Snapchat

Build me a private ephemeral photo-messaging app, snaps for one friend group that opts in. Requirements:

- Node 22 + Fastify + better-sqlite3, and a vanilla-JS installable PWA served from
  /public with no build step: manifest, service worker, an offline shell that caches
  the UI but never caches snaps.
- Core loop: open the camera with getUserMedia, capture a photo, type or draw a
  caption overlay on a canvas, send it to one or more friends.
- A snap is viewable exactly once for up to 10 seconds; the server deletes the image
  file immediately after the view and keeps only a minimal sent/opened log row.
- Accounts are invite-code only: the admin seeds codes with a CLI script, signup is
  username plus passcode, sessions are httpOnly cookies.
- Per-pair daily streaks tracked server-side, shown next to each friend.
- Group stories: a snap posted to my story is visible to all members and hard-deleted
  after 24 hours by a sweep job.
- Media lives as files on disk outside the web root; metadata in SQLite with WAL mode.
- Web push for new snaps behind a permission prompt; the app must work fully without
  it, and the README says iOS web push is best-effort. VAPID keys and session secret
  in .env, with a documented script that generates them and a .env.example.
- HTTPS is required for camera and push: document local dev with a self-signed cert
  and production behind Caddy on a cheap VPS.
- Be honest in the UI: label view-once as deleted from our server, and state plainly
  that screenshots cannot be detected on the web.
- Tests for delete-after-view, the 24-hour story sweep, and streak day-boundary math
  with a fake clock.
- Out of scope: AR lenses and face filters, Snap Map, Discover or Spotlight feeds,
  video calls, screenshot detection, analytics, and third-party auth.
- README: setup, deploying, where data lives, how deletion actually works, and how
  to invite the first two friends.

# AGENTS.md — Build guide for Snapchat

## Project scope
Snap a photo with a caption overlay and send it to an invited friend group; each snap deletes after one timed view, with daily streaks and 24-hour group stories.

Catalogue verdict: no. The mechanics one-shot fine: ephemeral photo messages, 24-hour stories and streak counters are CRUD plus a delete timer. None of that is the product. Snapchat is where your friends already are · the value of a disappearing photo is who is on the other end, and a self-hosted clone with two users is a group chat with extra steps. Add the AR lens stack built on years of face-tracking models, screenshot detection that needs OS-level app privileges, and media infrastructure moving billions of snaps a day, and the honest verdict is that the network is the app. The prompt below is the consolation build: a private snap relay for one friend group that opts in.
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 small VPS or free-tier Node host with HTTPS (camera and push APIs require it)
- friends willing to install the PWA and actually use it

## Stack and architecture
- Node 22 + Fastify + better-sqlite3, and a vanilla-JS installable PWA served from /public with no build step: manifest, service worker, an offline shell that caches the UI but never caches snaps.
- Model sources or channels, posts, dated observations, drafts, and reports; keep stable source IDs and timestamps.
- Interface for this ephemeral messaging + stories workflow: a focused ephemeral messaging + stories input, review, and export interface.

## Security and data integrity
- Node 22 + Fastify + better-sqlite3, and a vanilla-JS installable PWA served from /public with no build step: manifest, service worker, an offline shell that caches the UI but never caches snaps.
- Validate imported records and file paths; keep user data within the storage location named in the prompt.
- State the practical limit: the people: everyone you snap with is on Snapchat, not on your server.

## Agent implementation rules
- Project rule, data: Model sources or channels, posts, dated observations, drafts, and reports; keep stable source IDs and timestamps.
- Project rule, behavior: Core loop: open the camera with getUserMedia, capture a photo, type or draw a caption overlay on a canvas, send it to one or more friends.
- Project rule, recovery: Node 22 + Fastify + better-sqlite3, and a vanilla-JS installable PWA served from /public with no build step: manifest, service worker, an offline shell that caches the UI but never caches snaps.

## 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 ephemeral messaging + stories operation with sample or user-owned data: Core loop: open the camera with getUserMedia, capture a photo, type or draw a caption overlay on a canvas, send it to one or more friends.
- Show a concrete result or export: Be honest in the UI: label view-once as deleted from our server, and state plainly that screenshots cannot be detected on the web.
- State the practical limit: the people: everyone you snap with is on Snapchat, not on your server.

## Engineering roadmap
1. Phase 1, architecture and data: Node 22 + Fastify + better-sqlite3, and a vanilla-JS installable PWA served from /public with no build step: manifest, service worker, an offline shell that caches the UI but never caches snaps. Model sources or channels, posts, dated observations, drafts, and reports; keep stable source IDs and timestamps.
2. Phase 2, implement: Core loop: open the camera with getUserMedia, capture a photo, type or draw a caption overlay on a canvas, send it to one or more friends.
3. Phase 3, implement: Accounts are invite-code only: the admin seeds codes with a CLI script, signup is username plus passcode, sessions are httpOnly cookies.
4. Phase 4, review and output: Group stories: a snap posted to my story is visible to all members and hard-deleted after 24 hours by a sweep job. Be honest in the UI: label view-once as deleted from our server, and state plainly that screenshots cannot be detected on the web.
5. Phase 5, recovery and acceptance: Node 22 + Fastify + better-sqlite3, and a vanilla-JS installable PWA served from /public with no build step: manifest, service worker, an offline shell that caches the UI but never caches snaps. Verify this invariant with a saved fixture: A failed platform call retains the draft and cannot be marked published; retries use a stable delivery key. State the practical limit: the people: everyone you snap with is on Snapchat, not on your server.

## Paid-product capabilities outside this build
- the people: everyone you snap with is on Snapchat, not on your server
- AR lenses and filters backed by years of face-tracking models
- screenshot detection · a web app cannot see or stop screenshots
- Snap Map, Discover, Spotlight and the creator ecosystem
- reliable mobile push · web push on iOS is best-effort, not messenger-grade

## Implementation prompt
Build me a private ephemeral photo-messaging app, snaps for one friend group that opts in. Requirements:

- Node 22 + Fastify + better-sqlite3, and a vanilla-JS installable PWA served from
  /public with no build step: manifest, service worker, an offline shell that caches
  the UI but never caches snaps.
- Core loop: open the camera with getUserMedia, capture a photo, type or draw a
  caption overlay on a canvas, send it to one or more friends.
- A snap is viewable exactly once for up to 10 seconds; the server deletes the image
  file immediately after the view and keeps only a minimal sent/opened log row.
- Accounts are invite-code only: the admin seeds codes with a CLI script, signup is
  username plus passcode, sessions are httpOnly cookies.
- Per-pair daily streaks tracked server-side, shown next to each friend.
- Group stories: a snap posted to my story is visible to all members and hard-deleted
  after 24 hours by a sweep job.
- Media lives as files on disk outside the web root; metadata in SQLite with WAL mode.
- Web push for new snaps behind a permission prompt; the app must work fully without
  it, and the README says iOS web push is best-effort. VAPID keys and session secret
  in .env, with a documented script that generates them and a .env.example.
- HTTPS is required for camera and push: document local dev with a self-signed cert
  and production behind Caddy on a cheap VPS.
- Be honest in the UI: label view-once as deleted from our server, and state plainly
  that screenshots cannot be detected on the web.
- Tests for delete-after-view, the 24-hour story sweep, and streak day-boundary math
  with a fake clock.
- Out of scope: AR lenses and face filters, Snap Map, Discover or Spotlight feeds,
  video calls, screenshot detection, analytics, and third-party auth.
- README: setup, deploying, where data lives, how deletion actually works, and how
  to invite the first two friends.

## 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.