feat(docker): overview findings say when the problem began

#5013 "Overview findings for containers and Swarm services carry since=null"

- Container problems are dated from their own evidence: a crash or restart
  loop from its first death in the hour, an OOM kill or error exit from the
  death that ended it, a failing healthcheck from its last turn to unhealthy.
  list_containers and get_container carry problem_since / problem_age_s.
- Swarm services carry trouble_since: a crash loop's first failure in the
  hour, a short service's oldest troubled task in each failing slot, a
  recovered service's first failure in 24h. list_swarm_services shows it.
- get_overview findings from the docker plugin now have since and age_s,
  so they rank by how long they have stood.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/plugins/docker/test_swarm_view.py

@@ -3,7 +3,9 @@ import json
 from datetime import datetime, timedelta, timezone
 from types import SimpleNamespace
 
-from plugins.docker.swarm_view import build_swarm_services, last_task_error, task_failures
+from plugins.docker.swarm_view import (
+    build_swarm_services, last_task_error, task_failures, trouble_since,
+)
 
 NODE_HOSTNAME = {"nA": "docker01", "nB": "docker02", "nC": "docker03"}
 HOST_NAME = {"h1": "docker01", "h2": "docker02"}  # agents run on docker01/02 only
@@ -172,3 +174,40 @@ def test_the_newest_manager_report_wins():
     (svc,) = _view([], [old, new])["services"]
     assert svc["tasks_known"] is True and svc["failures_1h"] == 1
 
+
+
+def _ago(minutes):
+    return NOW - timedelta(minutes=minutes)
+
+
+def test_trouble_since_for_each_kind_of_trouble():
+    loop = [_task("t1", state="failed", ago_min=2), _task("t2", state="failed", ago_min=20),
+            _task("t3", state="failed", ago_min=45), _task("t4", state="failed", ago_min=90)]
+    # A crash loop: its first failure inside the hour.
+    assert trouble_since(loop, "down", True, NOW) == _ago(45)
+    # Down: the oldest of the newest troubled tasks, back to a running one.
+    down = [_task("t1", state="pending", ago_min=1, error="no suitable node"),
+            _task("t2", state="rejected", ago_min=30, error="No such image"),
+            _task("t3", state="running", desired="running", ago_min=600),
+            _task("t4", state="failed", ago_min=900)]
+    assert trouble_since(down, "degraded", False, NOW) == _ago(30)
+    # Another slot's newer, healthy task does not hide the failing one.
+    two = [_task("a2", state="running", desired="running", ago_min=5, slot=1),
+           _task("b1", state="failed", ago_min=8, slot=2),
+           _task("b0", state="failed", ago_min=40, slot=2),
+           _task("a1", state="failed", ago_min=300, slot=1)]
+    assert trouble_since(two, "degraded", False, NOW) == _ago(40)
+    # Healthy again, but a task failed today: dated from that failure.
+    recovered = [_task("t1", state="running", desired="running", ago_min=10),
+                 _task("t2", state="failed", ago_min=60 * 5),
+                 _task("t3", state="failed", ago_min=60 * 30)]
+    assert trouble_since(recovered, "healthy", False, NOW) == _ago(60 * 5)
+    # No task records: unknown.
+    assert trouble_since([], "down", False, NOW) is None
+
+
+def test_the_view_dates_a_down_service():
+    tasks = [_task("t1", state="failed", ago_min=3, exit_code=1),
+             _task("t2", state="failed", ago_min=70, exit_code=1)]
+    (s,) = _view([], [_svc("db", 0, 1, [], tasks=tasks)])["services"]
+    assert s["state"] == "down" and s["trouble_since"] == _ago(70)