Tighten spec-charter brownfield and cross-skill helper wording

[sungjunlee]

Context

The writing-great-skills review found two small predictability issues in spec-charter:

• Brownfield follow-up guidance repeats the same system-map-before-grill idea in multiple places.
• Reassess mode says to resolve helper scripts from the installed dev-backlog skill directory, but does not clearly mark this as a cross-skill helper dependency.

Affected file:

• skills/spec-charter/SKILL.md

Goal

Reduce duplication and make cross-skill helper resolution explicit.

Suggested Direction

• Keep one clear brownfield follow-up rule: create spec/system-map.md first when absent; recommend spec-grill only when capability candidates are evidence-backed.
• Change the reassess helper-script wording to name the cross-skill dependency on dev-backlog scripts such as capabilities-doctor.js and component-lint.js.

Acceptance Criteria

• Brownfield follow-up guidance has one authoritative wording instead of repeated equivalent instructions.
• Reassess mode clearly says the helper scripts are cross-skill helpers from dev-backlog.
• The edit preserves existing routing: charter direction stays with spec-charter, system shape with spec-system-map, capability contracts with spec-grill.
• npx --yes skills add . -l still discovers all five skills.

[coderabbitai]

🔗 Related PRs

#106 - docs(backlog-charter): create-mode interview + signals + seed-Decisions guidance (#93 #94 #96) [merged]
#156 - [codex] Fix backlog-charter skill metadata [merged]
#160 - [codex] split spec charter and grill skills [merged]
#182 - feat(spec): add report-first capability grill workflow [merged]
#188 - [codex] clarify spec evidence and coverage boundaries [merged]

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