Add session payments

import express from 'express';
import { initialise } from '@prudra/core';
import { walletMiddleware, payMiddleware, vaultMiddleware } from '@prudra/express';

initialise({ apiKey: process.env.PRUDRA_API_KEY! });

const app = express();
app.use(express.json());

app.post(
  '/agent/step',
  walletMiddleware({ walletId: process.env.BYO_WALLET_ID }),
  payMiddleware({
    price:          '0.01',
    description:    'Agent step',
    acceptSessions: true,   // Enable session payments
  }),
  vaultMiddleware(),
  async (req, res) => {
    const { step, query } = req.body as { step: string; query: string };
    const vault           = req.vault!;

    // Simulate step-specific work
    const result = { step, query, output: `Completed: ${step}` };

    // All session requests share this vault — documents accumulate
    await vault.emit('agent.step', { step, completedAt: new Date().toISOString() });
    await vault.addDocument(result, `Step: ${step}`);

    res.json({
      vaultId:   vault.id,        // same across all session requests
      sessionId: req.sessionId,   // return so agent can include in next request
      step,
      result,
    });
  }
);

app.post(
  '/agent/finish',
  walletMiddleware({ walletId: process.env.BYO_WALLET_ID }),
  payMiddleware({ price: '0.00', acceptSessions: true }),
  vaultMiddleware(),
  async (req, res) => {
    const vault = req.vault!;

    // Persist before sealing — keeps vault alive after session expires
    await vault.persist();
    await vault.seal('Agent session complete');

    const manifest = await vault.getManifest();

    res.json({
      vaultId:   vault.id,
      status:    'complete',
      documents: manifest.documents,
      files:     manifest.files,
    });
  }
);

# Step 1: First request — creates session (pays with stub mode)
curl -i -X POST http://localhost:4004/agent/step \
  -H "Content-Type: application/json" \
  -H "X-PAYMENT: stub_payment_accepted" \
  -d '{"step": "search", "query": "latest AI papers"}'

HTTP/1.1 200 OK
X-PRUDRA-SESSION-ID: sess_clx1abc123
Content-Type: application/json

{
  "vaultId": "vlt_clx1def456",
  "sessionId": "sess_clx1abc123",
  "step": "search",
  "result": { "step": "search", "query": "latest AI papers", "output": "Completed: search" }
}

# Step 2: Subsequent request — no payment needed, include session ID
curl -X POST http://localhost:4004/agent/step \
  -H "Content-Type: application/json" \
  -H "X-PRUDRA-SESSION-ID: sess_clx1abc123" \
  -d '{"step": "summarise", "query": "latest AI papers"}'

{
  "vaultId": "vlt_clx1def456",
  "sessionId": "sess_clx1abc123",
  "step": "summarise",
  "result": { "step": "summarise", "output": "Completed: summarise" }
}