diff --git a/CHANGELOG.md b/CHANGELOG.md
index f5285c7de..1001a91ce 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,11 +1,28 @@
 ## 4.2.0 (TBD)
 
+- Enhancements
+    - `@with_annotated` argument groups can now contain an `ArgumentBlock`'s arguments. A `Group`
+      member names a command-line argument, and a block expands into one argument per field, so its
+      fields are named: `Group("host", "port")`.
+- Breaking Changes
+    - A `Group` member now names an argument rather than a parameter. The two differ only for an
+      `ArgumentBlock` parameter, which is expanded away and has no argument of its own:
+      `Group("conn")` now raises `ValueError` pointing at the block's fields. It previously produced
+      an empty argument group in `groups=` and a `KeyError` in `mutually_exclusive_groups=`.
+    - Whether a `Group` member exists is now validated when the parser is built rather than at
+      decoration time, because a block's field names cannot be known without resolving its type
+      hint, and resolving hints eagerly would break forward-referenced annotations. A typo in a
+      member name still raises `ValueError`, but on first use of that command rather than at class
+      definition. The spec-shape rules (a member listed twice, a member in two groups,
+      `required=True` on a plain group, the mutex nesting rules) are unaffected and still hard-fail
+      at decoration time.
 - Bug Fixes
     - Fixed `@with_annotated(base_command=True)` not listing its subcommands under the positional
       arguments section of the parent command's `--help`, unlike `argparse` and
       `Cmd2ArgumentParser`. They were placed in an untitled section of their own instead. Passing
       `subcommand_title` or `subcommand_description` still gives the subcommands a dedicated section
       ([#1715](https://github.com/python-cmd2/cmd2/issues/1715)).
+    - Fix `@with_annotated` decorator so using `ArgumentBlock` works with groups
 
 ## 4.1.2 (July 16, 2026)
 
diff --git a/cmd2/annotated.py b/cmd2/annotated.py
index b059c8c5a..cf54251bc 100644
--- a/cmd2/annotated.py
+++ b/cmd2/annotated.py
@@ -552,25 +552,20 @@ def __init__(
     ) -> None:
         """Initialise an argument group definition.
 
-        :param members: parameter names to place in the group (at least one)
+        :param members: argument names to place in the group (at least one).  A plain parameter's name is its
+                        argument name; for an ``ArgumentBlock`` name its fields.
         :param title: group title shown as a help section header
         :param description: group description shown under the title
         :param required: ``mutually_exclusive_groups`` only -- require exactly one member.
                          On a ``groups=`` entry it raises ``ValueError``.
         """
         if not members:
-            raise ValueError("Group requires at least one member parameter name")
+            raise ValueError("Group requires at least one member argument name")
         self.members = members
         self.title = title
         self.description = description
         self.required = required
 
-    def _validate_members(self, *, all_param_names: set[str], group_type: str) -> None:
-        """Validate that every referenced member parameter exists."""
-        for name in self.members:
-            if name not in all_param_names:
-                raise ValueError(f"{group_type} references nonexistent parameter {name!r}")
-
 
 #: Metadata extracted from ``Annotated[T, meta]``, or ``None`` for plain types.
 ArgMetadata = Argument | Option | None
@@ -2072,6 +2067,39 @@ def _shared_field_dest(dc_type: type, field_name: str) -> str:
     return constants.cmd2_private_attr_name(f"shared_{id(dc_type):x}_{field_name}")
 
