Lifts the 'an agent uses a SKILL.md pack' concept out of a host and into the
harness:
- run.Ports.SkillPacks (SkillPackActivator) — nil-safe port; the executor folds
a loaded agent's pack catalog into the system prompt and adds a skill_use
loader tool to the toolbox (uses the existing ra.SystemPrompt + toolbox seams)
- run.RunnableAgent.SkillPacks + persona.Agent.SkillPacks (+ skill_packs YAML,
extends-inherit, ToRunnable) — the Agent noun is now pack-aware
- skillpack.Activator — the battery's default port impl (resolve names → packs →
catalog + skill_use), with a per-run BundleStager factory the host plumbs;
satisfies the port structurally (no import of run)
- agentbuiltins: ships gifsmith, a portable focused GIF/MP4 render agent that
uses the gif pack — references tool/tier/pack NAMES only, no host coupling
A host now wires run.Ports.SkillPacks instead of carrying its own activation
glue. Tests: Activator resolution + gifsmith loads through persona→RunnableAgent.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
