taskgraph_ts/tasks/implementation/graph/mutation.md

id, name, status, depends_on, scope, risk, impact, level

id	name	status	depends_on	scope	risk	impact	level
graph/mutation	Implement TaskGraph mutation methods (remove, update, updateEdgeAttributes)	completed	graph/taskgraph-class	narrow	low	component	implementation

Description

Implement mutation methods in src/graph/mutation.ts and integrate on TaskGraph. These methods modify the graph in-place.

Acceptance Criteria

• removeTask(id: string): void — No-op if node doesn't exist. Removes node and cascades edge removal (graphology handles this automatically).
• removeDependency(prerequisite: string, dependent: string): void — No-op if edge doesn't exist. Uses deterministic edge key ${prerequisite}->${dependent} to identify the edge.
• updateTask(id: string, attributes: Partial<TaskGraphNodeAttributes>): void — Throws TaskNotFoundError if ID doesn't exist. Uses mergeNodeAttributes for shallow merge of provided attributes.
• updateEdgeAttributes(prerequisite: string, dependent: string, attrs: Partial<TaskGraphEdgeAttributes>): void — Throws TaskNotFoundError (actually TaskNotFoundError for the edge itself, but per the spec, edge attributes need both endpoints to exist) if the edge doesn't exist. Uses mergeEdgeAttributes for shallow merge.
• All mutations maintain the deterministic edge key format
• Unit tests: remove nonexistent node/edge is no-op, update nonexistent throws, partial updates merge correctly

References

• docs/architecture/api-surface.md — mutation methods
• docs/architecture/errors-validation.md — mutation operation behavior table
• docs/architecture/graph-model.md — edge attributes, mutation semantics

Notes

Implementation follows the architecture spec precisely:

• Standalone functions in mutation.ts take TaskGraphInner as first arg
• TaskGraph class methods delegate to standalone functions
• removeTask/removeDependency are no-ops on missing targets (idempotent removal)
• updateTask/updateEdgeAttributes throw TaskNotFoundError on missing targets
• Deterministic edge key format ${prerequisite}->${dependent} used throughout

Summary

Implemented all four TaskGraph mutation methods with standalone functions and class integration.

• Created: test/mutation.test.ts (27 tests)
• Modified: src/graph/mutation.ts, src/graph/construction.ts
• Tests: 284 total, all passing (27 new mutation tests)