diff --git a/hermit/agent/evolver/methods/mwm/evolver.py b/hermit/agent/evolver/methods/mwm/evolver.py
index 4ae8ac0d..9b3f473b 100644
--- a/hermit/agent/evolver/methods/mwm/evolver.py
+++ b/hermit/agent/evolver/methods/mwm/evolver.py
@@ -456,6 +456,9 @@ def _notes(admission: dict | None) -> str:
 
     # ------------------------------------------------------------------ steps
     def setup(self, ctx: Context) -> None:
+        if ctx.params.get("backend", "codex") not in ("codex", "claude"):   # its session texts, homes and sign-ins
+            raise ValueError("the mwm Evolver's learner is a Codex or Claude Code session: evolver.params.backend is "
+                             f"codex or claude, not {ctx.params.get('backend')!r}")
         if "network_isolation" in ctx.params:
             raise ValueError("evolver.params.network_isolation was removed: the learner runs in the run's evolver "
                              "sandbox, whose network reaches only its models, the tool endpoint and "
diff --git a/hermit/agent/evolver/methods/rrsi_adapter/evolver.py b/hermit/agent/evolver/methods/rrsi_adapter/evolver.py
index 0ac28a4e..31add202 100644
--- a/hermit/agent/evolver/methods/rrsi_adapter/evolver.py
+++ b/hermit/agent/evolver/methods/rrsi_adapter/evolver.py
@@ -417,6 +417,9 @@ def setup(self, ctx) -> None:
         """What every step needs, checked once: a broken hyperparameter file or domain, or an unset web_search,
         stops the run here rather than failing each step."""
         _require_rrsi()
+        if ctx.params.get("backend", "codex") not in ("codex", "claude"):   # its roles' settings are those CLIs'
+            raise ValueError("the RRSI Adapter's proposer and roles are Codex or Claude Code sessions: "
+                             f"evolver.params.backend is codex or claude, not {ctx.params.get('backend')!r}")
         if not isinstance(ctx.params.get("web_search"), bool):
             raise ValueError("evolver.params.web_search must be set, true or false")
         role = ctx.params.get("roles") or {}
diff --git a/tests/methods/mwm/test_mwm_evolver.py b/tests/methods/mwm/test_mwm_evolver.py
index 687f028b..edcaacf1 100644
--- a/tests/methods/mwm/test_mwm_evolver.py
+++ b/tests/methods/mwm/test_mwm_evolver.py
@@ -148,6 +148,16 @@ def make(tmp: Path, monkeypatch, steps: int = 2, deployment_param: bool = False)
     return path
 
 
+def test_a_learner_that_is_not_codex_or_claude_code_is_refused_at_setup():
+    """mwm's session is Codex's or Claude Code's (its texts, homes and sign-ins): another CLI Base Agent, which the
+    config takes as evolver.base (pi), is refused before any step rather than run without its model (mwm's session
+    settings carry no `provider`)."""
+    from types import SimpleNamespace
+    from hermit.agent.evolver.methods.mwm.evolver import MwmEvolver
+    with pytest.raises(ValueError, match="backend is codex or claude, not 'pi'"):
+        MwmEvolver().setup(SimpleNamespace(params={"backend": "pi"}))
+
+
 def test_bootstrap_review_mounts_and_records(tmp_path, monkeypatch):
     cfg = Config.load(make(tmp_path, monkeypatch), [])
     stale = tmp_path / "taskdir" / "evidence" / "block000"   # a record already in the store: hidden from the bootstrap
diff --git a/tests/methods/rrsi_adapter/test_rrsi_adapter.py b/tests/methods/rrsi_adapter/test_rrsi_adapter.py
index 787b6782..1be09dca 100644
--- a/tests/methods/rrsi_adapter/test_rrsi_adapter.py
+++ b/tests/methods/rrsi_adapter/test_rrsi_adapter.py
@@ -818,6 +818,8 @@ def test_setup_checks_what_every_step_needs(tmp_path):
     ev.setup(ctx)
     with pytest.raises(ValueError, match="web_search"):
         ev.setup(context(ws, 1, dom, tmp_path, web_search=None))
+    with pytest.raises(ValueError, match="backend is codex or claude, not 'pi'"):   # its roles' settings are not Pi's
+        ev.setup(context(ws, 1, dom, tmp_path, backend="pi"))
     with pytest.raises(Exception):
         ev.setup(context(ws, 1, str(tmp_path / "dom" / "missing.py") + ":ToyDomain", tmp_path))
     with pytest.raises(ValueError, match="roles.model"):