Webhook-Triggered Sequencer — reactive personalized outreach on demand

You are helping me build a webhook-triggered sequencer. This is different from the cron-based GTM Email Sequencer: instead of polling a leads table on a schedule, this agent fires whenever an upstream system POSTs a lead payload to its webhook endpoint. Per fire: read the lead fields from the payload, write a single hyper-personalized email, push to Instantly via createLead, post a notification to Slack.

Use this pattern when you want sequencer firing to be reactive — every lead arrives with rich context and gets a tailored email immediately, not at the next 5-minute tick.

REFERENCE DOCS
- agntdata API documentation: https://agnt.mintlify.app/apis/overview
- agntdata Instantly integration: `createLead` (single-lead variant of bulkAddLeads)
- agntdata Slack connector: `slack_post_message`

ABOUT MY MOTION
- Product name: <YOUR PRODUCT>
- Product URL: <YOUR PRODUCT URL>
- Sender voice: <SENDER NAME, role at company, sign-off style>
- Instantly campaign id (UUID): <CAMPAIGN_ID>
- Slack channel for run notifications: <SLACK_CHANNEL_ID>
- The trigger: what upstream system POSTs to this agent? <UPSTREAM_TRIGGER — e.g. "another agnt_ agent emits a webhook when a qualified lead is ready", "Stripe new-customer webhook", "Calendly demo booked", etc.>

WEBHOOK PAYLOAD SHAPE
List the fields the upstream sender will POST. The agent reads them and substitutes into the email. A canonical shape:
- `signals.first_name` — lead's first name
- `signals.org_name` — their company
- `signals.website_url` — optional company URL
- `signals.company_description` — what their company does (sharpens personalization)
- `signals.qualification_notes` — why this person was targeted (tone calibration)
- `cta_url` — the link to put in the email (demo, claim, signup, …)
- `user_id` — for deterministic A/B subject-line selection (optional)

If your payload looks different, adapt the email template to your fields.

EMAIL FORMAT (under 100 words)
1. **Greeting** — "Hey <first_name>,"
2. **Hook** — one strong sentence that captures the *outcome* the lead gets. Made specific to their world via `signals.company_description` + `signals.qualification_notes`.
3. **CTA** — link the `cta_url`. One sentence max.
4. **Optional closer** — a single human line. Avoid emojis and corporate filler.
5. **Sign-off** — sender name + role.

NEVER:
- Reference what the lead "said", "posted", or "did" — that reads as AI-trying-too-hard.
- Compliment the lead or their company.
- Use filler ("I know you're busy", "given your focus on…").

A/B SUBJECT VARIANTS (optional)
If you pass a `user_id` in the payload, the agent picks between two subject styles deterministically based on the last char of the UUID:
- 0–4 → Variant A: personalized natural subject ("built an agent to find your next 100 leads at <company>")
- 5–f → Variant B: fixed evergreen subject (configured per deploy)

This lets you A/B test subjects without juggling code.

WHAT TO BUILD
- A webhook-triggered agent (claude-sonnet-4-6 — personalization quality matters here).
- One webhook endpoint exposed for upstream POSTs. Document the payload schema in the agent's description.
- Per webhook fire: parse payload → write email → createLead to Instantly → slack_post_message summary.
- No DB writes required — this agent is stateless; the upstream system already persisted the lead.

GUARDRAILS
- One email per webhook. If the payload arrives malformed, surface the error to Slack and skip the Instantly call.
- Don't loop or retry — webhook senders should handle retries. This agent does its work and returns.
- Every payload field must be substituted; never send a template with `<first_name>` unfilled.

When you're ready, ask me the ABOUT MY MOTION + WEBHOOK PAYLOAD SHAPE blocks.