fix(workflows): reject non-list input 'enum' instead of crashing (#3601)

A workflow input whose `enum` is a scalar or string (e.g. `enum: 5`,
`enum: "abc"`) previously slipped past `validate_workflow` and crashed
at run time. The `value not in enum_values` membership test in
`_coerce_input` raises a raw `TypeError` ("argument of type 'int' is
not iterable") for a scalar, and a bare string turns enum membership
into a silent substring test. The `TypeError` also escapes
`validate_workflow`'s `except ValueError`, breaking its documented
"return a list of errors, never raise" contract.

This is the same unvalidated-`execute()` crash class as the fan-in
`wait_for` (#3482) and fan-out step-template (#3537) fixes: `validate()`
should reject the value, but the value can still reach the engine via
`execute()`, which accepts unvalidated definitions.

Fix:
- `_coerce_input` requires a list `enum` (or `None`), raising a clean
  ValueError for any other shape — so both `validate_workflow` and
  runtime `_resolve_inputs` fail fast with a clear message.
- `validate_workflow` checks `enum` shape directly (not only via the
  default-coercion path, which is reached only when a `default` exists),
  and strips a malformed `enum` before coercing the default so the
  wrong-typed-default error is not duplicated as an enum-shape error.
- The `integration: auto` sentinel only strips a *list* `enum`; a
  non-list `enum` stays in the definition so it is rejected rather than
  silently exempted by the `auto` membership skip.

Tests cover all three layers: `_coerce_input` directly, authoring-time
`validate_workflow` (with no default present), and runtime
`_resolve_inputs`, plus the `integration: auto` interaction.

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

src/specify_cli/workflows/engine.py

@@ -201,6 +201,20 @@ def validate_workflow(definition: WorkflowDefinition) -> list[str]:
                     f"Must be 'string', 'number', or 'boolean'."
                 )
 
+            # ``enum`` must be a list. Checked here — not only via the
+            # ``_coerce_input`` call below — because that call is reached only
+            # when a ``default`` is present, and the ``integration: auto`` case
+            # strips ``enum`` before coercing; a scalar/string ``enum`` on an
+            # input with no default (or the auto-integration default) would
+            # otherwise slip through here and then crash ``_resolve_inputs`` with
+            # a raw ``TypeError`` at run time. ``None`` means "no enum".
+            enum_values = input_def.get("enum")
+            if enum_values is not None and not isinstance(enum_values, list):
+                errors.append(
+                    f"Input {input_name!r} has invalid 'enum': must be a list, "
+                    f"got {type(enum_values).__name__}."
+                )
+
             # Validate the default eagerly so authoring mistakes (e.g. a
             # default not in the declared enum, or a non-numeric default for
             # a number input) surface at install/validation time instead of
@@ -209,13 +223,28 @@ def validate_workflow(definition: WorkflowDefinition) -> list[str]:
             # enum-membership check is exempted for that exact case — the
             # declared type is still enforced (e.g. ``type: number`` paired
             # with ``default: "auto"`` is still rejected).
+            enum_is_valid = enum_values is None or isinstance(enum_values, list)
             if "default" in input_def:
                 default_value = input_def["default"]
                 is_auto_integration = (
                     input_name == "integration" and default_value == "auto"
                 )
+                # Strip ``enum`` from the definition handed to ``_coerce_input``
+                # when either:
+                #   * this is the auto-integration sentinel (enum-membership is
+                #     a runtime concern, exempted for ``"auto"``), or
+                #   * the ``enum`` is malformed (non-list) and already reported
+                #     above — leaving it in would make ``_coerce_input`` re-raise
+                #     the same enum-shape error re-framed as an "invalid default"
+                #     (a confusing duplicate).
+                # Removing *only* ``enum`` (rather than skipping the check
+                # entirely) preserves the default's type validation: a
+                # ``type: string`` input with ``default: 5, enum: 5`` still
+                # reports the wrong-typed default alongside the enum error,
+                # instead of hiding it.
+                strip_enum = is_auto_integration or not enum_is_valid
                 validation_input_def: dict[str, Any] = input_def
-                if is_auto_integration and "enum" in input_def:
+                if strip_enum and "enum" in input_def:
                     validation_input_def = {
                         key: value
                         for key, value in input_def.items()
@@ -1400,11 +1429,18 @@ class WorkflowEngine:
             # definition (``string`` rejects non-strings, ``number`` rejects
             # bools and uncoercible values, ``boolean`` rejects non-bools),
             # so ill-typed values still fail fast here.
+            #
+            # ``execute()`` accepts unvalidated definitions, so a malformed
+            # (non-list) ``enum`` can reach here. Only strip a *list* ``enum``:
+            # a scalar/string ``enum`` must stay in the definition so
+            # ``_coerce_input`` raises the clean shape ``ValueError`` instead of
+            # being silently exempted by the ``auto`` membership skip (which
+            # would otherwise let ``enum: 5`` resolve successfully).
             coerce_input_def = input_def
             if (
                 name == "integration"
                 and value == "auto"
-                and "enum" in input_def
+                and isinstance(input_def.get("enum"), list)
             ):
                 coerce_input_def = {
                     key: val
@@ -1450,6 +1486,22 @@ class WorkflowEngine:
         input_type = input_def.get("type", "string")
         enum_values = input_def.get("enum")
 
