From cfc0bddb1f0be7bffc07946c8dab4b1039ab1dd3 Mon Sep 17 00:00:00 2001
From: Dejvino <dejvino@gmail.com>
Date: Wed, 28 Oct 2026 15:33:07 +0100
Subject: [PATCH] =?UTF-8?q?Metabolism:=20browser=20fix=20=E2=80=94=20the?=
 =?UTF-8?q?=20arena=20stays=20a=20plain=20ArrayBuffer=20unless=20a=20regio?=
 =?UTF-8?q?n=20pool=20will=20share=20it;=20vite=20serves=20cross-origin-is?=
 =?UTF-8?q?olation=20headers=20so=20the=20browser=20can=20opt=20into=20SAB?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 metabolism/src/sim/world.js | 10 +++++++++-
 metabolism/vite.config.js   | 16 ++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/metabolism/src/sim/world.js b/metabolism/src/sim/world.js
index 3260c9e..a01255e 100644
--- a/metabolism/src/sim/world.js
+++ b/metabolism/src/sim/world.js
@@ -209,7 +209,15 @@ export class World {
         const fcSide0 = Math.max(16, Math.round(field / 2));   // the layout needs the coarse shape
         const spec = layout ?? arenaLayout(field, this.m, B0, fcSide0);
         this.layout = spec;
-        this.arena = sab ?? new SharedArrayBuffer((spec.bytes + 3) & ~3);
+        // The arena is shared ONLY when a region pool will actually spawn:
+        // browsers expose SharedArrayBuffer solely under cross-origin
+        // isolation, and the serial world must never require it.
+        const wantPool = !bare && workers > 1 && !!workerCtor() &&
+            typeof SharedArrayBuffer !== 'undefined';
+        if (!wantPool) workers = 0;
+        this.arena = sab ?? ((wantPool)
+            ? new SharedArrayBuffer((spec.bytes + 3) & ~3)
+            : new ArrayBuffer((spec.bytes + 3) & ~3));
         {
             let off = 0;
             for (const it of spec.items) { it.offset = off; off += (it.bytes + 3) & ~3; }
diff --git a/metabolism/vite.config.js b/metabolism/vite.config.js
index 29c7440..3af11c0 100644
--- a/metabolism/vite.config.js
+++ b/metabolism/vite.config.js
@@ -142,4 +142,20 @@ function songBankPlugin() {
 
 export default defineConfig({
     plugins: [songBankPlugin()],
+    // Cross-origin isolation: browsers expose SharedArrayBuffer only when
+    // both headers are present. The region pool needs it once the sim runs
+    // inside a browser worker; the demo is fully same-origin, so requiring
+    // corp costs nothing here.
+    server: {
+        headers: {
+            'Cross-Origin-Opener-Policy': 'same-origin',
+            'Cross-Origin-Embedder-Policy': 'require-corp',
+        },
+    },
+    preview: {
+        headers: {
+            'Cross-Origin-Opener-Policy': 'same-origin',
+            'Cross-Origin-Embedder-Policy': 'require-corp',
+        },
+    },
 });
\ No newline at end of file