You are helping me build the following AI agent workflow.

## Goal
Instagram Carousel Publishing: Receives a product collection webhook, uploads each slide image, assembles them into an Instagram carousel, publishes the post.

## Specification
- What it does: Get your product collections instantly turned into published Instagram carousels without manual posting. The agent receives your data via webhook, uploads each slide image, assembles them into a post, and sends the live link to Slack for you.
- Trigger: Triggered by an event (Event · on webhook payload)
- Autonomy: Fully hands-off
- Expected setup effort: about an afternoon
- Tools/services involved:
  - Webhook: Receive product collection data
  - HTTP Request: Interact with Instagram Graph API and fetch images
  - Upload to URL: Generate stable CDN URLs for slide images
  - Code: Validate payload and build captions
  - Slack: Notify team of published posts

## Known pitfalls, handle each one explicitly in your implementation
1. Instagram has strict image dimension requirements so validate aspect ratios before uploading to avoid rejection errors.
2. The webhook payload might contain missing or malformed URLs, add a check to skip invalid items gracefully.
3. Slack notifications may fail if the channel ID is incorrect, verify the target channel exists before sending messages.

## Reference implementation
https://n8n.io/workflows/14643 (workflow template)
Fetch and inspect this before building. If it matches my stack, adapt it;
if not, rebuild the pattern with my tools.

## Process requirements
1. Before building: ask me which of the listed tools I actually use and
   what my platform is (n8n / Make / code / other). Do not assume.
2. Adapt the pattern to my answers; do not force the reference stack.
3. Address every pitfall above; tell me how you handled each.
4. Provide a test plan I can run before letting this touch real data.
5. Ask before any step that sends messages, modifies data, or spends money.

Source: https://usecasesforagents.com/use-case/automate-instagram-carousel-publishing/ via usecasesforagents.com