feat(schema/input-schemas): define TaskInput, DependencyEdge schemas and Nullable re-export

- Add TaskInput schema with all fields per architecture (id, name, dependsOn,
  categorical fields as Optional(Nullable(...)), metadata fields)
- Add DependencyEdge schema with from, to, qualityRetention fields
- Re-export Nullable helper from task.ts for convenience
- Add type aliases: TaskInput, DependencyEdge via Static<typeof>
- Add 49 tests covering validation, nullable fields, edge cases, type correctness

tasks/implementation/schema/input-schemas.md

@@ -1,7 +1,7 @@
 ---
 id: schema/input-schemas
 name: Define TaskInput, DependencyEdge, and Nullable helper
-status: pending
+status: completed
 depends_on:
   - schema/enums
 scope: narrow
@@ -16,14 +16,14 @@ Define the `TaskInput` and `DependencyEdge` input schemas in `src/schema/task.ts
 
 ## Acceptance Criteria
 
-- [ ] `src/schema/task.ts` exports `Nullable` helper: `const Nullable = <T extends TSchema>(T: T) => Type.Union([T, Type.Null()])`
-- [ ] `TaskInput` schema defined with all fields per [schemas.md](../../../docs/architecture/schemas.md):
+- [x] `src/schema/task.ts` exports `Nullable` helper: `const Nullable = <T extends TSchema>(T: T) => Type.Union([T, Type.Null()])` — Re-exported from enums.ts
+- [x] `TaskInput` schema defined with all fields per [schemas.md](../../../docs/architecture/schemas.md):
   - `id: Type.String()`, `name: Type.String()`, `dependsOn: Type.Array(Type.String())`
   - Categorical fields: `Type.Optional(Nullable(TaskXxxEnum))` for status, scope, risk, impact, level, priority
   - Metadata fields: `tags`, `assignee`, `due`, `created`, `modified`
-- [ ] `DependencyEdge` schema: `from: Type.String()`, `to: Type.String()`, `qualityRetention: Type.Optional(Type.Number({ default: 0.9 }))`
-- [ ] Type aliases derived: `type TaskInput = Static<typeof TaskInput>`, `type DependencyEdge = Static<typeof DependencyEdge>`
-- [ ] Re-exported from `src/schema/index.ts`
+- [x] `DependencyEdge` schema: `from: Type.String()`, `to: Type.String()`, `qualityRetention: Type.Optional(Type.Number({ default: 0.9 }))`
+- [x] Type aliases derived: `type TaskInput = Static<typeof TaskInput>`, `type DependencyEdge = Static<typeof DependencyEdge>`
+- [x] Re-exported from `src/schema/index.ts`
 
 ## References
 
@@ -32,8 +32,11 @@ Define the `TaskInput` and `DependencyEdge` input schemas in `src/schema/task.ts
 
 ## Notes
 
-> To be filled by implementation agent
+`Nullable` was already defined in `src/schema/enums.ts` by the `schema/enums` task. It is re-exported from `src/schema/task.ts` for convenience, satisfying the acceptance criteria. All other schemas (`TaskInput`, `DependencyEdge`) are brand new.
 
 ## Summary
 
-> To be filled on completion
+Implemented TaskInput and DependencyEdge input schemas in `src/schema/task.ts`, plus re-exported Nullable helper.
+- Modified: `src/schema/task.ts` (implemented TaskInput, DependencyEdge schemas with type aliases)
+- Modified: `test/schema.test.ts` (added 49 tests for TaskInput, DependencyEdge, Nullable re-export, type alias verification)
+- All 126 tests passing, lint clean.