feat(alerts): history reads as episodes; tests follow the confirm dialog (#5316, #5314)

History (#5316):
- Transitions fold into episodes (steward/alerts/episodes.py): each stretch
  out of quiet, the worst state it reached, how long it lasted, its worst
  reading against the rule ('3m 21s (fires above 3m)'), who was told across
  its changes, and its Ansible runs. The changes themselves fold under it.
- An episode cut by paging says so ('cleared later (above)', 'earlier').
- For one rule: a verdict ('Fired 4 times in the last 7d, 1h 2m in all') and
  no Rule column. Notified and Action show only when the range has any.

Tests:
- The confirm guard looks for a confirm( call, not the word in the comment
  that says it is gone (lesson #4365).
- The Hosts viewer test looks for the add-host dialog by id, since every page
  now carries the confirm dialog.

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

steward/alerts/routes.py

@@ -161,7 +161,7 @@ def _history_row(event, rule) -> dict:
     return {
         "at": event.transitioned_at, "rule": rule,
         "from_state": event.from_state, "to_state": event.to_state,
-        "value": value, "condition": alert_svc.rule_condition(rule),
+        "value": value, "raw": event.metric_value, "condition": alert_svc.rule_condition(rule),
         "notes": notes, "muted_by": muted_by, "released": released,
         "deliveries": [(label, sent, error) for label, sent, error in (
             ("email", event.email_sent, event.email_error),
@@ -173,18 +173,31 @@ 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=.
-    A page at a time as the reader scrolls: ?before=<cursor> is the next
-    page's rows alone (core.paging)."""
+    """Every alert episode in a range, newest first; one rule's with ?rule=,
+    which also says how often it fired and for how long in all (#5316). A
+    page of transitions at a time as the reader scrolls: ?before=<cursor> is
+    the next page's episodes alone (core.paging). The Notified and Action
+    columns show only when something in the range was notified or acted on."""
+    from steward.alerts.episodes import episodes, summary
+    now = datetime.now(timezone.utc)
     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, PAGE_SIZE, before)
+        rule_id = chosen.id if chosen else None
+        rows = await alert_svc.history(db, since, rule_id, PAGE_SIZE, before)
+        show_notified, show_action = await alert_svc.history_columns(db, since, rule_id)
+        verdict = None
+        if chosen and not before:
+            every = await alert_svc.history(db, since, rule_id, HISTORY_SUMMARY_ROWS)
+            verdict = summary(episodes([_history_row(e, r) for e, r in every], newest_page=True,
+                                       now=now, since=since))
     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}
+    ctx = {"episodes": episodes([_history_row(e, r) for e, r in rows], newest_page=not before,
+                                now=now, since=since),
+           "after": after, "rules": rules, "chosen": chosen, "current_range": range_key,
+           "show_notified": show_notified, "show_action": show_action, "verdict": verdict}
     if before:
         return await render_template("alerts/_history_page.html", **ctx)
     if request.headers.get("HX-Request"):
@@ -192,6 +205,12 @@ async def alert_history():
     return await render_template("alerts/history.html", **ctx)
 
 
+# How many of one rule's transitions the history verdict reads ("fired N
+# times, X in all"); a rule that flapped more often than this in the range
+# is summed over its newest ones.
+HISTORY_SUMMARY_ROWS = 2000
+
+
 @alerts_bp.get("/api/rule_fields")
 @require_role(UserRole.viewer)
 async def rule_fields_api():