[LTP] [PATCH] doc/developers: document tst_/tse_/tso_ library namespaces

[Li Wang]

This helps contributors choose the correct layer when adding new library
code and clarifies expectations around legacy components.

Follow-up: eef750db28 ("libs: adopt tse_ prefix for extended (non-core) library")
Follow-up: 751df4fa64 ("include/old: rename legacy headers to tso_* namespace")
Signed-off-by: Li Wang <liwang@redhat.com>
---
 doc/developers/ltp_library.rst | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/doc/developers/ltp_library.rst b/doc/developers/ltp_library.rst
index f76cbb75e..bb2677622 100644
--- a/doc/developers/ltp_library.rst
+++ b/doc/developers/ltp_library.rst
@@ -15,6 +15,34 @@ for :doc:`writing tests <../developers/writing_tests>`
 #. Do not add new API functions to the old API. Add new functions to
    ``tst_.[ch]`` files.
 
+Library naming and scope
+------------------------
+
+To keep the library API easy to navigate and to make layering explicit, LTP
+library components follow these naming rules:
+
+- **tst_**: Core LTP library API (located in ``lib/``).
+
+  - Stable, widely used interfaces intended for general consumption by tests.
+  - New public APIs should normally live here (in ``tst_*.h`` / ``tst_*.c``).
+
+- **tse_**: Non-core / extended library code (located in ``libs/``).
+
+  - Optional or specialized helpers that are not part of the core API.
+  - May have narrower scope or fewer stability guarantees than ``tst_``.
+  - Can be promoted to ``tst_`` later if it becomes broadly useful and stable.
+
+- **tso_**: Legacy / old library code.
+
+  - Kept for backward compatibility.
+  - No new features should be added; only minimal fixes are acceptable (e.g. build fixes, correctness fixes, security fixes).
+  - New code should not depend on ``tso_`` unless strictly necessary.
+
+**Notes:**
+
+- Prefer adding new code to ``tst_`` or ``tse_``; avoid introducing new ``tso_`` components.
+- When adding a new public interface, document where it belongs (``tst_`` vs ``tse_``) and why.
+
 Shell API
 ---------
 
-- 
2.52.0