Tekton Pipelines is a Kubernetes-native CI/CD engine that defines and reconciles custom resources (Task, Pipeline, TaskRun, PipelineRun, StepAction, ResolutionRequest, etc.) to execute containerized workflows. The architecture follows the Kubernetes operator pattern using Knative's controller framework: admission webhooks for validation/defaulting, reconcilers that manage the lifecycle of each resource type, and a sidecar entrypoint binary for step execution. Key subsystems include a pluggable remote resolution framework (git, OCI bundles, HTTP, cluster, hub), CloudEvents-based notifications, SPIRE-based workload identity and provenance, and a DAG scheduler for pipeline task ordering. External dependencies include Kubernetes client-go, Knative/pkg, OpenTelemetry, CloudEvents SDK, sigstore, and various cloud SDKs. The codebase is well-structured with extensive unit and e2e tests, but carries some duplication between legacy and modern resolution packages.