diff --git a/.github/actions/setup-ci-job/action.yml b/.github/actions/setup-ci-job/action.yml
index 08bdf3ac..369add5f 100644
--- a/.github/actions/setup-ci-job/action.yml
+++ b/.github/actions/setup-ci-job/action.yml
@@ -584,7 +584,15 @@ runs:
         # one transitive dependency sends pip backtracking through sixty
         # releases of scikit-build-core before reporting it, burying the real
         # message under a wall of version lists.
-        pip install 'scikit-build-core>=0.10' nanobind cmake ninja
+        # nanobind is capped below 3.0 to match pypto's own build requirement.
+        # It has to be pinned here rather than inherited: the pypto build below
+        # passes --no-build-isolation, so the extension is compiled against this
+        # install and pypto's [build-system] requires is never consulted.
+        # nanobind 3.0 stopped binding a null holder to a parameter typed after a
+        # bound class, which is what pypto's TileView uses for `start_offset`, so
+        # `ir.TileView()` no longer matches its own all-defaulted overload and
+        # every `pl.Tile` annotation fails to parse.
+        pip install 'scikit-build-core>=0.10' 'nanobind<3' cmake ninja
         # torch BEFORE pypto is built. pypto declares torch>=2.0.0, and if it is
         # not installed yet pip resolves that from the default index, where the
         # aarch64 wheel now drags ~1.5 GB of CUDA onto an Ascend host. Under
@@ -658,7 +666,8 @@ runs:
       run: |
         source activate.sh
         # torch is installed in the build step above, before pypto is resolved.
-        pip install nanobind transformers safetensors numpy fastapi uvicorn pytest msgspec
+        # 'nanobind<3': same cap as the build step above.
+        pip install 'nanobind<3' transformers safetensors numpy fastapi uvicorn pytest msgspec
         # --no-deps: pyproject declares none, and the runtime stack above is
         # deliberately assembled by hand (CPU torch, from-source pypto).
         pip install --no-deps -e .