fix(lint): prefer-const in context.ts; fix GET /sessions/:id isGenerating routing

- context.ts: let engine → const engine (prefer-const lint rule)
- register-chat-routes.ts GET /sessions/🆔 use per-project chatManager
  for isGenerating enrichment (addresses Greptile P2 comment)

packages/dashboard/src/routes/context.ts

@@ -81,7 +81,7 @@ export async function getProjectContext(
   const engineManager = options?.engineManager;
 
   if (projectId && engineManager) {
-    let engine = engineManager.getEngine(projectId);
+    const engine = engineManager.getEngine(projectId);
     if (!engine) {
       // Trigger lazy engine start as fire-and-forget so this request is not
       // blocked while the engine initialises (engine.start() may take several

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

@@ -253,7 +253,8 @@ export function registerChatRoutes(ctx: ApiRoutesContext, deps: ChatRouteDeps):
       }
 
       const enriched: EnrichedChatSession = session;
-      enriched.isGenerating = options?.chatManager?.isGenerating?.(sessionId) ?? false;
+      const chatManager = await resolveScopedChatManager(req.query.projectId as string | undefined).catch(() => options?.chatManager);
+      enriched.isGenerating = chatManager?.isGenerating?.(sessionId) ?? false;
 
       res.json({ session: enriched });
     } catch (err: unknown) {