decompose architecture into 38 atomic tasks across 12 parallel generations

Decompose the reviewed architecture specs into taskgraph-managed tasks:
- 2 setup tasks (project init, test infrastructure)
- 4 schema tasks (enums, node attrs, edge attrs, graph schemas)
- 1 error hierarchy task
- 6 graph tasks (FlowGraph class, 3 construction paths, queries, validation)
- 5 analysis tasks (type-compat, build-type-edges, ordering, template-validation, defaults)
- 5 component tasks (Operation, Sequential, Parallel, Conditional, Map)
- 2 host config tasks (GraphologyHostConfig, ReactiveHostConfig)
- 4 reactive tasks (WorkflowRoot, node-status, max-concurrency, retry-semantics)
- 3 review tasks (foundation, reactive-and-hosts, complete-library)
- 5 meta cluster tasks (schema, graph, component, reactive, analysis layers)
- 1 API exports task

Validated with taskgraph: zero cycles, 38 tasks, 12 parallel generations.
Critical path: 12 tasks through reactive execution layer.

tasks/error-hierarchy.md

@@ -0,0 +1,46 @@
+---
+id: error/hierarchy
+name: Implement FlowgraphError hierarchy with all error classes and validation result types
+status: pending
+depends_on:
+  - setup/project-init
+scope: narrow
+risk: low
+impact: component
+level: implementation
+---
+
+## Description
+
+Implement the complete error hierarchy per [error-handling.md](../docs/architecture/error-handling.md). This includes thrown error classes (for construction invariant violations) and structured result types (for validation functions that never throw).
+
+## Acceptance Criteria
+
+- [ ] `src/error/index.ts` exports all error classes and result types
+- [ ] `FlowgraphError` base class extending `Error` with `name: "FlowgraphError"`
+- [ ] `ConstructionError` extending `FlowgraphError` — base for construction-time errors
+- [ ] `DuplicateNodeError` extending `ConstructionError` — `key` property
+- [ ] `DuplicateEdgeError` extending `ConstructionError` — `source`, `target` properties
+- [ ] `NodeNotFoundError` extending `ConstructionError` — `key` property
+- [ ] `CycleError` extending `ConstructionError` — `cycles: string[][]` property
+- [ ] `InvalidInputError` extending `ConstructionError` — `errors: ValidationError[]` property
+- [ ] `InvalidTransitionError` extending `FlowgraphError` — `requestId`, `from: CallStatus`, `to: CallStatus` properties
+- [ ] `ValidationError` interface — `{ type: "schema", nodeKey, field, message, value? }`
+- [ ] `GraphValidationError` interface — `{ type: "graph", category: "cycle" | "dangling-reference" | "orphan-node" | "status-inconsistency", details: unknown }`
+- [ ] `TypeIncompatError` interface — `{ type: "type-compat", sourceKey, targetKey, compatible: false, mismatches: TypeMismatch[] }`
+- [ ] `TypeMismatch` interface — `{ path, expected, actual }`
+- [ ] `AnyValidationError` union type — `ValidationError | GraphValidationError | TypeIncompatError`
+- [ ] Throwing vs returning contract clearly documented in JSDoc
+- [ ] Unit tests: each error class constructs correctly, result types validate, `instanceof` checks work
+
+## References
+
+- docs/architecture/error-handling.md — complete error hierarchy, throwing vs returning contract
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion