taskgraph_ts/tasks/implementation/frontmatter/splitter.md

id, name, status, depends_on, scope, risk, impact, level

id	name	status	depends_on	scope	risk	impact	level
frontmatter/splitter	Implement frontmatter delimiter splitter (~40 lines)	completed	setup/project-init	single	trivial	component	implementation

Description

Implement the self-contained --- delimited frontmatter splitter in src/frontmatter/parse.ts. This is a ~40 line function that extracts the YAML data string and markdown content body from a markdown string. No gray-matter dependency.

Per frontmatter.md, the splitter:

1. Checks for opening --- delimiter (not ----)
2. Finds closing \n--- delimiter
3. Extracts YAML data string and markdown content body
4. Returns { data: string, content: string } or null if no valid frontmatter

Acceptance Criteria

• splitFrontmatter(markdown: string): { data: string; content: string } | null
• Opening --- must be at the start of the file (or after optional BOM/whitespace on first line)
• ---- (4+ dashes) is NOT a valid delimiter — only exact ---
• Closing delimiter requires \n--- (newline before dashes)
• Returns null if no valid frontmatter found
• Returns { data: "", content: "" } if frontmatter is present but empty (e.g., ---\n---)
• Content body starts after the closing --- + newline
• Handles edge cases: no closing delimiter (returns null), file with only ---\n---, file with no --- at all
• Unit tests: standard frontmatter, no frontmatter, empty frontmatter, multi-line content, dashes in content body (shouldn't be treated as delimiters), 4+ dashes ignored

References

• docs/architecture/frontmatter.md — splitter design, supply chain decision

Notes

Self-contained splitFrontmatter function implemented with no external dependencies. Uses regex for opening delimiter match and manual scan for closing delimiter to enforce exact 3-dash rule. Handles BOM stripping and empty frontmatter.

Summary

Implemented the splitFrontmatter function in src/frontmatter/parse.ts per architecture spec.

• Modified: src/frontmatter/parse.ts (added splitFrontmatter function, ~65 lines including JSDoc)
• Modified: src/frontmatter/index.ts (exported splitFrontmatter)
• Modified: test/frontmatter.test.ts (18 comprehensive tests)
• Tests: 18 splitFrontmatter tests + 4 existing placeholder tests, all passing (22 total)
• TypeScript check: passing