jerry/buzz

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Wes f0234f1449 fix(desktop): eliminate mounted-view CPU burn — compositor-safe shimmer, observer append fast path, poll-tick disk reads (#6198 )

## Summary

Live 0.5.16 review (Royal Court thread) traced the sustained 20–25%
WebContent CPU burn in any large mounted channel with a working agent to
three defects, in descending impact:

1. **Shimmer animation forces per-frame style + compositing walks.**
`.buzz-shimmer` animated `background-position` under
`-webkit-background-clip: text`, which WebKit cannot run on the
compositor: every frame did a full document style resolve plus a
recursive compositing-hierarchy update over the timeline's layer tree.
The highlight now lives on an `aria-hidden` overlay child duplicating
the label text and animates **opacity only** (compositor-accelerated); a
real element is used instead of `::after` generated content so screen
readers never see the duplicate text. Visual: the moving sweep becomes a
gentle pulse. `prefers-reduced-motion` removes the overlay entirely —
static muted label, exactly as before.
2. **Observer journal whole-journal dedup + re-sort per append.** Every
one-per-second observer frame rebuilt a dedup Set over up to 3000
retained events and re-sorted the whole journal with a
`Date.parse`-per-comparison comparator. In-order batches (the ordinary
live path, same condition as the existing incremental transcript fold)
now dedup within the batch and concat; out-of-order/replayed arrivals
keep the full path.
3. **Redundant disk reads in the 5s agent-list poll.**
`build_managed_agent_summary` re-read the global config from disk per
call despite receiving it as a parameter, and re-read the teams store
per tracked pair — 2N redundant reads per poll tick for N agents. Both
are now caller-supplied; one-shot command paths use a
`summarize_from_disk` helper. Same stores, same `unwrap_or_default`
failure posture, read once.

## Evidence (mechanism attribution, live 0.5.16-block, mounted
~1500-event channel)

- True-idle mounted view (working-state UI live): **25.08% mean / 24.15%
median** WebContent CPU; post working-state decay: **6.33% / 3.50%**.
- Reduce Motion A/B during a live agent turn (isolates the shimmer,
working UI still mounted): **19.50% mean → 5.39% mean** (72% collapse).
Native 10s samples: `Document::resolveStyle` 379 samples → 1;
`updateCompositingLayersAfterStyleChange` 378 → 0; recursive
`updateBackingAndHierarchy` 363 → 6.
- The shimmer mechanism predates 0.5.16 (CSS unchanged since #3151);
current multi-agent workloads exposed and amplified it. The mention
regression itself was fixed separately in #6182.

## Testing

- `desktop` observer store suites: 55/55 pass, including 5 new tests
pinning the fast-path invariants (equal-timestamp seq ordering,
duplicate-batch redelivery, intra-batch duplicates, overlapping late
arrival takes the slow path, transcript-equals-replay on both paths).
- `cargo test --lib managed_agents` (1016 passed) and `--lib commands`
(727 passed); `cargo clippy` clean; `pnpm typecheck` + biome clean.
- Release gate for the patched build (per Mongo): active-turn mounted
CPU must collapse from the ~21–25% baseline with no per-frame
style/compositing walk in a native sample — measured on Wes's workspace
once a build with this branch is running.

Findings and raw samples:
`RESEARCH/LIVE_0_5_16_WEBKIT_ATTRIBUTION_2026_08_18.md`,
`RESEARCH/RENDERER_STEADY_STATE_LOOP_AUDIT_2026_08_18.md`,
`.scratch/live-app-review/` (Carl/Donut/Mongo/Brain, Royal Court thread
01a7fe75).

---
*Opened by Brain (agent) via @wesbillman's account on his behalf —
coordinated in Buzz channel agent-mention-policy-royal-court, thread
01a7fe75.*

---------

Signed-off-by: Wes <wesbillman@users.noreply.github.com>
Co-authored-by: Brain <21994759fc7a6fa6b965551d35cfd7897d262f2495467f2d78694ddcfa6a5c7e@buzz.block.builderlab.xyz>

2026-08-18 05:47:53 -07:00