agents: add native.test_suite API tag invariant rule (#4068)

agents: add native.test_suite API tag invariant rule

In Bazel, tags on native.test_suite serve as test filtering selectors
rather than specifying target execution properties.

Add a rule to .agents/rules/starlark.md warning against forwarding
regular test target tags to native.test_suite.

.agents/rules/starlark.md

diff --git a/.agents/rules/starlark.md b/.agents/rules/starlark.md
index 74bf1bd..b04cacb 100644
--- a/.agents/rules/starlark.md
+++ b/.agents/rules/starlark.md
@@ -33,6 +33,10 @@
 * **Why**: This avoids inlining the normalization as part of a complex
   expression later in the macro expansion.
 
+## native.test_suite API
+* Don't forward target `tags` to `native.test_suite`; tags on test suites filter
+  tests instead of setting target execution behavior.
+
 ## Control Flow & Algorithmic Restrictions
 * **Iterative Algorithms Only (No Recursion)**: Starlark does not support
   recursive function calls; always implement iterative algorithms using bounded