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.

Pipelines-as-Code is a Kubernetes-native CI/CD controller that triggers Tekton PipelineRuns in response to Git webhook events from multiple providers (GitHub, GitLab, Gitea/Forgejo, Bitbucket Cloud/Data Center). In production, it listens for webhook payloads on a configurable endpoint, detects and validates the provider, matches events to PipelineRun templates stored in the repository's `.tekton/` directory using CEL expressions and annotations, resolves remote tasks and pipelines via hub or URL, creates PipelineRun resources with appropriate parameters and secrets, and reports status back to the Git provider (commit statuses, check runs, comments). It supports ChatOps commands (`/test`, `/retest`, `/cancel`), GitOps-style push commands, concurrency limits, automatic cleanup of old PipelineRuns, and optional LLM-driven failure analysis. The architecture consists of three main controllers (controller, watcher, webhook) plus a CLI tool (`tkn-pac`) for bootstrapping, repository management, and local testing. The codebase is well-structured, with clean provider abstractions, a modular queue system, extensive OpenTelemetry instrumentation, and comprehensive test coverage across all providers. While the multi-provider support introduces some duplication, the core patterns (event matching, pipeline resolution, status reporting) are cleanly separated and reusable.