fix(rlm): fall back to no sub-agents when the interpreter rejects the facade shim with SyntaxError

Restricted interpreters (e.g. RestrictedPython) reject the shim's _dspy_* names at
compile time and raise SyntaxError, which _setup_facade did not catch, so every RLM
call crashed before the first iteration. Treat it like CodeExecutionError.

Amp-Thread-ID: https://ampcode.com/threads/T-01a12205-9d20-7108-b7b8-057a602a6ba2
Co-authored-by: Isaac Miller <isaac@cmpnd.ai>

Author: ampagent

dspy/predict/rlm.py

@@ -588,8 +588,9 @@ def _setup_facade(
         )
         try:
             invocation.install(repl)
-        except CodeExecutionError as e:
-            # The runtime cannot host the shim (e.g. it runs code in the host's memory): no sub-agents this call.
+        except (CodeExecutionError, SyntaxError) as e:
+            # The runtime cannot host the shim (e.g. it runs code in the host's memory, or a restricted compiler
+            # rejects the shim's `_dspy_*` names): no sub-agents this call.
             for name in (CONSTRUCT_TOOL, CALL_TOOL):
                 repl.tools.pop(name, None)
             logger.warning("RLM sub-agents are unavailable on %s: %s", type(repl).__name__, e)

tests/predict/test_rlm.py

@@ -1989,6 +1989,26 @@ def test_interpreter_in_the_host_memory_runs_without_sub_agents(self, caplog):
         assert "Sub-agents (dspy)" not in seen[0].instructions
         assert "host's memory" in caplog.text
 
+    def test_interpreter_that_rejects_the_shim_as_syntax_error_runs_without_sub_agents(self, caplog):
+        # Restricted compilers (e.g. RestrictedPython) reject the shim's `_dspy_*` names at compile time.
+        from dspy.primitives import facade
+
+        def execute(code, variables):
+            if code == facade.SHIM_SETUP:
+                raise SyntaxError('"_dspy_sys" is an invalid variable name because it starts with "_"')
+            return FinalOutput({"answer": "42"})
+
+        factory = MockInterpreterFactory(execute_fn=execute)
+        rlm = RLM("query -> answer", max_iters=1, interpreter_factory=factory)
+        rlm.generate_action, seen = _recording_predictor('SUBMIT("42")')
+
+        with caplog.at_level("WARNING", logger="dspy.predict.rlm"):
+            assert rlm(query="q").answer == "42"
+
+        assert "Sub-agents (dspy)" not in seen[0].instructions
+        assert not {facade.CONSTRUCT_TOOL, facade.CALL_TOOL} & factory.instances[0].tools.keys()
+        assert "sub-agents are unavailable on MockInterpreter" in caplog.text
+
     def test_facade_reserves_sandbox_names(self):
         with pytest.raises(ValueError, match="conflict"):
             RLM("dspy -> answer")