While mesh networking for edge settings (e.g., smart buildings, farms, battlefields, etc.) has received much attention, the layer of control over such meshes remains largely centralized and cloud-based. This paper focuses on applications with sense-trigger-actuate (STA) workloads -- these are similar to the abstraction of routines popular in smart homes, but applied to larger-scale edge IoT deployments. We present CoMesh, which tackles the challenge of building local, non-cloud, and decentralized solutions for control of sense-trigger-actuate applications. At its core CoMesh uses an abstraction called k-groups to spread in a fine-grained way, the load of STA actions. Coordination within the k-group uses selective fast and cheap mechanisms rather than expensive off-the-shelf solutions. k-group selection is proactively dynamic, and occurs by using a combination of zero-message-exchange mechanisms (to reduce load) and locality sensitive hashing (to be aware of physical layout of devices). We analyze and theoretically prove the safety of CoMesh's mechanisms. Our evaluations using both simulation and Raspberry Pi lab deployments show that CoMesh is load-balanced, fast, and fault-tolerant.