fix(context): bound the complete retrieval response by the caller's limit

The continuation hint was reserved only against the global page cap, so a
small caller-supplied limit bounded content alone and the appended hint pushed
the complete response past the requested maximum. Reserve the hint out of the
effective ceiling (min of limit and the global cap) so content plus hint always
honours the caller's limit, flooring content so pages still make progress.

tests/test_output_store.py

@@ -120,10 +120,14 @@ def test_read_stored_output_paginates(tmp_path: Path) -> None:
         bound_and_store(text, max_lines=4, max_bytes=1_000_000),
     )
     assert output_id is not None
-    page = read_stored_output(output_id.group(1), offset=0, limit=10)
+    # A small caller limit bounds the *complete* response (content + hint).
+    page = read_stored_output(output_id.group(1), offset=0, limit=200)
     assert page.startswith("0\n1")
     assert "more;" in page
-    assert "offset=10" in page
+    assert len(page.encode("utf-8")) <= 200
+    # The continuation offset advances past the returned content.
+    match = re.search(r"offset=(\d+)", page)
+    assert match is not None and int(match.group(1)) > 0
 
 
 def test_read_stored_output_page_including_hint_stays_within_ceiling(tmp_path: Path) -> None: