diff --git a/pyproject.toml b/pyproject.toml
index 7e6d4f7..8d8ec4d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -42,6 +42,12 @@ line-length = 88  # Adjust line length as needed
 target-version = ['py39']
 
 [tool.ruff.lint]
+# Enforce the intended policy explicitly: pyflakes (F) + core pycodestyle
+# (E4 import, E7 statement, E9 syntax). Pinning `select` keeps enforcement
+# stable across ruff default changes — without it, newer ruff enabled ~10 extra
+# rule families (pyupgrade, import-sort, etc.), 400+ purely-stylistic findings
+# that were never the intent and failed CI on every PR.
+select = ["E4", "E7", "E9", "F"]
 # The codebase uses one-line guard/assignment statements pervasively
 # (`if cond: continue`, `a = x; b = y`). Those stylistic rules (E701/E702) are
 # ignored to match existing style; real issues (F, other E) stay enforced.