refactor(source/cloud-storage): move max-read constant into source package

DefaultMaxReadBytes doesn't belong in errors.go — the limit is a source-side
invariant, not an error-classification concern. The sentinel
ErrReadSizeLimitExceeded stays in cloudstoragecommon because the classifier
still needs to recognize it.

Author: huangjiahua

internal/sources/cloudstorage/cloudstorage.go

@@ -32,6 +32,11 @@ import (
 
 const SourceType string = "cloud-storage"
 
+// defaultMaxReadBytes caps the payload ReadObject will return per call,
+// protecting the server from OOM and keeping LLM contexts manageable. Objects
+// or ranges exceeding this are rejected with ErrReadSizeLimitExceeded.
+const defaultMaxReadBytes int64 = 8 << 20 // 8 MiB
+
 // validate interface
 var _ sources.SourceConfig = Config{}
 
@@ -136,18 +141,19 @@ func (s *Source) ListObjects(ctx context.Context, bucket, prefix, delimiter stri
 // offset and length follow storage.ObjectHandle.NewRangeReader semantics:
 // length == -1 means "read to end of object"; a negative offset means "suffix
 // from end" (in which case length must be -1). Reads larger than
-// cloudstoragecommon.DefaultMaxReadBytes are rejected with
-// ErrReadSizeLimitExceeded so the caller can narrow the range.
+// defaultMaxReadBytes are rejected with
+// cloudstoragecommon.ErrReadSizeLimitExceeded so the caller can narrow the
+// range.
 func (s *Source) ReadObject(ctx context.Context, bucket, object string, offset, length int64) (map[string]any, error) {
 	reader, err := s.Client.Bucket(bucket).Object(object).NewRangeReader(ctx, offset, length)
 	if err != nil {
 		return nil, fmt.Errorf("failed to open object %q in bucket %q: %w", object, bucket, err)
 	}
 	defer reader.Close()
 
-	if remain := reader.Remain(); remain > cloudstoragecommon.DefaultMaxReadBytes {
+	if remain := reader.Remain(); remain > defaultMaxReadBytes {
 		return nil, fmt.Errorf("object %q: %d bytes exceeds %d byte limit: %w",
-			object, remain, cloudstoragecommon.DefaultMaxReadBytes,
+			object, remain, defaultMaxReadBytes,
 			cloudstoragecommon.ErrReadSizeLimitExceeded)
 	}
 

internal/tools/cloudstorage/cloudstoragecommon/errors.go

@@ -13,7 +13,7 @@
 // limitations under the License.
 
 // Package cloudstoragecommon holds helpers shared across the Cloud Storage
-// tool implementations, including error classification and read-size limits.
+// tool implementations, chiefly error classification.
 package cloudstoragecommon
 
 import (
@@ -26,14 +26,10 @@ import (
 	"google.golang.org/api/googleapi"
 )
 
-// DefaultMaxReadBytes is the default cap for ReadObject payloads. Objects (or
-// ranges) larger than this are rejected with ErrReadSizeLimitExceeded so they
-// can't OOM the server or blow an LLM's context window.
-const DefaultMaxReadBytes int64 = 8 << 20 // 8 MiB
-
-// ErrReadSizeLimitExceeded is returned by the source when an object/range would
-// exceed the configured byte limit. ProcessGCSError maps this to an Agent
-// error because the LLM can fix the call by narrowing the 'range' parameter.
+// ErrReadSizeLimitExceeded is returned by the source when an object/range
+// would exceed the source's configured byte limit. ProcessGCSError maps this
+// to an Agent error because the LLM can fix the call by narrowing the 'range'
+// parameter.
 var ErrReadSizeLimitExceeded = errors.New("cloud storage read size limit exceeded")
 
 // ProcessGCSError classifies an error from the Cloud Storage Go client into