Merge frontmatter/parsing: parseFrontmatter with YAML 1.2, TypeBox validation, InvalidInputError

tasks/implementation/frontmatter/parsing.md

@@ -1,7 +1,7 @@
 ---
 id: frontmatter/parsing
 name: Implement parseFrontmatter with YAML parsing and TypeBox validation
-status: pending
+status: completed
 depends_on:
   - frontmatter/splitter
   - schema/input-schemas
@@ -24,17 +24,17 @@ Per [frontmatter.md](../../../docs/architecture/frontmatter.md), the function us
 
 ## Acceptance Criteria
 
-- [ ] `parseFrontmatter(markdown: string): TaskInput`:
+- [x] `parseFrontmatter(markdown: string): TaskInput`:
   - Calls splitter to extract YAML string
   - Throws `InvalidInputError` if no valid frontmatter found (not `null` return — the caller expects TaskInput)
   - Calls `yaml.parse(yamlString)` for YAML 1.2 parsing
   - Runs `Value.Clean(TaskInput, parsed)` to strip unknown properties
   - Runs `Value.Check(TaskInput, cleaned)` — if fails, runs `Value.Errors()` and throws `InvalidInputError` with structured field/path/message/value details
   - Returns validated `TaskInput`
-- [ ] `InvalidInputError` is populated with field-level details from `Value.Errors()` output
-- [ ] YAML 1.2 used exclusively (the `yaml` package default) — no YAML 1.1 type coercion
-- [ ] Handles YAML `null` values (e.g., `risk:` with no value) correctly — becomes `null` in the TaskInput (distinction from absent field)
-- [ ] Unit tests: valid frontmatter, missing required fields, invalid enum values, unknown fields stripped, null categorical values preserved
+- [x] `InvalidInputError` is populated with field-level details from `Value.Errors()` output
+- [x] YAML 1.2 used exclusively (the `yaml` package default) — no YAML 1.1 type coercion
+- [x] Handles YAML `null` values (e.g., `risk:` with no value) correctly — becomes `null` in the TaskInput (distinction from absent field)
+- [x] Unit tests: valid frontmatter, missing required fields, invalid enum values, unknown fields stripped, null categorical values preserved
 
 ## References
 
@@ -44,8 +44,11 @@ Per [frontmatter.md](../../../docs/architecture/frontmatter.md), the function us
 
 ## Notes
 
-> To be filled by implementation agent
+All acceptance criteria verified by unit tests and type-checker.
 
 ## Summary
 
-> To be filled on completion
+Implemented `parseFrontmatter(markdown: string): TaskInput` with full YAML 1.2 parsing and TypeBox validation pipeline.
+- Modified: `src/frontmatter/parse.ts` — replaced stub with full implementation (splitter → yaml.parse → Value.Clean → Value.Check → Value.Errors → InvalidInputError)
+- Modified: `test/frontmatter.test.ts` — added 23 new tests for parseFrontmatter (total 41 tests in file)
+- Tests: 41 frontmatter tests, all passing; 211 total across all test files, all passing