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

tests/api/fleet/test_mutate_interval.py

@@ -0,0 +1,91 @@
+"""
+Tests for the mutate interval API endpoint.
+"""
+
+import json
+import pytest
+import httpx
+from unittest.mock import patch, MagicMock
+from pathlib import Path
+
+import decnet.config
+from decnet.config import DeckyConfig, DecnetConfig
+
+
+def _decky(name: str = "decky-01") -> DeckyConfig:
+    return DeckyConfig(
+        name=name, ip="192.168.1.10", services=["ssh"],
+        distro="debian", base_image="debian", hostname="test-host",
+        build_base="debian:bookworm-slim", nmap_os="linux",
+        mutate_interval=30,
+    )
+
+
+def _config() -> DecnetConfig:
+    return DecnetConfig(
+        mode="unihost", interface="eth0", subnet="192.168.1.0/24",
+        gateway="192.168.1.1", deckies=[_decky()],
+    )
+
+
+class TestMutateInterval:
+    @pytest.mark.asyncio
+    async def test_unauthenticated_returns_401(self, client: httpx.AsyncClient):
+        resp = await client.put(
+            "/api/v1/deckies/decky-01/mutate-interval",
+            json={"mutate_interval": 60},
+        )
+        assert resp.status_code == 401
+
+    @pytest.mark.asyncio
+    async def test_no_active_deployment(self, client: httpx.AsyncClient, auth_token: str):
+        with patch("decnet.web.router.fleet.api_mutate_interval.load_state", return_value=None):
+            resp = await client.put(
+                "/api/v1/deckies/decky-01/mutate-interval",
+                headers={"Authorization": f"Bearer {auth_token}"},
+                json={"mutate_interval": 60},
+            )
+        assert resp.status_code == 500
+
+    @pytest.mark.asyncio
+    async def test_decky_not_found(self, client: httpx.AsyncClient, auth_token: str):
+        config = _config()
+        with patch("decnet.web.router.fleet.api_mutate_interval.load_state",
+                    return_value=(config, Path("test.yml"))):
+            resp = await client.put(
+                "/api/v1/deckies/nonexistent/mutate-interval",
+                headers={"Authorization": f"Bearer {auth_token}"},
+                json={"mutate_interval": 60},
+            )
+        assert resp.status_code == 404
+
+    @pytest.mark.asyncio
+    async def test_successful_interval_update(self, client: httpx.AsyncClient, auth_token: str):
+        config = _config()
+        with patch("decnet.web.router.fleet.api_mutate_interval.load_state",
+                    return_value=(config, Path("test.yml"))):
+            with patch("decnet.web.router.fleet.api_mutate_interval.save_state") as mock_save:
+                resp = await client.put(
+                    "/api/v1/deckies/decky-01/mutate-interval",
+                    headers={"Authorization": f"Bearer {auth_token}"},
+                    json={"mutate_interval": 120},
+                )
+        assert resp.status_code == 200
+        assert resp.json()["message"] == "Mutation interval updated"
+        mock_save.assert_called_once()
+        # Verify the interval was actually updated on the decky config
+        assert config.deckies[0].mutate_interval == 120
+
+    @pytest.mark.asyncio
+    async def test_null_interval_removes_mutation(self, client: httpx.AsyncClient, auth_token: str):
+        config = _config()
+        with patch("decnet.web.router.fleet.api_mutate_interval.load_state",
+                    return_value=(config, Path("test.yml"))):
+            with patch("decnet.web.router.fleet.api_mutate_interval.save_state"):
+                resp = await client.put(
+                    "/api/v1/deckies/decky-01/mutate-interval",
+                    headers={"Authorization": f"Bearer {auth_token}"},
+                    json={"mutate_interval": None},
+                )
+        assert resp.status_code == 200
+        assert config.deckies[0].mutate_interval is None