 
+def _check_group_members_exist(
+    by_name: dict[str, _ArgparseArgument],
+    block_param_names: set[str],
+    func_qualname: str,
+    *specs: tuple[Group, ...] | None,
+) -> None:
+    """Reject a ``Group`` member that names no command-line argument, once every argument is built.
+
+    :func:`_validate_group_specs` cannot do this at decoration time: an ArgumentBlock's arguments are its
+    dataclass fields, which only resolving the block's type hint would reveal, and resolving hints there
+    would break forward-referenced annotations.  So this is where a bad member name is finally caught.
+
+    Naming the block parameter itself is the likely mistake -- it reads natural but the parameter is expanded
+    away and has no argument -- so it gets its own message pointing at the fields to name instead.
+    """
+    for spec_group in specs:
+        for spec in spec_group or ():
+            for name in spec.members:
+                if name in by_name:
+                    continue
+                if name in block_param_names:
+                    raise ValueError(
+                        f"group in {func_qualname} references {name!r}, which is an ArgumentBlock parameter "
+                        f"and not a command-line argument: a block is expanded into one argument per field, "
+                        f"so name those fields instead."
+                    )
+                raise ValueError(
+                    f"group in {func_qualname} references {name!r}, which is not a command-line argument. "
+                    f"Members name arguments: a plain parameter is its own argument, and an ArgumentBlock's "
+                    f"arguments are its field names."
+                )
+
+
 def _link_mutex_group_membership(
     by_name: dict[str, _ArgparseArgument],
     mutually_exclusive_groups: tuple[Group, ...] | None,
@@ -2079,8 +2107,7 @@ def _link_mutex_group_membership(
     """Append each mutex group's 1-based index to its member arguments' ``mutex_group_indices``.
 
     This membership is the fact behind the required-member constraint row.  Member references are
-    validated upstream by :func:`_validate_group_specs` before this runs, so every member name
-    resolves to a built argument.
+    resolved to built arguments upstream by :func:`_check_group_members_exist` before this runs.
     """
     if not mutually_exclusive_groups:
         return
@@ -2352,6 +2379,7 @@ def _resolve_parameters(
     *,
     skip_params: frozenset[str] = _SKIP_PARAMS,
     base_command: bool = False,
+    groups: tuple[Group, ...] | None = None,
     mutually_exclusive_groups: tuple[Group, ...] | None = None,
 ) -> tuple[list[_ArgparseArgument], set[type]]:
     """Resolve a function signature into argparse-argument builders and inheritable-block types.
@@ -2378,6 +2406,7 @@ def _resolve_parameters(
     resolved: list[_ArgparseArgument] = []
     inherited_field_names: set[str] = set()
     base_args_types: set[type] = set()
+    block_param_names: set[str] = set()
 
     # Skip the first parameter by position (self/cls for methods)
     params = list(sig.parameters.items())
@@ -2398,6 +2427,7 @@ def _resolve_parameters(
                     f"cannot have a default value; remove the default."
                 )
             inherited_field_names.update(_init_field_names(inherited))
+            block_param_names.add(name)
             continue
 
         # An ArgumentBlock-typed parameter is an argument block: expand its fields in place (flat) instead of
@@ -2416,6 +2446,7 @@ def _resolve_parameters(
                 block_hint, func_qualname=func.__qualname__, base_command=base_command, shared=name == NS_ATTR_BASE_ARGS
             )
             _reject_field_shadowing_block_param(block_hint, name, func.__qualname__)
+            block_param_names.add(name)
             resolved.extend(expanded)
             continue
         # The magic name requires a bare ArgumentBlock; a non-block annotation on it is a clear mistake.
@@ -2480,6 +2511,7 @@ def _resolve_parameters(
     for arg in positionals[:-1]:  # every positional except the last has a following positional
         arg.has_following_positional = True
     by_name = {arg.name: arg for arg in resolved}
+    _check_group_members_exist(by_name, block_param_names, func.__qualname__, groups, mutually_exclusive_groups)
     _link_mutex_group_membership(by_name, mutually_exclusive_groups)
     for arg in resolved:
         arg._check_constraints()
@@ -2539,30 +2571,22 @@ def _filtered_namespace_kwargs(
 
 
 def _validate_group_specs(
-    func: Callable[..., Any],
-    *,
-    skip_params: frozenset[str],
     groups: tuple[Group, ...] | None,
     mutually_exclusive_groups: tuple[Group, ...] | None,
 ) -> None:
-    """Validate ``groups=`` / ``mutually_exclusive_groups=`` specs from parameter names alone.
-
-    Runs at decoration time (from both the regular-command and subcommand decoration paths, and
-    again from :func:`build_parser_from_function` for direct callers), so a misconfigured group
-    hard-fails when the class is defined instead of on first command use, where cmd2's runtime
-    handler turns the error into a printed message.  Reads only parameter names and the ``Group``
-    specs -- never the type hints -- so forward-referenced annotations still decorate.  The one
-    group rule that needs the annotations (a required member in a mutually exclusive group) stays
-    in :data:`_CONSTRAINTS` and fires when the parser is built.
+    """Validate the *shape* of ``groups=`` / ``mutually_exclusive_groups=`` specs.
+
+    Runs at decoration time (from both the regular-command and subcommand decoration paths, and again from
+    :func:`build_parser_from_function` for direct callers), so a misshapen group hard-fails when the class is
+    defined instead of on first command use, where cmd2's runtime handler turns the error into a printed
+    message.  Reads only the ``Group`` specs -- never the signature or the type hints -- so
+    forward-referenced annotations still decorate.
     """
     if not groups and not mutually_exclusive_groups:
         return
-    params = list(inspect.signature(func).parameters)[1:]  # skip self/cls by position
-    all_param_names = {name for name in params if name not in skip_params}
 
     group_entry_for: dict[str, int] = {}
     for index, spec in enumerate(groups or (), start=1):
-        spec._validate_members(all_param_names=all_param_names, group_type="groups")
         if spec.required:
             raise ValueError(
                 "Group(required=True) is only valid in mutually_exclusive_groups; "
@@ -2580,7 +2604,6 @@ def _validate_group_specs(
 
     mutex_entry_for: dict[str, int] = {}
     for index, spec in enumerate(mutually_exclusive_groups or (), start=1):
-        spec._validate_members(all_param_names=all_param_names, group_type="mutually_exclusive_groups")
         for name in spec.members:
             previous = mutex_entry_for.get(name)
             if previous == index:
@@ -2721,7 +2744,7 @@ def build_parser_from_function(
     from . import argparse_utils
 
     # The decorator already ran this at decoration time; direct callers get the same checks here.
-    _validate_group_specs(func, skip_params=skip_params, groups=groups, mutually_exclusive_groups=mutually_exclusive_groups)
+    _validate_group_specs(groups, mutually_exclusive_groups)
 
     parser_cls = parser_class or argparse_utils.DEFAULT_ARGUMENT_PARSER
     if "description" not in parser_kwargs:
@@ -2735,6 +2758,7 @@ def build_parser_from_function(
     resolved, base_args_types = _resolve_parameters(
         func,
         skip_params=skip_params,
+        groups=groups,
         mutually_exclusive_groups=mutually_exclusive_groups,
     )
 
