fix(tracker): is_processed now checks expires_at, not just file existence 🐛

Previously is_processed() returned True for any record file that existed,
relying entirely on cleanup_expired() (called at __init__) to delete stale
files. Because cleanup runs at container startup — before Akahu transactions
are fetched — any record that expired exactly on that startup would be deleted
and then immediately missed, letting the duplicate through.

Fix: is_processed() reads the expires_at field from the JSON and returns False
if the record has expired, regardless of whether cleanup has run.

Also adds migrate_ttl.py script to retroactively extend expires_at on existing
records that were written under a shorter TTL, and bumps version to 0.1.3.

scripts/migrate_ttl.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+"""
+Migrate existing transaction records to a new TTL.
+
+Reads all .json record files in the given storage directory and rewrites
+expires_at to processed_at + ttl_days. Records that have already expired
+are left untouched (they will be cleaned up on next startup).
+
+Usage:
+    python migrate_ttl.py <storage_dir> <ttl_days>
+
+Example (run on the server):
+    python migrate_ttl.py /opt/data/transaction_records 14
+"""
+import json
+import os
+import sys
+from datetime import datetime, timedelta
+
+
+def migrate(storage_dir: str, ttl_days: int) -> None:
+    if not os.path.isdir(storage_dir):
+        print(f"Directory not found: {storage_dir}")
+        sys.exit(1)
+
+    now = datetime.now()
+    updated = skipped = errors = 0
+
+    for filename in os.listdir(storage_dir):
+        if not filename.endswith(".json"):
+            continue
+        path = os.path.join(storage_dir, filename)
+        try:
+            with open(path) as f:
+                record = json.load(f)
+
+            processed_at = datetime.fromisoformat(record["processed_at"])
+            current_expires = datetime.fromisoformat(record["expires_at"])
+
+            if current_expires <= now:
+                skipped += 1
+                continue
+
+            new_expires = processed_at + timedelta(days=ttl_days)
+            if new_expires <= current_expires:
+                skipped += 1
+                continue
+
+            record["expires_at"] = new_expires.isoformat()
+            with open(path, "w") as f:
+                json.dump(record, f)
+            updated += 1
+
+        except (json.JSONDecodeError, KeyError, ValueError, OSError) as e:
+            print(f"  ERROR {filename}: {e}")
+            errors += 1
+
+    print(f"Done: {updated} updated, {skipped} skipped (already expired or TTL already sufficient), {errors} errors")
+
+
+if __name__ == "__main__":
+    if len(sys.argv) != 3:
+        print(__doc__)
+        sys.exit(1)
+    migrate(sys.argv[1], int(sys.argv[2]))