fix: Validate session_id exists before memory insert (CF-194)

- Added session existence check before INSERT
- Graceful degradation: sets session_id to null if invalid
- Prevents FK constraint violation
- Memory still stored without session link

src/tools/memories.ts

@@ -45,7 +45,18 @@ interface MemoryListArgs {
  * Add a new memory/learning (enhanced with session_id and task_id)
  */
 export async function memoryAdd(args: MemoryAddArgs): Promise<string> {
-  const { category, title, content, context, project, session_id, task_id } = args;
+  let { category, title, content, context, project, session_id, task_id } = args;
+
+  // Validate session_id exists if provided (graceful degradation)
+  if (session_id) {
+    const sessionExists = await queryOne<{ exists: boolean }>(
+      'SELECT EXISTS(SELECT 1 FROM sessions WHERE id = $1)',
+      [session_id]
+    );
+    if (!sessionExists?.exists) {
+      session_id = undefined; // Set to null if session doesn't exist
+    }
+  }
 
   // Generate embedding for semantic search
   const embedText = `${title}. ${content}`;