⚡ Homepage PageSpeed: CLS and TBT are holding the score down

TL;DR

The homepage scores ~42 on PageSpeed Insights (mobile). Two metrics account for essentially all of the loss — CLS (~0.6–0.7, score 0.12) and TBT (~770 ms, score 0.38). Everything else is already healthy, so work should be confined to those two.

What's actually healthy — don't spend time here

Already fixed

• Icon bundle — import * as on three react-icons sets shipped 4.76 MB to every page; now 42 KB (#4887).
• ButtonRow forced reflow — geometry reads moved into the ResizeObserver callback; chunk 9148 has dropped off the forced-reflow list entirely (#4884).
• Hero image weight + deviceSizes srcset gap (#4884).

Ruled out — do not chase

• Footer logo flagged as "Unsized image element": the SVG is exactly 332×98, matching its declared dimensions, so the delta on load is 0.0 px. Lighthouse false positive on height:auto.
• v3Events: server-rendered via preloaded events.
• Globe / office accordion: hidden lg:block, desktop-only — cannot affect the mobile score. A previous fix targeted this desktop path, which is why the CLS number never moved.
• JotFormEmbed (ssr:false): not on the homepage.

Order of work

Sub-issues are ordered by score impact per unit of effort and risk. 1 and 2 are the high-value, low-risk items; 3 is a genuine refactor; 4 is cleanup.

Measurement of record is PageSpeed Insights (mobile). Note the shift only reproduces under real throttling — simulated throttling reports CLS 0, so verify with devtools/real throttling or PSI itself.

Update — deduplicated against #4894

#4894 (AI for Business Leaders event page) covers overlapping site-wide infrastructure. Reconciled as follows:

Correction to this PBI's earlier analysis: the claim that tinacms/dist/react imports were "fine" understated the problem. #4896 found TinaMarkdown (tinacms/dist/rich-text) pulls sanitizeUrl from @tinacms/mdx — a 1.97 MB package — across 65 components. That is the larger chain and is tracked in #4896.

Also verified: #4887 is deployed. Chunk 3b0ee722 on production went from 4.76 MB to ~0 MB with Simple Icons gone, so #4895 can be closed.

Start with the linked work items #4890, #4891, and #4893, then measure the homepage with PageSpeed Insights on mobile or real throttling. Done means addressing the remaining CLS and TBT causes without revisiting the ruled-out items, and confirming that the metrics improve.