Hand off HubSpot closed-won deals to Loops and Slack

Build me a sales-to-customer-success handoff that fires whenever a HubSpot deal moves to the Closed Won stage. It should seed the new customer in Loops, kick off the onboarding sequence, and ping our CS team in Slack.

Trigger: a webhook from HubSpot on deal stage change. Only run the flow when the new stage is closedwon (default sales pipeline) so we don't fire on every stage move.

On each fire, run this sequence:

1. HubSpot Get Deal by ID. Request the deal amount, our plan_tier property, industry, close date, and the deal owner, plus the associated primary contact. If the deal has more than one contact associated, use the primary one.

2. HubSpot Get Contact for that primary contact. Pull email, first name, last name, job title, and company name.

3. Loops List Mailing Lists. Find the mailing list named "Customers" and grab its ID so we can subscribe the new customer to it.

4. Loops Update Contact (upsert) using the contact's email as the identifier. Set firstName, lastName, and put company name and job title on the contact. Then include custom top-level camelCase properties: planTier, dealAmount, industry, and companySize when we have it. In the mailingLists object, set the Customers list ID to true so we subscribe them. Remember that custom properties are top-level camelCase keys, not nested under a "properties" object, and mailingLists is an object mapping list ID to boolean (never the list name).

5. Loops Send Event to kick off the pre-built onboarding sequence. Pick the event name by deal amount: if the amount is at or above $25,000, use customer_onboarding_started_enterprise; otherwise use customer_onboarding_started_smb. Pass plan tier and deal owner name as event properties so the Loops sequence can personalize. Include an Idempotency-Key header derived from the HubSpot deal ID (for example the deal ID itself) so a webhook retry does not re-fire the onboarding sequence.

6. Slack Send a Message (as the bot) to our #cs-handoffs channel. Summarize the deal: name, amount, plan tier, industry, close date, deal owner (call them out by @-mention if you can resolve the Slack user by email, otherwise plain name), and primary contact (name, title, email). Include a link back to the HubSpot deal record and a link to the HubSpot contact record. Close the message with a one-line reminder of what the first onboarding email will do so CS knows what the customer is about to see.

Guardrails the agent should apply on its own:

- If the deal has no primary contact, or the contact has no valid email, skip both the Loops upsert and the Loops Send Event so we don't create an orphan customer. Still post the Slack message, but flag it clearly at the top (something like "heads up: no contact email on this deal, CS please gather it before starting onboarding").

- If the deal amount is missing or unparseable, default to the SMB event name rather than skipping the fire.

- Never re-fire the Loops event for the same deal close. The Idempotency-Key tied to the deal ID enforces this, and the agent should not remove it on retry.

- Read the amount in USD; if HubSpot returns a different currency, note it in the Slack message but still use the numeric amount for the enterprise-versus-SMB decision.