Retry a failed job, cancel a running build, or unblock a blocked ('Block pipeline') job in Buildkite via the REST API, including required scopes and the state each action requires.

Documented steps

1. Retry a job: `PUT /v2/organizations/{org.slug}/jobs/{job.id}/retry` (org-scoped) or the build-scoped `.../builds/{build.number}/jobs/{job.id}/retry`. Requires `write_builds`. Only retries a job that is `failed`, `timed_out`, or whose step has `permit_on_passed: true`. Returns `200 OK` with the NEW job object (new `job.id`). See https://buildkite.com/docs/apis/rest-api/jobs#retry-a-job
2. Each `job.id` can only be retried once — retry the new `job.id` from the prior response to retry again.
3. Cancel a build: `PUT /v2/organizations/{org.slug}/pipelines/{pipeline.slug}/builds/{number}/cancel` (build NUMBER, not UUID). Requires `write_builds`. Only succeeds if state is `scheduled`, `running`, or `failing`; otherwise `422`. See https://buildkite.com/docs/apis/rest-api/builds#cancel-a-build
4. There is no standalone 'cancel a job' endpoint — cancel the parent build to stop a specific job; job-level actions are limited to retry/reprioritize/unblock.
5. Unblock a job: `PUT /v2/organizations/{org.slug}/jobs/{job.id}/unblock` or the build-scoped equivalent. Requires `write_builds`. Optional JSON body: `{"unblocker": "<user-id>", "fields": {"<key>": "<value>"}}`. Example: `curl -H "Authorization: Bearer $TOKEN" -X PUT ".../jobs/{job.id}/unblock" -H "Content-Type: application/json" -d '{"fields": {"release-name": "Flying Dolphin"}}'`. See https://buildkite.com/docs/apis/rest-api/jobs#unblock-a-job
6. Check the job's `unblockable` boolean (from a build/job fetch) before calling `/unblock`; its `unblock_url` field names the exact endpoint. Success returns `200 OK` with `state: "unblocked"`.