fix(chat): resolve ChatManager before flushing SSE headers

Move resolveScopedChatManager() before res.flushHeaders() in the
POST /messages route so that failures (e.g. project DB cannot be
opened) produce a proper HTTP error instead of silently closing the
SSE connection.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/src/routes/register-chat-routes.ts

@@ -566,6 +566,10 @@ export function registerChatRoutes(ctx: ApiRoutesContext, deps: ChatRouteDeps):
         throw notFound(`Chat session ${sessionId} not found`);
       }
 
+      // Resolve per-project ChatManager before opening the SSE stream so
+      // failures (e.g. project DB cannot be opened) produce a proper HTTP error.
+      const chatManager = await resolveScopedChatManager(req.query.projectId as string | undefined);
+
       // Set SSE headers
       res.setHeader("Content-Type", "text/event-stream");
       res.setHeader("Cache-Control", "no-cache");
@@ -602,9 +606,6 @@ export function registerChatRoutes(ctx: ApiRoutesContext, deps: ChatRouteDeps):
         }
       }
 
-      // Resolve per-project ChatManager (falls back to global when no projectId)
-      const chatManager = await resolveScopedChatManager(req.query.projectId as string | undefined);
-
       // Allocate a generation up front so subscription and sendMessage broadcasts
       // share the same id. This filters out stragglers from a prior, just-cancelled
       // generation that would otherwise hit this fresh subscriber and falsely look