feat(ui): audit log, alert history and Ansible runs load as you scroll (#5211)

#5211 "Lists load as you scroll: audit, alert history, Ansible runs"
(milestone 477), per preference 172.

- core/paging.py: keyset paging over (time, id), newest first, with an
  opaque "<iso>|<id>" cursor; a page reads one row past itself to know
  whether another follows. No OFFSET, so rows added while someone scrolls
  never shift the pages after them.
- _macros.html scroll_more / scroll_end and static/scroll-more.js, written
  once: an IntersectionObserver with a 600px margin fetches the next page
  before the reader reaches the end; "Loading more…" while in flight,
  "End of the list." at the end, and a failed page says so with a Retry
  button instead of re-firing on every scroll.
- Audit log: no "Load more" link and no 500-row cap.
- Alert history: no 200-row stop with "pick a shorter range";
  alert_svc.history takes the cursor, so the MCP tool and the page share
  one query.
- Ansible runs: no silent cap of 50.

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

steward/alerts/routes.py

@@ -5,6 +5,7 @@ from steward.core.audit import log_audit
 from sqlalchemy import select
 from steward.auth.middleware import require_role
 from steward.alerts import service as alert_svc
+from steward.core.paging import PAGE_SIZE, next_page
 from steward.core.time_range import parse_range
 from steward.ansible import sources as src_module
 from steward.models.alerts import AlertRule, AlertOperator, AlertState, MaintenanceWindow
@@ -117,9 +118,6 @@ async def active_fragment():
     return await render_template("alerts/_active.html", active=active)
 
 
-HISTORY_LIMIT = 200
-
-
 def _history_row(event, rule) -> dict:
     """One transition as the history page shows it."""
     from steward.core.alerts import MUTED, RELEASED
@@ -147,15 +145,20 @@ def _history_row(event, rule) -> dict:
 @alerts_bp.get("/history")
 @require_role(UserRole.viewer)
 async def alert_history():
-    """Every alert transition in a range, newest first; one rule's with ?rule=."""
+    """Every alert transition in a range, newest first; one rule's with ?rule=.
+    A page at a time as the reader scrolls: ?before=<cursor> is the next
+    page's rows alone (core.paging)."""
     since, range_key = parse_range(request.args.get("range") or "7d")
+    before = request.args.get("before")
     async with current_app.db_sessionmaker() as db:
         rules = await alert_svc.list_rules(db)
         chosen = next((r for r in rules if r.id == request.args.get("rule")), None)
-        rows = await alert_svc.history(db, since, chosen.id if chosen else None, HISTORY_LIMIT)
-    ctx = {"events": [_history_row(e, r) for e, r in rows[:HISTORY_LIMIT]],
-           "truncated": len(rows) > HISTORY_LIMIT, "limit": HISTORY_LIMIT,
+        rows = await alert_svc.history(db, since, chosen.id if chosen else None, PAGE_SIZE, before)
+    rows, after = next_page(rows, lambda row: (row[0].transitioned_at, row[0].id))
+    ctx = {"events": [_history_row(e, r) for e, r in rows], "after": after,
            "rules": rules, "chosen": chosen, "current_range": range_key}
+    if before:
+        return await render_template("alerts/_history_page.html", **ctx)
     if request.headers.get("HX-Request"):
         return await render_template("alerts/_history_rows.html", **ctx)
     return await render_template("alerts/history.html", **ctx)

steward/alerts/service.py

@@ -241,17 +241,18 @@ async def list_rules(db) -> list[AlertRule]:
 
 
 async def history(db, since: datetime, rule_id: str | None = None,
-                  limit: int = 200) -> list[tuple[AlertEvent, AlertRule]]:
+                  limit: int = 200, before: str | None = None) -> list[tuple[AlertEvent, AlertRule]]:
     """Alert transitions since `since`, newest first, with their rule; one
-    rule's when `rule_id` is given. Returns up to limit+1 rows so a caller can
-    tell the list was cut."""
+    rule's when `rule_id` is given; only those older than the `before` cursor
+    when given (core.paging). Returns up to limit+1 rows so a caller can tell
+    the list was cut."""
+    from steward.core.paging import keyset
     stmt = (select(AlertEvent, AlertRule)
             .join(AlertRule, AlertEvent.rule_id == AlertRule.id)
-            .where(AlertEvent.transitioned_at >= since)
-            .order_by(AlertEvent.transitioned_at.desc())
-            .limit(limit + 1))
+            .where(AlertEvent.transitioned_at >= since))
     if rule_id:
         stmt = stmt.where(AlertEvent.rule_id == rule_id)
+    stmt = keyset(stmt, AlertEvent.transitioned_at, AlertEvent.id, before, limit)
     return [tuple(row) for row in (await db.execute(stmt)).all()]