Wire up nostr-signer-capacitor-plugin for Amber login and signing

- Add CapacitorAmberSigner: a full NostrSigner implementation backed by
  the native nostr-signer-capacitor-plugin (login, signEvent, nip04,
  nip44 all go through Amber via native Android intents)
- LoginDialog: on Capacitor, call getAmberPublicKeyViaPlugin() directly
  instead of the intent:// URL redirect — returns a Promise, no
  callback URL or polling needed. Shows clear error if Amber not installed.
- useCurrentUser: on Capacitor amber logins use CapacitorAmberSigner
  so every publish/sign goes through the plugin, not window.location.href
- Web/PWA path unchanged — still uses URL redirect + AmberSigner

Co-authored-by: shakespeare.diy <assistant@shakespeare.diy>

src/components/auth/LoginDialog.tsx

@@ -16,6 +16,7 @@ import { useLoginActions } from '@/hooks/useLoginActions';
 import { useToast } from '@/hooks/useToast';
 import { cn } from '@/lib/utils';
 import { openAmberForLogin, subscribeToAmberReturn } from '@/lib/amber';
+import { getAmberPublicKeyViaPlugin, isAmberInstalled } from '@/lib/capacitorAmberSigner';
 
 
 interface LoginDialogProps {
@@ -44,34 +45,47 @@ export const LoginDialog: React.FC<LoginDialogProps> = ({ isOpen, onClose, onLog
   // Detect if running inside a Capacitor native app
   const isCapacitor = !!(window as unknown as { Capacitor?: { isNativePlatform?: () => boolean } }).Capacitor?.isNativePlatform?.();
 
-  // Step 1: open Amber via proper intent:// URL with a callbackUrl so Amber
-  // redirects back to the app after approval (works in both web PWA and Capacitor APK).
-  // openAmberForLogin() handles building the correct intent: URL with the callback.
-  const handleAmberLogin = () => {
+  // Step 1: open Amber
+  // - On Capacitor (ZapStore APK): use the native plugin — direct Promise, no redirects needed
+  // - On web/PWA: use intent:// URL with callbackUrl so Amber redirects back
+  const handleAmberLogin = async () => {
     setAmberStep('loading');
+    setAmberError('');
+
+    if (isCapacitor) {
+      // ── Native path (ZapStore/Capacitor APK) ────────────────────────────────
+      // Check Amber is installed first for a clear error message
+      const installed = await isAmberInstalled();
+      if (!installed) {
+        setAmberError('Amber is not installed. Install it from the ZapStore or GitHub.');
+        setAmberStep('error');
+        return;
+      }
+      try {
+        // This opens Amber natively, user approves, pubkey comes back as a Promise
+        const pubkey = await getAmberPublicKeyViaPlugin();
+        completeAmberLogin(pubkey);
+      } catch (e: unknown) {
+        // User cancelled or Amber threw
+        const msg = (e as Error)?.message ?? 'Amber login failed';
+        setAmberError(msg.includes('cancelled') || msg.includes('cancel')
+          ? 'Login cancelled. Tap "Open Amber" to try again.'
+          : msg);
+        setAmberStep('error');
+      }
+      return;
+    }
+
+    // ── Web/PWA path ─────────────────────────────────────────────────────────
     // Store return path before navigating away
     const currentPath = window.location.hash.replace(/^#/, '') || '/';
     localStorage.setItem('amber_return_path', currentPath);
-    // On Capacitor the deep-link fires appUrlOpen, not a page redirect, so we
-    // also need to poll localStorage for the pubkey written by AmberCallbackPage.
-    if (isCapacitor) {
-      // Listen for when app regains focus — Amber will have fired the deep link
-      const unsub = subscribeToAmberReturn(() => {
-        // Give DeepLinkHandler 300 ms to process the URL and write to localStorage
-        setTimeout(checkAmberPendingPubkey, 300);
-      });
-      // Store unsub so we can clean up (store in ref-like closure)
-      window.__amberUnsubRef = unsub;
-    }
+    // Listen for app regaining focus (after Amber redirect)
+    const unsub = subscribeToAmberReturn(() => {
+      checkAmberPendingPubkey();
+    });
+    window.__amberUnsubRef = unsub;
     openAmberForLogin();
-    // Fallback: if somehow we stay on the same page (no redirect happened),
-    // switch to the manual paste step after the dialog loses/regains focus.
-    if (!isCapacitor) {
-      const unsub = subscribeToAmberReturn(() => {
-        checkAmberPendingPubkey();
-      });
-      window.__amberUnsubRef = unsub;
-    }
   };
 
   // Check if AmberCallbackPage already wrote a pubkey to localStorage

src/hooks/useCurrentUser.ts

@@ -4,6 +4,7 @@ import { useCallback, useMemo } from 'react';
 
 import { useAuthor } from './useAuthor.ts';
 import { AmberSigner } from '@/lib/amber';
+import { CapacitorAmberSigner } from '@/lib/capacitorAmberSigner';
 import type { AmberLoginType } from './useLoginActions';
 
