Preload poteto-mode in the Claude poteto-agent

[RomiSinghio]

Problem

Claude Code starts custom subagents with isolated context. The shipped poteto-agent tells the child to read poteto-mode, but its frontmatter does not preload that skill. A live claude --agent pstack:poteto-agent probe reports NOT PRELOADED when file reads and Skill invocation are withheld. External pstack Claude lanes also disable ambient skill dispatch by design, so prose alone does not provide the skill body.

Proposed change

Add skills: [pstack:poteto-mode] to the Claude poteto-agent definition. Keep the shared skill tree unchanged. Add a static invariant so future upstream syncs preserve the Claude-only preload field.

Acceptance criteria

• The packaged poteto-agent preloads pstack:poteto-mode through Claude Code's supported skills frontmatter.
• The skill remains one shared tree for Claude Code and Codex.
• A static check fails if the preload binding disappears.
• The exact candidate passes the repository test, typecheck, static-invariant, and plugin-validation commands.
• A live Claude Code run with the packaged candidate can name content from poteto-mode without invoking Skill or reading the skill from disk.

Evidence

Baseline command used Claude Code 2.1.258 with open-pstack 1.2.1. The agent returned NOT PRELOADED and explained that only the skill name and description were visible.