Decompose architecture into 28 atomic implementation tasks

Break the @alkdev/taskgraph architecture specs into dependency-ordered
implementation tasks across 8 component directories: setup, schema,
error, graph, analysis, cost-benefit, frontmatter, api, and review.
Each task has clear acceptance criteria referencing specific architecture
docs. Three review tasks serve as quality gates at critical junction
points (schemas-and-errors, graph-complete, complete-library). The
dependency graph is validated acyclic with 9 topological levels enabling
significant parallelism across independent work streams.

tasks/implementation/review/complete-library.md

@@ -0,0 +1,48 @@
+---
+id: review/complete-library
+name: Final review — validate full library against architecture docs
+status: pending
+depends_on:
+  - api/public-exports
+  - review/graph-complete
+  - frontmatter/file-io-and-serialize
+  - cost-benefit/workflow-cost
+  - cost-benefit/risk-analysis
+scope: broad
+risk: low
+impact: project
+level: review
+---
+
+## Description
+
+Final review of the complete library. Verify the full API surface matches architecture docs, all analysis functions produce correct results, and the library achieves its stated purpose: pure TypeScript task graph library with graphology, replicating and extending the essential graph algorithms and cost-benefit math from the Rust CLI.
+
+## Acceptance Criteria
+
+- [ ] Public API matches [api-surface.md](../../../docs/architecture/api-surface.md) exactly — no missing exports, no extra exports
+- [ ] All construction paths work: fromTasks, fromRecords, fromJSON, incremental
+- [ ] DAG-propagation cost model produces results consistent with Python research model examples
+- [ ] Independent model available as degenerate case (set `propagationMode: 'independent'` or `defaultQualityRetention: 1.0`)
+- [ ] Frontmatter parsing round-trips correctly: `parseFrontmatter(serializeFrontmatter(task))` ≈ task
+- [ ] `Value.Clean()` and `Value.Errors()` used correctly throughout (no `Value.Assert()` where structured errors needed)
+- [ ] No gray-matter, no js-yaml, no Zod anywhere in the dependency tree
+- [ ] `npm pack` produces a valid package with correct exports
+- [ ] All tests pass: `npm test`
+- [ ] TypeScript strict mode compilation succeeds with no errors
+- [ ] Build output (`dist/`) is correct: ESM + CJS + declarations
+
+## References
+
+- docs/architecture/README.md
+- docs/architecture/api-surface.md
+- docs/architecture/build-distribution.md
+- docs/architecture/cost-benefit.md
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion