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

[Copilot]

Summary

• What changed: Added JSDoc requirement to guardrails using @returns tag; added ERRORS.md entry for missing JSDoc on new functions
• Why: Recent PRs introduced functions without JSDoc headers; codifies this as an always-on constraint
• Supersedes / Related: N/A

Scope

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

Validation

• npm run lint (not applicable - docs only)
• npm test (not applicable - docs only)
• Manual checks done: Verified @returns usage matches existing codebase convention (e.g., modules/tasks/repositories/tasks.repository.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 requirement	Implicit/unenforced	Explicit guardrail	Uses @returns to match codebase
Error tracking	No entry	ERRORS.md entry added	Captures recurring mistake pattern

• Upstream parity target / source: N/A
• Automation or policy impact (CI, Dependabot, auto-merge, majors, permissions): None
• Rollback plan: Git revert if needed

Notes for reviewers

• Security considerations: None
• Mergeability considerations: Standardized on @returns (not @return) to match existing Node codebase convention in repositories and services
• Follow-up tasks (optional): None

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