docs(guardrails): enforce JSDoc on every new or modified function

[Copilot]

Summary

• What changed: Added JSDoc requirement to AI guardrails in CLAUDE.md, copilot-instructions.md, and ERRORS.md
• Why: Recent PRs introduced undocumented functions; enforce documentation at authoring time rather than review time
• Supersedes / Related: Addresses bot reviewer feedback on original PR

Scope

• Modules impacted: Documentation only (CLAUDE.md, .github/copilot-instructions.md, ERRORS.md)
• Cross-module impact: none
• Risk level: low

Validation

• npm run lint (N/A - docs only)
• npm run test:unit (N/A - docs only)
• npm run build (N/A - docs only)
• Manual checks done: verified @return convention matches codebase (theme.js, tools.js, model.js)

Guardrails check

• No secrets or credentials introduced (.env*, secrets/**, keys, tokens)
• No risky rename/move of core stack paths
• Changes remain merge-friendly for downstream projects
• Tests added or updated when behavior changed (N/A - docs only)

Optional: Infra/Stack alignment details

Before vs After (key changes only)

Area	Before	After	Notes
JSDoc tag	Used @returns initially	Use @return	Matches codebase convention (7+ files use @return, only 1 uses @returns)
Async clarity	Not specified	Always document resolved value	Clarifies what promises resolve to
Sync status	Only in CLAUDE.md	All 3 AI instruction files	Consistent enforcement across Copilot and Claude

• Upstream parity target / source: N/A
• Automation or policy impact (CI, Dependabot, auto-merge, majors, permissions): None - pure documentation
• Rollback plan: Revert commit if needed; no runtime impact

Notes for reviewers

• Security considerations: None
• Mergeability considerations: Minimal diff, documentation-only change safe for downstream merges
• Follow-up tasks (optional): None

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