test(clink): regression tests for the audit fixes

Locks in the protocol-layer fixes that were previously only compile-checked:
- offerLargePriceRoundTripIsUnsigned: a price > Int.MAX_VALUE round-trips as a
  positive Long (guards the unsigned-decode fix).
- cannotDecryptAuthoredEventMissingRecipient: an authored event with no p tag
  can't be decrypted by anyone (guards the no-self-fallback conversationPeer).
- manageCreateRequestSerializesNested + manageFailureResponseParsesField: the
  Manage request nests under offer.fields, payer_data is a string list, and the
  failure response carries field (guards the 21003 shape fix).

All CLINK tests pass.

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/experimental/clink/ClinkEventTest.kt

@@ -21,6 +21,10 @@
 package com.vitorpamplona.quartz.experimental.clink
 
 import com.vitorpamplona.quartz.experimental.clink.debits.DebitResponse
+import com.vitorpamplona.quartz.experimental.clink.manage.ManageOffer
+import com.vitorpamplona.quartz.experimental.clink.manage.ManageRequest
+import com.vitorpamplona.quartz.experimental.clink.manage.ManageResponse
+import com.vitorpamplona.quartz.experimental.clink.manage.OfferFields
 import com.vitorpamplona.quartz.experimental.clink.offers.OfferEvent
 import com.vitorpamplona.quartz.experimental.clink.offers.OfferRequest
 import com.vitorpamplona.quartz.experimental.clink.offers.OfferResponse
@@ -88,6 +92,23 @@ class ClinkEventTest {
         assertFalse(request.canDecrypt(stranger))
     }
 
+    @Test
+    fun cannotDecryptAuthoredEventMissingRecipient() {
+        // A malformed event I authored but with no `p` tag: my own key must NOT be used as
+        // the conversation peer (no self-fallback), so neither party can derive a key.
+        val noRecipient =
+            OfferEvent(
+                id = "a".repeat(64),
+                pubKey = payer.pubKey,
+                createdAt = 1L,
+                tags = arrayOf(ClinkVersionTag.assemble()),
+                content = "encrypted-placeholder",
+                sig = "b".repeat(128),
+            )
+        assertFalse(noRecipient.canDecrypt(payer))
+        assertFalse(noRecipient.canDecrypt(service))
+    }
+
     // --- JSON DTOs ---
 
     @Test
@@ -136,4 +157,32 @@ class ClinkEventTest {
         assertTrue(parsed.isOk())
         assertEquals("deadbeef", parsed.preimage)
     }
+
+    @Test
+    fun manageCreateRequestSerializesNested() {
+        val request =
+            ManageRequest(
+                resource = ManageRequest.RESOURCE_OFFER,
+                action = ManageRequest.ACTION_CREATE,
+                offer = ManageOffer(fields = OfferFields("Coffee", 1500L, "https://x/cb", listOf("email", "name"))),
+            )
+        val json = OptimizedJsonMapper.toJson(request)
+
+        // Offer data is nested under offer.fields (not flat).
+        assertTrue(json.contains("\"offer\""), json)
+        assertTrue(json.contains("\"fields\""), json)
+
+        val parsed = OptimizedJsonMapper.fromJsonTo<ManageRequest>(json)
+        assertEquals("Coffee", parsed.offer?.fields?.label)
+        assertEquals(1500L, parsed.offer?.fields?.price_sats)
+        // payer_data is a list of field names, not a map.
+        assertEquals(listOf("email", "name"), parsed.offer?.fields?.payer_data)
+    }
+
+    @Test
+    fun manageFailureResponseParsesField() {
+        val parsed = OptimizedJsonMapper.fromJsonTo<ManageResponse>("""{"res":"GFY","code":5,"error":"bad","field":"price_sats"}""")
+        assertFalse(parsed.isOk())
+        assertEquals("price_sats", parsed.field)
+    }
 }

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/experimental/clink/pointers/ClinkPointerTest.kt

@@ -52,6 +52,19 @@ class ClinkPointerTest {
         assertEquals(offer, parsed)
     }
 
+    @Test
+    fun offerLargePriceRoundTripIsUnsigned() {
+        // A price with the high bit set (> Int.MAX_VALUE) must round-trip as a positive
+        // Long — the price is an unsigned 4-byte big-endian integer, so reading it signed
+        // would wrap it negative.
+        val price = 3_000_000_000L
+        val offer = NOffer(pubKey, listOf(relay), null, OfferPriceType.FIXED, price)
+        val parsed = ClinkPointerParser.parse(offer.encode()) as NOffer
+
+        assertEquals(price, parsed.price)
+        assertEquals(offer, parsed)
+    }
+
     @Test
     fun debitStaticRoundTrip() {
         val debit = NDebit(pubKey, listOf(relay), "pointer-7", null)