Improve translation reliability and progress feedback

backend/sessions.py

@@ -7,8 +7,12 @@ from typing import Any
 from backend.models import TranslationSession
 
 
+class SessionConflictError(Exception):
+    """Raised when a long-running phase tries to update a changed session."""
+
+
 class SessionStore:
-    """Thread-safe-ish in-memory dict for translation sessions.
+    """Process-local in-memory store for user-owned translation sessions.
 
     Each session is keyed by a UUID and has a 24-hour TTL.
     Expired sessions are lazily cleaned on access.
@@ -18,18 +22,26 @@ class SessionStore:
         self._store: dict[str, dict[str, Any]] = {}
         self.ttl_hours = ttl_hours
 
-    def create(self, session_data: TranslationSession) -> str:
+    def create(self, session_data: TranslationSession, owner_id: str) -> str:
         session_id = uuid.uuid4().hex[:16]
         self._store[session_id] = {
             "data": session_data.model_dump(),
+            "owner_id": owner_id,
+            "version": 0,
             "created_at": datetime.now(timezone.utc),
             "updated_at": datetime.now(timezone.utc),
         }
         return session_id
 
-    def get(self, session_id: str) -> TranslationSession | None:
+    def get(self, session_id: str, owner_id: str) -> TranslationSession | None:
+        result = self.get_with_version(session_id, owner_id)
+        return result[0] if result else None
+
+    def get_with_version(
+        self, session_id: str, owner_id: str
+    ) -> tuple[TranslationSession, int] | None:
         entry = self._store.get(session_id)
-        if entry is None:
+        if entry is None or entry["owner_id"] != owner_id:
             return None
         # Check TTL
         now = datetime.now(timezone.utc)
@@ -39,22 +51,51 @@ class SessionStore:
             return None
         # Touch (refresh TTL)
         entry["updated_at"] = now
-        return TranslationSession(**entry["data"])
+        return TranslationSession(**entry["data"]), entry["version"]
 
-    def update(self, session_id: str, data: dict[str, Any]) -> TranslationSession | None:
+    def update(
+        self,
+        session_id: str,
+        data: dict[str, Any],
+        owner_id: str,
+        expected_version: int | None = None,
+    ) -> TranslationSession | None:
         entry = self._store.get(session_id)
-        if entry is None:
+        if entry is None or entry["owner_id"] != owner_id:
             return None
+        now = datetime.now(timezone.utc)
+        if now - entry["updated_at"] > timedelta(hours=self.ttl_hours):
+            del self._store[session_id]
+            return None
+        if expected_version is not None and entry["version"] != expected_version:
+            raise SessionConflictError
         entry["data"].update(data)
-        entry["updated_at"] = datetime.now(timezone.utc)
+        entry["version"] += 1
+        entry["updated_at"] = now
         return TranslationSession(**entry["data"])
 
-    def delete(self, session_id: str) -> bool:
-        if session_id in self._store:
+    def delete(self, session_id: str, owner_id: str) -> bool:
+        entry = self._store.get(session_id)
+        if entry is not None and entry["owner_id"] == owner_id:
             del self._store[session_id]
             return True
         return False
 
+    def set_progress(
+        self, session_id: str, progress: dict[str, Any] | None, owner_id: str
+    ) -> bool:
+        """Update transient progress without changing the semantic session version."""
+        entry = self._store.get(session_id)
+        if entry is None or entry["owner_id"] != owner_id:
+            return False
+        now = datetime.now(timezone.utc)
+        if now - entry["updated_at"] > timedelta(hours=self.ttl_hours):
+            del self._store[session_id]
+            return False
+        entry["data"]["progress"] = progress
+        entry["updated_at"] = now
+        return True
+
     def cleanup_expired(self):
         """Remove all expired sessions."""
         now = datetime.now(timezone.utc)