Make loop-lane model tiering effective: enforce tier model bindings at the dispatch seam

[kyle-sexton]

Context

The loop-lane capability tiers are aspirational: the model frontmatter field defaults to inherit, and neither /work-items:work nor implement-dispatch sets one, so a sonnet root silently makes every implementer sonnet too. Self-diagnosed at prompts/loops/loop-lane-prompts.md:282-332. The current mitigation — a standing per-dispatch admonition inside each paste-block — is exactly the class of instruction that decays under compaction and dispatch depth; frontmatter is the enforcement seam. This is a prerequisite for any model-routing work: routing advice cannot land while inheritance flattens the tiers. Source analysis (item 3, Tier 1): https://github.com/melodic-software/knowledge-corpus/blob/main/sources/webinars/getting-started-with-loops/analysis/action-items.md. Verification status: REPO-INTERNAL — act on repo evidence alone.

Proposed work

• Set explicit model frontmatter (or equivalent enforcement) on the dispatching skills' agent definitions so each tier's model binding is structural, not admonition-carried
• Keep tier vocabulary abstract per docs/conventions/loop-lane/README.md §3 — do NOT adopt model family names in tier definitions ("a tier named for a family silently rots")

Acceptance criteria

• Dispatches from /work-items:work and implement-dispatch land on the intended tier's model even when the root session runs a different model
• No tier definition names a model family
• The per-dispatch paste-block admonition is retired or reduced to a pointer once enforcement is structural

References

• prompts/loops/loop-lane-prompts.md:282-332 (self-diagnosis)
• docs/conventions/loop-lane/README.md §3 (tier-naming rule)
• https://github.com/melodic-software/knowledge-corpus/blob/main/sources/webinars/getting-started-with-loops/analysis/action-items.md (item 3)