fix(backend): prevent seed opinion creation failure due to read replica lag (#407)

When creating conversations with seed opinions in production, the seed opinion
creation was failing with "Conversation slugId not found" errors. This occurred
because postNewOpinion queried the conversation by slugId immediately after
creation, hitting the read replica before replication completed.

Changes:
- Add optional conversationMetadata parameter to postNewOpinion interface
- When metadata is provided, skip database lookup and use provided values
- Skip lock check for seed opinions (just-created conversations cannot be locked)
- Pass conversation metadata from createNewPost when creating seed opinions
- Eliminates 2 unnecessary database queries per seed opinion

This fix resolves the production-only race condition while improving efficiency
by avoiding redundant database queries for data already available in scope.

Author: nicobao

services/api/src/service/comment.ts

@@ -1090,6 +1090,13 @@ interface PostNewOpinionProps {
     userAgent: string;
     now: Date;
     isSeed: boolean;
+    conversationMetadata?: {
+        conversationId: number;
+        conversationContentId: number;
+        conversationAuthorId: string;
+        conversationIsIndexed: boolean;
+        conversationIsLoginRequired: boolean;
+    };
 }
 
 export async function postNewOpinion({
@@ -1102,31 +1109,51 @@ export async function postNewOpinion({
     userAgent,
     now,
     isSeed,
+    conversationMetadata,
 }: PostNewOpinionProps): Promise<CreateCommentResponse> {
-    const { getPostMetadataFromSlugId } = useCommonPost();
-    const {
-        id: conversationId,
-        contentId: conversationContentId,
-        authorId: conversationAuthorId,
-        isIndexed: conversationIsIndexed,
-        isLoginRequired: conversationIsLoginRequired,
-    } = await getPostMetadataFromSlugId({
-        db: db,
-        conversationSlugId: conversationSlugId,
-    });
+    // Use provided metadata if available (for seed opinions), otherwise fetch from DB
+    let conversationId: number;
+    let conversationContentId: number | null;
+    let conversationAuthorId: string;
+    let conversationIsIndexed: boolean;
+    let conversationIsLoginRequired: boolean;
+
+    if (conversationMetadata) {
+        conversationId = conversationMetadata.conversationId;
+        conversationContentId = conversationMetadata.conversationContentId;
+        conversationAuthorId = conversationMetadata.conversationAuthorId;
+        conversationIsIndexed = conversationMetadata.conversationIsIndexed;
+        conversationIsLoginRequired =
+            conversationMetadata.conversationIsLoginRequired;
+    } else {
+        const { getPostMetadataFromSlugId } = useCommonPost();
+        const metadata = await getPostMetadataFromSlugId({
+            db: db,
+            conversationSlugId: conversationSlugId,
+        });
+        conversationId = metadata.id;
+        conversationContentId = metadata.contentId;
+        conversationAuthorId = metadata.authorId;
+        conversationIsIndexed = metadata.isIndexed;
+        conversationIsLoginRequired = metadata.isLoginRequired;
+    }
+
     if (conversationContentId == null) {
         throw httpErrors.gone("Cannot comment on a deleted post");
     }
 
-    const isLocked = await useCommonPost().isPostSlugIdLocked({
-        postSlugId: conversationSlugId,
-        db: db,
-    });
-    if (isLocked) {
-        return {
-            success: false,
-            reason: "conversation_locked",
-        };
+    // Skip lock check if metadata provided (seed opinions on just-created conversations)
+    if (!conversationMetadata) {
+        const isLocked = await useCommonPost().isPostSlugIdLocked({
+            postSlugId: conversationSlugId,
+            db: db,
+        });
+        if (isLocked) {
+            return {
+                success: false,
+                reason: "conversation_locked",
+            };
+        }
     }
 
     try {

services/api/src/service/post.ts

@@ -282,6 +282,13 @@ export async function createNewPost({
                 userAgent: "Seed Opinion Creation",
                 now,
                 isSeed: true,
+                conversationMetadata: {
+                    conversationId,
+                    conversationContentId,
+                    conversationAuthorId: authorId,
+                    conversationIsIndexed: isIndexed,
+                    conversationIsLoginRequired: isIndexed ? true : isLoginRequired,
+                },
             });
         }
     }