+        # ``enum`` must be a list. A scalar (``enum: 5``, ``enum: true``) makes
+        # the ``value not in enum_values`` membership test below raise a raw
+        # ``TypeError`` ("argument of type 'int' is not ... iterable"), which
+        # escapes ``validate_workflow``'s ``except ValueError`` and breaks its
+        # "return errors, never raise" contract — and crashes ``_resolve_inputs``
+        # outright at run time. A bare string is just as wrong: ``value in "abc"``
+        # is a silent substring/character test, not enum membership. Require a
+        # list so both forms fail fast with a clear message. ``None`` means "no
+        # enum" and is left alone.
+        if enum_values is not None and not isinstance(enum_values, list):
+            msg = (
+                f"Input {name!r} has invalid 'enum': must be a list, got "
+                f"{type(enum_values).__name__}."
+            )
+            raise ValueError(msg)
+
         if input_type == "number":
             # Reject bools explicitly: ``bool`` is a subclass of ``int`` so
             # ``float(True)`` succeeds and would silently coerce a YAML

tests/test_workflows.py

@@ -4349,6 +4349,108 @@ steps:
         assert WorkflowEngine._coerce_input("count", 5.0, {"type": "number"}) == 5
         assert WorkflowEngine._coerce_input("count", 3.5, {"type": "number"}) == 3.5
 
+    def test_coerce_input_rejects_non_list_enum_cleanly(self):
+        """A non-list ``enum`` (scalar or string) must raise a clean ValueError,
+        not the raw ``TypeError`` from the ``value not in enum`` membership test.
+
+        A scalar (``enum: 5``) makes ``value not in 5`` raise
+        ``TypeError: argument of type 'int' is not iterable``. A bare string
+        (``enum: "abc"``) is silently wrong instead — ``value in "abc"`` is a
+        substring test, not enum membership — so it must be rejected too.
+        """
+        from specify_cli.workflows.engine import WorkflowEngine
+
+        for bad_enum in (5, True, "abc", {"a": 1}):
+            with pytest.raises(ValueError, match="invalid 'enum': must be a list"):
+                WorkflowEngine._coerce_input(
+                    "scope", "x", {"type": "string", "enum": bad_enum}
+                )
+        # A valid list ``enum`` still works, and ``None`` means "no enum".
+        assert (
+            WorkflowEngine._coerce_input(
+                "scope", "a", {"type": "string", "enum": ["a", "b"]}
+            )
+            == "a"
+        )
+        assert (
+            WorkflowEngine._coerce_input("scope", "x", {"type": "string"}) == "x"
+        )
+
+    def test_validate_workflow_rejects_non_list_enum(self):
+        """A non-list ``enum`` must be reported as an error, not crash
+        ``validate_workflow``. The membership test would raise ``TypeError``,
+        which escapes its ``except ValueError`` and breaks the "return a list of
+        errors, never raise" contract. This must surface even with no ``default``
+        present (the coercion path that would otherwise catch it is only reached
+        when a default exists).
+        """
+        from specify_cli.workflows.engine import WorkflowDefinition, validate_workflow
+
+        definition = WorkflowDefinition.from_string("""
+schema_version: "1.0"
+workflow:
+  id: "bad-enum"
+  name: "Bad Enum"
+  version: "1.0.0"
+inputs:
+  scope:
+    type: string
+    enum: 5
+steps:
+  - id: noop
+    type: gate
+    message: "noop"
+    options: [approve]
+""")
+        errors = validate_workflow(definition)
+        assert any("invalid 'enum': must be a list" in e for e in errors), errors
+
+    def test_resolve_inputs_rejects_non_list_enum_at_runtime(self, project_dir):
+        """``execute()`` accepts unvalidated definitions, so a non-list ``enum``
+        can reach ``_resolve_inputs`` at run time. It must fail with a clean
+        ValueError rather than the raw ``TypeError`` from the membership test.
+        """
+        from specify_cli.workflows.engine import WorkflowEngine, WorkflowDefinition
+
+        definition = WorkflowDefinition.from_string("""
+schema_version: "1.0"
+workflow:
+  id: "runtime-bad-enum"
+  name: "Runtime Bad Enum"
+  version: "1.0.0"
+inputs:
+  scope:
+    type: string
+    enum: 5
+""")
+        engine = WorkflowEngine(project_dir)
+        with pytest.raises(ValueError, match="invalid 'enum': must be a list"):
+            engine._resolve_inputs(definition, {"scope": "x"})
+
+    def test_non_list_enum_on_integration_auto_still_rejected(self, project_dir):
+        """The ``integration: auto`` sentinel strips a *list* ``enum`` before
+        coercion (enum-membership is a runtime concern for ``auto``). A non-list
+        ``enum`` must NOT be silently stripped by that path — it is still an
+        authoring error and must fail with the clean shape ValueError.
+        """
+        from specify_cli.workflows.engine import WorkflowEngine, WorkflowDefinition
+
+        definition = WorkflowDefinition.from_string("""
+schema_version: "1.0"
+workflow:
+  id: "auto-bad-enum"
+  name: "Auto Bad Enum"
+  version: "1.0.0"
+inputs:
+  integration:
+    type: string
+    default: "auto"
+    enum: 5
+""")
+        engine = WorkflowEngine(project_dir)
+        with pytest.raises(ValueError, match="invalid 'enum': must be a list"):
+            engine._resolve_inputs(definition, {})
+
     def test_validate_workflow_rejects_infinite_default_for_number_type(self):
         """``type: number`` with an infinite default (YAML ``.inf``) must be
         reported as an error, not raise. ``int(inf)`` raises OverflowError during