Invoice attachment access (pre-signed URLs)

# Instructions — Access to supporting documents

## ⚠️ URLs with a limited lifetime: 1 hour

URLs returned by `get_payable_attachments` are **pre-signed AWS S3 links**.

```
X-Amz-Expires=3600 → expires 1 hour after generation
```

**Never:**
- Store these URLs in a database
- Cache them in a long conversational context
- Pass them to a third-party system that would use them later

**Always:** share the URL immediately and tell the user it expires in 1h.

## ⚠️ Tool cache = 3300s (55min)

The tool itself is cached for 55 minutes.
If the URL was retrieved at the start of the cache window, it will only have **5 minutes** left at the end of the cache window.
→ For interactive use, don't hesitate to call the tool again if the time between two uses exceeds 30 minutes.

## Step 1 — Get the payableId

Call `get_payables` with the appropriate filter to find the target payable.
```json
{
  "companyId": "...",
  "filters": { "field": "documentaryEvidenceStatus", "operator": "=", "value": ["provided"] },
  "pageSize": 20
}
```
→ Extract the `id` field of the payable you're interested in.

## Step 2 — Retrieve the attachments

```json
{ "companyId": "...", "payableId": "<payable-id>" }
```

## Step 3 — Interpret the fields

For each attachment:
- `url`: direct download link (valid for 1h) — to share immediately
- `mimetype`: MIME type (`image/jpeg`, `application/pdf`, `image/png`, etc.) — inform the user
- `checksum`: MD5 hash of the file for integrity verification
- `attachedAt`: attachment date (format `YYYY-MM-DD`, not datetime)

## Step 4 — Present the result

```
Supporting document found for invoice [description]:
- Type: image/jpeg
- Attached on: 2023-01-11
- Download link: [URL]
⚠️ This link expires in 1 hour. After expiry, call the command again to get a new link.
```

## Live example (real data)

```json
{
  "mimetype": "image/jpeg",
  "checksum": "107fc4b2a439cbeb84c91c9764b9744d",
  "attachedAt": "2023-01-11",
  "url": "https://spx-production.s3.eu-west-1.amazonaws.com/invoices/nTtrU1GKV_5633342?X-Amz-Expires=3600..."
}
```
→ S3 bucket: `spx-production.s3.eu-west-1.amazonaws.com` (EU region)
→ Expiry: 3600s confirmed live

## Example prompt

- "Show me the supporting document for the Airbnb invoice" → get_payables search + get_payable_attachments
- "Download the PDF of last month's Oracle invoice" → filter supplier + get_payable_attachments
- "Check that the attachment isn't corrupted" → compare local checksum vs API checksum