TOOLING-ITD-003: Custom Lint Rules

CONTEXT

Generic markdown linting doesn't understand our document types. An ITD must have specific sections (Context, Problem, Options, Reasoning, Implications). A Data Structure needs an Overview.

PROBLEM

How should we enforce document-type-specific structure?

OPTIONS CONSIDERED

1. Manual review only - Reviewers check structure

2. ✅ Custom markdownlint rules - Automated validation per doc type

3. Schema validation - YAML frontmatter with JSON schema

REASONING

Option 1 (Manual): Reviewers forget. Inconsistent enforcement.

Option 2 (Custom rules): Markdownlint supports custom rules in JavaScript. We can validate ITD sections, naming conventions, and required content automatically.

Option 3 (Schema): Adds complexity. Frontmatter is friction. Markdown-native validation is simpler.

IMPLICATIONS

Custom rules implemented:

• itd-required-sections - ITDs must have all five sections

• itd-valid-sections - No unexpected sections in ITDs

• itd-single-selected-option - Exactly one option marked with ✅

• itd-naming-convention - Title matches folder prefix

• ds-required-sections - Data Structures need Overview

Rules live in tooling/lint-rules/ and run via markdownlint config.