Receipt validity check (documentary evidence)

# Instructions — Validity of receipts (documentary evidence)

## ⚠️ Critical distinction

| Filter | What it means | What it does NOT mean |
|--------|-------------------|--------------------------|
| `documentaryEvidenceStatus=provided` | A file is attached | That the document is valid or compliant |
| `documentaryEvidenceStatus=providedAndDpr` | File attached + DPR processing | That the document is valid |
| `documentaryEvidenceStatus=missing` | No file attached | |
| `documentaryEvidenceStatus=declaredAsInvalid` | Marked invalid by the user | |

**For actual validity**: read `documentaryEvidence.validity.valid` (boolean) and `documentaryEvidence.compliances` on each payable.

## Use case 1 — Identify expenses without a receipt

Call `get_payables` with:
```json
{ "field": "documentaryEvidenceStatus", "operator": "=", "value": ["missing", "declaredAsInvalid"] }
```

→ All expenses requiring receipt follow-up.

## Use case 2 — Check compliance of attached receipts

Step 1: Retrieve payables with an attached receipt
```json
{ "field": "documentaryEvidenceStatus", "operator": "=", "value": ["provided", "providedAndDpr"] }
```

Step 2: For each payable, inspect:
```
documentaryEvidence.validity.valid       → true/false
documentaryEvidence.compliances          → {} (empty) or { compliance rules }
documentaryEvidence.type                 → "invoice" | "creditNote" | ...
documentaryEvidence.invoiceNumber        → present if invoice
```

Step 3: Flag cases where `validity.valid=false` or `compliances` contains errors.

## Full structure of the documentaryEvidence field

```json
{
  "validity": {
    "valid": true/false
  },
  "compliances": {
    // business compliance rules (can be empty {} on accounts without strict compliance)
  },
  "type": "invoice" | "creditNote" | "other",
  "invoiceNumber": "XXXX",              // if type=invoice
  "creditNoteNumber": "XXXX",           // if type=creditNote
  "referenceInvoiceNumber": "XXXX"      // if credit note with a reference
}
```

## Use case 3 — Full receipt audit

For a full audit, combine both searches:

1. No receipt: `status=["missing","declaredAsInvalid"]`
2. With a potentially invalid receipt: `status=["provided","providedAndDpr"]` + filter on `validity.valid=false` client-side

Display:
- % of payables with a valid receipt
- List of problematic cases (no receipt + invalid receipt)
- Priority on high amounts

## Note on the demo account

On the Spendesk demo account, all `provided` receipts have `validity.valid=true` and `compliances={}`. In production with compliance rules enabled, `compliances` can contain validation errors (missing VAT, invalid date, unreadable amount, etc.).

## Example prompts

- "Which expenses have no receipt?" → filter status=missing
- "Are there any receipts attached but non-compliant?" → provided + validity.valid=false
- "Audit missing receipts before closing" → missing + declaredAsInvalid