Refactors duplicate payment check in Fava

Improves payment recording logic by fetching recent entries and filtering using Python, replacing the BQL query.

This addresses issues with matching against set types in BQL, enhancing reliability.

tasks.py

@@ -152,18 +152,28 @@ async def on_invoice_paid(payment: Payment) -> None:
     fava = get_fava_client()
 
     try:
-        # Query Fava for existing payment entry
-        query = f"SELECT * WHERE links ~ 'ln-{payment.payment_hash[:16]}'"
-        async with httpx.AsyncClient(timeout=5.0) as client:
-            response = await client.get(
-                f"{fava.base_url}/query",
-                params={"query_string": query}
-            )
-            result = response.json()
+        # Check if payment already recorded by fetching recent entries
+        # Note: We can't use BQL query with `links ~ 'pattern'` because links is a set type
+        # and BQL doesn't support regex matching on sets. Instead, fetch entries and filter in Python.
+        link_to_find = f"ln-{payment.payment_hash[:16]}"
 
-            if result.get('data', {}).get('rows'):
-                logger.info(f"Payment {payment.payment_hash} already recorded in Fava, skipping")
-                return
+        async with httpx.AsyncClient(timeout=5.0) as client:
+            # Get recent entries from Fava's journal endpoint
+            response = await client.get(
+                f"{fava.base_url}/api/journal",
+                params={"time": ""}  # Get all entries
+            )
+
+            if response.status_code == 200:
+                data = response.json()
+                entries = data.get('entries', [])
+
+                # Check if any entry has our payment link
+                for entry in entries:
+                    entry_links = entry.get('links', [])
+                    if link_to_find in entry_links:
+                        logger.info(f"Payment {payment.payment_hash} already recorded in Fava, skipping")
+                        return
 
     except Exception as e:
         logger.warning(f"Could not check Fava for duplicate payment: {e}")