[BLCCoreStudio]

Summary

Upgrades tool/containerd from a short schema-v2 overview into a schema-v3 technical reference focused on its real place in the container stack.

Changes

• separate containerd from Docker, Kubernetes, and low-level OCI runtimes
• explain the daemon/plugin architecture and native API boundary
• cover content, descriptors, images, snapshotters, containers, tasks, namespaces, GC/leases, Runtime v2/shims, root/state, events, and observability
• explain Kubernetes CRI, runtime classes, cgroups, CNI-facing behavior, and NRI integration
• distinguish ctr, nerdctl, and crictl by interface and diagnostic role
• add security boundaries, performance characteristics, upgrade considerations, failure modes, and an operational troubleshooting workflow
• add Technology Universe coverage metadata
• connect the module deliberately to Containers, Docker, and Kubernetes
• expand the source set to current containerd documentation, OCI standards, and official Kubernetes CRI documentation

Quality bar

The module follows the existing deep-dive standard without copying the Docker article mechanically. Its organizing model is containerd's object/lifecycle architecture and the boundaries operators actually debug on a node.