Warm containers, cloneable agents, resident sub-agents (v1.23.2 to v1.28.0)

Three interlocking arcs across seven releases. RFC BI P2 hardens the sandbox: durable per-principal workspaces via sandbox_open workspace: (bind-mounted /work, fenced as //, build caches survive container reap and sidecar restart), attested run tagging via the X-Loom-Root-Run header loomcycle forwards (server-set, unforgeable), sandbox_touch keepalive + sandbox_close_run bulk close, plus a static-MCP re-probe at run start so a sidecar that comes up second recovers on the next run. RFC BJ personalizes chat agents: a Library Clone action derives a new agent whose tool list is editable and may widen (only over the operator bearer, never from an in-run LLM), chat agents get self-service SkillDef, the fork ceiling check is now glob-aware, and POST /v1/sessions/{id}/replay copies a transcript into a new session bound to a possibly different target agent (cross-provider safe, reasoning stripped, optional compress). Adapters bump to 1.25.0 for replaySession. RFC BK ships resident sub-agents: Agent open/send/close keeps a child alive across turns with a warm sandbox container and full conversation state, then bounded and interruptible via timeout_ms + poll + cancel, then Web UI visibility with per-run listing + close + turn-cancel. Composes into a real compile-test-fix loop.