FN-6018: allow stopping and deleting failed agents

Let failed agents be stopped and deleted consistently across the dashboard and agent lifecycle.

- allow agents in the error state to transition to paused and cover the new lifecycle path in core tests
- expose delete controls for failed agents in the agents list and mobile detail view with dashboard regression coverage
- update CLI stop-tool guidance and add a patch changeset for the published package

Files changed:
 .changeset/fn-6018-agent-error-stop-delete.md      |  7 ++++
 packages/cli/src/__tests__/extension.test.ts       | 16 ++++++++
 packages/cli/src/extension.ts                      |  4 +-
 packages/core/src/__tests__/agent-store.test.ts    | 16 ++++++++
 packages/core/src/types.ts                         |  2 +-
 .../dashboard/app/components/AgentDetailView.tsx   |  4 ++
 packages/dashboard/app/components/AgentsView.tsx   |  2 +-
 .../__tests__/AgentDetailView.core.test.tsx        | 24 +++++++++++-
 .../app/components/__tests__/AgentsView.test.tsx   | 44 +++++++++++++++++++++-
 9 files changed, 112 insertions(+), 7 deletions(-)

Fusion-Task-Id: FN-6018

Fusion-Task-Lineage: 40159b9b-4d14-4f1e-9bd9-d018e54db7ee

packages/cli/src/__tests__/extension.test.ts

@@ -153,6 +153,22 @@ describe("fn pi extension tool copy guardrails", () => {
     expect(guidelines).toMatch(/soft.?delete/i);
     expect(guidelines).not.toMatch(/permanent|cannot be recovered|cannot be undone|deleted immediately|irrecoverable/i);
   });
+
+  it("describes fn_agent_stop as allowing error-state agents to be paused (FN-6018)", () => {
+    const api = createMockAPI();
+    kbExtension(api);
+
+    const tool = api.tools.get("fn_agent_stop") as
+      | { description?: string; promptGuidelines?: string[] }
+      | undefined;
+
+    expect(tool).toBeDefined();
+
+    const guidelines = (tool?.promptGuidelines ?? []).join(" ");
+    expect(guidelines).toMatch(/running, active, or in error/i);
+    expect(guidelines).toMatch(/idle.*already-paused/i);
+    expect(guidelines).not.toMatch(/idle, 'error', or already-paused/i);
+  });
 });
 
 // Audited in FN-3189: this exhaustive suite is expensive (~62s) and stale

packages/cli/src/extension.ts

@@ -3592,9 +3592,9 @@ export default function kbExtension(pi: ExtensionAPI) {
       "Transitions the agent from running/active to paused state.",
     promptSnippet: "Stop (pause) a running Fusion agent",
     promptGuidelines: [
-      "Use to pause an agent that is currently running or active",
+      "Use to pause an agent that is currently running, active, or in error",
       "Stopped agents can be resumed with fn_agent_start",
-      "Agents in 'idle', 'error', or already-paused state cannot be stopped",
+      "Agents in 'idle' or already-paused state cannot be stopped",
     ],
     parameters: Type.Object({
       id: Type.String({ description: "Agent ID to stop (e.g., agent-abc123)" }),