feat(infer): messages starting with "other:" are not monthly fees

When the bank message starts with "other:" (case-insensitive),
inference does not look for a month, neither in the text nor from the
payment date. The trimmed message is written to Purpose, so reconcile
books the payment as an "other" transaction for the person instead of
a monthly fee. Messages containing "other:" elsewhere are unchanged.

- matching.IsOtherPurpose / is_other_purpose shared by inference and
  reconcile
- reconcile applies the rule to rows not yet processed by inference
- no person found: Purpose is still written, row shows as unmatched
- implemented in Go and legacy Python; four new parity fixtures

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

legacy/scripts/_fixture_seeds.py

@@ -358,6 +358,36 @@ SEEDS[("infer_transaction_details", "serial_date")] = {
     "member_names": _ROSTER,
     "default_year": 2026,
 }
+SEEDS[("infer_transaction_details", "other_prefix")] = {
+    "tx": {
+        "sender": "Jana Novakova",
+        "message": "other: tournament leden 2026",
+        "user_id": "",
+        "date": {"type": "string", "value": "2026-04-15"},
+    },
+    "member_names": _ROSTER,
+    "default_year": 2026,
+}
+SEEDS[("infer_transaction_details", "other_prefix_uppercase")] = {
+    "tx": {
+        "sender": "Test Payer",
+        "message": " Other: Dres ",
+        "user_id": "",
+        "date": {"type": "string", "value": "2026-04-15"},
+    },
+    "member_names": _ROSTER,
+    "default_year": 2026,
+}
+SEEDS[("infer_transaction_details", "other_not_at_start")] = {
+    "tx": {
+        "sender": "Jana Novakova",
+        "message": "leden other: dres",
+        "user_id": "",
+        "date": {"type": "string", "value": "2026-04-15"},
+    },
+    "member_names": _ROSTER,
+    "default_year": 2026,
+}
 SEEDS[("infer_transaction_details", "no_member_no_month")] = {
     "tx": {
         "sender": "Unknown Person",
@@ -476,6 +506,14 @@ SEEDS[("reconcile", "07_other_purpose_split")] = _reconcile_seed(
     transactions=[_tx("2026-01-10", 800, "Alice Dvořák, Bob Kratochvíl", "other:tournament", sender="Alice Dvořák")],
 )
 
+# 11 — message starts with "other:" on a row not yet inferred (empty Person/Purpose):
+# goes to the other ledger, the month stays unpaid
+SEEDS[("reconcile", "11_other_message_fallback")] = _reconcile_seed(
+    members=[_member("Alice Dvořák", "A", {"2026-01": (750, 3)})],
+    sorted_months=["2026-01"],
+    transactions=[_tx("2026-01-10", 300, "", "", sender="Alice Dvořák", message="other: tournament")],
+)
+
 # 08 — junior with attendance=1 (expected=0 in reconcile, unknown in UI)
 SEEDS[("reconcile", "08_junior_question_mark")] = _reconcile_seed(
     members=[_member("Karel Junior", "A", {"2026-01": (0, 1)})],

legacy/scripts/match_payments.py

@@ -150,27 +150,48 @@ def match_members(
 # Reconciliation
 # ---------------------------------------------------------------------------
 
+def is_other_purpose(text) -> bool:
+    """True when text marks a payment that is not a monthly fee.
+
+    It starts with "other:" (case-insensitive, leading whitespace ignored).
+    Used for both the Purpose column and the bank message.
+    """
+    return str(text or "").strip().lower().startswith("other:")
+
+
 def infer_transaction_details(tx: dict, member_names: list[str]) -> dict:
     """Infer member(s) and month(s) for a single transaction.
-    
+
+    A message that starts with "other:" is not a monthly fee: no month is
+    inferred (neither from the text nor from the date) and 'months' holds the
+    trimmed message as the single purpose.
+
     Returns:
         {
             'members': [(name, confidence)],
-            'months': [YYYY-MM],
+            'months': [YYYY-MM] or ['other:…'],
             'matched_text': str
         }
     """
     # Combine sender + message for searching
     search_text = f"{tx.get('sender', '')} {tx.get('message', '')} {tx.get('user_id', '')}"
     matched_members = match_members(search_text, member_names)
-    matched_months = parse_month_references(
-        tx.get("message", "") + " " + tx.get("user_id", "")
-    )
 
     if not matched_members:
         # Try matching sender name alone with more lenient matching
         matched_members = match_members(tx.get("sender", ""), member_names)
 
+    if is_other_purpose(tx.get("message", "")):
+        return {
+            "members": matched_members,
+            "months": [str(tx.get("message", "")).strip()],
+            "search_text": search_text
+        }
+
+    matched_months = parse_month_references(
+        tx.get("message", "") + " " + tx.get("user_id", "")
+    )
+
     if not matched_months:
         # If no month specified, try to infer from payment date
         tx_date = tx.get("date")
@@ -394,7 +415,7 @@ def reconcile(
         
         # Strip markers like [?]
         person_str = re.sub(r"\[\?\]\s*", "", person_str)
-        is_other = purpose_str.lower().startswith("other:")
+        is_other = is_other_purpose(purpose_str)
 
         if person_str and purpose_str:
             # We have pre-matched data (either from script or manual)
@@ -415,6 +436,10 @@ def reconcile(
             inference = infer_transaction_details(tx, member_names)
             matched_members = inference["members"]
             matched_months = inference["months"]
+            # A message starting with "other:" is inferred as a non-fee payment.
+            if len(matched_months) == 1 and is_other_purpose(matched_months[0]):
+                is_other = True
+                purpose_str = matched_months[0]
             amount = tx.get("amount", 0)
             try:
                 amount = float(amount)