Add session mode for pre-funded request processing

Implement session-based API endpoints for creating, managing, and interacting with pre-funded sessions, including deposit and top-up invoice generation, macaroon authentication, and per-request debiting of compute costs.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 418bf6f8-212b-4bb0-a7a5-8231a061da4e
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 2dc3847e-7186-4a22-9c7e-16cd31bca8d9
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/9f85e954-647c-46a5-90a7-396e495a805a/418bf6f8-212b-4bb0-a7a5-8231a061da4e/sPDHkg8
Replit-Helium-Checkpoint-Created: true

artifacts/api-server/src/lib/agent.ts

@@ -3,6 +3,8 @@ import { anthropic } from "@workspace/integrations-anthropic-ai";
 export interface EvalResult {
   accepted: boolean;
   reason: string;
+  inputTokens: number;
+  outputTokens: number;
 }
 
 export interface WorkResult {
@@ -49,7 +51,12 @@ Respond ONLY with valid JSON: {"accepted": true, "reason": "..."} or {"accepted"
       throw new Error(`Failed to parse eval JSON: ${block.text}`);
     }
 
-    return { accepted: Boolean(parsed.accepted), reason: parsed.reason ?? "" };
+    return {
+      accepted: Boolean(parsed.accepted),
+      reason: parsed.reason ?? "",
+      inputTokens: message.usage.input_tokens,
+      outputTokens: message.usage.output_tokens,
+    };
   }
 
   async executeWork(requestText: string): Promise<WorkResult> {