feat(rules+trigger): conversations Firestore rules, onMessageWritten listens on conversations path, gitignore

- firestore.rules: conversations doc read/write rules with ciphertext validation, messages subcollection create rules (image or ciphertext text)
- onMessageWritten: trigger path changed from question_threads to conversations, passes conversation_id in FCM data, removed questionId resolution (no longer needed)
- .gitignore: deduplicate ClaudeReport.md entry

.gitignore

@@ -71,3 +71,4 @@ docs/img/qa.jpeg
 docs/img/sam.jpg
 ClaudeReport.md
 ClaudeReport.md
+ClaudeReport.md

firestore.rules

@@ -413,6 +413,39 @@ service cloud.firestore {
         }
       }
 
+      // Conversations: the Messages inbox. Each conversation (the couple chat or a per-question
+      // discussion) holds E2E-encrypted messages; only metadata + the encrypted last-message
+      // preview live on the conversation doc.
+      match /conversations/{conversationId} {
+        allow read: if isCouplesMember(coupleId);
+        // Members may create/merge-update the conversation doc within the allowed shape; any
+        // last-message preview must be ciphertext (encrypted on-device before write).
+        allow write: if isCouplesMember(coupleId)
+          && request.resource.data.keys().hasOnly(
+               ['type', 'questionId', 'createdAt', 'lastMessageAt', 'lastMessagePreview', 'lastMessageSenderId', 'reads'])
+          && (!('lastMessagePreview' in request.resource.data)
+               || isCiphertext(request.resource.data.lastMessagePreview));
+
+        // Messages: author-only create; text is ciphertext OR it's an image message pointing at
+        // encrypted Storage bytes; immutable after creation.
+        match /messages/{messageId} {
+          allow read: if isCouplesMember(coupleId);
+          allow create: if isCouplesMember(coupleId)
+            && coupleEncryptionEnabled(coupleId)
+            && request.resource.data.authorUserId == request.auth.uid
+            && request.resource.data.keys().hasOnly(['authorUserId', 'text', 'createdAt', 'type', 'mediaUrl'])
+            && (
+              (request.resource.data.get('type', 'text') == 'image'
+                && request.resource.data.mediaUrl is string
+                && request.resource.data.mediaUrl.size() > 0)
+              ||
+              (request.resource.data.get('type', 'text') == 'text'
+                && isCiphertext(request.resource.data.text))
+            );
+          allow update, delete: if false;
+        }
+      }
+
       // Date swipes: per-couple, per-date partner swipe state. The action is E2E
       // ciphertext so the server can't read date preferences; only swipedAt is plaintext.
       match /date_swipes/{dateIdeaId} {

functions/src/questions/onMessageWritten.ts

@@ -3,18 +3,18 @@ import * as admin from 'firebase-admin'
 
 /**
  * Firestore trigger that notifies the other partner when a chat message is
- * sent in a question thread.
+ * sent in a conversation (the couple chat or a per-question discussion).
  *
- * Path: couples/{coupleId}/question_threads/{threadId}/messages/{messageId}
+ * Path: couples/{coupleId}/conversations/{conversationId}/messages/{messageId}
  *
  * Respects the recipient's `notifChatMessage` preference (default: enabled).
  */
 export const onMessageWritten = functions.firestore
-  .document('couples/{coupleId}/question_threads/{threadId}/messages/{messageId}')
+  .document('couples/{coupleId}/conversations/{conversationId}/messages/{messageId}')
   .onCreate(async (snap, context) => {
-    const { coupleId, threadId, messageId } = context.params as {
+    const { coupleId, conversationId, messageId } = context.params as {
       coupleId: string
-      threadId: string
+      conversationId: string
       messageId: string
     }
 
@@ -39,14 +39,6 @@ export const onMessageWritten = functions.firestore
       return
     }
 
-    // The conversation deep link + the client's "am I already in this thread?" suppression both
-    // key off questionId, so resolve it from the thread doc and pass it through.
-    const threadDoc = await db
-      .collection('couples').doc(coupleId)
-      .collection('question_threads').doc(threadId)
-      .get()
-    const questionId = (threadDoc.data()?.questionId as string | undefined) ?? ''
-
     const partnerUserDoc = await db.collection('users').doc(partnerId).get()
 
     // Respect the partner's notification preference (opt-out; default is enabled).
@@ -95,8 +87,7 @@ export const onMessageWritten = functions.firestore
       data: {
         type: 'chat_message',
         couple_id: coupleId,
-        thread_id: threadId,
+        conversation_id: conversationId,
-        ...(questionId ? { question_id: questionId } : {}),
         ...(authorPhotoUrl ? { sender_avatar_url: authorPhotoUrl } : {}),
       },
     }
@@ -119,6 +110,6 @@ export const onMessageWritten = functions.firestore
     }
 
     console.log(
-      `[onMessageWritten] notified partner ${partnerId} for thread ${threadId} in couple ${coupleId}`
+      `[onMessageWritten] notified partner ${partnerId} for conversation ${conversationId} in couple ${coupleId}`
     )
   })