Agentic systems should be proactive, reliable and cost-effective.

const SLACK_CHANNEL = 'accounts';1Currency formatting by hand → listen-fire has a helperfunction formatAmount(cents, currency) {  const cur = String(currency || 'usd').toUpperCase();  const zeroDecimal = ['BIF','CLP','DJF','GNF','JPY','KMF','KRW','MGA','PYG','RWF','UGX','VND','VUV','XAF','XOF','XPF'];  const major = zeroDecimal.includes(cur) ? cents : cents / 100;  const whole = Number.isInteger(major);  try {    return new Intl.NumberFormat('en-US', {      style: 'currency', currency: cur,      minimumFractionDigits: whole ? 0 : 2, maximumFractionDigits: whole ? 0 : 2,    }).format(major);  } catch (e) {    return `${whole ? major : major.toFixed(2)} ${cur}`;  }}async function alertAccounts(text) {  await slack.post({ channel: SLACK_CHANNEL, text });}async function handler(event) {2Is this the right event → listen-fire guarantees it  if (!event || event.type !== 'invoice.payment_failed') {    console.log('ignored event type', event && event.type);    return { ignored: true };  }3Guard against duplicates → listen-fire deduplicates automatically  const doneKey = `done:${event.id}`;  if (event.id && (await kv.get(doneKey))) {    console.log('duplicate event, already handled', event.id);    return { duplicate: true };  }4Safety guards everywhere → listen-fire provides live type safety  const inv = event.data && event.data.object;  if (!inv) throw new Error('payment_failed event has no data.object');  const stripeEmail = (inv.customer_email || '').trim();  const amount = formatAmount(inv.amount_due, inv.currency);  const invoiceLink = inv.hosted_invoice_url;4  const who = `${inv.customer_name || stripeEmail || inv.customer || 'unknown customer'}`;  const invoiceRef = `${inv.number || inv.id || ''}`.trim();  if (!stripeEmail) {    await alertAccounts(`:warning: Payment of ${amount} failed (invoice ${invoiceRef}, Stripe customer ${inv.customer}) but the invoice has no customer email, so I couldn't look them up in the CRM. No email was sent.`);8Manual auditing → all writes automatically logged    if (event.id) await kv.set(doneKey, 'alerted-no-email');    return { alerted: 'no-email' };  }5Handle the format of every API → every system gets the same interface with the engineering handled  const res = await crm.request('POST', '/v2/objects/people/records/query', {    filter: { email_addresses: stripeEmail },    limit: 5,  });  if (res.status !== 200) {    throw new Error(`CRM lookup failed: ${res.status} ${JSON.stringify(res.body)}`);  }6Cautious double-checking → confidence from live typing  const matches = (res.body.data || []).filter(r =>    ((r.values.email_addresses) || []).some(e => (e.email_address || '').toLowerCase() === stripeEmail.toLowerCase()));  if (matches.length !== 1) {    const why = matches.length === 0 ? 'no CRM record matches' : `${matches.length} CRM records match`;    await alertAccounts(`:warning: Payment of ${amount} failed for ${who} <${stripeEmail}> (invoice ${invoiceRef}), but ${why} that email, so I couldn't tell their plan. No email was sent; please follow up manually.${invoiceLink ? ' Invoice: ' + invoiceLink : ''}`);8    if (event.id) await kv.set(doneKey, 'alerted-lookup');    return { alerted: why };  }7Field juggling from concerns about missing values → confidence from live typing  const person = matches[0];  const v = person.values;  const planTitle = (((v.plan || [])[0] || {}).option || {}).title || '';  const plan = planTitle.toLowerCase();  const name = ((v.name || [])[0] || {}).full_name || inv.customer_name || 'there';  const manager = ((v.account_manager || [])[0] || {}).value;  const company = ((v.company || [])[0] || {}).value;  if (plan === 'monthly') {    if (!invoiceLink) {      await alertAccounts(`:warning: Payment of ${amount} failed for ${name} <${stripeEmail}> (monthly), but the invoice has no hosted_invoice_url, so the retry email wasn't sent.`);8      if (event.id) await kv.set(doneKey, 'alerted-no-link');      return { alerted: 'no-link' };    }    await email.send({      to: stripeEmail,      subject: "Your Ledgerline payment didn't go through",      body:`Hi ${name},We tried to take your Ledgerline payment of ${amount} and it didn't go through. It's usually an expired card or a bank check.You can update your card and pay here: ${invoiceLink}We'll try again in a few days. If anything's changed, just reply to this email.The Ledgerline team`,    });8    if (event.id) await kv.set(doneKey, 'emailed');    return { emailed: stripeEmail };  }  if (plan === 'yearly' || plan === 'annual') {    const mgr = manager ? `Account manager: ${manager}.` : 'No account manager is set in the CRM for this account.';    await alertAccounts(`:warning: Annual-plan payment of ${amount} failed for ${name}${company ? ' (' + company + ')' : ''} <${stripeEmail}>. ${mgr}${invoiceLink ? ' Invoice: ' + invoiceLink : ''}`);8    if (event.id) await kv.set(doneKey, 'slacked');    return { slacked: true };  }  await alertAccounts(`:warning: Payment of ${amount} failed for ${name} <${stripeEmail}>, but their CRM plan is ${planTitle ? '"' + planTitle + '"' : 'not set'} (not monthly or yearly). No email was sent; please follow up manually.${invoiceLink ? ' Invoice: ' + invoiceLink : ''}`);8  if (event.id) await kv.set(doneKey, 'alerted-plan');  return { alerted: 'unknown-plan' };}