Add portable NIP-46 crypto + protocol parsing to :shared/commonMain

BunkerSigner wraps Quartz's NostrSignerInternal for sign/nip44/nip04
encrypt-decrypt; BunkerMethod/BunkerRequestPayload mirror Amber's
existing bunker-request method dispatch and per-method params layout
(app/src/main/java/.../service/BunkerRequestUtils.kt) as pure,
platform-agnostic functions with unit tests running on the JVM target.

shared/src/commonMain/kotlin/com/greenart7c3/nostrsigner/shared/BunkerMethod.kt

@@ -0,0 +1,38 @@
+package com.greenart7c3.nostrsigner.shared
+
+/** The NIP-46 bunker RPC methods a signer can be asked to perform. */
+enum class BunkerMethod {
+    CONNECT,
+    SIGN_EVENT,
+    NIP04_ENCRYPT,
+    NIP04_DECRYPT,
+    NIP44_ENCRYPT,
+    NIP44_DECRYPT,
+    NIP44_V3_ENCRYPT,
+    NIP44_V3_DECRYPT,
+    GET_PUBLIC_KEY,
+    DECRYPT_ZAP_EVENT,
+    PING,
+    SWITCH_RELAYS,
+    SIGN_PSBT,
+    LOGOUT,
+    INVALID,
+}
+
+fun bunkerMethodOf(method: String): BunkerMethod = when (method) {
+    "connect" -> BunkerMethod.CONNECT
+    "sign_event" -> BunkerMethod.SIGN_EVENT
+    "get_public_key" -> BunkerMethod.GET_PUBLIC_KEY
+    "nip04_encrypt" -> BunkerMethod.NIP04_ENCRYPT
+    "nip04_decrypt" -> BunkerMethod.NIP04_DECRYPT
+    "nip44_encrypt" -> BunkerMethod.NIP44_ENCRYPT
+    "nip44_decrypt" -> BunkerMethod.NIP44_DECRYPT
+    "nip44v3_encrypt" -> BunkerMethod.NIP44_V3_ENCRYPT
+    "nip44v3_decrypt" -> BunkerMethod.NIP44_V3_DECRYPT
+    "decrypt_zap_event" -> BunkerMethod.DECRYPT_ZAP_EVENT
+    "ping" -> BunkerMethod.PING
+    "switch_relays" -> BunkerMethod.SWITCH_RELAYS
+    "sign_psbt" -> BunkerMethod.SIGN_PSBT
+    "logout" -> BunkerMethod.LOGOUT
+    else -> BunkerMethod.INVALID
+}

shared/src/commonMain/kotlin/com/greenart7c3/nostrsigner/shared/BunkerRequestPayload.kt

@@ -0,0 +1,40 @@
+package com.greenart7c3.nostrsigner.shared
+
+import com.vitorpamplona.quartz.nip46RemoteSigner.BunkerRequest
+
+/**
+ * Pure helpers for reading the fields a [BunkerRequest]'s NIP-46 `params` array carries,
+ * mirroring the NIP-46 spec's per-method param layout. No signing/encryption happens here —
+ * see [BunkerSigner] for that.
+ */
+object BunkerRequestPayload {
+    /** The event JSON (for `sign_event`), ciphertext/plaintext payload, or PSBT hex a request carries, if any. */
+    fun payload(bunkerRequest: BunkerRequest): String = when (bunkerMethodOf(bunkerRequest.method)) {
+        BunkerMethod.SIGN_EVENT -> bunkerRequest.params.firstOrNull() ?: ""
+        BunkerMethod.NIP04_ENCRYPT, BunkerMethod.NIP04_DECRYPT,
+        BunkerMethod.NIP44_ENCRYPT, BunkerMethod.NIP44_DECRYPT,
+        BunkerMethod.DECRYPT_ZAP_EVENT,
+        -> bunkerRequest.params.getOrElse(1) { "" }
+        // NIP-44 v3 NIP-46 layout: [pubkey, kind, scope, payload]. For
+        // `nip44v3_encrypt` the payload is base64-encoded plaintext; for
+        // `nip44v3_decrypt` it is the v3 ciphertext.
+        BunkerMethod.NIP44_V3_ENCRYPT, BunkerMethod.NIP44_V3_DECRYPT -> bunkerRequest.params.getOrElse(3) { "" }
+        BunkerMethod.SIGN_PSBT -> bunkerRequest.params.firstOrNull() ?: ""
+        else -> ""
+    }
+
+    /** The counterparty pubkey a NIP-04/NIP-44 encrypt/decrypt request targets, if any. */
+    fun counterpartyPubKey(bunkerRequest: BunkerRequest): String? = when (bunkerMethodOf(bunkerRequest.method)) {
+        BunkerMethod.NIP04_ENCRYPT, BunkerMethod.NIP04_DECRYPT,
+        BunkerMethod.NIP44_ENCRYPT, BunkerMethod.NIP44_DECRYPT,
+        BunkerMethod.NIP44_V3_ENCRYPT, BunkerMethod.NIP44_V3_DECRYPT,
+        -> bunkerRequest.params.firstOrNull()
+        else -> null
+    }
+
+    /** Extract `kind` from a NIP-44 v3 bunker request; null if missing/invalid. */
+    fun nip44v3Kind(bunkerRequest: BunkerRequest): Int? = bunkerRequest.params.getOrNull(1)?.toIntOrNull()
+
+    /** Extract `scope` from a NIP-44 v3 bunker request; defaults to empty per spec. */
+    fun nip44v3Scope(bunkerRequest: BunkerRequest): String = bunkerRequest.params.getOrElse(2) { "" }
+}

