fix(spend-logs): keep main's stored tail for a negative prompt length limit

At a negative MAX_STRING_LENGTH_PROMPT_IN_DB the shared truncation helper stored one more character of each value than main, since it dropped main's clamp of the end slice to the limit minus the start

litellm/proxy/spend_tracking/spend_tracking_utils.py

@@ -1205,7 +1205,7 @@ def _truncated_for_db(value: str, max_length: int) -> str:
         f"{value[:start_chars]}"
         f"... ({LITELLM_TRUNCATED_PAYLOAD_FIELD} skipped {len(value) - start_chars - end_chars} chars. "
         f"{LITELLM_TRUNCATION_DB_SAFEGUARD_NOTE}) ..."
-        f"{value[-end_chars:]}"
+        f"{value[-min(end_chars, max_length - start_chars) :]}"
     )
 
 

tests/unit/proxy/spend_tracking/test_spend_tracking_utils.py

@@ -668,14 +668,17 @@ def test_large_request_no_truncation_threshold():
     assert "skipped" in truncated_content
 
 
-@pytest.mark.parametrize("max_string_length_prompt_in_db", [0, 1])
-def test_a_limit_under_two_still_stores_the_whole_value_after_the_marker(max_string_length_prompt_in_db: int):
+@pytest.mark.parametrize(
+    ("max_string_length_prompt_in_db", "stored_tail"),
+    [(0, "claude-sonnet-5-5"), (1, "claude-sonnet-5-5"), (-1, "laude-sonnet-5-5"), (-2, "aude-sonnet-5-5")],
+)
+def test_a_limit_under_two_keeps_mains_tail_after_the_marker(max_string_length_prompt_in_db: int, stored_tail: str):
     sanitized: Final = _sanitize_request_body_for_spend_logs_payload(
         {"model": "claude-sonnet-5-5"}, max_string_length_prompt_in_db=max_string_length_prompt_in_db
     )
 
     assert sanitized["model"].startswith("...")
-    assert sanitized["model"].endswith("claude-sonnet-5-5")
+    assert sanitized["model"].endswith(f") ...{stored_tail}")
 
 
 def test_small_request_no_truncation():