@@ -2864,12 +2888,7 @@ def _build_subcommand_handler(
     # Validate the group specs eagerly (decoration time) so a misconfigured group hard-fails when
     # the class is defined; the name-only checks never resolve type hints, so forward-referenced
     # annotations still decorate and the parser build stays deferred.
-    _validate_group_specs(
-        func,
-        skip_params=_SKIP_PARAMS,
-        groups=options.groups,
-        mutually_exclusive_groups=options.mutually_exclusive_groups,
-    )
+    _validate_group_specs(options.groups, options.mutually_exclusive_groups)
     if base_command:
         # Validate eagerly (decoration time); the base-command rows in _CONSTRAINTS fire here.
         # skip_params is spelled out so this call cannot silently diverge from the parser build below.
@@ -3053,12 +3072,7 @@ def decorator(fn: Callable[..., Any]) -> Callable[..., Any]:
         # Validate the group specs eagerly (decoration time) so a misconfigured group hard-fails when
         # the class is defined; the name-only checks never resolve type hints, so forward-referenced
         # annotations still decorate and the parser build stays deferred.
-        _validate_group_specs(
-            fn,
-            skip_params=skip_params,
-            groups=options.groups,
-            mutually_exclusive_groups=options.mutually_exclusive_groups,
-        )
+        _validate_group_specs(options.groups, options.mutually_exclusive_groups)
         if base_command:
             # Validate eagerly (decoration time); the base-command rows in _CONSTRAINTS fire here.
             _resolve_parameters(fn, skip_params=skip_params, base_command=True)
diff --git a/docs/features/annotated.md b/docs/features/annotated.md
index 6895a03ec..98d087a97 100644
--- a/docs/features/annotated.md
+++ b/docs/features/annotated.md
@@ -445,8 +445,8 @@ token to convert. Both raise `TypeError` at decoration time.
 - `help` -- help text for an annotated subcommand (only valid with `subcommand_to`)
 - `aliases` -- aliases for an annotated subcommand (only valid with `subcommand_to`)
 - `deprecated` -- mark the subcommand as deprecated in `--help` (only valid with `subcommand_to`)
-- `groups` -- `Group` instances assigning parameter names to argument groups
-- `mutually_exclusive_groups` -- `Group` instances of mutually exclusive parameters
+- `groups` -- `Group` instances assigning argument names to argument groups
+- `mutually_exclusive_groups` -- `Group` instances of mutually exclusive arguments
 - `parser_class` -- a custom parser class (defaults to the configured default)
 - `**parser_kwargs` -- every other `Cmd2ArgumentParser` constructor kwarg, forwarded through PEP 692
   [`Unpack[Cmd2ParserKwargs]`][cmd2.annotated.Cmd2ParserKwargs]. See
@@ -549,13 +549,35 @@ both places, a mutex that sits only partly in a `groups=` entry, or one that spa
 raises `ValueError`. The other three nestings (an argument group inside another group or a mutex, or
 a mutex inside a mutex) are removed in argparse on Python 3.14 and cannot be expressed here.
 
-All of these group-spec rules -- member references, a parameter assigned to two groups,
+A `Group` member names a command-line **argument**. For a plain parameter the argument is the
+parameter, so the name is the same either way. An `ArgumentBlock` parameter is different: it is
+expanded into one argument per field (field name == argument name), so you name its fields rather
+than the block:
+
+```python
+@dataclass
+class Conn(ArgumentBlock):
+    host: Annotated[str, Option("--host")] = "localhost"
+    port: Annotated[int, Option("--port")] = 8080
+
+@with_annotated(groups=(Group("host", "port", title="connection"),))
+def do_connect(self, conn: Conn) -> None: ...
+```
+
+Naming the block parameter itself (`Group("conn")`) raises `ValueError`: the parameter is expanded
+away and has no argument of its own. Naming a block's fields individually is also what lets you say
+which fields are alternatives -- put `Group("json", "csv")` in `mutually_exclusive_groups` and only
+those two exclude each other, rather than every field of the block they happen to live in.
+
+The group-spec **shape** rules -- a member listed twice, a member assigned to two groups,
 `required=True` on a plain group, and the mutex nesting rules above -- are validated when the
-decorator runs, so a misconfigured group raises `ValueError` at class definition time instead of on
-first command use. The checks read only parameter names, never the type hints, so forward-referenced
-annotations still decorate cleanly. The one group rule that depends on the annotations (a member of
-a mutually exclusive group must be omittable -- have a default or be `T | None`) fires when the
-parser is built.
+decorator runs, so a misshapen group raises `ValueError` at class definition time instead of on
+first command use. Those checks read only the `Group` specs, never the signature or the type hints,
+so forward-referenced annotations still decorate cleanly.
+
+The rules that depend on what a member _is_ fire when the parser is built, because a block's field
+names cannot be known without resolving its type hint: that every member names a real argument, and
+that a member of a mutually exclusive group is omittable (has a default or is `T | None`).
 
