In-session skill counterparts to `pnpm work decompose --execute` and
`pnpm work dispatch --execute`. They dispatch sub-agents — a decomposer
for /work-decompose; separate worktree-isolated implementer and
read-only reviewer sub-agents for /work-dispatch's implement-review loop.
Single source of truth: the skills read `.sandcastle/*.prompt.md` at
dispatch time and never copy them — the prompt files stay authoritative
for both Sandcastle and the skills, so the role definitions cannot
drift. `.sandcastle/` and `pnpm work` are untouched; this is additive.
Danijel Martinek
c33e0b2669