> [!NOTE]
> This PR was authored by Coder Agents on behalf of @jeremyruppel.
Part 4 of DEVEX-277 (POST /api/v2/templatebuilder/compose).
Adds the HTTP handler, route wiring, and integration tests for the
compose endpoint.
The handler accepts a JSON request with a base template ID and optional
modules with variable overrides, renders them via `Compose`/`BundleTar`,
and returns the tar archive directly with `Content-Type:
application/x-tar`. The registry URL comes from the deployment config
(`CODER_TEMPLATE_BUILDER_REGISTRY_URL`).
RBAC uses `policy.ActionCreate` on
`rbac.ResourceTemplate.AnyOrganization()`.
Integration tests cover: base-only compose, base with modules, unknown
base/module errors, missing base template ID, and feature-disabled 404.
