fix(context): keep tool-output retrieval reliable and stream pages

Exempt read_tool_output from result-bounding so paging a large stored
output isn't re-spilled under a new id, byte-cap each page in place, and
stream the requested window with islice instead of loading the whole
file per page.

tests/test_agent_factory_shell.py

@@ -110,3 +110,14 @@ async def test_chat_completions_filesystem_custom_tool_becomes_function_tool() -
     factory._configure_filesystem_tools(toolset, chat_completions=True)
 
     assert isinstance(toolset.read_file, FunctionTool)
+
+
+def test_read_tool_output_is_not_result_bounded() -> None:
+    # Every other FunctionTool gets the result-bounding wrapper, but the
+    # retrieval tool must be exempt or paging a large stored output would be
+    # re-spilled under a new id.
+    agent = factory.build_strix_agent(is_root=True)
+    by_name = {t.name: t for t in agent.tools}
+
+    assert getattr(by_name["read_tool_output"], "_strix_bounded", False) is False
+    assert getattr(by_name["think"], "_strix_bounded", False) is True

tests/test_output_store.py

@@ -114,6 +114,25 @@ def test_read_stored_output_paginates(tmp_path: Path) -> None:
     assert "offset=10" in page
 
 
+def test_read_stored_output_page_is_bounded_without_new_spill(tmp_path: Path) -> None:
+    # A page of very long lines must be byte-capped in place, never re-spilled
+    # under a fresh output_id (which would make paging loop forever).
+    configure_output_store(tmp_path)
+    text = "\n".join("z" * 5_000 for _ in range(50))
+    output_id = re.search(
+        r'output_id="([0-9a-f]{32})"',
+        bound_and_store(text, max_lines=4, max_bytes=1_000),
+    )
+    assert output_id is not None
+
+    page = read_stored_output(output_id.group(1), offset=0, limit=2_000)
+
+    assert len(page.encode("utf-8")) <= 60 * 1024
+    # No brand-new spill id in the returned page.
+    ids = re.findall(r'output_id="([0-9a-f]{32})"', page)
+    assert ids == [output_id.group(1)] or ids == []
+
+
 def test_read_stored_output_rejects_traversal(tmp_path: Path) -> None:
     configure_output_store(tmp_path)
     assert "Invalid output_id" in read_stored_output("../../etc/passwd")