Customer.io

Build me a focused customer messaging workflow for the personal core of Customer.io. Requirements:

- Use exactly this stack: Next.js 15 + TypeScript + PostgreSQL. Model subscribers, consent records, campaigns, delivery attempts, and suppression state; keep stable source IDs and timestamps.
- Paid product context: Behavior-triggered email, push, SMS, in-app messages, and data pipelines. Build only this DIY scope: Build a small customer messaging editor and subscriber database that exports clean HTML and sends only through a reputable user-supplied email provider.
- For customer messaging, import subscribers with consent source, status, and suppression flag.
- Compose a campaign, preview HTML/plain text, and queue an authorized send by stable message ID.
- Process delivery, bounce, and unsubscribe events before publishing the archive or report.
- Use a local web page with input, progress, review, and export views. Required input or access: transactional or bulk email provider key in .env. Keep credentials in .env.
- Acceptance: with one labelled sample, show the input, saved intermediate state, and exported result; verify this invariant: Unsubscribed or bounced addresses must stay suppressed; retrying an ambiguous provider response cannot silently send twice.
- Out of scope: large-scale segmentation and automation; payments, recommendations, and audience network. Keep this a personal, inspectable workflow.
- Include a README with setup, a sample input, required keys or permissions, data location, and the supported scope.

# AGENTS.md — Build guide for Customer.io

## Project scope
Build a small customer messaging editor and subscriber database that exports clean HTML and sends only through a reputable user-supplied email provider.

Catalogue verdict: no. Do not mistake the interface for the product. Customer.io's durable value is deliverability, reputation, network, which a solo one-shot build cannot reproduce responsibly. The prompt therefore builds only the closest honest personal consolation tool.
Use the implementation prompt below to define the deliverable. Complete each phase's acceptance checks before extending the scope.

## Working agreement
- Inspect the repository and its existing instructions before choosing paths, dependencies or commands. Keep one coherent stack and explain changes to the proposed architecture.
- Plan a vertical slice that accepts a real input and produces the useful output described below. Persist only the state the prompt calls for; respect memory-only and upstream-managed workflows. Use fixtures only when they are clearly labelled.
- After scaffolding, document the actual install, development, check and build commands in README and keep them synchronized with the package or project manifest. Do not report commands as successful unless they ran.
- Work in small steps. At handoff, list implemented flows, checks actually performed, remaining blockers, and any credentials or provider setup the owner must supply.
- Do not publish, spend money, contact customers, delete source data or run irreversible migrations without the project owner's authorization.

## Prerequisites
- Node.js 22
- PostgreSQL
- transactional or bulk email provider key in .env
- Explicit README warning that this is a consolation build, not a production replacement

## Stack and architecture
- Use exactly this stack: Next.js 15 + TypeScript + PostgreSQL.
- Model subscribers, consent records, campaigns, delivery attempts, and suppression state; keep stable source IDs and timestamps.
- Interface for this customer messaging workflow: a local web page with input, progress, review, and export views.

## Security and data integrity
- Unsubscribed or bounced addresses must stay suppressed; retrying an ambiguous provider response cannot silently send twice.
- Validate imported records and file paths; keep user data within the storage location named in the prompt.
- State the practical limit: large-scale segmentation and automation.

## Agent implementation rules
- Project rule, data: Model subscribers, consent records, campaigns, delivery attempts, and suppression state; keep stable source IDs and timestamps.
- Project rule, behavior: For customer messaging, import subscribers with consent source, status, and suppression flag.
- Project rule, recovery: Unsubscribed or bounced addresses must stay suppressed; retrying an ambiguous provider response cannot silently send twice.

## Optional agent skills and references
No installable skill is listed for this guide; use the project rules and the stack documentation.

Read the linked SKILL.md and its dependencies before adding a skill. Select only the skills matching this project's runtime and task; their documentation does not supply API access, credentials or approval to perform external actions. Pin the reviewed revision where the tool supports it. Follow the chosen agent's documented project-level installation mechanism.

## Distribution ideas
These are optional planning notes. Obtain the owner's approval before publishing or contacting anyone.
- Demonstrate this customer messaging operation with sample or user-owned data: For customer messaging, import subscribers with consent source, status, and suppression flag.
- Show a concrete result or export: Process delivery, bounce, and unsubscribe events before publishing the archive or report.
- State the practical limit: large-scale segmentation and automation.

## Engineering roadmap
1. Phase 1, architecture and data: Use exactly this stack: Next.js 15 + TypeScript + PostgreSQL. Model subscribers, consent records, campaigns, delivery attempts, and suppression state; keep stable source IDs and timestamps.
2. Phase 2, implement: For customer messaging, import subscribers with consent source, status, and suppression flag.
3. Phase 3, implement: Compose a campaign, preview HTML/plain text, and queue an authorized send by stable message ID.
4. Phase 4, review and output: Process delivery, bounce, and unsubscribe events before publishing the archive or report.
5. Phase 5, recovery and acceptance: Verify this invariant with a saved fixture: Unsubscribed or bounced addresses must stay suppressed; retrying an ambiguous provider response cannot silently send twice. State the practical limit: large-scale segmentation and automation.

## Paid-product capabilities outside this build
- large-scale segmentation and automation
- payments, recommendations, and audience network
- sender reputation, deliverability, and suppression handling
- sender reputation and deliverability operations
- bounce, complaint, and suppression handling

## Implementation prompt
Build me a focused customer messaging workflow for the personal core of Customer.io. Requirements:

- Use exactly this stack: Next.js 15 + TypeScript + PostgreSQL. Model subscribers, consent records, campaigns, delivery attempts, and suppression state; keep stable source IDs and timestamps.
- Paid product context: Behavior-triggered email, push, SMS, in-app messages, and data pipelines. Build only this DIY scope: Build a small customer messaging editor and subscriber database that exports clean HTML and sends only through a reputable user-supplied email provider.
- For customer messaging, import subscribers with consent source, status, and suppression flag.
- Compose a campaign, preview HTML/plain text, and queue an authorized send by stable message ID.
- Process delivery, bounce, and unsubscribe events before publishing the archive or report.
- Use a local web page with input, progress, review, and export views. Required input or access: transactional or bulk email provider key in .env. Keep credentials in .env.
- Acceptance: with one labelled sample, show the input, saved intermediate state, and exported result; verify this invariant: Unsubscribed or bounced addresses must stay suppressed; retrying an ambiguous provider response cannot silently send twice.
- Out of scope: large-scale segmentation and automation; payments, recommendations, and audience network. Keep this a personal, inspectable workflow.
- Include a README with setup, a sample input, required keys or permissions, data location, and the supported scope.

## Completion evidence
Demonstrate the prompt's acceptance scenarios against the scoped workflow. Include setup from a clean checkout and failure recovery. Check persistence across restart and export/restore only for the state the prompt says to store; for memory-only tools, confirm that temporary content is discarded as specified. Record actual results and remaining limitations. A detailed plan alone does not establish a working replacement.