feat(syslog): a source's lines to read and search, on its page, its host's and its SNMP device's, and over MCP (#6000)

- /plugins/syslog/sources/<id>: the lines newest first, loading as you
  scroll, filtered by severity and worse, app, text and time, with day
  dividers and times to the second in the reader's zone.
- The Syslog page links each source and shows its lines in the last hour.
- A Syslog panel on a host's page and an SNMP device's: the newest lines of
  the sources bound to it or at its address.
- MCP: list_syslog_sources and search_syslog (source, host, text, severity
  and worse, app, range, paging by next_before).
- Shared: escape_like moves to steward/core/like.py and cut_middle to the
  MCP shaping module, replacing four inline copies; |when takes seconds=.

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

tests/plugins/syslog/test_syslog_page.py

@@ -20,7 +20,7 @@ def _source(name, state, level=6, line="nfsd: server not responding", host=None)
             "hostname_seen": "synnas", "host": host, "first_seen_at": now - timedelta(days=1),
             "last_seen_at": now - timedelta(minutes=3), "lines_total": 1204,
             "severity": "err" if level == 3 else "info", "level": level, "last_line": line,
-            "suggested_host": "h1"}
+            "suggested_host": "h1", "rate": 12 if state == "accepted" else None}
 
 
 async def _render(app, role, **ctx):
@@ -49,7 +49,8 @@ async def test_an_offered_sender_can_be_added_or_ignored_by_an_admin(app):
 async def test_a_viewer_sees_sources_but_no_controls(app):
     page = await _render(app, "viewer", sources=[_source("SynNAS", "accepted", host=NS(id="h1", name="SynNAS"))],
                          offered=[_source("router", "offered")])
-    assert 'href="/hosts/h1"' in page and "/plugins/syslog/sources/" not in page
+    assert 'href="/hosts/h1"' in page and 'href="/plugins/syslog/sources/id-SynNAS"' in page
+    assert "/add" not in page and "/ignore" not in page and "/edit" not in page
     assert "Sending, not added" in page
 
 
@@ -71,3 +72,62 @@ async def test_the_edit_page_has_its_trail_and_a_remove(app):
     page = " ".join(page.split())
     assert 'href="/plugins/syslog/">Syslog</a>' in page
     assert 'action="/plugins/syslog/sources/s1/delete"' in page and "data-confirm=" in page
+
+
+def _line(i, level=6, app="kernel", message="nfsd: server not responding", minutes=1):
+    now = datetime.now(timezone.utc)
+    return {"id": f"l{i}", "received_at": now - timedelta(minutes=minutes), "sent_at": None,
+            "level": level, "severity": {3: "err", 4: "warning"}.get(level, "info"),
+            "facility": "kern", "hostname": "synnas", "app": app, "message": message,
+            "group": "Today", "opens_group": i == 0}
+
+
+async def test_a_source_page_filters_its_lines_and_scrolls_on(app):
+    from quart import session
+    from plugins.syslog.service import SEVERITY_CHOICES, LineFilter
+    src = {**_source("SynNAS", "accepted"), "rate": 42}
+    async with app.test_request_context("/plugins/syslog/sources/id-SynNAS"):
+        session["user_role"] = "viewer"
+        page = await render_plugin_template(
+            app, "syslog", "syslog/source.html", source=src, f=LineFilter(severity=3), filtered=True,
+            lines=[_line(0, level=3), _line(1, app="", message="a <b> tag")],
+            more_url="/plugins/syslog/sources/id-SynNAS?severity=3&before=x", severities=SEVERITY_CHOICES,
+            apps=["kernel", "nfsd"], ranges=["1h", "24h"])
+    page = " ".join(page.split())
+    assert 'href="/plugins/syslog/">Syslog</a>' in page                      # its trail
+    assert "42 lines in the last hour" in page
+    assert '<option value="3" selected>Errors and worse</option>' in page
+    assert '<tr class="table-divider"><th colspan="4" scope="rowgroup">Today</th></tr>' in page
+    assert '<span class="tone-crit">err</span>' in page and "a &lt;b&gt; tag" in page
+    assert 'hx-get="/plugins/syslog/sources/id-SynNAS?severity=3&amp;before=x"' in page
+    assert "/edit" not in page                                               # a viewer
+    main = page[page.index("<main"):]
+    assert "font-weight:600" not in main and not hex_colours(main), hex_colours(main)
+
+
+async def test_a_filtered_source_with_no_lines_offers_them_all_back(app):
+    from quart import session
+    from plugins.syslog.service import LineFilter
+    async with app.test_request_context("/plugins/syslog/sources/id-SynNAS"):
+        session["user_role"] = "viewer"
+        table = await render_plugin_template(
+            app, "syslog", "syslog/_lines_table.html", source=_source("SynNAS", "accepted"),
+            f=LineFilter(text="nope"), filtered=True, lines=[], more_url=None)
+    assert "No lines match these filters." in table and 'href="/plugins/syslog/sources/id-SynNAS"' in table
+
+
+async def test_the_panel_names_each_source_when_there_are_several(app):
+    from quart import session
+    lines = [{**_line(0, level=4), "source": "SynNAS", "source_id": "s1"},
+             {**_line(1), "source": "router", "source_id": "s2"}]
+    async with app.test_request_context("/plugins/syslog/panel"):
+        session["user_role"] = "viewer"
+        one = await render_plugin_template(app, "syslog", "syslog/panel.html", lines=lines[:1],
+                                           sources=[{"id": "s1", "name": "SynNAS"}])
+        two = await render_plugin_template(app, "syslog", "syslog/panel.html", lines=lines,
+                                           sources=[{"id": "s1", "name": "SynNAS"}, {"id": "s2", "name": "router"}])
+        none = await render_plugin_template(app, "syslog", "syslog/panel.html", lines=[],
+                                            sources=[{"id": "s1", "name": "SynNAS"}])
+    assert "<th>Source</th>" not in one and '<span class="tone-warn">warning</span>' in one
+    assert "<th>Source</th>" in two and 'href="/plugins/syslog/sources/s2">router</a>' in two
+    assert "No lines in the last day." in none