Bundle pinned copies of 7 CE pipeline-stage skills (strategy, ideate,
brainstorm, plan, work, code-review, compound) under src/skills/ and declare
them via PluginSkillContribution. Empirical finding: the skills contribution
alone does not make a SKILL.md resolvable in a session -- the engine ingests it
as a name only. So onLoad runs an idempotent, isolation-guarded physical install
into a plugin-local .fusion-ce-skills/ dir (never a global ~/.claude/skills),
which the engine skill-resolver can then discover. Proven against the real
loadSkills + resolveSessionSkills pipeline.