FN-5652: add goal retrieval tool for agent execution

Expose goal details to agents during task execution workflows.

- add fn_goal_show tool to the CLI extension with goal lookup, formatted output, and not-found error details
- add focused tests for goal tool registration and execution behavior
- mark fn_goal_show as execution-safe in engine gating classifications and test coverage
- update Fusion skill/reference docs to include the new goal retrieval capability
- add a changeset for @runfusion/fusion patch release

Files changed:
 .changeset/fn-5652-goal-show.md                    |   7 +
 packages/cli/skill/fusion/SKILL.md                 |   2 +-
 .../cli/skill/fusion/references/extension-tools.md |  16 +++
 .../skill/fusion/references/fusion-capabilities.md |   1 +
 .../cli/src/__tests__/extension-goal-tools.test.ts | 148 +++++++++++++++++++++
 packages/cli/src/extension.ts                      |  43 ++++++
 .../src/__tests__/gating-classifications.test.ts   |   7 +
 packages/engine/src/gating-classifications.ts      |   2 +
 8 files changed, 225 insertions(+), 1 deletion(-)

Fusion-Task-Id: FN-5652

Fusion-Task-Lineage: 98c2c417-0887-4794-81b1-6b47ab0f708f

packages/cli/skill/fusion/SKILL.md

@@ -30,7 +30,7 @@ Mission → Milestone → Slice → Feature → Task
 - **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`, `fn_feature_update`, `fn_milestone_update`
-- **Goal tools** — `fn_goal_list`, `fn_goal_create`, `fn_goal_archive`
+- **Goal tools** — `fn_goal_list`, `fn_goal_create`, `fn_goal_archive`, `fn_goal_show`
 - **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

@@ -301,6 +301,14 @@ Archive a goal by ID.
 |-----------|------|----------|-------------|
 | `id` | string | ✓ | Goal ID (G-…) to archive |
 
+### fn_goal_show
+
+Show full details for a single goal by ID.
+
+| Parameter | Type | Required | Description |
+|-----------|------|----------|-------------|
+| `id` | string | ✓ | Goal ID (G-…) |
+
 ## Agent Tools
 
 ### fn_agent_stop
@@ -523,6 +531,14 @@ Group kept experiment runs into reviewable branches and finalize the session. Us
 | `summary` | string | — | Optional finalize summary |
 
 <!-- END: extension-tools -->
+
+## Goal retrieval contract notes
+
+### Goal-show response contract
+
+- **Success:** returns `details.goal` as the complete goal JSON object (`id`, `title`, optional `description`, `status`, `createdAt`, `updatedAt`) and `content[0].text` with those same human-readable fields.
+- **Not found:** returns `isError: true` with `details.code: "GOAL_NOT_FOUND"` and `details.goalId` set to the requested id.
+
 ## Dashboard Command
 
 ### /fn

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

@@ -46,6 +46,7 @@ All skill/extension tool invocations in this catalog use the public `fn_*` names
 | `fn_goal_list` | List goals by status with active-goal warning details. |
 | `fn_goal_create` | Create a new project goal. |
 | `fn_goal_archive` | Archive a goal by ID. |
+| `fn_goal_show` | Show full details for a single goal by ID. |
 | `fn_mission_show` | Show mission details with full hierarchy: milestones → slices → features. |
 | `fn_mission_delete` | Delete a mission and all its milestones, slices, and features. Cannot be undone. |
 | `fn_milestone_add` | Add a milestone to a mission. Milestones represent phases of work. |