fix: align createCard due-date contract with api client ownership

app/src/main/java/space/hackenslacker/kanbn4droid/app/auth/KanbnApiClient.kt

@@ -4,6 +4,7 @@ import java.io.IOException
 import java.net.HttpURLConnection
 import java.net.URL
 import java.time.Instant
+import java.time.LocalDate
 import org.json.JSONArray
 import org.json.JSONObject
 import kotlinx.coroutines.Dispatchers
@@ -79,7 +80,7 @@ interface KanbnApiClient {
         listPublicId: String,
         title: String,
         description: String?,
-        dueDate: String?,
+        dueDate: LocalDate?,
         tagPublicIds: List<String>,
     ): BoardsApiResult<CreatedEntityRef> {
         return BoardsApiResult.Failure("Card creation is not implemented.")
@@ -300,16 +301,18 @@ class HttpKanbnApiClient : KanbnApiClient {
         appendIndex: Int,
     ): BoardsApiResult<CreatedEntityRef> {
         return withContext(Dispatchers.IO) {
-            val payload = JSONObject()
-                .put("boardPublicId", boardPublicId)
-                .put("name", title)
-                .put("index", appendIndex)
+            val payload =
+                "{" +
+                    "\"boardPublicId\":\"${jsonEscape(boardPublicId)}\"," +
+                    "\"name\":\"${jsonEscape(title)}\"," +
+                    "\"index\":$appendIndex" +
+                    "}"
             request(
                 baseUrl = baseUrl,
                 path = "/api/v1/lists",
                 method = "POST",
                 apiKey = apiKey,
-                body = payload.toString(),
+                body = payload,
             ) { code, body ->
                 if (code in 200..299) {
                     parseCreatedEntityRef(body)
@@ -328,23 +331,29 @@ class HttpKanbnApiClient : KanbnApiClient {
         listPublicId: String,
         title: String,
         description: String?,
-        dueDate: String?,
+        dueDate: LocalDate?,
         tagPublicIds: List<String>,
     ): BoardsApiResult<CreatedEntityRef> {
         return withContext(Dispatchers.IO) {
-            val payload = JSONObject()
-                .put("listPublicId", listPublicId)
-                .put("title", title)
-                .put("description", description ?: "")
-                .put("dueDate", dueDate)
-                .put("index", 0)
-                .put("labelPublicIds", JSONArray(tagPublicIds))
+            val payloadFields = mutableListOf(
+                "\"listPublicId\":\"${jsonEscape(listPublicId)}\"",
+                "\"title\":\"${jsonEscape(title)}\"",
+                "\"index\":0",
+                "\"labelPublicIds\":${jsonStringArray(tagPublicIds)}",
+            )
+            if (description != null) {
+                payloadFields += "\"description\":\"${jsonEscape(description)}\""
+            }
+            if (dueDate != null) {
+                payloadFields += "\"dueDate\":\"${dueDate}T00:00:00Z\""
+            }
+            val payload = "{${payloadFields.joinToString(",")}}"
             request(
                 baseUrl = baseUrl,
                 path = "/api/v1/cards",
                 method = "POST",
                 apiKey = apiKey,
-                body = payload.toString(),
+                body = payload,
             ) { code, body ->
                 if (code in 200..299) {
                     parseCreatedEntityRef(body)
@@ -890,6 +899,10 @@ class HttpKanbnApiClient : KanbnApiClient {
         return builder.toString()
     }
 
+    private fun jsonStringArray(values: List<String>): String {
+        return values.joinToString(prefix = "[", postfix = "]", separator = ",") { "\"${jsonEscape(it)}\"" }
+    }
+
     private class MiniJsonParser(private val input: String) {
         private var index = 0
 

app/src/main/java/space/hackenslacker/kanbn4droid/app/boarddetail/BoardDetailRepository.kt

@@ -3,6 +3,7 @@ package space.hackenslacker.kanbn4droid.app.boarddetail
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
+import java.time.LocalDate
 import space.hackenslacker.kanbn4droid.app.auth.ApiKeyStore
 import space.hackenslacker.kanbn4droid.app.auth.KanbnApiClient
 import space.hackenslacker.kanbn4droid.app.auth.LabelDetail
@@ -73,7 +74,7 @@ class BoardDetailRepository(
         listId: String,
         title: String,
         description: String?,
-        dueDate: String?,
+        dueDate: LocalDate?,
         tagIds: Collection<String>,
     ): BoardsApiResult<CreatedEntityRef> {
         val normalizedListId = listId.trim()
@@ -87,7 +88,6 @@ class BoardDetailRepository(
         }
 
         val normalizedDescription = description?.trim()?.takeIf { it.isNotBlank() }
-        val normalizedDueDate = dueDate?.trim()?.takeIf { it.isNotBlank() }
         val normalizedTagIds = tagIds
             .map { it.trim() }
             .filter { it.isNotBlank() }
@@ -104,7 +104,7 @@ class BoardDetailRepository(
             listPublicId = normalizedListId,
             title = normalizedTitle,
             description = normalizedDescription,
-            dueDate = normalizedDueDate,
+            dueDate = dueDate,
             tagPublicIds = normalizedTagIds,
         )
     }

app/src/test/java/space/hackenslacker/kanbn4droid/app/auth/HttpKanbnApiClientBoardDetailParsingTest.kt

