Testing: Stabilized test suite and achieved 93% total coverage.

- Fixed CLI tests by patching local imports at source (psutil, os, Path).
- Fixed Collector tests by globalizing docker.from_env mock.
- Stabilized SSE stream tests via AsyncMock and immediate generator termination to prevent hangs.
- Achieved >80% coverage on CLI (84%), Collector (97%), and DB Repository (100%).
- Implemented SMTP Relay service tests (100%).

tests/api/fleet/test_mutate_decky.py

@@ -0,0 +1,41 @@
+"""
+Tests for the mutate decky API endpoint.
+"""
+
+import pytest
+import httpx
+from unittest.mock import patch
+
+
+class TestMutateDecky:
+    @pytest.mark.asyncio
+    async def test_unauthenticated_returns_401(self, client: httpx.AsyncClient):
+        resp = await client.post("/api/v1/deckies/decky-01/mutate")
+        assert resp.status_code == 401
+
+    @pytest.mark.asyncio
+    async def test_successful_mutation(self, client: httpx.AsyncClient, auth_token: str):
+        with patch("decnet.web.router.fleet.api_mutate_decky.mutate_decky", return_value=True):
+            resp = await client.post(
+                "/api/v1/deckies/decky-01/mutate",
+                headers={"Authorization": f"Bearer {auth_token}"},
+            )
+        assert resp.status_code == 200
+        assert "Successfully mutated" in resp.json()["message"]
+
+    @pytest.mark.asyncio
+    async def test_failed_mutation_returns_404(self, client: httpx.AsyncClient, auth_token: str):
+        with patch("decnet.web.router.fleet.api_mutate_decky.mutate_decky", return_value=False):
+            resp = await client.post(
+                "/api/v1/deckies/decky-01/mutate",
+                headers={"Authorization": f"Bearer {auth_token}"},
+            )
+        assert resp.status_code == 404
+
+    @pytest.mark.asyncio
+    async def test_invalid_decky_name_returns_422(self, client: httpx.AsyncClient, auth_token: str):
+        resp = await client.post(
+            "/api/v1/deckies/INVALID NAME!!/mutate",
+            headers={"Authorization": f"Bearer {auth_token}"},
+        )
+        assert resp.status_code == 422