feat(backend): add cyclone.store with BatchRecord and InMemoryStore

backend/src/cyclone/store.py

@@ -0,0 +1,68 @@
+"""In-memory batch store for parsed X12 files.
+
+Lives at module scope so route handlers and tests can import a single
+singleton. Single-process only — no cross-process coordination. Threading:
+a re-entrant lock guards every public method so FastAPI's threadpool
+request handlers can call them concurrently.
+"""
+
+from __future__ import annotations
+
+import threading
+from datetime import datetime, timezone
+from typing import Iterable, Literal
+
+from pydantic import BaseModel, ConfigDict, Field
+
+from cyclone.parsers.models import ParseResult
+from cyclone.parsers.models_835 import ParseResult835
+
+
+BatchKind = Literal["837p", "835"]
+
+
+class BatchRecord(BaseModel):
+    """One parsed file, with a stable uuid4 id and the full ParseResult."""
+
+    model_config = ConfigDict(extra="ignore")
+
+    id: str
+    kind: BatchKind
+    input_filename: str
+    parsed_at: str  # ISO 8601 UTC, e.g. "2026-06-19T12:00:00Z"
+    result: ParseResult | ParseResult835 = Field(discriminator=None)
+
+
+class InMemoryStore:
+    """Thread-safe list of BatchRecord, newest-first on `list`."""
+
+    def __init__(self) -> None:
+        self._batches: list[BatchRecord] = []
+        self._lock = threading.RLock()
+
+    def add(self, record: BatchRecord) -> None:
+        with self._lock:
+            self._batches.append(record)
+
+    def list(self, *, limit: int = 100) -> list[BatchRecord]:
+        with self._lock:
+            return list(reversed(self._batches[-limit:]))
+
+    def get(self, batch_id: str) -> BatchRecord | None:
+        with self._lock:
+            for b in self._batches:
+                if b.id == batch_id:
+                    return b
+            return None
+
+    def all(self) -> list[BatchRecord]:
+        with self._lock:
+            return list(self._batches)
+
+
+store = InMemoryStore()
+
+
+def utcnow_iso() -> str:
+    """ISO 8601 UTC timestamp, second precision, suffixed with 'Z'."""
+    return datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")