From e16f572252b954d455141b40d369c12cff7f1ed8 Mon Sep 17 00:00:00 2001
From: Linus Rath <139418639+rathlinus@users.noreply.github.com>
Date: Mon, 18 May 2026 11:00:05 +0200
Subject: [PATCH] fix: use plugin slot offer snapshots for useSyncExternalStore

---
 components/plugins/plugin-slot.tsx |  7 ++---
 hooks/use-plugin-slot-offers.ts    |  7 ++---
 lib/plugin-sandbox/registry.ts     | 41 +++++++++++++++++++++++++-----
 3 files changed, 38 insertions(+), 17 deletions(-)

diff --git a/components/plugins/plugin-slot.tsx b/components/plugins/plugin-slot.tsx
index ea00587a..babdc534 100644
--- a/components/plugins/plugin-slot.tsx
+++ b/components/plugins/plugin-slot.tsx
@@ -12,11 +12,8 @@ interface PluginSlotProps {
 }
 
 export function PluginSlot({ name, className, extraProps }: PluginSlotProps) {
-  const offers = useSyncExternalStore(
-    subscribe,
-    () => offersForSlot(name),
-    () => [],
-  );
+  const getSnapshot = () => offersForSlot(name);
+  const offers = useSyncExternalStore(subscribe, getSnapshot, getSnapshot);
 
   if (offers.length === 0) return null;
 
diff --git a/hooks/use-plugin-slot-offers.ts b/hooks/use-plugin-slot-offers.ts
index 2501cc05..8a235812 100644
--- a/hooks/use-plugin-slot-offers.ts
+++ b/hooks/use-plugin-slot-offers.ts
@@ -9,9 +9,6 @@ import type { SlotName } from '@/lib/plugin-types';
 import { offersForSlot, subscribe } from '@/lib/plugin-sandbox/registry';
 
 export function usePluginSlotOffers(slotName: SlotName) {
-  return useSyncExternalStore(
-    subscribe,
-    () => offersForSlot(slotName),
-    () => [],
-  );
+  const getSnapshot = () => offersForSlot(slotName);
+  return useSyncExternalStore(subscribe, getSnapshot, getSnapshot);
 }
diff --git a/lib/plugin-sandbox/registry.ts b/lib/plugin-sandbox/registry.ts
index 85870543..6b4a4e28 100644
--- a/lib/plugin-sandbox/registry.ts
+++ b/lib/plugin-sandbox/registry.ts
@@ -1,6 +1,10 @@
 // Process-wide registry of active sandboxed plugins. The loader populates it
 // after a successful boot; PluginIframeSlot reads it to spawn slot iframes
 // and to call evaluateShouldShow on the background instance.
+//
+// `offersForSlot` results are memoised per slot name so that
+// `useSyncExternalStore` sees a stable reference between unrelated renders.
+// The cache is invalidated whenever the set of active plugins changes.
 
 import type { Disposable, InstalledPlugin, SlotName } from '../plugin-types';
 import type { SandboxInstance } from './host-bridge';
@@ -20,21 +24,36 @@ export interface ActivePlugin {
   hookDisposables: Disposable[];
 }
 
+export interface ResolvedSlotOffer {
+  pluginId: string;
+  order: number;
+  hasShouldShow: boolean;
+}
+
 const active = new Map<string, ActivePlugin>();
 const listeners = new Set<() => void>();
 
-function emit(): void { for (const l of listeners) try { l(); } catch { /* ignore */ } }
+// Per-slot snapshot cache. Cleared on any registry mutation.
+const offersCache = new Map<SlotName, readonly ResolvedSlotOffer[]>();
+const EMPTY: readonly ResolvedSlotOffer[] = Object.freeze([]);
+
+function invalidate(): void {
+  offersCache.clear();
+  for (const l of listeners) {
+    try { l(); } catch { /* ignore */ }
+  }
+}
 
 export function register(entry: ActivePlugin): void {
   active.set(entry.plugin.id, entry);
-  emit();
+  invalidate();
 }
 
 export function deregister(pluginId: string): ActivePlugin | undefined {
   const e = active.get(pluginId);
   if (!e) return undefined;
   active.delete(pluginId);
-  emit();
+  invalidate();
   return e;
 }
 
@@ -46,9 +65,15 @@ export function all(): ActivePlugin[] {
   return [...active.values()];
 }
 
-/** Returns active plugins ordered by `order`, that offer the requested slot. */
-export function offersForSlot(slot: SlotName): Array<{ pluginId: string; order: number; hasShouldShow: boolean }> {
-  const out: Array<{ pluginId: string; order: number; hasShouldShow: boolean }> = [];
+/**
+ * Returns the cached, frozen list of plugins offering this slot, sorted by
+ * `order`. The returned array is referentially stable until the active-plugin
+ * set changes, so it is safe to pass to `useSyncExternalStore`.
+ */
+export function offersForSlot(slot: SlotName): readonly ResolvedSlotOffer[] {
+  const cached = offersCache.get(slot);
+  if (cached) return cached;
+  const out: ResolvedSlotOffer[] = [];
   for (const entry of active.values()) {
     for (const offer of entry.slotOffers) {
       if (offer.name === slot) {
@@ -57,7 +82,9 @@ export function offersForSlot(slot: SlotName): Array<{ pluginId: string; order:
     }
   }
   out.sort((a, b) => a.order - b.order);
-  return out;
+  const snapshot = out.length === 0 ? EMPTY : Object.freeze(out);
+  offersCache.set(slot, snapshot);
+  return snapshot;
 }
 
 export function subscribe(listener: () => void): () => void {