chore(deps): React 18 → 19 (react + react-dom + types) with JSX namespace fix

[oratis]

Supersedes #170 and #171.

Why these couldn't merge as-is

Dependabot split the React upgrade across two PRs — #170 bumps react + @types/react, #171 bumps react-dom + @types/react-dom. Neither can merge alone: each leaves the tree with react@19 + react-dom@18 (or the reverse), which is an unsupported combination. That's why #170 has been red since June.

Both are also missing the code change React 19 requires.

The code change

React 19's @types/react removed the global JSX namespace. It now lives under React.JSX and is re-exported as a named type from 'react'. This repo has 38 JSX.Element annotations across 25 desktop files that resolved against the old global, and every one fails with TS2503: Cannot find namespace 'JSX' under the new types.

Each file now imports the type explicitly, merged into its existing 'react' import where one exists so no duplicate-import lint warning appears — root lint is --max-warnings=0 as of #210.

-import { useCallback, useEffect, useState } from 'react';
+import { useCallback, useEffect, useState, type JSX } from 'react';

A note on how this was verified

My first local run of pnpm typecheck passed and it was wrong. tsc -b is incremental and reused .tsbuildinfo, silently skipping the desktop project — the exact project the breakage was in. CI caught what the local incremental build hid.

Everything below was re-run with tsc -b --force:

• tsc -b --force — clean
• pnpm lint (--max-warnings=0) — clean
• pnpm format:check — clean
• pnpm test — 1033 tests across 8 packages pass
• pnpm build — clean
• pnpm --filter @deepcode/desktop test:e2e — desktop Playwright protocol journey, 4/4 pass

The browser journey matters here specifically: React 19 changes runtime behaviour, not just types, so a green typecheck alone would not have been sufficient evidence. The fixture from #193 exercises the real renderer bridge.

Scope

Types-only change to application code — no component logic, no hooks, no rendering behaviour touched. Versions land at react@19.2.8, react-dom@19.2.8, @types/react@19.2.18, @types/react-dom@19.2.3.

🤖 Generated with Claude Code