 `parents=` mirrors argparse's standard parents mechanism for sharing argument definitions across
 parsers. `argument_default=argparse.SUPPRESS` is not supported and raises `TypeError`. It removes an
diff --git a/tests/test_annotated.py b/tests/test_annotated.py
index 6ed8f15e3..6f39699f7 100644
--- a/tests/test_annotated.py
+++ b/tests/test_annotated.py
@@ -1034,7 +1034,7 @@ def test_groups_and_mutex_applied(self) -> None:
         assert {"force", "dry_run"} in mutex_groups
 
     def test_group_nonexistent_param_raises(self) -> None:
-        with pytest.raises(ValueError, match="nonexistent parameter"):
+        with pytest.raises(ValueError, match="'missing', which is not a command-line argument"):
             build_parser_from_function(_func_grouped, groups=(Group("missing"),))
 
     def test_param_in_multiple_groups_raises(self) -> None:
@@ -1178,7 +1178,7 @@ def test_nonexistent_member_reported_over_required_member(self) -> None:
 
         def func(self, local: Annotated[str, Option("--local")], remote: str | None = None) -> None: ...
 
-        with pytest.raises(ValueError, match=r"nonexistent parameter 'ghost'"):
+        with pytest.raises(ValueError, match=r"'ghost', which is not a command-line argument"):
             build_parser_from_function(func, mutually_exclusive_groups=(Group("local", "ghost"),))
 
     def test_argument_group(self) -> None:
@@ -1376,10 +1376,6 @@ def team_add(self, name: str) -> None:
 
 
 class TestGroupHelpers:
-    def test_validate_group_members_rejects_nonexistent_param(self) -> None:
-        with pytest.raises(ValueError, match="nonexistent"):
-            Group("verbose", "nonexistent")._validate_members(all_param_names={"verbose"}, group_type="groups")
-
     def test_build_argument_group_targets(self) -> None:
         parser = argparse.ArgumentParser()
         target_for, argument_group_for = _build_argument_group_targets(parser, groups=(Group("src", "dst"),))
@@ -1436,33 +1432,154 @@ def func(self, src: str = "a", dst: str = "b") -> None: ...
 
         with pytest.raises(ValueError, match="different argument groups"):
             _validate_group_specs(
-                func,
-                skip_params=frozenset(),
                 groups=(Group("src"), Group("dst")),
                 mutually_exclusive_groups=(Group("src", "dst"),),
             )
 
 
-class TestEagerGroupSpecValidation:
-    """Group specs hard-fail at decoration time (class definition), not on first command use.
+class TestBuildTimeMemberValidation:
+    """A Group member names an argument, and that is checked once the arguments are built.
 
-    The decorator runs the name-only spec checks before deferring the parser build, so a
-    misconfigured group raises while the class body executes instead of surfacing as a swallowed
-    runtime error the first time the command runs.  Type hints are never resolved by these checks,
-    so forward-referenced annotations still decorate (the parser build stays deferred for them).
+    It cannot be checked at decoration time: an ArgumentBlock expands into one argument per field, and the
+    field names live inside the dataclass, reachable only by resolving the block's type hint -- which the
+    decoration-time checks never do, so forward references keep working.
     """
 
