Proactive cron prompt-evolution nudge (v2 of cron↔skill linking)

Context

v1 of cron↔skill linking (spec: docs/superpowers/specs/2026-06-15-cron-skill-linking-design.md, commit 83f0227d) makes cron-prompt evolution reactive: the right-cron skill instructs the agent to slim a cron's prompt toward its linked skills when it is already editing/reasoning about that cron (cron_update + cron_list introspection). There is intentionally no proactive trigger in v1.

Ask (v2)

Add a pull-only proactive signal that surfaces to the agent when a recurring cron accumulates one or more newly auto-linked skills, prompting it to consider migrating that cron from a fat hand-written prompt toward a thin "what" prompt + skill references.

Hard constraints (inherited from project ethos)

• Never a silent platform rewrite of cron_specs.prompt — mutation stays on the agent-driven cron_update path, visible to the user.
• Never a noisy unsolicited bot message to the end user.
• Pull-only: a signal the agent consumes and acts on with judgment; auditable.

Why deferred from v1

The functional benefit (deterministic skill pull) is delivered immediately by auto-link + the runtime directive. Prompt slimming is token-only and non-urgent, so lazy/reactive evolution is correct and churn-free for v1. (The 2026-06-14 cron-then-continuation spec already documents churn from agent prompt self-rewrites — a proactive nudge must avoid reintroducing it.)

Sketch of acceptance

• When auto-link attaches a new skill to a recurring cron, record a lightweight signal (e.g. a flag/row, not a message).
• The agent's next foreground turn that touches crons (or a bounded curator-time pass) surfaces "cron X grew skill Y; its prompt may be slimmable".
• The agent decides whether to cron_update the prompt and tells the user what it simplified.

Start with docs/superpowers/specs/2026-06-15-cron-skill-linking-design.md and commit 83f0227d, then trace the auto-link, cron_update, and cron_list paths described in the issue. Done means a new auto-linked skill records a pull-only signal that a later cron-related agent turn can surface, while mutation remains agent-driven and user-visible.