Route fava_client.add_account writes per account type

The Fava-backed ledger is being split into purpose-specific files (see
aiolabs/server-deploy#4): accounts/chart.beancount for static + admin-managed
opens, accounts/users.beancount for libra-appended per-user opens.

Add a `target_file` parameter to `add_account` that defaults to inference
from the account name (`:User-[0-9a-f]{8}$` -> users.beancount, otherwise
chart.beancount). Drop the now-redundant `GET /api/options` call that was
only used to discover the root file path. Callers that need explicit
control (e.g. the upcoming admin chart-edit endpoint) can pass
`target_file=` directly.

The retry loop, write lock, and insertion-point search are unchanged --
each included file is a self-contained source the existing logic operates
on cleanly.

Refs: aiolabs/libra#28

fava_client.py

@@ -18,6 +18,7 @@ See: https://github.com/beancount/fava/blob/main/src/fava/json_api.py
 """
 
 import asyncio
+import re
 import httpx
 from typing import Any, Dict, List, Optional
 from decimal import Decimal
@@ -30,6 +31,19 @@ class ChecksumConflictError(Exception):
     pass
 
 
+# Per-user account names end with :User-{user_id[:8]} (8 hex chars). Anything
+# matching is routed to accounts/users.beancount; anything else goes to
+# accounts/chart.beancount. See `_infer_target_file` and `add_account`.
+_USER_ACCT_RE = re.compile(r":User-[0-9a-f]{8}$")
+
+
+def _infer_target_file(account_name: str) -> str:
+    """Pick the Beancount include file for an Open directive based on account name."""
+    if _USER_ACCT_RE.search(account_name):
+        return "accounts/users.beancount"
+    return "accounts/chart.beancount"
+
+
 class FavaClient:
     """
     Async client for Fava REST API.
@@ -1487,13 +1501,20 @@ class FavaClient:
         currencies: list[str],
         opening_date: Optional[date] = None,
         metadata: Optional[Dict[str, Any]] = None,
+        target_file: Optional[str] = None,
         max_retries: int = 3
     ) -> Dict[str, Any]:
         """
         Add an account to the Beancount ledger via an Open directive.
 
         NOTE: Fava's /api/add_entries endpoint does NOT support Open directives.
-        This method uses /api/source to directly edit the Beancount file.
+        This method uses /api/source to directly edit a Beancount file.
+
+        The ledger is split across multiple include files
+        (see modules/services/fava-seeds.nix in server-deploy). Per-user
+        opens go to accounts/users.beancount; admin/static chart opens go to
+        accounts/chart.beancount. If `target_file` is not passed, it is
+        inferred from the account name via `_infer_target_file`.
 
         This method implements optimistic concurrency control with retry logic:
         - Acquires a global write lock before modifying the ledger
@@ -1506,6 +1527,8 @@ class FavaClient:
             currencies: List of currencies for this account (e.g., ["EUR", "SATS"])
             opening_date: Date to open the account (defaults to today)
             metadata: Optional metadata for the account
+            target_file: Beancount file path (relative to ledger root) to append
+                the Open directive to. Defaults to inference from `account_name`.
             max_retries: Maximum number of retry attempts on checksum conflict (default: 3)
 
         Returns:
@@ -1515,17 +1538,18 @@ class FavaClient:
             ChecksumConflictError: If all retry attempts fail due to concurrent modifications
 
         Example:
-            # Add a user's receivable account
+            # User-account names route to accounts/users.beancount automatically.
             result = await fava.add_account(
-                account_name="Assets:Receivable:User-abc123",
+                account_name="Assets:Receivable:User-abc12345",
                 currencies=["EUR", "SATS", "USD"],
-                metadata={"user_id": "abc123", "description": "User receivables"}
+                metadata={"user_id": "abc12345", "description": "User receivables"}
             )
 
-            # Add a user's payable account
+            # Static / admin-added chart entries route to accounts/chart.beancount.
             result = await fava.add_account(
-                account_name="Liabilities:Payable:User-abc123",
+                account_name="Expenses:NewCategory",
-                currencies=["EUR", "SATS"]
+                currencies=["EUR"],
+                target_file="accounts/chart.beancount",
             )
         """
         from datetime import date as date_type
@@ -1533,6 +1557,9 @@ class FavaClient:
         if opening_date is None:
             opening_date = date_type.today()
 
+        if target_file is None:
+            target_file = _infer_target_file(account_name)
+
         last_error = None
 
         for attempt in range(max_retries):
@@ -1540,18 +1567,10 @@ class FavaClient:
             async with self._write_lock:
                 try:
                     async with httpx.AsyncClient(timeout=self.timeout) as client:
-                        # Step 1: Get the main Beancount file path from Fava
+                        # Step 1: Get current source file (fresh read on each attempt)
-                        options_response = await client.get(f"{self.base_url}/options")
-                        options_response.raise_for_status()
-                        options_data = options_response.json()["data"]
-                        file_path = options_data["beancount_options"]["filename"]
-
-                        logger.debug(f"Fava main file: {file_path}")
-
-                        # Step 2: Get current source file (fresh read on each attempt)
                         response = await client.get(
                             f"{self.base_url}/source",
-                            params={"filename": file_path}
+                            params={"filename": target_file}
                         )
                         response.raise_for_status()
                         source_data = response.json()["data"]
@@ -1559,12 +1578,12 @@ class FavaClient:
                         sha256sum = source_data["sha256sum"]
                         source = source_data["source"]
 
-                        # Step 3: Check if account already exists (may have been created by concurrent request)
+                        # Step 2: Check if account already exists (may have been created by concurrent request)
                         if f"open {account_name}" in source:
-                            logger.info(f"Account {account_name} already exists in Beancount file")
+                            logger.info(f"Account {account_name} already exists in {target_file}")
                             return {"data": sha256sum, "mtime": source_data.get("mtime", "")}
 
-                        # Step 4: Find insertion point (after last Open directive AND its metadata)
+                        # Step 3: Find insertion point (after last Open directive AND its metadata)
                         lines = source.split('\n')
                         insert_index = 0
                         for i, line in enumerate(lines):
@@ -1575,7 +1594,7 @@ class FavaClient:
                                 while insert_index < len(lines) and lines[insert_index].startswith((' ', '\t')) and lines[insert_index].strip():
                                     insert_index += 1
 
-                        # Step 5: Format Open directive as Beancount text
+                        # Step 4: Format Open directive as Beancount text
                         currencies_str = ", ".join(currencies)
                         open_lines = [
                             "",
@@ -1591,15 +1610,15 @@ class FavaClient:
                                 else:
                                     open_lines.append(f'  {key}: {value}')
 
-                        # Step 6: Insert into source
+                        # Step 5: Insert into source
                         for i, line in enumerate(open_lines):
                             lines.insert(insert_index + i, line)
 
                         new_source = '\n'.join(lines)
 
-                        # Step 7: Update source file via PUT /api/source
+                        # Step 6: Update source file via PUT /api/source
                         update_payload = {
-                            "file_path": file_path,
+                            "file_path": target_file,
                             "source": new_source,
                             "sha256sum": sha256sum
                         }
@@ -1612,7 +1631,7 @@ class FavaClient:
                         response.raise_for_status()
                         result = response.json()
 
-                        logger.info(f"Added account {account_name} to Beancount file with currencies {currencies}")
+                        logger.info(f"Added account {account_name} to {target_file} with currencies {currencies}")
                         return result
 
                 except httpx.HTTPStatusError as e: