fix(core): StreamedBytesIO ignores negative read size and drops seek(SEEK_END) position (#3136)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

packages/dbgpt-core/src/dbgpt/core/interface/file.py

@@ -997,7 +997,7 @@ class StreamedBytesIO(io.BytesIO):
             bytes: The read data
         """
         left_off_at = self._bytes.tell()
-        if size is None:
+        if size is None or size < 0:
             self._load_all()
         else:
             goal_position = left_off_at + size
@@ -1006,20 +1006,22 @@ class StreamedBytesIO(io.BytesIO):
         self._bytes.seek(left_off_at)
         return self._bytes.read(size)
 
-    def seek(self, position: int, whence: int = io.SEEK_SET):
+    def seek(self, position: int, whence: int = io.SEEK_SET) -> int:
         """Seek to a position in the stream.
 
         Args:
             position (int): The position
             whence (int, optional): The reference point. Defaults to io.SEEK
 
+        Returns:
+            int: The new absolute position.
+
         Raises:
             ValueError: If the reference point is invalid
         """
         if whence == io.SEEK_END:
             self._load_all()
-        else:
-            self._bytes.seek(position, whence)
+        return self._bytes.seek(position, whence)
 
     def __enter__(self):
         """Enter the context manager."""

packages/dbgpt-core/src/dbgpt/core/interface/tests/test_file.py

@@ -13,6 +13,7 @@ from ..file import (
     InMemoryStorage,
     LocalFileStorage,
     SimpleDistributedStorage,
+    StreamedBytesIO,
 )
 
 
@@ -504,3 +505,16 @@ def test_simple_distributed_storage_delete_file_remote(
         f"http://{remote_node_address}/api/v2/serve/file/files/{bucket}/{file_id}",
         timeout=360,
     )
+
+
+class TestStreamedBytesIO:
+    def test_read_negative_size_reads_all(self):
+        stream = StreamedBytesIO(iter([b"hello ", b"world"]))
+        assert stream.read(-1) == b"hello world"
+
+    def test_seek_end_loads_all_and_returns_position(self):
+        stream = StreamedBytesIO(iter([b"hello ", b"world"]))
+        position = stream.seek(-5, io.SEEK_END)
+        assert position == 6
+        assert stream.tell() == 6
+        assert stream.read() == b"world"