Cross-skill canonical invocation: standardize on /slash form for shared skills

[sridherj]

Source: sub-phase 2.4 (correctness sanity + remediation + LinkedOut-coupling spike).

Context

`bin/audit-interdependencies --mode=cross-skill` finds two shared skills invoked with mixed forms across the fleet:

• `cast-child-delegation` — slash×14, bare×1.
• `cast-interactive-questions` — bare×10, slash×1.

Mixed invocation is yellow (not red) but degrades discoverability — Claude Code's slash-command palette only recognizes the `/cast-...` form; bare prose mentions are advisory only.

Decision

Adopt `/cast-skill-name` (slash form) as the canonical invocation across the fleet. It is the form the dispatcher recognizes and is already the majority pattern.

Why deferred to Phase 3a

This is a shared-skill content fix. Phase 2.4's deferral rule says any change that touches shared skills should batch with Phase 3a's behavior upgrades to avoid merge-conflict-within-3a risk.

Action

• Phase 3a sub-phase: rewrite all bare `cast-child-delegation` and `cast-interactive-questions` mentions in agent prompts to `/cast-child-delegation` and `/cast-interactive-questions`.
• 2.4 records the 26 yellow cross-skill findings as Deferred to this issue.

Verification

After Phase 3a, `bin/audit-interdependencies --mode=cross-skill --json` reports zero yellow findings.