shared/src/commonTest/kotlin/com/greenart7c3/nostrsigner/shared/BunkerRequestPayloadTest.kt

@@ -0,0 +1,39 @@
+package com.greenart7c3.nostrsigner.shared
+
+import com.vitorpamplona.quartz.nip46RemoteSigner.BunkerRequest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+class BunkerRequestPayloadTest {
+    @Test
+    fun signEventPayload() {
+        val request = BunkerRequest("id-1", "sign_event", arrayOf("{\"kind\":1}"))
+        assertEquals(BunkerMethod.SIGN_EVENT, bunkerMethodOf(request.method))
+        assertEquals("{\"kind\":1}", BunkerRequestPayload.payload(request))
+    }
+
+    @Test
+    fun nip44EncryptPayload() {
+        val request = BunkerRequest("id-2", "nip44_encrypt", arrayOf("deadbeef", "plaintext"))
+        assertEquals(BunkerMethod.NIP44_ENCRYPT, bunkerMethodOf(request.method))
+        assertEquals("plaintext", BunkerRequestPayload.payload(request))
+        assertEquals("deadbeef", BunkerRequestPayload.counterpartyPubKey(request))
+    }
+
+    @Test
+    fun nip44v3Payload() {
+        val request = BunkerRequest("id-3", "nip44v3_encrypt", arrayOf("deadbeef", "7", "scope", "cGF5bG9hZA=="))
+        assertEquals(BunkerMethod.NIP44_V3_ENCRYPT, bunkerMethodOf(request.method))
+        assertEquals("cGF5bG9hZA==", BunkerRequestPayload.payload(request))
+        assertEquals(7, BunkerRequestPayload.nip44v3Kind(request))
+        assertEquals("scope", BunkerRequestPayload.nip44v3Scope(request))
+    }
+
+    @Test
+    fun unknownMethodIsInvalid() {
+        val request = BunkerRequest("id-4", "not_a_real_method", arrayOf())
+        assertEquals(BunkerMethod.INVALID, bunkerMethodOf(request.method))
+        assertNull(BunkerRequestPayload.counterpartyPubKey(request))
+    }
+}

shared/src/commonTest/kotlin/com/greenart7c3/nostrsigner/shared/BunkerSignerTest.kt

@@ -0,0 +1,30 @@
+package com.greenart7c3.nostrsigner.shared
+
+import com.vitorpamplona.quartz.nip01Core.crypto.KeyPair
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlinx.coroutines.test.runTest
+
+class BunkerSignerTest {
+    @Test
+    fun nip44RoundTrip() = runTest {
+        val alice = BunkerSigner(KeyPair())
+        val bob = BunkerSigner(KeyPair())
+
+        val cipherText = alice.nip44Encrypt("hello bunker", bob.pubKey)
+        val plainText = bob.nip44Decrypt(cipherText, alice.pubKey)
+
+        assertEquals("hello bunker", plainText)
+    }
+
+    @Test
+    fun nip04RoundTrip() = runTest {
+        val alice = BunkerSigner(KeyPair())
+        val bob = BunkerSigner(KeyPair())
+
+        val cipherText = alice.nip04Encrypt("hello bunker nip04", bob.pubKey)
+        val plainText = bob.nip04Decrypt(cipherText, alice.pubKey)
+
+        assertEquals("hello bunker nip04", plainText)
+    }
+}