-    def test_member_typo_fails_at_decoration(self) -> None:
-        def do_x(self, a: str = "v") -> None: ...
+    def test_block_fields_can_be_named_in_an_argument_group(self) -> None:
+        """The #1714 case: a block's arguments are its fields, so its fields are what a group names."""
+
+        @dataclass
+        class Conn(ArgumentBlock):
+            host: Annotated[str, Option("--host")] = "localhost"
+            port: Annotated[int, Option("--port")] = 8080
+
+        def func(self, conn: Conn, verbose: bool = False) -> None: ...
+
+        parser = build_parser_from_function(func, groups=(Group("host", "port", title="Connection"),))
+        section = next(g for g in parser._action_groups if g.title == "Connection")
+        assert {a.dest for a in section._group_actions} == {"host", "port"}
+
+    def test_block_fields_can_be_named_in_a_mutex_group(self) -> None:
+        """Fields that are genuinely alternatives are named individually, so the meaning is explicit."""
+
+        @dataclass
+        class Format(ArgumentBlock):
+            json: Annotated[bool, Option("--json")] = False
+            csv: Annotated[bool, Option("--csv")] = False
+
+        def func(self, fmt: Format, verbose: bool = False) -> None: ...
+
+        parser = build_parser_from_function(func, mutually_exclusive_groups=(Group("json", "csv"),))
+        assert {a.dest for a in parser._mutually_exclusive_groups[0]._group_actions} == {"json", "csv"}
+        with pytest.raises(SystemExit):
+            parser.parse_args(["--json", "--csv"])
+
+    def test_a_group_can_mix_block_fields_and_plain_parameters(self) -> None:
+        """Members name arguments, so where an argument came from stops mattering once it is built.
+
+        The block's own `port` is left out to pin down that a group takes the fields it names rather
+        than the whole block that one of them happens to belong to.
+        """
+
+        @dataclass
+        class Conn(ArgumentBlock):
+            host: Annotated[str, Option("--host")] = "localhost"
+            port: Annotated[int, Option("--port")] = 8080
+
+        def func(self, conn: Conn, verbose: bool = False) -> None: ...
+
+        parser = build_parser_from_function(func, groups=(Group("host", "verbose", title="Mixed"),))
+        section = next(g for g in parser._action_groups if g.title == "Mixed")
+        assert {a.dest for a in section._group_actions} == {"host", "verbose"}
+        ns = parser.parse_args(["--host", "h", "--verbose"])
+        assert (ns.host, ns.verbose) == ("h", True)
+
+    def test_a_mutex_can_mix_a_block_field_and_a_plain_parameter(self) -> None:
+        """A block field and a plain parameter can be genuine alternatives to each other."""
+
+        @dataclass
+        class Conn(ArgumentBlock):
+            host: Annotated[str, Option("--host")] = "localhost"
+
+        def func(self, conn: Conn, verbose: bool = False) -> None: ...
+
+        parser = build_parser_from_function(func, mutually_exclusive_groups=(Group("host", "verbose"),))
+        assert {a.dest for a in parser._mutually_exclusive_groups[0]._group_actions} == {"host", "verbose"}
+        assert parser.parse_args(["--host", "h"]).host == "h"
+        assert parser.parse_args(["--verbose"]).verbose is True
+        with pytest.raises(SystemExit):
+            parser.parse_args(["--host", "h", "--verbose"])
+
+    def test_naming_the_block_parameter_is_rejected(self) -> None:
+        """The block parameter is expanded away and has no argument, so it cannot be a member."""
+
+        @dataclass
+        class Conn(ArgumentBlock):
+            host: Annotated[str, Option("--host")] = "localhost"
+
+        def func(self, conn: Conn, verbose: bool = False) -> None: ...
+
+        with pytest.raises(ValueError, match="'conn', which is an ArgumentBlock parameter"):
+            build_parser_from_function(func, groups=(Group("conn", title="Connection"),))
+
+    def test_naming_the_block_parameter_in_a_mutex_is_rejected_too(self) -> None:
+        """Same rule in both spec kinds -- there is no groups=/mutex asymmetry to remember."""
+
+        @dataclass
+        class Conn(ArgumentBlock):
+            host: Annotated[str, Option("--host")] = "localhost"
+
+        def func(self, conn: Conn, verbose: bool = False) -> None: ...
+
+        with pytest.raises(ValueError, match="'conn', which is an ArgumentBlock parameter"):
+            build_parser_from_function(func, mutually_exclusive_groups=(Group("conn", "verbose"),))
 
