feat: Add NIP-44 validation and better gift wrap error diagnostics

- Validate signer has NIP-44 support before attempting decryption
  - NIP-59 gift wraps REQUIRE NIP-44 encryption
  - Fail early with helpful message if signer lacks nip44
  - Suggests using compatible extensions (Alby, nos2x-fox, etc.)

- Add specific error messages for common decryption failures
  - JSON parse errors → "Decrypted content is not valid JSON"
  - Missing event properties → "Seal is missing required properties"
  - Author mismatch → "Seal and rumor authors don't match"
  - Includes event ID in error messages for debugging

- Add test for signer without NIP-44 support

This helps diagnose the two production errors:
1. "Unexpected token 'T', "This is to"..." → JSON parse failure
2. "can't serialize event" → malformed seal event

Users will now see clear error messages explaining the issue
(incompatible extension, malformed gift wrap, etc.)

src/services/gift-wrap.test.ts

@@ -53,6 +53,32 @@ describe("unwrapAndUnseal", () => {
   });
 
   describe("validation", () => {
+    it("should reject signer without NIP-44 support", async () => {
+      const giftWrap: NostrEvent = {
+        id: "test-id",
+        pubkey: "ephemeral-key",
+        created_at: 1234567890,
+        kind: 1059,
+        tags: [],
+        content: "encrypted-content",
+        sig: "signature",
+      };
+
+      // Signer without nip44
+      const signerWithoutNip44: ISigner = {
+        getPublicKey: vi.fn().mockResolvedValue("mock-pubkey"),
+        signEvent: vi.fn(),
+      };
+
+      await expect(
+        unwrapAndUnseal(giftWrap, signerWithoutNip44),
+      ).rejects.toThrow(GiftWrapError);
+
+      await expect(
+        unwrapAndUnseal(giftWrap, signerWithoutNip44),
+      ).rejects.toThrow("does not support NIP-44");
+    });
+
     it("should reject non-1059 events", async () => {
       const invalidGiftWrap: NostrEvent = {
         id: "test-id",

src/services/gift-wrap.ts

@@ -89,6 +89,16 @@ export async function unwrapAndUnseal(
     throw new GiftWrapError("Gift wrap content is empty", "MISSING_CONTENT");
   }
 
+  // CRITICAL: Validate signer has NIP-44 support
+  // NIP-59 gift wraps REQUIRE NIP-44 encryption
+  if (!signer.nip44) {
+    throw new GiftWrapError(
+      "Signer does not support NIP-44 encryption (required for NIP-59 gift wraps). " +
+        "Please use a browser extension that supports NIP-44 (e.g., Alby, nos2x-fox, Nostr-Connect).",
+      "NO_SIGNER",
+    );
+  }
+
   // CRITICAL: Add to event store before unlocking
   // Applesauce requires the event to be in the store for caching to work
   // We wrap in try-catch because the event might not be valid for the event store
@@ -147,6 +157,34 @@ export async function unwrapAndUnseal(
 
     const message = error instanceof Error ? error.message : String(error);
 
+    // Provide helpful error messages for common issues
+    if (message.includes("Unexpected token") || message.includes("JSON")) {
+      throw new GiftWrapError(
+        `Decrypted content is not valid JSON. This gift wrap may be malformed or use incompatible encryption. ` +
+          `Event ID: ${giftWrap.id.slice(0, 16)}... (${message})`,
+        "INVALID_SEAL",
+      );
+    }
+
+    if (
+      message.includes("can't serialize") ||
+      message.includes("wrong or missing properties")
+    ) {
+      throw new GiftWrapError(
+        `Decrypted seal is missing required event properties. This gift wrap may be malformed. ` +
+          `Event ID: ${giftWrap.id.slice(0, 16)}... (${message})`,
+        "INVALID_SEAL",
+      );
+    }
+
+    if (message.includes("Seal author does not match rumor author")) {
+      throw new GiftWrapError(
+        `Seal and rumor authors don't match - possible tampering. ` +
+          `Event ID: ${giftWrap.id.slice(0, 16)}...`,
+        "INVALID_SEAL",
+      );
+    }
+
     // Map decryption errors
     if (
       message.includes("decrypt") ||