 /** Extended login type that includes Amber */
@@ -23,7 +24,13 @@ export function useCurrentUser() {
         return NUser.fromExtensionLogin(login);
       case 'amber': { // Nostr login with Amber (NIP-55)
         const amberLogin = login as AmberLoginType;
-        const signer = new AmberSigner(amberLogin.pubkey);
+        // On Capacitor (ZapStore APK) use the native plugin signer so all
+        // signing operations go through Amber via native intents.
+        // On web/PWA fall back to the URL-redirect based AmberSigner.
+        const isCapacitor = !!(window as unknown as { Capacitor?: { isNativePlatform?: () => boolean } }).Capacitor?.isNativePlatform?.();
+        const signer = isCapacitor
+          ? new CapacitorAmberSigner(amberLogin.pubkey)
+          : new AmberSigner(amberLogin.pubkey);
         return new NUser({ pubkey: amberLogin.pubkey, signer });
       }
       // Other login types can be defined here

src/lib/capacitorAmberSigner.ts

@@ -0,0 +1,120 @@
+/**
+ * CapacitorAmberSigner
+ *
+ * A NostrSigner implementation that delegates all cryptographic operations
+ * to the nostr-signer-capacitor-plugin, which in turn communicates with
+ * Amber (or any NIP-55 compatible signer app) via native Android intents.
+ *
+ * This ONLY works inside a Capacitor native app. On web/PWA use AmberSigner
+ * (the intent:// URL redirect approach) instead.
+ *
+ * Usage:
+ *   const signer = new CapacitorAmberSigner(pubkeyHex);
+ *   const event = await signer.signEvent({ kind: 1, content: 'hello', tags: [], created_at: ... });
+ */
+
+import type { NostrEvent, NostrSigner } from '@nostrify/nostrify';
+import { nip19 } from 'nostr-tools';
+
+// Amber's package name on Android — used to target the correct signer app.
+const AMBER_PACKAGE_NAME = 'com.greenart7c3.nostrsigner';
+
+/**
+ * Lazy-load the plugin and set the package name once.
+ * Returns null if not running inside Capacitor (web/PWA fallback).
+ */
+async function getPlugin() {
+  try {
+    const mod = await import('nostr-signer-capacitor-plugin');
+    const plugin = mod.default ?? mod.NostrSignerPlugin;
+    if (!plugin) return null;
+    await plugin.setPackageName({ packageName: AMBER_PACKAGE_NAME });
+    return plugin;
+  } catch {
+    return null;
+  }
+}
+
+export class CapacitorAmberSigner implements NostrSigner {
+  readonly pubkey: string;
+
+  constructor(pubkeyHex: string) {
+    this.pubkey = pubkeyHex;
+  }
+
+  async getPublicKey(): Promise<string> {
+    return this.pubkey;
+  }
+
+  async signEvent(event: Omit<NostrEvent, 'id' | 'sig'>): Promise<NostrEvent> {
+    const plugin = await getPlugin();
+    if (!plugin) throw new Error('Capacitor Amber plugin not available');
+
+    const { event: signedJson } = await plugin.signEvent({
+      eventJson: JSON.stringify(event),
+    });
+
+    return JSON.parse(signedJson) as NostrEvent;
+  }
+
+  readonly nip04 = {
+    encrypt: async (pubkey: string, plaintext: string): Promise<string> => {
+      const plugin = await getPlugin();
+      if (!plugin) throw new Error('Capacitor Amber plugin not available');
+      const { result } = await plugin.nip04Encrypt({ pubKey: pubkey, plainText: plaintext });
+      return result;
+    },
+    decrypt: async (pubkey: string, ciphertext: string): Promise<string> => {
+      const plugin = await getPlugin();
+      if (!plugin) throw new Error('Capacitor Amber plugin not available');
+      const { result } = await plugin.nip04Decrypt({ pubKey: pubkey, encryptedText: ciphertext });
+      return result;
+    },
+  };
+
+  readonly nip44 = {
+    encrypt: async (pubkey: string, plaintext: string): Promise<string> => {
+      const plugin = await getPlugin();
+      if (!plugin) throw new Error('Capacitor Amber plugin not available');
+      const { result } = await plugin.nip44Encrypt({ pubKey: pubkey, plainText: plaintext });
+      return result;
+    },
+    decrypt: async (pubkey: string, ciphertext: string): Promise<string> => {
+      const plugin = await getPlugin();
+      if (!plugin) throw new Error('Capacitor Amber plugin not available');
+      const { result } = await plugin.nip44Decrypt({ pubKey: pubkey, encryptedText: ciphertext });
+      return result;
+    },
+  };
+}
+
+/**
+ * Check if the Amber signer app is installed on the device.
+ * Returns false on web/PWA (plugin not available).
+ */
+export async function isAmberInstalled(): Promise<boolean> {
+  const plugin = await getPlugin();
+  if (!plugin) return false;
+  try {
+    const { installed } = await plugin.isExternalSignerInstalled();
+    return installed;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Request the public key from Amber via the Capacitor plugin.
+ * Returns the hex pubkey string, or throws on failure/cancel.
+ */
+export async function getAmberPublicKeyViaPlugin(): Promise<string> {
+  const plugin = await getPlugin();
+  if (!plugin) throw new Error('Capacitor Amber plugin not available — are you on a native build?');
+
+  const { npub } = await plugin.getPublicKey();
+
+  // Plugin returns npub — decode to hex
+  const decoded = nip19.decode(npub);
+  if (decoded.type !== 'npub') throw new Error('Unexpected key format from Amber plugin');
+  return decoded.data as string;
+}