Migrate from Segment to Twilio Buildkite

[AnkitSegment]

Summary

Fixes the Buildkite pipeline on the Twilio locked-down general-039 agents. The previous pipeline still depended on Segment-only infrastructure and failed every run.

Verified green on build #11 (Build and Test + SauceLabs both passed).

Root causes fixed

• Segment cache-buildkite-plugin → shasum: command not found + S3 403 on the locked-down agents. Removed.
• No browser in the test image — tests run Karma ChromeHeadless, but node:*-alpine ships no browser. Added a CI image with Chromium.
• No public internet egress — docker.io pulls TLS-timeout, so apk add chromium can't reach the public Alpine CDN. Chromium is installed from the Twilio base-alpine apk mirror.
• phantomjs-prebuilt postinstall download (the real blocker) — several integrations pull it as a devDependency; its install downloads a binary from a public CDN and fails yarn install. It has no skip flag, so a tiny phantomjs stub on PATH reporting 2.1.1 makes its installer skip the download. The phantom launcher is unused — tests only run ChromeHeadless.
• SauceLabs used an unauthenticated Segment ECR image; moved to the same compose CI image.

Changes

File	Change
.buildkite/Dockerfile.ci	CI image: node (Twilio ECR mirror) + Chromium (Twilio base-alpine apk mirror) + phantomjs stub
docker-compose-ci.yml	Compose service that builds the CI image and runs the suite
.buildkite/pipeline.yml	Build/Test + SauceLabs steps via the docker-compose plugin with mount-checkout
karma.conf.js	ChromeHeadlessNoSandbox launcher (container runs as root)
.npmrc	Twilio Artifactory virtual-npm registry

Notes / follow-ups

• On a branch with no integration changes, yarn test runs --since master and reports "no packages" — passes without exercising integration tests. The CI infra is verified working; a branch touching an integration will exercise real Chrome runs.
• The Upload Assets steps still call ./.buildkite/upload.sh / publish.sh, which rely on Segment agent hooks (SEGMENT_LIB_PATH, run-with-role). Being verified separately on staging.

🤖 Generated with Claude Code

Testing

Testing not required as migrating from Segment to Twilio BK.