# Phase 19 — Expandable UPS power-events list

**Source:** `TODO.md` L4 — "The UPS tab should have an expandable, clear list of last incidents with dates/times"
**Story:** n/a
**Context:** `src/dashboards/web/pages/ups.html` lines 72–76 (the `Power events` card: `<header><h3>` + a `ul.events#events` holding a `loading…` placeholder), `src/dashboards/web/static/page-ups.js` (`refreshEvents()` at line 430 — fetches `/api/events?limit=200&source=ups` and hands the rows to `Dash.eventsPager` with the date/time + severity-chip + host row shape; called unconditionally from `refresh()` at line 427, which the page's `poll(refresh, state.pollMs)` loop drives, `state.pollMs` from `config.ups.poll_ms || 5000`), `src/dashboards/web/static/app.js` (`Dash.eventsPager` — 50 rows a page, paging state in a `WeakMap` keyed by the `<ul>`, rows re-written only when their markup changed), `src/dashboards/web/static/dash.css` (`details.charts-box` at lines 714–727 — the summary marker `▸`/`▾`, hidden webkit marker, hover; the `.events` bounded 320px scroll and `.events-pager` strip), and the pattern this phase mirrors — `/system`'s per-host Charts disclosure (`system.html` line 81, `page-system.js` line 315: "a `<details>` renders nothing, so … nothing is built or drawn while the stack is shut") and its pin `test_system_history_charts_are_collapsed_behind_a_toggle`

## Objective

The `/ups` power-events list becomes what the TODO asks for — *expandable*: the card is collapsed by default behind a `<details>` disclosure in the repo's own `charts-box` style, nothing is fetched or drawn while it is shut (the `/system` rule), the first expand fetches and builds, a re-expand paints from the data in hand unless it is stale, and the page's poll loop refreshes the list only while the disclosure is open. The "clear" half already ships and stays: every row carries its date/time, the severity chip, and the host, and the 50-per-page pager bounds the list. No new API surface — the existing `/api/events?source=ups` is the whole backend.

## Dependencies
- `18_nav_hamburger` (todo) — both phases touch `ups.html` (the masthead, the events card); landing 18 first keeps this phase's diff confined to the events section. No shared code between them.

## Tasks
1. `01_events_disclosure.md` — the `ups.html` markup: the card body becomes a collapsed-by-default `<details class="events-box">`
2. `02_events_lazy_loading.md` — `page-ups.js`: no fetch while closed, first-expand fetch, re-expand stale rule, poll-while-open
3. `03_disclosure_css.md` — `dash.css`: the `details.events-box` summary styling in the `charts-box` shape, pager and bounded list inside
4. `04_tests_and_verification.md` — the served-page pins (disclosure present and unopened, the lazy rule, the unchanged row shape) and the closed/open browser verification

## Testing & Quality
- Unit/integration: `tests/test_api.py` — the served-page pins (see task 04), alongside the untouched `Dash.eventsPager` behaviour (a re-paint with the same data keeps the reader's page — the `WeakMap` rule, pinned by the existing event-feed tests)
- Coverage: **>90%** on new/modified code (the phase is markup + JS + CSS; the gate applies to the changed Python test files)
- The phase is "Complete" only when the **entire** project test suite passes 100% (every test in the project, not just this phase's)

## Documentation & Consistency

- The final pass reviews `README.md` and `AGENTS.md` in full against the project as it stands after this phase — fixing every inconsistency found, **including pre-existing ones not caused by this phase**.
- AGENTS.md's `UI conventions` section already documents the event pager ("An event feed is a window, not a printout") and the `/system` Charts disclosure; it gains the `/ups` disclosure's sentence (collapsed by default, lazy-built, poll-while-open, the stale rule) in the section's voice. The README's `/ups` table row ("power events") stays true — the list is on the page, now behind a summary.

## Completion Criteria
- [ ] `/ups` loads with the Power events card collapsed (a summary line, no list visible, no `/api/events` request in the page's first poll) and the expand shows the bounded, paged list with date/time rows
- [ ] closing and re-opening within one poll interval paints the cached rows without a refetch; a stale cache refetches on open; while open, the poll loop keeps the list current
- [ ] `uv run pytest` green, coverage not down, `ruff` + `pyright` clean
- [ ] `bash .agents/validate.sh` green (including `node --check` of the modified `page-ups.js`)
- [ ] closed- and open-state screenshots in `data/logs/` against the running dev server (invariant 10)
- [ ] no behavior change in completed work: every other element on `/ups` (cards, charts, dialog, pager behaviour) is unchanged