@@ -6,6 +6,7 @@ import java.net.InetSocketAddress
 import java.net.ServerSocket
 import java.net.Socket
 import java.time.Instant
+import java.time.LocalDate
 import java.util.concurrent.CopyOnWriteArrayList
 import java.util.concurrent.Executors
 import java.util.concurrent.TimeUnit
@@ -21,6 +22,52 @@ import space.hackenslacker.kanbn4droid.app.boards.BoardsApiResult
 
 class HttpKanbnApiClientBoardDetailParsingTest {
 
+    @Test
+    fun createCardFormatsLocalDateAsUtcMidnightInPayload() = runTest {
+        TestServer().use { server ->
+            server.register(path = "/api/v1/cards", method = "POST", status = 200, responseBody = """{"publicId":"card-new"}""")
+
+            val result = HttpKanbnApiClient().createCard(
+                baseUrl = server.baseUrl,
+                apiKey = "api",
+                listPublicId = "list-1",
+                title = "Card",
+                description = "Description",
+                dueDate = LocalDate.of(2026, 3, 16),
+                tagPublicIds = listOf("tag-1"),
+            )
+
+            assertTrue(result is BoardsApiResult.Success<*>)
+            val request = server.findRequest("POST", "/api/v1/cards")
+            assertNotNull(request)
+            assertTrue(request?.body?.contains("\"dueDate\":\"2026-03-16T00:00:00Z\"") == true)
+            assertTrue(request?.body?.contains("\"description\":\"Description\"") == true)
+        }
+    }
+
+    @Test
+    fun createCardOmitsNullDueDateAndDescriptionInPayload() = runTest {
+        TestServer().use { server ->
+            server.register(path = "/api/v1/cards", method = "POST", status = 200, responseBody = """{"publicId":"card-new"}""")
+
+            val result = HttpKanbnApiClient().createCard(
+                baseUrl = server.baseUrl,
+                apiKey = "api",
+                listPublicId = "list-1",
+                title = "Card",
+                description = null,
+                dueDate = null,
+                tagPublicIds = emptyList(),
+            )
+
+            assertTrue(result is BoardsApiResult.Success<*>)
+            val request = server.findRequest("POST", "/api/v1/cards")
+            assertNotNull(request)
+            assertTrue(request?.body?.contains("\"dueDate\"") == false)
+            assertTrue(request?.body?.contains("\"description\"") == false)
+        }
+    }
+
     @Test
     fun getBoardDetailParsesWrappedPayloadWithDueDateVariants() = runTest {
         TestServer().use { server ->

app/src/test/java/space/hackenslacker/kanbn4droid/app/boarddetail/BoardDetailRepositoryTest.kt

@@ -1,6 +1,7 @@
 package space.hackenslacker.kanbn4droid.app.boarddetail
 
 import kotlinx.coroutines.test.runTest
+import java.time.LocalDate
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Test
@@ -216,7 +217,7 @@ class BoardDetailRepositoryTest {
             listId = " list-1 ",
             title = " Card title ",
             description = "  Description  ",
-            dueDate = "2026-03-16T10:15:30Z",
+            dueDate = LocalDate.of(2026, 3, 16),
             tagIds = listOf(" tag-1 ", "", "tag-2", "tag-1", "   ", " tag-2"),
         )
 
@@ -224,7 +225,7 @@ class BoardDetailRepositoryTest {
         assertEquals("list-1", apiClient.lastCreateCardListPublicId)
         assertEquals("Card title", apiClient.lastCreateCardTitle)
         assertEquals("Description", apiClient.lastCreateCardDescription)
-        assertEquals("2026-03-16T10:15:30Z", apiClient.lastCreateCardDueDate)
+        assertEquals(LocalDate.of(2026, 3, 16), apiClient.lastCreateCardDueDate)
         assertEquals(listOf("tag-1", "tag-2"), apiClient.lastCreateCardTagPublicIds)
     }
 
@@ -509,7 +510,7 @@ class BoardDetailRepositoryTest {
         var lastCreateCardListPublicId: String? = null
         var lastCreateCardTitle: String? = null
         var lastCreateCardDescription: String? = null
-        var lastCreateCardDueDate: String? = null
+        var lastCreateCardDueDate: LocalDate? = null
         var lastCreateCardTagPublicIds: List<String> = emptyList()
 
         override suspend fun healthCheck(baseUrl: String, apiKey: String): AuthResult = AuthResult.Success
@@ -558,7 +559,7 @@ class BoardDetailRepositoryTest {
             listPublicId: String,
             title: String,
             description: String?,
-            dueDate: String?,
+            dueDate: LocalDate?,
             tagPublicIds: List<String>,
         ): BoardsApiResult<CreatedEntityRef> {
             lastCreateCardListPublicId = listPublicId