fix(workflows): fail switch step on non-mapping cases instead of crashing (#3481)

`SwitchStep.validate()` already rejects a non-mapping `cases`, but the
engine's `execute()` path does not auto-validate (see
`WorkflowEngine.load_workflow`, whose docstring notes the definition is
"not yet validated"). On an unvalidated run, `execute` called
`cases.items()` on the raw value, so a list or scalar `cases` authoring
mistake raised `AttributeError` and took down the whole run — the engine
invokes `step_impl.execute()` with no surrounding try/except.

Guard `execute` to return a FAILED StepResult naming the type error
instead, mirroring the fan-out step's non-list `items` handling. The
expression is still evaluated first, so its value is surfaced in the
step output for downstream context.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/specify_cli/workflows/steps/switch/__init__.py

@@ -26,6 +26,20 @@ class SwitchStep(StepBase):
         str_value = str(value) if value is not None else ""
 
         cases = config.get("cases", {})
+        if not isinstance(cases, dict):
+            # The engine does not auto-validate step config, so an unvalidated
+            # run with a non-mapping ``cases`` (a list/scalar authoring mistake)
+            # would otherwise raise AttributeError from ``.items()`` below and
+            # crash the whole run. Fail this step loudly instead, mirroring the
+            # fan-out step's non-list ``items`` handling.
+            return StepResult(
+                status=StepStatus.FAILED,
+                error=(
+                    f"Switch step {config.get('id', '?')!r}: 'cases' must be a "
+                    f"mapping, got {type(cases).__name__}."
+                ),
+                output={"matched_case": None, "expression_value": value},
+            )
         for case_key, case_steps in cases.items():
             if str(case_key) == str_value:
                 return StepResult(