Lazy-load the Mermaid code block

[nolannbiron]

CodeBlock only renders MermaidCodeBlock when the block's syntax is mermaid, but the import was static. Next inlines every 'use client' module reachable from a route's server graph into that route's client entry (next-flight-client-entry-loader emits import(/* webpackMode: "eager" */ …)), so a runtime conditional in a server component doesn't split anything — the diagram viewer's dependencies shipped on every page that has any code block at all.

Moving the boundary into a 'use client' wrapper puts them in an on-demand chunk instead. ssr: true is kept so real diagram blocks still server-render their skeleton.

Verified on a production build of this branch: @panzoom/panzoom and the Mermaid wrapper no longer appear in the route's entry chunks.

Initial client JS for the docs route:

nolann/perf-shiki-split (base)	1616.3 KB
this branch	1604.2 KB
	−12.1 KB

The byte saving is deliberately small — the Mermaid engine itself was already behind import('mermaid'). What changes is that pages with code blocks but no diagram stop loading the viewer's wrapper and its dependencies at all.

[changeset-bot]

🦋 Changeset detected

Latest commit: e545766

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
gitbook	Patch

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[github-actions]

Summary of the deployments:

Version	URL	Status
Vercel	https://gitbook-v2-pvs1wubah-gitbook.vercel.app	✅
Cloudflare	https://30390a70-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-pvs1wubah-gitbook.vercel.app/url/gitbook.com/docs	https://30390a70-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-pvs1wubah-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://30390a70-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.gitbook.io/test-gitbook-open

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Build	Status	Details	Updated (UTC)
customers-v2-cloudflare (Inspect)	👍 Approved by Nolann Biron	38 changed, 4 ignored	Aug 5, 2026, 2:39 PM
customers-v2-vercel (Inspect)	👍 Approved by Nolann Biron	13 changed, 31 ignored	Aug 5, 2026, 2:37 PM
v2-cloudflare (Inspect)	👍 Approved by Nolann Biron	8 changed, 1 ignored	Aug 5, 2026, 2:40 PM
v2-vercel (Inspect)	👍 Approved by Nolann Biron	8 changed, 1 ignored	Aug 5, 2026, 2:38 PM