-        with pytest.raises(ValueError, match="groups references nonexistent parameter 'typo'"):
-            with_annotated(groups=(Group("typo"),))(do_x)
+    def test_naming_the_block_class_is_rejected(self) -> None:
+        """The class name is not a parameter or an argument; only fields are."""
+
+        @dataclass
+        class Conn(ArgumentBlock):
+            host: Annotated[str, Option("--host")] = "localhost"
+
+        def func(self, conn: Conn, verbose: bool = False) -> None: ...
+
+        with pytest.raises(ValueError, match="'Conn', which is not a command-line argument"):
+            build_parser_from_function(func, groups=(Group("Conn", title="Connection"),))
+
+    def test_parent_args_block_parameter_is_rejected(self) -> None:
+        """cmd2_parent_args declares no arguments of its own; its fields come from the parent."""
+
+        @dataclass
+        class Base(ArgumentBlock):
+            dry: Annotated[bool, Option("--dry")] = False
+
+        def func(self, cmd2_parent_args: Base, verbose: bool = False) -> None: ...
+
+        with pytest.raises(ValueError, match="'cmd2_parent_args', which is an ArgumentBlock parameter"):
+            build_parser_from_function(func, groups=(Group("cmd2_parent_args", title="Inherited"),))
+
+    def test_member_typo_fails_at_build(self) -> None:
+        """A typo still hard-fails -- at the parser build rather than at decoration."""
 
-    def test_mutex_member_typo_fails_at_decoration(self) -> None:
         def do_x(self, a: str = "v") -> None: ...
 
-        with pytest.raises(ValueError, match="mutually_exclusive_groups references nonexistent parameter 'typo'"):
-            with_annotated(mutually_exclusive_groups=(Group("typo"),))(do_x)
+        with_annotated(groups=(Group("typo"),))(do_x)  # decorates: existence is not knowable yet
+        with pytest.raises(ValueError, match="'typo', which is not a command-line argument"):
+            build_parser_from_function(do_x, groups=(Group("typo"),))
+
+
+class TestEagerGroupSpecValidation:
+    """Spec-*shape* rules hard-fail at decoration time (class definition), not on first command use.
+
+    The decorator runs the spec-shape checks before deferring the parser build, so a misshapen group
+    raises while the class body executes instead of surfacing as a swallowed runtime error the first
+    time the command runs.  These checks read the ``Group`` specs only -- never the signature and never
+    the type hints -- so forward-referenced annotations still decorate.
+
+    Whether a member *exists* is deliberately not among them: an ArgumentBlock's arguments are its
+    dataclass fields, which only resolving its hint would reveal, so that check runs at parser build
+    (see :class:`TestBuildTimeMemberValidation`).
+    """
 
     def test_param_in_two_argument_groups_fails_at_decoration(self) -> None:
         def do_x(self, a: str = "v") -> None: ...
@@ -1503,19 +1620,13 @@ def do_x(self, a: str = "v", b: str = "w") -> None: ...
                 mutually_exclusive_groups=(Group("a", "b", title="U"),),
             )(do_x)
 
-    def test_subcommand_group_typo_fails_at_decoration(self) -> None:
-        def team_add(self, a: str = "v") -> None: ...
-
-        with pytest.raises(ValueError, match="nonexistent parameter 'typo'"):
-            with_annotated(subcommand_to="team", groups=(Group("typo"),))(team_add)
-
     def test_eager_validation_does_not_resolve_type_hints(self) -> None:
-        # The group error fires even though the annotation can never resolve: the checks read
-        # parameter names only, so the unresolvable hint is not touched.
+        # The shape error fires even though the annotation can never resolve: the checks read the
+        # Group specs only, so the unresolvable hint is not touched.
         def do_x(self, a: "NoSuchType" = None) -> None: ...  # noqa: F821
 
-        with pytest.raises(ValueError, match="nonexistent parameter 'typo'"):
-            with_annotated(groups=(Group("typo"),))(do_x)
+        with pytest.raises(ValueError, match="only valid in mutually_exclusive_groups"):
+            with_annotated(groups=(Group("a", required=True),))(do_x)
 
     def test_unresolvable_hints_with_valid_groups_decorate(self) -> None:
         # Valid specs + an unresolvable annotation must decorate without raising; type resolution