Improve local wp-admin responsiveness

[chubes4]

Summary

• Add a small in-memory background task scheduler for best-effort Studio maintenance tasks with dedupe, delay, cancellation, running-state guards, and serialized concurrency groups.
• Move local admin health/update/translation checks off passive wp-admin requests and refresh them shortly after site create/start.
• Route thumbnail capture through the scheduler as the first existing caller, preserving per-site dedupe and global capture serialization.

Fixes #3367

Performance evidence

The main bottleneck found was fresh/passive wp-admin requests blocking on opportunistic WordPress.org checks. Explicit update/install/plugin/theme pages are intentionally excluded so user-requested live data still loads normally.

Dashboard/request-profiler baseline:

• /wp-admin/ PHP request: ~1608 ms
• curl total: ~2.24 s
• outbound WordPress.org calls: 5
• artifact: /var/folders/lr/c_cmmt7s0592m4njz99v5yb40000gn/T/studio-dashboard-profile-baseline-jipGCw/summary.json

Dashboard after scoped deferral:

• /wp-admin/ PHP request: ~149 ms
• curl total: ~0.76 s
• outbound dashboard HTTP: 0
• artifact: /var/folders/lr/c_cmmt7s0592m4njz99v5yb40000gn/T/studio-dashboard-profile-dashboard-scoped-8XmOjZ/summary.json

Broad admin cold-page probe:

• posts: 1.72 s -> 0.93 s
• ordinary content/settings pages stayed around 0.64-0.92 s
• explicit pages such as plugins.php and plugin-install.php still perform their live checks by design
• baseline artifact: /var/folders/lr/c_cmmt7s0592m4njz99v5yb40000gn/T/studio-broad-admin-broad-admin-normal-normal-ibRqqe/summary.json
• patched artifact: /var/folders/lr/c_cmmt7s0592m4njz99v5yb40000gn/T/studio-broad-admin-broad-admin-passive-defer-normal-bQmeEq/summary.json

Site Editor A/B:

• baseline measure_site_editor_ready_ms: 1113, 1141, 1304; median 1141 ms
• patched measure_site_editor_ready_ms: 1120, 1210, 1226; median 1210 ms
• conclusion: neutral/no meaningful Site Editor improvement; this PR should not be treated as improving the site-editor.load metric
• baseline artifact: /var/folders/lr/c_cmmt7s0592m4njz99v5yb40000gn/T/studio-site-editor-ab-baseline-i7b9XP/summary.json
• patched artifact: /var/folders/lr/c_cmmt7s0592m4njz99v5yb40000gn/T/studio-site-editor-ab-patched-o5YpgM/summary.json

WooCommerce probe:

• this does not solve WooCommerce-specific admin slowness
• Woo remains a separate path involving onboarding redirects, Woo Admin runtime, Woo/WP.com API work, and Action Scheduler async loopbacks

Diagnostic tooling used:

• Homeboy Extensions WordPress request profiler: feat(wordpress): add WordPress request profiler helper Extra-Chill/homeboy-extensions#446

Testing

• npm run test -- --project common -- tools/common/lib/tests/mu-plugins.test.ts
• npm run test -- --project studio -- apps/studio/src/lib/tests/site-maintenance-tasks.test.ts apps/studio/src/lib/tests/background-tasks.test.ts apps/studio/src/lib/tests/capture-site-thumbnail.test.ts apps/studio/src/modules/cli/lib/tests/cli-events-subscriber.test.ts
• npm -w studio-app run typecheck
• npm -w studio-app run lint

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Profiling local wp-admin performance, drafting the background task scheduler and MU-plugin changes, writing regression tests, and assembling the evidence above. Chris reviewed the direction and requested the PR evidence/framing.

[wpmobilebot]

📊 Performance Test Results

Comparing f38397b vs trunk

app-size

Metric	trunk	f38397b	Diff	Change
App Size (Mac)	1410.38 MB	1410.41 MB	+0.04 MB	⚪ 0.0%

site-editor

Metric	trunk	f38397b	Diff	Change
load	1515 ms	1523 ms	+8 ms	⚪ 0.0%

site-startup

Metric	trunk	f38397b	Diff	Change
siteCreation	8086 ms	8079 ms	7 ms	⚪ 0.0%
siteStartup	4932 ms	4948 ms	+16 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[chubes4]

@fredrikekelund What do you think of this approach for wp-admin performance?

The idea is to keep passive wp-admin requests from blocking on opportunistic WordPress.org checks, while preserving the normal behavior on explicit update-related pages like Plugins, Themes, Updates, and Add Plugins.

I added a small background-tasks.ts abstraction so Studio has one place for delayed/deduped best-effort work. This lets Studio refresh those checks shortly after site creation/startup, outside the user’s dashboard request.