fix(handlers): add missing rows.Err() check in llm_billing_mode

readWorkspaceDeriveInputs iterated workspace_secrets via rows.Next()
but never checked rows.Err() after the loop. A transient iteration
error (network, cursor failure) would silently be ignored, causing
the resolver to derive billing mode from a partial secret set.

Add the standard post-Next rows.Err() check, logging the error and
continuing with whatever was gathered (fail-closed: incomplete inputs
cause DeriveProvider to default to platform_managed).

Closes internal#734 CWE-78 follow-up (last missing check in handlers).

workspace-server/internal/handlers/llm_billing_mode.go

@@ -377,6 +377,9 @@ func readWorkspaceDeriveInputs(ctx context.Context, workspaceID string) (runtime
 			availableAuthEnv = append(availableAuthEnv, k)
 		}
 	}
+	if err := rows.Err(); err != nil {
+		log.Printf("llm_billing_mode: rows iteration error for %s: %v (deriving with partial model/auth-env)", workspaceID, err)
+	}
 	return runtime, model, availableAuthEnv
 }