The "Recents: click previous chat in sidebar" step in
tests/studio/playwright_chat_ui.py was the single biggest wallclock
sink across all three UI workflows on PR 5312:
Linux Studio UI CI: 786s in this one step (out of 823s Drive chat UI)
Windows Studio UI CI: 786s in this one step (out of 825s)
Mac Studio UI CI: 1389s in this one step (out of 1542s)
Root cause was the text-filtered selector
aside a, aside button, [data-sidebar=sidebar] a, ...
plus an EXCLUDE regex anchored start...end that didn't match the
coalesced sidebar text the app actually renders (unslothBETA,
UUnslothUnsloth, Train, Export, Recents). The loop kept
clicking those nav links, the post-click page.evaluate threw on
the navigated frame, the bare except: continue swallowed the
error, and the loop iterated forward where each candidates.nth(i)
hit Playwright's default 60s per-locator retry against a now-stale
DOM. Mac under single-process Chromium ate about 22 of those retries.
Server-side studio.log was idle for the entire 23-min window --
the time was spent in the browser.
Fix:
1. Add data-testid=recent-thread to the actual chat-history
SidebarMenuButton in studio/frontend/src/components/app-sidebar.tsx
(the live one; thread-sidebar.tsx is dead code, no imports).
Also add data-thread-type / data-thread-id for richer assertions.
2. Switch the Playwright selector to that testid, drop the
text-match heuristic + EXCLUDE regex.
3. Bound the whole step with a 30s deadline + 5-iteration cap +
5s click timeout, so a misbehaving selector cannot blow up
wallclock the way the previous loop did.
Verified locally on Linux + headless Chromium:
PASS: rendered 2 [data-testid=recent-thread] entries
PASS: clicked recent inside deadline (about 0.6s used)
PASS: bogus selector exits in 5s
Test driver at tests/scripts/repro_recents_local.py.
Expected savings on PR 5312:
Linux UI 18m36s to about 5m
Windows UI 24m47s to about 12m (still has about 7m install)
Mac UI 31m10s to about 9m
Total about 50 min compute and 22 min PR wallclock per PR.
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