fix(vector): harden backup restore parity gates

harness/tht/adapters/vector/thoth_http.py

@@ -10,7 +10,7 @@ from tht.ports.vector import (
     VectorWriteUnavailable,
     require_positive_limit,
 )
-from tht.vectorstore.rest_client import VectorRestClient
+from tht.vectorstore.rest_client import VectorRestClient, VectorRestError
 from tht.vectorstore.store import hit_from_metadata
 from tht.adapters.vector.pgvector import (
     _collection,
@@ -102,7 +102,10 @@ class ThothHttpVectorStore:
         hits: list[VectorHit] = []
         for collection in collections:
             _collection("vectors", collection)
-            rows = self._reader.search_similar(collection, embedding, limit, kinds=kinds)
+            try:
+                rows = self._reader.search_similar(collection, embedding, limit, kinds=kinds)
+            except VectorRestError as exc:
+                raise VectorStoreError(str(exc)) from exc
             hits.extend(
                 hit_from_metadata(row.get("similarity", 0.0), row.get("metadata"))
                 for row in rows
@@ -120,7 +123,10 @@ class ThothHttpVectorStore:
     def existing_hashes(self, collection: str, kinds: list[str]) -> dict[str, str]:
         _collection("vectors", collection)
         _validate_collection_kinds(collection, kinds)
-        return self._require_writer().existing_hashes(collection, kinds)
+        try:
+            return self._require_writer().existing_hashes(collection, kinds)
+        except VectorRestError as exc:
+            raise VectorStoreError(str(exc)) from exc
 
     def upsert(self, collection: str, records: list[VectorWriteRecord]) -> int:
         writer = self._require_writer()
@@ -133,7 +139,10 @@ class ThothHttpVectorStore:
             ):
                 raise VectorStoreError("Embedding dimension does not match configured dimension")
         rows = [self._row(record) for record in records]
-        return writer.upsert_records(collection, rows)
+        try:
+            return writer.upsert_records(collection, rows)
+        except VectorRestError as exc:
+            raise VectorStoreError(str(exc)) from exc
 
     @staticmethod
     def _row(write_record: VectorWriteRecord) -> dict: