diff --git a/gateway/platforms/discord.py b/gateway/platforms/discord.py
index 28286d48c0..660ed46dd8 100644
--- a/gateway/platforms/discord.py
+++ b/gateway/platforms/discord.py
@@ -1081,6 +1081,8 @@ class DiscordAdapter(BasePlatformAdapter):
         chat_id: str,
         message_id: str,
         content: str,
+        *,
+        finalize: bool = False,
     ) -> SendResult:
         """Edit a previously sent Discord message."""
         if not self._client:
diff --git a/gateway/platforms/feishu.py b/gateway/platforms/feishu.py
index 0531bff487..4b4fa0da4e 100644
--- a/gateway/platforms/feishu.py
+++ b/gateway/platforms/feishu.py
@@ -1468,6 +1468,8 @@ class FeishuAdapter(BasePlatformAdapter):
         chat_id: str,
         message_id: str,
         content: str,
+        *,
+        finalize: bool = False,
     ) -> SendResult:
         """Edit a previously sent Feishu text/post message."""
         if not self._client:
diff --git a/gateway/platforms/matrix.py b/gateway/platforms/matrix.py
index cdd67b337d..a5f9352b55 100644
--- a/gateway/platforms/matrix.py
+++ b/gateway/platforms/matrix.py
@@ -825,7 +825,7 @@ class MatrixAdapter(BasePlatformAdapter):
 
 
     async def edit_message(
-        self, chat_id: str, message_id: str, content: str
+        self, chat_id: str, message_id: str, content: str, *, finalize: bool = False
     ) -> SendResult:
         """Edit an existing message (via m.replace)."""
 
diff --git a/gateway/platforms/mattermost.py b/gateway/platforms/mattermost.py
index 18367a8e44..10539bf646 100644
--- a/gateway/platforms/mattermost.py
+++ b/gateway/platforms/mattermost.py
@@ -304,7 +304,7 @@ class MattermostAdapter(BasePlatformAdapter):
         )
 
     async def edit_message(
-        self, chat_id: str, message_id: str, content: str
+        self, chat_id: str, message_id: str, content: str, *, finalize: bool = False
     ) -> SendResult:
         """Edit an existing post."""
         formatted = self.format_message(content)
diff --git a/gateway/platforms/slack.py b/gateway/platforms/slack.py
index ba444c53e8..5455c0fa56 100644
--- a/gateway/platforms/slack.py
+++ b/gateway/platforms/slack.py
@@ -316,6 +316,8 @@ class SlackAdapter(BasePlatformAdapter):
         chat_id: str,
         message_id: str,
         content: str,
+        *,
+        finalize: bool = False,
     ) -> SendResult:
         """Edit a previously sent Slack message."""
         if not self._app:
diff --git a/gateway/platforms/telegram.py b/gateway/platforms/telegram.py
index 0b74c4e15f..1bc4ec2b10 100644
--- a/gateway/platforms/telegram.py
+++ b/gateway/platforms/telegram.py
@@ -1081,6 +1081,8 @@ class TelegramAdapter(BasePlatformAdapter):
         chat_id: str,
         message_id: str,
         content: str,
+        *,
+        finalize: bool = False,
     ) -> SendResult:
         """Edit a previously sent Telegram message."""
         if not self._bot:
diff --git a/gateway/platforms/whatsapp.py b/gateway/platforms/whatsapp.py
index d1de5b8568..78b1b92f77 100644
--- a/gateway/platforms/whatsapp.py
+++ b/gateway/platforms/whatsapp.py
@@ -655,6 +655,8 @@ class WhatsAppAdapter(BasePlatformAdapter):
         chat_id: str,
         message_id: str,
         content: str,
+        *,
+        finalize: bool = False,
     ) -> SendResult:
         """Edit a previously sent message via the WhatsApp bridge."""
         if not self._running or not self._http_session:
diff --git a/tests/gateway/test_stream_consumer.py b/tests/gateway/test_stream_consumer.py
index 0a0e0631db..7ae587dadd 100644
--- a/tests/gateway/test_stream_consumer.py
+++ b/tests/gateway/test_stream_consumer.py
@@ -133,6 +133,43 @@ class TestFinalizeCapabilityGate:
         assert picky.edit_message.call_args[1]["finalize"] is True
 
 
+class TestEditMessageFinalizeSignature:
+    """Every concrete platform adapter must accept the ``finalize`` kwarg.
+
+    stream_consumer._send_or_edit always passes ``finalize=`` to
+    ``adapter.edit_message(...)`` (see gateway/stream_consumer.py).  An
+    adapter that overrides edit_message without accepting finalize raises
+    TypeError the first time streaming hits a segment break or final edit.
+    Guard the contract with an explicit signature check so it cannot
+    silently regress — existing tests use MagicMock which swallows any
+    kwarg and cannot catch this.
+    """
+
+    @pytest.mark.parametrize(
+        "module_path,class_name",
+        [
+            ("gateway.platforms.telegram", "TelegramAdapter"),
+            ("gateway.platforms.discord", "DiscordAdapter"),
+            ("gateway.platforms.slack", "SlackAdapter"),
+            ("gateway.platforms.matrix", "MatrixAdapter"),
+            ("gateway.platforms.mattermost", "MattermostAdapter"),
+            ("gateway.platforms.feishu", "FeishuAdapter"),
+            ("gateway.platforms.whatsapp", "WhatsAppAdapter"),
+            ("gateway.platforms.dingtalk", "DingTalkAdapter"),
+        ],
+    )
+    def test_edit_message_accepts_finalize(self, module_path, class_name):
+        import inspect
+
+        module = pytest.importorskip(module_path)
+        cls = getattr(module, class_name)
+        params = inspect.signature(cls.edit_message).parameters
+        assert "finalize" in params, (
+            f"{class_name}.edit_message must accept 'finalize' kwarg; "
+            f"stream_consumer._send_or_edit passes it unconditionally"
+        )
+
+
 class TestSendOrEditMediaStripping:
     """Verify _send_or_edit strips MEDIA: before sending to the platform."""