fix(engine): scale Chrome memory budget and frame cache to available RAM

On low-memory systems (<4GB free), Chrome's --force-gpu-mem-available-mb=4096
causes the renderer to allocate more GPU texture memory than the system can
provide, leading to OOM crashes during frame capture ("Target closed").

Changes:
- Scale --force-gpu-mem-available-mb to match available system RAM
  (512MB when <2GB free, 1024MB when <4GB, 4096MB otherwise)
- Add --js-flags=--max-old-space-size=N on low-memory systems to cap
  Chrome's V8 heap (256MB when <2GB free, 512MB when <4GB)
- Scale frame data URI cache defaults: 32 entries/128MB when <2GB free,
  64 entries/256MB when <4GB, unchanged otherwise

Closes #1072

packages/engine/src/config.ts

@@ -208,6 +208,29 @@ export const DEFAULT_CONFIG: EngineConfig = {
   debug: false,
 };
 
+function getSystemFreeMb(): number {
+  try {
+    const { freemem } = require("os") as typeof import("os");
+    return Math.floor(freemem() / (1024 * 1024));
+  } catch {
+    return 8192;
+  }
+}
+
+function memoryAdaptiveCacheLimit(): number {
+  const free = getSystemFreeMb();
+  if (free < 2048) return 32;
+  if (free < 4096) return 64;
+  return DEFAULT_CONFIG.frameDataUriCacheLimit;
+}
+
+function memoryAdaptiveCacheBytesMb(): number {
+  const free = getSystemFreeMb();
+  if (free < 2048) return 128;
+  if (free < 4096) return 256;
+  return DEFAULT_CONFIG.frameDataUriCacheBytesLimitMb;
+}
+
 /**
  * Resolve configuration by merging: defaults ← env vars ← explicit overrides.
  * Env vars provide backward compatibility during migration; explicit config
@@ -298,14 +321,11 @@ export function resolveConfig(overrides?: Partial<EngineConfig>): EngineConfig {
     audioGain: envNum("PRODUCER_AUDIO_GAIN", DEFAULT_CONFIG.audioGain),
     frameDataUriCacheLimit: Math.max(
       32,
-      envNum("PRODUCER_FRAME_DATA_URI_CACHE_LIMIT", DEFAULT_CONFIG.frameDataUriCacheLimit),
+      envNum("PRODUCER_FRAME_DATA_URI_CACHE_LIMIT", memoryAdaptiveCacheLimit()),
     ),
     frameDataUriCacheBytesLimitMb: Math.max(
       64,
-      envNum(
-        "PRODUCER_FRAME_DATA_URI_CACHE_BYTES_MB",
-        DEFAULT_CONFIG.frameDataUriCacheBytesLimitMb,
-      ),
+      envNum("PRODUCER_FRAME_DATA_URI_CACHE_BYTES_MB", memoryAdaptiveCacheBytesMb()),
     ),
 
     playerReadyTimeout: envNum(

packages/engine/src/services/browserManager.ts

@@ -8,7 +8,7 @@
 import type { Browser, PuppeteerNode } from "puppeteer-core";
 import { existsSync, readdirSync } from "fs";
 import { join } from "path";
-import { homedir } from "os";
+import { freemem, homedir } from "os";
 import { DEFAULT_CONFIG, type EngineConfig } from "../config.js";
 
 let _puppeteer: PuppeteerNode | undefined;
@@ -476,6 +476,24 @@ export function _setPuppeteerForTests(mock: PuppeteerNode | undefined): void {
   _puppeteer = mock;
 }
 
+function getFreeMb(): number {
+  return Math.floor(freemem() / (1024 * 1024));
+}
+
+function getGpuMemBudgetMb(): number {
+  const free = getFreeMb();
+  if (free < 2048) return 512;
+  if (free < 4096) return 1024;
+  return 4096;
+}
+
+function getLowMemoryFlags(): string[] {
+  const free = getFreeMb();
+  if (free >= 4096) return [];
+  const heapMb = free < 2048 ? 256 : 512;
+  return [`--js-flags=--max-old-space-size=${heapMb}`];
+}
+
 export interface BuildChromeArgsOptions {
   width: number;
   height: number;
@@ -530,9 +548,10 @@ export function buildChromeArgs(
     "--disable-print-preview",
     "--no-pings",
     "--no-zygote",
-    // Memory
-    "--force-gpu-mem-available-mb=4096",
+    // Memory — scale GPU budget to available system RAM
+    `--force-gpu-mem-available-mb=${getGpuMemBudgetMb()}`,
     "--disk-cache-size=268435456",
+    ...getLowMemoryFlags(),
     // Disable features that add overhead
     "--disable-features=AudioServiceOutOfProcess,IsolateOrigins,site-per-process,Translate,BackForwardCache,IntensiveWakeUpThrottling",
   ];