feat: Generate pi-coding-agent compatible slash-command prompts from schema #818

Problem Statement

Related: #817

pi-coding-agent uses .pi/prompts/opsx-*.md slash templates (/opsx:propose <desc>) to generate OpenSpec changes scaffold + artifacts.

Current:

Manual prompts w/ hardcoded steps/instructions (fragile, dupes schema logic).

Describe the solution you'd like

openspec CLI gen pi prompts from schema:

openspec gen pi --artifacts prompts --workflow propose > .pi/prompts/opsx-propose.md
openspec gen pi --artifacts prompts --workflow apply > .pi/prompts/opsx-apply.md

etc.

• --provider pi / --template pi-slash
• Interp schema: artifacts/deps/status/instructions → dynamic steps.
• Placeholders: $@ for user args (change name/desc).
• Reload: pi /reload.

Ex output (propose.md snippet):

Input: Args: $@. Derive name/desc.

1. openspec new change "$1 || kebab($@)"
2. Loop artifacts via openspec status --json
...

Benefits:

• Schema changes → auto prompt updates.
• Consistent w/ OpenSpec.
• Shareable pi packages.

Describe alternatives you've considered

• Manual prompts (.pi/skills/openspec-*-change/SKILL.md): Dup maint.
• Custom extension: Reinvents schema parsing.

Additional context

Ex repo using: taqtiqa-mark/zeptoclaw (.pi/prompts/opsx-*.md).
Tested v1.2.0: Works w/ arg sub → full artifacts.

Ex generated change: chore-add-containerized-test-lint-scripts (from `/opsx:propose "Create
container scripts..." ).