feat(graph/queries): implement query methods — hasCycles, findCycles, topologicalOrder, dependencies, dependents, taskCount, getTask

- hasCycles(): uses graphology-dag.hasCycle() as fast boolean check
- findCycles(): SCC pre-check + custom 3-color DFS for cycle path extraction
- topologicalOrder(): graphology-dag.topologicalSort + CircularDependencyError on cycle
- dependencies/dependents: inNeighbors/outNeighbors with TaskNotFoundError
- taskCount(): graph.order, getTask(): node attributes or undefined
- 45 unit tests covering all acceptance criteria

tasks/implementation/graph/queries.md

@@ -1,7 +1,7 @@
 ---
 id: graph/queries
 name: Implement TaskGraph query methods (hasCycles, findCycles, topologicalOrder, dependencies, dependents, taskCount, getTask)
-status: pending
+status: completed
 depends_on:
   - graph/taskgraph-class
 scope: moderate
@@ -21,21 +21,21 @@ Per [errors-validation.md](../../../docs/architecture/errors-validation.md):
 
 ## Acceptance Criteria
 
-- [ ] `hasCycles(): boolean` — uses `graphology-dag.hasCycle()` or `graphology-components` SCC check as fast pre-check
-- [ ] `findCycles(): string[][]`:
+- [x] `hasCycles(): boolean` — uses `graphology-dag.hasCycle()` or `graphology-components` SCC check as fast pre-check
+- [x] `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[]`:
+- [x] `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
+- [x] `dependencies(taskId: string): string[]` — returns prerequisite task IDs (inNeighbors). Throws `TaskNotFoundError` if ID doesn't exist.
+- [x] `dependents(taskId: string): string[]` — returns dependent task IDs (outNeighbors). Throws `TaskNotFoundError` if ID doesn't exist.
+- [x] `taskCount(): number` — returns number of nodes
+- [x] `getTask(taskId: string): TaskGraphNodeAttributes | undefined` — returns node attributes or undefined
+- [x] Unit tests: cycle detection on known cyclic/acyclic graphs, topologicalOrder on DAG, topologicalOrder throws on cyclic graph, dependency/dependent queries
 
 ## References
 
@@ -46,8 +46,11 @@ Per [errors-validation.md](../../../docs/architecture/errors-validation.md):
 
 ## Notes
 
-> To be filled by implementation agent
+findCycles uses a custom 3-color DFS (WHITE/GREY/BLACK) as specified — graphology-components only gives SCCs, not cycle paths. The DFS traces the recursion stack on back edges to extract ordered cycle paths.
 
 ## Summary
 
-> To be filled on completion
+Implemented all 7 query methods in `src/graph/queries.ts` as free functions operating on the inner graphology graph, and integrated them as instance methods on `TaskGraph`.
+- Created: `src/graph/queries.ts`, `test/queries.test.ts`
+- Modified: `src/graph/construction.ts` (added query method imports and 7 instance methods)
+- Tests: 45, all passing (full suite: 302 passing)