Model omitted active plugin constraints when writing a handoff prompt

Model: claude-fable-5 (Claude Fable 5), Claude Code session with the ponytail plugin (v4.9.0) active in ultra mode.

What happened: While writing a handoff prompt for another agent, Claude omitted the active ponytail plugin's style discipline (YAGNI/shortest-diff rules) even though the skill was loaded and enforced in its own session. The user had to notice the omission and ask; only then did Claude supply the missing block.

Failure mode: Active behavioral constraints (loaded skill/plugin rules) were not treated as part of the state to hand off when generating a prompt for a different agent.

Expected: A handoff prompt should carry every constraint governing the work, including active plugin/skill disciplines, without the user having to audit it.

Filed at the user's request as model-behavior feedback.