feat(FN-4569): add fn_feature_update mission tool

Fusion-Task-Id: FN-4569
Fusion-Task-Lineage: c6736466-c317-4d6c-b1a6-225554e8fc0f

packages/cli/skill/fusion/SKILL.md

@@ -29,7 +29,7 @@ Mission → Milestone → Slice → Feature → Task
 <!-- BEGIN: tool-categories (auto-generated by scripts/sync-fusion-skill-tools.mjs — do not edit by hand) -->
 - **Task tools** — `fn_task_create`, `fn_task_update`, `fn_task_list`, `fn_task_show`, `fn_task_attach`, `fn_task_pause`, `fn_task_unpause`, `fn_task_retry`, `fn_task_duplicate`, `fn_task_refine`, `fn_task_archive`, `fn_task_unarchive`, `fn_task_delete`, `fn_task_plan`
 - **GitHub tools** — `fn_task_import_github`, `fn_task_import_github_issue`, `fn_task_browse_github_issues`
-- **Mission tools** — `fn_mission_create`, `fn_mission_list`, `fn_mission_show`, `fn_mission_delete`, `fn_milestone_add`, `fn_slice_add`, `fn_feature_add`, `fn_slice_activate`, `fn_feature_link_task`
+- **Mission tools** — `fn_mission_create`, `fn_mission_list`, `fn_mission_show`, `fn_mission_delete`, `fn_milestone_add`, `fn_slice_add`, `fn_feature_add`, `fn_slice_activate`, `fn_feature_link_task`, `fn_feature_update`
 - **Agent tools** — `fn_agent_stop`, `fn_agent_start`, `fn_agent_create`, `fn_agent_delete`, `fn_list_agents`, `fn_delegate_task`, `fn_agent_show`, `fn_agent_org_chart`
 - **Skills tools** — `fn_skills_search`, `fn_skills_install`
 - **Insight tools** — `fn_insight_list`, `fn_insight_show`, `fn_insight_run_list`, `fn_insight_run_show`

packages/cli/skill/fusion/references/extension-tools.md

@@ -248,6 +248,28 @@ Link a feature to a fn task for implementation. Updates the feature status to 't
 | `featureId` | string | ✓ | Feature ID to link (e.g., F-001) |
 | `taskId` | string | ✓ | Task ID to link to (e.g., FN-001) |
 
+### fn_feature_update
+
+Update an existing feature's title, description, or acceptance criteria. Partial patches leave untouched fields intact.
+
+| Parameter | Type | Required | Description |
+|-----------|------|----------|-------------|
+| `id` | string | ✓ | Feature ID to update (e.g., F-001) |
+| `title` | string | — | Updated feature title |
+| `description` | string | — | Updated feature description |
+| `acceptanceCriteria` | string | — | Updated acceptance criteria for completing the feature |
+
+**Example:**
+
+```json
+{
+  "id": "F-001",
+  "acceptanceCriteria": "Runs deterministic verification and updates notes"
+}
+```
+
+**Returns:** Updated feature summary and details including `featureId`, `sliceId`, `title`, `description`, `acceptanceCriteria`, and `status`.
+
 ## Agent Tools
 
 ### fn_agent_stop

packages/cli/skill/fusion/references/fusion-capabilities.md

@@ -49,6 +49,7 @@ All skill/extension tool invocations in this catalog use the public `fn_*` names
 | `fn_feature_add` | Add a feature to a slice. Features are deliverables that can be linked to tasks. |
 | `fn_slice_activate` | Activate a pending slice for implementation. Sets status to 'active' and enables task linking for its features. |
 | `fn_feature_link_task` | Link a feature to a fn task for implementation. Updates the feature status to 'triaged' and associates it with the task. |
+| `fn_feature_update` | Update an existing feature's title, description, or acceptance criteria. Partial patches leave untouched fields intact. |
 | `fn_agent_stop` | Stop a running agent — pauses its execution. Transitions the agent from running/active to paused state. |
 | `fn_agent_start` | Start a stopped agent — resumes its execution. Transitions the agent from paused to active state. |
 | `fn_agent_create` | Create a new non-ephemeral agent. |