.id}`, { recursive: true });