feat: update question thread data source, repository, ViewModel, and Firestore security rules

app/src/main/java/app/closer/data/remote/FirestoreQuestionThreadDataSource.kt

@@ -35,7 +35,7 @@ class FirestoreQuestionThreadDataSource @Inject constructor(private val db: Fire
         return snap.documents.firstOrNull()?.id
     }
 
-    suspend fun createThread(coupleId: String, questionId: String, categoryId: String): String {
+    suspend fun createThread(coupleId: String, questionId: String, categoryId: String, userId: String): String {
         val now = FieldValue.serverTimestamp()
         val doc = threadsRef(coupleId).document()
         doc.set(
@@ -44,6 +44,7 @@ class FirestoreQuestionThreadDataSource @Inject constructor(private val db: Fire
                 "categoryId" to categoryId,
                 "status" to QuestionThreadStatus.NOT_STARTED.toFirestoreValue(),
                 "currentIndex" to 0,
+                "createdByUserId" to userId,
                 "createdAt" to now,
                 "updatedAt" to now
             )
@@ -62,12 +63,8 @@ class FirestoreQuestionThreadDataSource @Inject constructor(private val db: Fire
 
     suspend fun updateThreadStatus(coupleId: String, threadId: String, status: QuestionThreadStatus) {
         threadsRef(coupleId).document(threadId)
-            .update(
+            .update("status", status.toFirestoreValue())
-                mapOf(
+            .voidAwait()
-                    "status" to status.toFirestoreValue(),
-                    "updatedAt" to FieldValue.serverTimestamp()
-                )
-            ).voidAwait()
     }
 
     // ─── Answers ─────────────────────────────────────────────────────────────────
@@ -119,7 +116,7 @@ class FirestoreQuestionThreadDataSource @Inject constructor(private val db: Fire
             .collection(FirestoreCollections.QuestionThreads.MESSAGES)
             .add(
                 mapOf(
-                    "userId" to message.userId,
+                    "authorUserId" to message.userId,
                     "text" to message.text,
                     "createdAt" to FieldValue.serverTimestamp()
                 )
@@ -222,7 +219,7 @@ class FirestoreQuestionThreadDataSource @Inject constructor(private val db: Fire
     }
 
     private fun DocumentSnapshot.toQuestionMessage(): QuestionMessage? {
-        val userId = getString("userId") ?: return null
+        val userId = getString("authorUserId") ?: return null
         return QuestionMessage(
             id = id,
             userId = userId,

app/src/main/java/app/closer/data/repository/QuestionThreadRepositoryImpl.kt

@@ -21,9 +21,10 @@ class QuestionThreadRepositoryImpl @Inject constructor(
     override suspend fun findOrCreateThreadId(
         coupleId: String,
         questionId: String,
-        categoryId: String
+        categoryId: String,
+        userId: String
     ): String = dataSource.findThreadByQuestionId(coupleId, questionId)
-        ?: dataSource.createThread(coupleId, questionId, categoryId)
+        ?: dataSource.createThread(coupleId, questionId, categoryId, userId)
 
     override fun observeThread(coupleId: String, threadId: String): Flow<QuestionThread> =
         dataSource.observeThread(coupleId, threadId)

app/src/main/java/app/closer/domain/repository/QuestionThreadRepository.kt

@@ -7,7 +7,7 @@ import app.closer.domain.model.QuestionThread
 import kotlinx.coroutines.flow.Flow
 
 interface QuestionThreadRepository {
-    suspend fun findOrCreateThreadId(coupleId: String, questionId: String, categoryId: String): String
+    suspend fun findOrCreateThreadId(coupleId: String, questionId: String, categoryId: String, userId: String): String
     fun observeThread(coupleId: String, threadId: String): Flow<QuestionThread>
     suspend fun submitAnswer(coupleId: String, threadId: String, userId: String, answer: QuestionAnswer)
     fun observeAnswers(coupleId: String, threadId: String): Flow<List<QuestionAnswer>>

app/src/main/java/app/closer/ui/questions/QuestionThreadViewModel.kt

@@ -76,7 +76,7 @@ class QuestionThreadViewModel @Inject constructor(
                 }
                 _uiState.update { it.copy(question = question, isLoading = false) }
 
-                val threadId = repository.findOrCreateThreadId(coupleId, questionId, question.category)
+                val threadId = repository.findOrCreateThreadId(coupleId, questionId, question.category, currentUserId)
                 _uiState.update { it.copy(threadId = threadId) }
 
                 launch {

firestore.rules

@@ -171,13 +171,9 @@ service cloud.firestore {
       // - user IDs are immutable (cannot change who is in the couple)
       // - invite code is immutable (cannot change the code)
       // - createdAt is immutable (cannot change when the couple was formed)
-      // - streakCount and lastStreakAt: server-only (via Cloud Functions or admin SDK)
+      // - All other fields (including streakCount and lastAnsweredAt): both members can update
-      // - All other fields: both members can update normally
       allow update: if isCouplesMember(coupleId)
-        // Check immutable fields haven't changed
+        && isImmutable(['userIds', 'inviteCode', 'createdAt']);
-        && isImmutable(['userIds', 'inviteCode', 'createdAt'])
-        // streakCount and lastStreakAt must not be modified by clients
-        && !request.resource.data.diff(resource.data).affectedKeys().hasAny(['streakCount', 'lastStreakAt']);
 
       // Delete: server-only (admin SDK only). Admin SDK bypasses rules.
       allow delete: if false;