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/api/public-exports.md

@@ -0,0 +1,57 @@
+---
+id: api/public-exports
+name: Wire up public API surface in src/index.ts
+status: pending
+depends_on:
+  - graph/taskgraph-class
+  - graph/construction
+  - graph/mutation
+  - graph/queries
+  - graph/subgraph-and-validation
+  - graph/export
+  - analysis/parallel-groups
+  - analysis/critical-path
+  - analysis/bottlenecks
+  - cost-benefit/ev-calculation
+  - cost-benefit/dag-propagation
+  - cost-benefit/workflow-cost
+  - cost-benefit/risk-analysis
+  - frontmatter/parsing
+  - frontmatter/file-io-and-serialize
+  - schema/numeric-methods-and-defaults
+scope: narrow
+risk: low
+impact: project
+level: implementation
+---
+
+## Description
+
+Wire up `src/index.ts` to re-export the full public API surface. This is the main entry point for consumers: everything they need should be importable from `@alkdev/taskgraph`.
+
+## Acceptance Criteria
+
+- [ ] `src/index.ts` re-exports all public API items:
+  - `TaskGraph` class (from `src/graph/index.ts`)
+  - All analysis functions: `parallelGroups`, `criticalPath`, `weightedCriticalPath`, `bottlenecks`, `riskPath`, `riskDistribution`, `shouldDecomposeTask`, `workflowCost`, `calculateTaskEv`
+  - All categorical numeric functions: `scopeCostEstimate`, `scopeTokenEstimate`, `riskSuccessProbability`, `riskWeight`, `impactWeight`, `resolveDefaults`
+  - All frontmatter functions: `parseFrontmatter`, `parseTaskFile`, `parseTaskDirectory`, `serializeFrontmatter`
+  - All schemas and types: all enum schemas, `TaskInput`, `DependencyEdge`, `TaskGraphNodeAttributes`, `TaskGraphEdgeAttributes`, `TaskGraphSerialized`, all result types
+  - All error classes: `TaskgraphError`, `TaskNotFoundError`, `CircularDependencyError`, `InvalidInputError`, `DuplicateNodeError`, `DuplicateEdgeError`
+- [ ] No internal implementation details leak through the public API
+- [ ] `package.json` `"exports"` field configured for ESM primary + CJS compat
+- [ ] TypeScript declarations (`tsc --emitDeclarationOnly`) verify the public surface compiles correctly
+- [ ] Consumer import `import { TaskGraph, workflowCost } from "@alkdev/taskgraph"` works
+
+## References
+
+- docs/architecture/api-surface.md — full public API
+- docs/architecture/build-distribution.md — package name, ESM primary
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion