docs: reorder & testing

gateway/internal/session/backend.go

@@ -1,50 +1,12 @@
 package session
 
-import (
-	"context"
-	"errors"
-	"fmt"
-)
+import "context"
 
-// BackendLookup describes the slice of `backendclient.RESTClient`
-// SessionCache depends on. The narrow interface keeps this package free
-// of any backendclient import.
+// BackendLookup is the slice of backend's REST surface that the
+// session-cache layer depends on. The narrow interface keeps this
+// package free of any backendclient import. The canonical
+// implementation is `*backendclient.RESTClient`; tests can supply a
+// fake.
 type BackendLookup interface {
 	LookupSession(ctx context.Context, deviceSessionID string) (Record, error)
 }
-
-// BackendCache resolves authenticated device sessions by issuing one
-// synchronous REST call to backend per request. The canonical implementation replaces the
-// previous Redis-backed projection with this thin wrapper; gateway no
-// longer keeps a process-local snapshot. See ARCHITECTURE.md §11
-// «backend (sync REST), no Redis projection».
-type BackendCache struct {
-	backend BackendLookup
-}
-
-// NewBackendCache constructs a Cache that delegates every Lookup to
-// backend over REST. backend must not be nil.
-func NewBackendCache(backend BackendLookup) (*BackendCache, error) {
-	if backend == nil {
-		return nil, errors.New("session.NewBackendCache: backend lookup must not be nil")
-	}
-	return &BackendCache{backend: backend}, nil
-}
-
-// Lookup resolves deviceSessionID via backend. ErrNotFound is forwarded
-// unchanged so callers can keep using the existing equality check.
-func (c *BackendCache) Lookup(ctx context.Context, deviceSessionID string) (Record, error) {
-	if c == nil {
-		return Record{}, errors.New("session backend cache: nil cache")
-	}
-	if c.backend == nil {
-		return Record{}, errors.New("session backend cache: nil backend lookup")
-	}
-	rec, err := c.backend.LookupSession(ctx, deviceSessionID)
-	if err != nil {
-		return Record{}, fmt.Errorf("session backend cache: %w", err)
-	}
-	return rec, nil
-}
-
-var _ Cache = (*BackendCache)(nil)