v0.6.0

Core runtime (sessions, fair scheduling, sandboxing, three backend drivers), markdown harness authoring with hot reload, container isolation, run cancellation, operations layer (backpressure, retries, hooks, metrics, quotas, secret scoping), harness packs (git/npm/tarball/local) with CLI, artifact stores (local + dependency-free S3), and real-CLI verification of the claude/codex drivers including warm resume.