security(deps): upgrade Next 14 → 15.5.16 + React 19 (AVO-3258, PR 2 of 3)

[ada-avo]

What & why

The final phase of the AVO-3258 docs remediation. PR 1 (#1729) cannot fully clear the Vanta test — 4 of the 6 next advisories are fixed only in 15.5.15 / 15.5.16, so full clearance requires the next 14 → 15 major upgrade (which requires React 19).

Clears: GHSA-h25m-26qc-wcjf (< 15.0.8), GHSA-q4gf-8mx6-v5v3 (< 15.5.15), CVE-2026-44573, CVE-2026-44578, GHSA-8h8q-6873-q5fj (< 15.5.16).

Pinned to 15.5.16 (the minimal version for clearance) rather than next@latest, which is now 16.x — a larger change beyond this remediation's scope and the approved decision (Next 15.5.16 + React 19).

Changes

Package	From	To	Why
next	^14.2.32	15.5.16	clears the 4 remaining advisories
react	^18.3.1	19.2.7	required by Next 15
react-dom	^18.3.1	19.2.7	required by Next 15
@types/react	^18.3.12	^19.2.17	React 19 types
@types/react-dom	^18.3.1	^19.2.3	React 19 types
react-medium-image-zoom	5.2.5	5.4.8	official React 19 support; used on the landing page (<Zoom>); clears its runtime peer warning

Code change — just one line

+import type { JSX } from 'react';
 import Document, { ... } from 'next/document';

@types/react 19 removed the global JSX namespace; _document.tsx's render(): JSX.Element now imports the type from react.

This is a Pages-router Nextra 3 site. The headline Next 15 breaking change — async cookies() / headers() / params — is app-router only and does not apply here. _document.tsx's getInitialProps is a standard Pages-router pattern, unaffected. next.config.mjs uses no Next-15-removed options (no swcMinify, no images.domains, no i18n). next-env.d.ts was regenerated by Next 15 (typed-routes reference).

Verification — production build + next start + browser spot-check (per the brief)

• yarn build ✅ · tsc --noEmit ✅ · yarn lint ✅ · yarn spellcheck ✅ (164 files, 0 issues)
• Chromium spot-check under React 19 (next start, real browser):
  • Landing, content pages, search, navigation all render correctly (full Nextra theme, sidebar, TOC, theme toggle).
  • Search — flexsearch index loads and returns highlighted results ("inspector" → 105, "tracking plan" → 98).
  • Navigation — sidebar links work.
  • react-medium-image-zoom — the zoom modal opens on click ✓.
  • mermaid / SVG render.
  • Zero uncaught exceptions and zero hydration warnings on every page.
  • The only console errors are external analytics CDNs (FullStory, GTM, iubenda, Segment) blocked by this sandbox's network egress — environmental, not code regressions (they load on Vercel).

Every bumped package was verified against the registry (publish age > 7 days, no preinstall/install/postinstall scripts, not deprecated, dependency-delta clean).

Known non-blocking items

• Remaining peer warning: nextra > @theguild/remark-mermaid@0.1.3 wants react@^18.2.0. It is a build-time remark plugin, not runtime React, and mermaid renders correctly — a Nextra transitive we don't control directly. Left as-is.
• next lint deprecation: Next 15.5 prints a notice that next lint is deprecated in favor of the ESLint CLI. Lint still passes; the migration is intentionally left out of this security PR to keep the diff focused.

Merge

Per the ticket, Solvi makes the merge call on PR 2 given the regression surface. Independent of #1729 / #1730 (they touch resolutions; this touches core dependencies); expect a trivial package.json reconciliation if merged after them.

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Generated by Claude Code

Summary by CodeRabbit

• Chores
  • Updated the app to newer platform and UI library versions for improved compatibility and support.
  • Added route type support from the latest build output to help keep TypeScript checks in sync with navigation changes.

[linear-code]

AVO-3258

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Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview, Comment	Jul 6, 2026 2:21pm

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📝 Walkthrough

Walkthrough

This PR upgrades core dependencies: next to 15.5.16, react and react-dom to 19.2.7, react-medium-image-zoom to 5.4.8, and @types/react to ^19.2.17. It also adds a routes.d.ts reference in next-env.d.ts and a type-only JSX import in pages/_document.tsx.

Changes

Dependency Upgrade

Layer / File(s)	Summary
Dependency version bumps package.json	Updates next, react, react-dom, react-medium-image-zoom in dependencies, and @types/react in devDependencies to new major versions.
TypeScript environment and import updates next-env.d.ts, pages/_document.tsx	Adds a reference directive for .next/types/routes.d.ts, updates the documentation URL comment, and adds a type-only JSX import from react.

Estimated code review effort: 2 (Simple) | ~10 minutes

Poem

Hop, hop, upgrade time is near,
New React, new Next, no need to fear,
A JSX import, a routes.d.ts line,
Small little tweaks, all working fine,
This bunny thumps with joy so bright! 🐇✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately summarizes the main change: upgrading Next.js 14 to 15.5.16 and React to 19.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/exciting-planck-lv2t8j-next15

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