fix: handle missing/empty interest list gracefully for $hashtags

- Remove #t from filter when $hashtags resolves to empty array
  (prevents unusable queries)
- Preserve other hashtags when $hashtags is empty
- Add UI warning banners for:
  - Interest list not found (kind 10015)
  - Interest list exists but has no hashtags
- Add interestListStatus computed state for UI feedback
- Add tests for empty $hashtags resolution scenarios

src/components/ReqViewer.tsx

@@ -704,6 +704,16 @@ export default function ReqViewer({
     [interestListEvent],
   );
 
+  // Compute interest list status for UI feedback
+  const interestListStatus = useMemo(() => {
+    if (!needsInterestList) return null;
+    if (!accountPubkey) return null; // Account required error handles this
+    if (interestListEvent === undefined) return "loading";
+    if (interestListEvent === null) return "not-found";
+    if (hashtags.length === 0) return "empty";
+    return "ok";
+  }, [needsInterestList, accountPubkey, interestListEvent, hashtags.length]);
+
   // Resolve $me, $contacts, and $hashtags aliases (memoized to prevent unnecessary object creation)
   const resolvedFilter = useMemo(
     () =>
@@ -1285,6 +1295,28 @@ export default function ReqViewer({
         </div>
       )}
 
+      {/* Interest List Warning Banner */}
+      {interestListStatus === "not-found" && (
+        <div className="border-b border-border px-4 py-2 bg-warning/10 flex items-center gap-2">
+          <Hash className="size-4 text-warning" />
+          <span className="text-xs text-warning">
+            No interest list found (kind 10015).{" "}
+            <code className="bg-muted px-1 py-0.5 rounded">$hashtags</code>{" "}
+            ignored.
+          </span>
+        </div>
+      )}
+      {interestListStatus === "empty" && (
+        <div className="border-b border-border px-4 py-2 bg-warning/10 flex items-center gap-2">
+          <Hash className="size-4 text-warning" />
+          <span className="text-xs text-warning">
+            Interest list has no hashtags.{" "}
+            <code className="bg-muted px-1 py-0.5 rounded">$hashtags</code>{" "}
+            ignored.
+          </span>
+        </div>
+      )}
+
       {/* Account Required Error */}
       {(needsAccount || needsInterestList) && !accountPubkey && (
         <div className="flex flex-col items-center justify-center h-full gap-4 p-8 text-center">

src/lib/nostr-utils.test.ts

@@ -428,13 +428,24 @@ describe("resolveFilterAliases", () => {
       expect(result["#t"]).not.toContain("$hashtags");
     });
 
-    it("should handle $hashtags with empty hashtag list", () => {
+    it("should remove #t from filter when $hashtags resolves to empty", () => {
       const filter: NostrFilter = { "#t": ["$hashtags"] };
       const result = resolveFilterAliases(filter, undefined, [], {
         hashtags: [],
       });
 
-      expect(result["#t"]).toEqual([]);
+      // Empty #t should be removed from filter entirely
+      expect(result["#t"]).toBeUndefined();
+    });
+
+    it("should preserve other hashtags when $hashtags resolves to empty", () => {
+      const filter: NostrFilter = { "#t": ["$hashtags", "nostr", "bitcoin"] };
+      const result = resolveFilterAliases(filter, undefined, [], {
+        hashtags: [],
+      });
+
+      // Other hashtags should be preserved
+      expect(result["#t"]).toEqual(["nostr", "bitcoin"]);
     });
 
     it("should preserve other hashtags when resolving $hashtags", () => {
@@ -520,7 +531,8 @@ describe("resolveFilterAliases", () => {
       const result = resolveFilterAliases(filter, accountPubkey, []);
 
       expect(result.authors).toEqual([accountPubkey]);
-      expect(result["#t"]).toEqual([]); // Empty when no hashtags provided
+      // Empty #t should be removed from filter entirely
+      expect(result["#t"]).toBeUndefined();
     });
   });
 

src/lib/nostr-utils.ts

@@ -236,7 +236,14 @@ export function resolveFilterAliases(
     }
 
     // Deduplicate
-    resolved["#t"] = Array.from(new Set(resolvedTTags));
+    const deduped = Array.from(new Set(resolvedTTags));
+
+    // If result is empty, remove #t from filter entirely to avoid unusable query
+    if (deduped.length === 0) {
+      delete resolved["#t"];
+    } else {
+      resolved["#t"] = deduped;
+    }
   }
 
   return resolved;