diff --git a/hermes_cli/gateway.py b/hermes_cli/gateway.py
index ccac2220a6b9..e3fa8d6339b7 100644
--- a/hermes_cli/gateway.py
+++ b/hermes_cli/gateway.py
@@ -5814,17 +5814,21 @@ def _builtin_setup_fn(key: str):
     from hermes_cli import setup as _s
 
     return {
-        # telegram moved into the plugin: setup_fn registered by
-        # plugins/platforms/telegram/adapter.py::register(). #41112.
         # discord moved into the plugin: setup_fn is registered by
         # plugins/platforms/discord/adapter.py::register() and dispatched
         # via the plugin path in _configure_platform().
-        # slack moved into the plugin: setup_fn is registered by
-        # plugins/platforms/slack/adapter.py::register() and dispatched
-        # via the plugin path in _configure_platform(). #41112.
-        # matrix moved into the plugin: setup_fn registered by
-        # plugins/platforms/matrix/adapter.py::register() and dispatched via
-        # the plugin path in _configure_platform(). #41112.
+        #
+        # telegram, slack, and matrix are built-in (not plugin-migrated —
+        # see the _PLATFORMS NOTE above). They keep their bespoke setup
+        # flows here because the generic _setup_standard_platform fallback
+        # treats the first `vars` entry (token_var) as mandatory and aborts
+        # the whole wizard if it's left empty. That breaks Matrix's
+        # documented "leave the access token empty for password login"
+        # path outright, and loses Telegram's token-format validation and
+        # Slack's manifest-regeneration prompt.
+        "telegram": _s._setup_telegram,
+        "slack": _s._setup_slack,
+        "matrix": _s._setup_matrix,
         # mattermost moved into the plugin: setup_fn is registered by
         # plugins/platforms/mattermost/adapter.py::register() and dispatched
         # via the plugin path in _configure_platform().
diff --git a/tests/hermes_cli/test_gateway_platform_gating.py b/tests/hermes_cli/test_gateway_platform_gating.py
index c16875687ce4..ebf648d03a61 100644
--- a/tests/hermes_cli/test_gateway_platform_gating.py
+++ b/tests/hermes_cli/test_gateway_platform_gating.py
@@ -15,6 +15,67 @@
 import sys
 
 
+# Every built-in adapter under gateway/platforms/ that is expected to have
+# a picker entry today. This intentionally excludes dingtalk/feishu/wecom/
+# wecom_callback — those were dropped by the same e39b468 refactor but are
+# tracked and restored separately (see .plans/missing-platform-plugin-shims.md
+# and the PR that follows it); asserting them here would make this test
+# depend on merge order between unrelated PRs.
+BUILTIN_ADAPTER_KEYS = frozenset(
+    {
+        "telegram",
+        "slack",
+        "matrix",
+        "whatsapp",
+        "email",
+        "sms",
+        "mattermost",
+        "signal",
+        "weixin",
+        "bluebubbles",
+        "qqbot",
+        "yuanbao",
+    }
+)
+
+
+class TestBuiltinAdaptersStayInPicker:
+    def test_every_builtin_adapter_key_is_in_all_platforms(self, monkeypatch):
+        """Regression guard for e39b468-style silent deletions.
+
+        A future refactor that deletes a _PLATFORMS entry (or claims a
+        built-in "moved to plugins" without actually creating the plugin)
+        should fail CI here instead of shipping a picker that's silently
+        missing a platform.
+        """
+        import hermes_cli.gateway as gateway_mod
+
+        monkeypatch.setattr(gateway_mod.sys, "platform", "linux")
+        keys = {p["key"] for p in gateway_mod._all_platforms()}
+        missing = BUILTIN_ADAPTER_KEYS - keys
+        assert not missing, (
+            f"Built-in adapter(s) {sorted(missing)} have no _all_platforms() "
+            "entry — they exist in gateway/platforms/ but are invisible to "
+            "`hermes setup gateway`."
+        )
+
+    def test_telegram_slack_matrix_use_bespoke_setup_fn(self, monkeypatch):
+        """Matrix's "leave the token empty for password login" path is real.
+
+        The generic _setup_standard_platform() fallback treats the first
+        `vars` entry (token_var) as mandatory and aborts the whole wizard
+        if left empty — which would silently break Matrix's documented
+        password-login path. These three must resolve to their bespoke
+        hermes_cli.setup functions, not fall through to the generic flow.
+        """
+        import hermes_cli.gateway as gateway_mod
+        from hermes_cli import setup as _s
+
+        assert gateway_mod._builtin_setup_fn("telegram") is _s._setup_telegram
+        assert gateway_mod._builtin_setup_fn("slack") is _s._setup_slack
+        assert gateway_mod._builtin_setup_fn("matrix") is _s._setup_matrix
+
+
 class TestMatrixHiddenOnWindows:
     def test_matrix_present_on_linux(self, monkeypatch):
         """Sanity: matrix is still in the picker on Linux/macOS."""