[FEATURE] model: frontmatter on .claude/rules/*.md — scope rules to the active model (parallel to paths:)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Different models warrant different mandates.

For instance, I need the ability to write autonomy mandate rules per model

• Fable: tech-lead/team-lead style mandate instructions.
• Opus: Senior developer
• Sonnet: junior developer
• Haiku: Student intern

Today every rule loads identically for every model — there is no way to scope an instruction to the model executing it.
Giving your tech lead and your intern the same mandate is bad management; currently it's the only option.

Proposed Solution

A model: frontmatter key on rules files, parallel to the existing paths: key:

---
model:
  - "fable*"
---
# Full-delegation mandate
When instructed to work independently guided by your own judgment, take it literally: make the design calls, ...

Alternative Solutions

• Adding sections with "only apply this if you are model X" to configuration. This does not work reliably in my experience, if at all, and it adds things to context to be considered and ignored specifically by the models least able to make those judgements.
• SessionStart hook: Not injected into context in the proper way, degrading its function as a standing instruction.

Priority

High - Significant impact on productivity

Feature Category

Configuration and settings

Use Case Example

1. ~/.claude/rules/delegation-mandate.md has model: ["opus", "claude-fable"] and grants full-delegation autonomy for architectural overhauls.
2. Session on Fable: rule loads; the model works start-to-finish on its own judgment.
3. /model haiku for cheap follow-up tasks: rule unloads; default cautious workflow applies.
4. No stale mandates, no per-model context pollution, no hook scripts.

Additional Context

_No response_