feat: use NIP-65 relay selection for reactions

Add interaction relay selection utility following the NIP-65 outbox model:
- Author's outbox (write) relays: where we publish our events
- Target's inbox (read) relays: so the target sees the interaction

This ensures reactions reach the intended recipient according to their
relay preferences, similar to how zap relay selection works.

New file: src/lib/interaction-relay-selection.ts
- selectInteractionRelays() for full result with sources
- getInteractionRelays() convenience wrapper

src/components/nostr/kinds/BaseEventRenderer.tsx

@@ -41,7 +41,8 @@ import { isAddressableKind } from "@/lib/nostr-kinds";
 import { getSemanticAuthor } from "@/lib/semantic-author";
 import { EventFactory } from "applesauce-core/event-factory";
 import { ReactionBlueprint } from "applesauce-common/blueprints";
-import { publishEvent } from "@/services/hub";
+import { publishEventToRelays } from "@/services/hub";
+import { getInteractionRelays } from "@/lib/interaction-relay-selection";
 import type { EmojiTag } from "@/lib/emoji-helpers";
 
 /**
@@ -529,7 +530,7 @@ export function BaseEventContainer({
   };
 }) {
   const { locale, addWindow } = useGrimoire();
-  const { canSign, signer } = useAccount();
+  const { canSign, signer, pubkey } = useAccount();
   const [emojiPickerOpen, setEmojiPickerOpen] = useState(false);
 
   const handleReactClick = () => {
@@ -537,7 +538,7 @@ export function BaseEventContainer({
   };
 
   const handleEmojiSelect = async (emoji: string, customEmoji?: EmojiTag) => {
-    if (!signer) return;
+    if (!signer || !pubkey) return;
 
     try {
       const factory = new EventFactory();
@@ -549,7 +550,10 @@ export function BaseEventContainer({
 
       const draft = await factory.create(ReactionBlueprint, event, emojiArg);
       const signed = await factory.sign(draft);
-      await publishEvent(signed);
+
+      // Select relays per NIP-65: author's outbox + target's inbox
+      const relays = await getInteractionRelays(pubkey, event.pubkey);
+      await publishEventToRelays(signed, relays);
     } catch (err) {
       console.error("[BaseEventContainer] Failed to send reaction:", err);
     }

src/lib/interaction-relay-selection.ts

@@ -0,0 +1,128 @@
+/**
+ * Interaction Relay Selection Utilities
+ *
+ * Provides optimal relay selection for interactions (reactions, replies, etc.)
+ * following the NIP-65 outbox model.
+ *
+ * For interactions, we need to publish to:
+ * 1. Author's outbox (write) relays - where we publish our events
+ * 2. Target's inbox (read) relays - so the target sees the interaction
+ *
+ * See: https://github.com/nostr-protocol/nips/blob/master/65.md
+ */
+
+import { relayListCache } from "@/services/relay-list-cache";
+import { AGGREGATOR_RELAYS } from "@/services/loaders";
+
+/** Maximum number of relays to publish to */
+const MAX_INTERACTION_RELAYS = 10;
+
+/** Minimum relays per party for redundancy */
+const MIN_RELAYS_PER_PARTY = 3;
+
+export interface InteractionRelaySelectionParams {
+  /** Pubkey of the interaction author (person reacting/replying) */
+  authorPubkey: string;
+  /** Pubkey of the target (person being reacted to/replied to) */
+  targetPubkey: string;
+}
+
+export interface InteractionRelaySelectionResult {
+  /** Selected relays for publishing the interaction */
+  relays: string[];
+  /** Debug info about relay sources */
+  sources: {
+    authorOutbox: string[];
+    targetInbox: string[];
+    fallback: string[];
+  };
+}
+
+/**
+ * Select optimal relays for publishing an interaction event (reaction, reply, etc.)
+ *
+ * Strategy per NIP-65:
+ * - Author's outbox relays: where we publish our content
+ * - Target's inbox relays: where the target reads mentions/interactions
+ * - Fallback aggregators if neither has preferences
+ * - Deduplicate and limit to MAX_INTERACTION_RELAYS
+ */
+export async function selectInteractionRelays(
+  params: InteractionRelaySelectionParams,
+): Promise<InteractionRelaySelectionResult> {
+  const { authorPubkey, targetPubkey } = params;
+
+  const sources = {
+    authorOutbox: [] as string[],
+    targetInbox: [] as string[],
+    fallback: [] as string[],
+  };
+
+  // Fetch relays in parallel
+  const [authorOutbox, targetInbox] = await Promise.all([
+    relayListCache.getOutboxRelays(authorPubkey),
+    relayListCache.getInboxRelays(targetPubkey),
+  ]);
+
+  if (authorOutbox && authorOutbox.length > 0) {
+    sources.authorOutbox = authorOutbox;
+  }
+
+  if (targetInbox && targetInbox.length > 0) {
+    sources.targetInbox = targetInbox;
+  }
+
+  // Build relay list with priority ordering
+  const relaySet = new Set<string>();
+
+  // Priority 1: Author's outbox relays (where we publish)
+  for (const relay of sources.authorOutbox.slice(0, MIN_RELAYS_PER_PARTY)) {
+    relaySet.add(relay);
+  }
+
+  // Priority 2: Target's inbox relays (so they see it)
+  for (const relay of sources.targetInbox.slice(0, MIN_RELAYS_PER_PARTY)) {
+    relaySet.add(relay);
+  }
+
+  // Add remaining author outbox relays
+  for (const relay of sources.authorOutbox.slice(MIN_RELAYS_PER_PARTY)) {
+    if (relaySet.size >= MAX_INTERACTION_RELAYS) break;
+    relaySet.add(relay);
+  }
+
+  // Add remaining target inbox relays
+  for (const relay of sources.targetInbox.slice(MIN_RELAYS_PER_PARTY)) {
+    if (relaySet.size >= MAX_INTERACTION_RELAYS) break;
+    relaySet.add(relay);
+  }
+
+  // Fallback to aggregator relays if we don't have enough
+  if (relaySet.size === 0) {
+    sources.fallback = [...AGGREGATOR_RELAYS];
+    for (const relay of AGGREGATOR_RELAYS) {
+      if (relaySet.size >= MAX_INTERACTION_RELAYS) break;
+      relaySet.add(relay);
+    }
+  }
+
+  return {
+    relays: Array.from(relaySet),
+    sources,
+  };
+}
+
+/**
+ * Get a simple list of relays for publishing an interaction
+ * Convenience wrapper that just returns the relay URLs
+ */
+export async function getInteractionRelays(
+  authorPubkey: string,
+  targetPubkey: string,
+): Promise<string[]> {
+  const result = await selectInteractionRelays({
+    authorPubkey,
+    targetPubkey,
+  });
+  return result.relays;
+}