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/graph/queries.md

@@ -0,0 +1,53 @@
+---
+id: graph/queries
+name: Implement TaskGraph query methods (hasCycles, findCycles, topologicalOrder, dependencies, dependents, taskCount, getTask)
+status: pending
+depends_on:
+  - graph/taskgraph-class
+scope: moderate
+risk: medium
+impact: component
+level: implementation
+---
+
+## Description
+
+Implement query methods in `src/graph/queries.ts` and integrate on `TaskGraph`. The `findCycles` implementation requires a custom 3-color DFS since `graphology-components` only gives SCCs, not cycle paths.
+
+Per [errors-validation.md](../../../docs/architecture/errors-validation.md):
+- `hasCycles()` returns boolean (uses `graphology-dag` or `graphology-components` for fast check)
+- `findCycles()` returns `string[][]` — each inner array is an ordered cycle path
+- `topologicalOrder()` throws `CircularDependencyError` with `cycles` populated when graph is cyclic (per ADR-003)
+
+## Acceptance Criteria
+
+- [ ] `hasCycles(): boolean` — uses `graphology-dag.hasCycle()` or `graphology-components` SCC check as fast pre-check
+- [ ] `findCycles(): string[][]`:
+  - Uses `stronglyConnectedComponents()` as pre-check: if zero multi-node SCCs and no self-loops, skip DFS
+  - Custom 3-color DFS (WHITE/GREY/BLACK) to extract cycle paths
+  - Returns one representative cycle per back edge, not exhaustive enumeration
+  - Each inner array is an ordered node sequence where last node has edge back to first
+- [ ] `topologicalOrder(): string[]`:
+  - Uses `graphology-dag.topologicalSort()` for the actual sort
+  - **Throws `CircularDependencyError`** (with `cycles` from `findCycles()`) when graph is cyclic
+  - Returns `string[]` of task IDs in prerequisite→dependent order
+- [ ] `dependencies(taskId: string): string[]` — returns prerequisite task IDs (inNeighbors). Throws `TaskNotFoundError` if ID doesn't exist.
+- [ ] `dependents(taskId: string): string[]` — returns dependent task IDs (outNeighbors). Throws `TaskNotFoundError` if ID doesn't exist.
+- [ ] `taskCount(): number` — returns number of nodes
+- [ ] `getTask(taskId: string): TaskGraphNodeAttributes | undefined` — returns node attributes or undefined
+- [ ] Unit tests: cycle detection on known cyclic/acyclic graphs, topologicalOrder on DAG, topologicalOrder throws on cyclic graph, dependency/dependent queries
+
+## References
+
+- docs/architecture/api-surface.md — query methods
+- docs/architecture/errors-validation.md — cycle handling, CircularDependencyError
+- docs/architecture/cost-benefit.md — findCycles algorithm description
+- docs/architecture/decisions/003-topo-order-throws-on-cycle.md — ADR-003
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion