# AGENTS.md — Build guide for DataFast

## Project scope
Record allowed campaign parameters, link an identified customer at signup and ingest verified Stripe events to attribute net collected revenue. Show first-touch and last-touch assumptions and unassigned revenue explicitly.

Catalogue verdict: kinda. The pageview half of DataFast is the same weekend build as Plausible or Umami. The revenue half is where it stops being a weekend. Attribution is only worth anything if the anonymous visitor who found your launch post on a phone is still recognisably the customer who pays from a laptop three weeks later, and that stitching is exactly what an agent will hand you a naive version of. A localStorage id plus an email match at signup does get you a channel table that is directionally right for a single-domain solo product, which is genuinely worth having. It also quietly under-counts every cross-device path, every privacy browser that clears storage between visits, and every customer who pays with a different address than they signed up with. You can build the dashboard in a weekend. Trusting it enough to move ad spend is the part that keeps costing you weekends.
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- Do not publish, spend money, contact customers, delete source data or run irreversible migrations without the project owner's authorization.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
- A supported Node release, PostgreSQL, HTTPS for a shared deployment, and a backup destination. Begin with one workspace and explicit owner/member permissions. Stripe integration requires the account keys, verified webhook secret and public HTTPS endpoint; start with sandbox fixtures before live payments.
- Implementation components: Next.js App Router and TypeScript for server-rendered pages and validated mutations. PostgreSQL with Drizzle migrations; Better Auth sessions for a small private workspace.
- Scope boundary: Cross-device identity, universal bot filtering and purchase-likelihood predictions are excluded.

## Stack and architecture
- Next.js App Router and TypeScript for server-rendered pages and validated mutations.
- PostgreSQL with Drizzle migrations; Better Auth sessions for a small private workspace.
- Domain model: first-party visits, consent states, campaign touches, explicit customer links, payment events and refunds

## Security and data integrity
- Authorize every record read and mutation on the server using its workspace membership; validate payloads, protect mutations against CSRF, and escape user-authored HTML.
- Correctness boundary: Do not stitch unrelated devices by guesswork; refunds and duplicate webhook IDs affect revenue once, and ambiguous customer matches stay unassigned.
- Commit related database changes in one transaction. Use version checks for competing edits and an outbox for external notifications; retry delivery independently of saving the record.
- Export versioned JSON plus attachments and a readable CSV summary. Restore into a separate database and compare record IDs and attachment checksums before switching.

## Agent implementation rules
- Project rule — data model: first-party visits, consent states, campaign touches, explicit customer links, payment events and refunds
- Project rule — preserve this invariant: Do not stitch unrelated devices by guesswork; refunds and duplicate webhook IDs affect revenue once, and ambiguous customer matches stay unassigned.
- Project rule — acceptance evidence: Replay a payment and refund callback and reconcile one net amount; a purchase without a consented visitor link remains in an unassigned bucket.

## Optional agent skills and references
- Optional external skill: [vercel-react-best-practices](https://github.com/vercel-labs/agent-skills/blob/main/skills/react-best-practices/SKILL.md) — Improve React and Next.js data fetching, rendering, bundle size and server performance. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission.
- Optional external skill: [supabase-postgres-best-practices](https://github.com/supabase/agent-skills/blob/main/skills/supabase-postgres-best-practices/SKILL.md) — Review PostgreSQL schemas, queries, indexes, pooling, concurrency and row-level security. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission.
- Optional external skill: [web-design-guidelines](https://github.com/vercel-labs/agent-skills/blob/main/skills/web-design-guidelines/SKILL.md) — Review web interfaces for accessibility, keyboard focus, forms, navigation and interaction quality. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission.
- Optional external skill: [stripe-best-practices](https://github.com/stripe/ai/blob/main/skills/stripe-best-practices/SKILL.md) — Plan Stripe checkout, subscriptions, webhooks, platform payments and secure API integration. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission.

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 the actual DataFast-inspired workflow with owned or clearly labeled sample data: Record allowed campaign parameters, link an identified customer at signup and ingest verified Stripe events to attribute net collected revenue. Show first-touch and last-touch assumptions and unassigned revenue explicitly.
- Publish a reproducible walkthrough with this observable result: Replay a payment and refund callback and reconcile one net amount; a purchase without a consented visitor link remains in an unassigned bucket.
- Explain who can operate this scoped tool, its setup and ongoing costs, and these remaining product gaps: Cross-device identity, universal bot filtering and purchase-likelihood predictions are excluded. Avoid guaranteed savings, performance scores or implied endorsement.

## Engineering roadmap
1. Phase 1 — Scope and fixtures. Implement this bounded workflow: Record allowed campaign parameters, link an identified customer at signup and ingest verified Stripe events to attribute net collected revenue. Show first-touch and last-touch assumptions and unassigned revenue explicitly. Record prerequisites, select representative user-owned fixtures and document the unsupported features: Cross-device identity, universal bot filtering and purchase-likelihood predictions are excluded.
2. Phase 2 — Durable model. Model first-party visits, consent states, campaign touches, explicit customer links, payment events and refunds Add migrations or a versioned document format, explicit validation, stable IDs and a visible import-error report. Preserve this rule: Do not stitch unrelated devices by guesswork; refunds and duplicate webhook IDs affect revenue once, and ambiguous customer matches stay unassigned.
3. Phase 3 — Complete the first useful path. Implement the workflow's input, review and output interface, with clear controls and explicit empty/error states. Commit related database changes in one transaction. Use version checks for competing edits and an outbox for external notifications; retry delivery independently of saving the record.
4. Phase 4 — Permissions and integration failure. Authorize every record read and mutation on the server using its workspace membership; validate payloads, protect mutations against CSRF, and escape user-authored HTML. Request integration credentials and permissions only for the enabled feature; show a disconnected state instead of mock results.
5. Phase 5 — Portable handoff. Export versioned JSON plus attachments and a readable CSV summary. Restore into a separate database and compare record IDs and attachment checksums before switching. Include setup, operating limits, fixture walkthrough and shutdown/restart instructions in the README.
6. Phase 6 — Acceptance scenarios. Replay a payment and refund callback and reconcile one net amount; a purchase without a consented visitor link remains in an unassigned bucket. Repeat the workflow after restart and with a denied permission or unavailable dependency; show recoverable failure rather than a success placeholder.

## Paid-product capabilities outside this build
- identity stitching across devices, browsers and cleared storage
- bot and AI-crawler filtering that stays current without you
- one-click installs for Shopify, Webflow, WordPress and 20 other platforms
- the live visitor feed and purchase-likelihood scoring
- the hosted MCP server and CLI for querying the data in plain English

## Implementation prompt
WORKING SLICE
Record allowed campaign parameters, link an identified customer at signup and ingest verified Stripe events to attribute net collected revenue. Show first-touch and last-touch assumptions and unassigned revenue explicitly.

Build this scoped DataFast-inspired workflow with a documented data model and visible failure states.

Architecture
- Next.js App Router and TypeScript for server-rendered pages and validated mutations.
- PostgreSQL with Drizzle migrations; Better Auth sessions for a small private workspace.

Prerequisites and limits
A supported Node release, PostgreSQL, HTTPS for a shared deployment, and a backup destination. Begin with one workspace and explicit owner/member permissions. Stripe integration requires the account keys, verified webhook secret and public HTTPS endpoint; start with sandbox fixtures before live payments.
Outside this release: Cross-device identity, universal bot filtering and purchase-likelihood predictions are excluded.

Data model and correctness
first-party visits, consent states, campaign touches, explicit customer links, payment events and refunds
Invariant: Do not stitch unrelated devices by guesswork; refunds and duplicate webhook IDs affect revenue once, and ambiguous customer matches stay unassigned.
Commit related database changes in one transaction. Use version checks for competing edits and an outbox for external notifications; retry delivery independently of saving the record.

Security and privacy
Authorize every record read and mutation on the server using its workspace membership; validate payloads, protect mutations against CSRF, and escape user-authored HTML.

Recovery and export
Export versioned JSON plus attachments and a readable CSV summary. Restore into a separate database and compare record IDs and attachment checksums before switching.

Implementation order
1. Phase 1 — Scope and fixtures. Implement this bounded workflow: Record allowed campaign parameters, link an identified customer at signup and ingest verified Stripe events to attribute net collected revenue. Show first-touch and last-touch assumptions and unassigned revenue explicitly. Record prerequisites, select representative user-owned fixtures and document the unsupported features: Cross-device identity, universal bot filtering and purchase-likelihood predictions are excluded.
2. Phase 2 — Durable model. Model first-party visits, consent states, campaign touches, explicit customer links, payment events and refunds Add migrations or a versioned document format, explicit validation, stable IDs and a visible import-error report. Preserve this rule: Do not stitch unrelated devices by guesswork; refunds and duplicate webhook IDs affect revenue once, and ambiguous customer matches stay unassigned.
3. Phase 3 — Complete the first useful path. Implement the workflow's input, review and output interface, with clear controls and explicit empty/error states. Commit related database changes in one transaction. Use version checks for competing edits and an outbox for external notifications; retry delivery independently of saving the record.
4. Phase 4 — Permissions and integration failure. Authorize every record read and mutation on the server using its workspace membership; validate payloads, protect mutations against CSRF, and escape user-authored HTML. Request integration credentials and permissions only for the enabled feature; show a disconnected state instead of mock results.
5. Phase 5 — Portable handoff. Export versioned JSON plus attachments and a readable CSV summary. Restore into a separate database and compare record IDs and attachment checksums before switching. Include setup, operating limits, fixture walkthrough and shutdown/restart instructions in the README.
6. Phase 6 — Acceptance scenarios. Replay a payment and refund callback and reconcile one net amount; a purchase without a consented visitor link remains in an unassigned bucket. Repeat the workflow after restart and with a denied permission or unavailable dependency; show recoverable failure rather than a success placeholder.

Acceptance
Replay a payment and refund callback and reconcile one net amount; a purchase without a consented visitor link remains in an unassigned bucket.
Use real source data or clearly labeled fixtures. Explain unsupported input and provider failures; do not fabricate analytics, delivery receipts, accuracy claims or security guarantees.

Optional agent guidance
Optional external skill: [vercel-react-best-practices](https://github.com/vercel-labs/agent-skills/blob/main/skills/react-best-practices/SKILL.md) — Improve React and Next.js data fetching, rendering, bundle size and server performance. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission.
Optional external skill: [supabase-postgres-best-practices](https://github.com/supabase/agent-skills/blob/main/skills/supabase-postgres-best-practices/SKILL.md) — Review PostgreSQL schemas, queries, indexes, pooling, concurrency and row-level security. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission.
Optional external skill: [web-design-guidelines](https://github.com/vercel-labs/agent-skills/blob/main/skills/web-design-guidelines/SKILL.md) — Review web interfaces for accessibility, keyboard focus, forms, navigation and interaction quality. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission.
Optional external skill: [stripe-best-practices](https://github.com/stripe/ai/blob/main/skills/stripe-best-practices/SKILL.md) — Plan Stripe checkout, subscriptions, webhooks, platform payments and secure API integration. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission.
Project rule — data model: first-party visits, consent states, campaign touches, explicit customer links, payment events and refunds
Project rule — preserve this invariant: Do not stitch unrelated devices by guesswork; refunds and duplicate webhook IDs affect revenue once, and ambiguous customer matches stay unassigned.
Project rule — acceptance evidence: Replay a payment and refund callback and reconcile one net amount; a purchase without a consented visitor link remains in an unassigned bucket.

## 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.