fix(matrix): block outbound media when maxMediaBytes is zero

nanobot/channels/matrix.py

@@ -496,7 +496,15 @@ class MatrixChannel(BaseChannel):
             )
             return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(filename)
 
-        if limit_bytes and size_bytes > limit_bytes:
+        if limit_bytes <= 0:
+            logger.warning(
+                "Matrix outbound attachment skipped: media limit {} blocks all uploads for {}",
+                limit_bytes,
+                resolved,
+            )
+            return MATRIX_ATTACHMENT_TOO_LARGE_TEMPLATE.format(filename)
+
+        if size_bytes > limit_bytes:
             logger.warning(
                 "Matrix outbound attachment skipped: {} bytes exceeds limit {} for {}",
                 size_bytes,

tests/test_matrix_channel.py

@@ -857,6 +857,29 @@ async def test_send_uses_server_upload_limit_when_smaller_than_local_limit(tmp_p
     assert client.room_send_calls[0]["content"]["body"] == "[attachment: tiny.txt - too large]"
 
 
+@pytest.mark.asyncio
+async def test_send_blocks_all_outbound_media_when_limit_is_zero(tmp_path) -> None:
+    channel = MatrixChannel(_make_config(max_media_bytes=0), MessageBus())
+    client = _FakeAsyncClient("", "", "", None)
+    channel.client = client
+
+    file_path = tmp_path / "empty.txt"
+    file_path.write_bytes(b"")
+
+    await channel.send(
+        OutboundMessage(
+            channel="matrix",
+            chat_id="!room:matrix.org",
+            content="",
+            media=[str(file_path)],
+        )
+    )
+
+    assert client.upload_calls == []
+    assert len(client.room_send_calls) == 1
+    assert client.room_send_calls[0]["content"]["body"] == "[attachment: empty.txt - too large]"
+
+
 @pytest.mark.asyncio
 async def test_send_omits_ignore_unverified_devices_when_e2ee_disabled() -> None:
     channel = MatrixChannel(_make_config(e2ee_enabled=False), MessageBus())