[hood]

defaults dev.preTransformRequests to true for every environment, not just client. cold SSR loads in dev go ~2x faster.

fixes #24093

why

ssr-transformed modules await their imports one by one, so with pre-transform off every module starts resolve/load/transform only after the previous one is done. turning it on lets importAnalysis warm up static imports while the runner is still busy upstream, same as on the client. Vite 5 did this for ssr already, it got lost in #16471 (#19272 noticed it too). details and history in the issue.

externalized imports return before the warmup call in importAnalysis, so nothing extra in node_modules gets transformed.

numbers

cold runner.import() of a seeded react+ts app, on a default config, comparing upstream f89888822 vs this branch, 7 interleaved runs, mac M1 Pro, nodejs v26:

app	upstream median (min-max)	this PR median (min-max)	wall	server CPU	peak RSS
1652 modules	3176 ms (3051-3477)	1499 ms (1416-1557)	-53%	3974 -> 3405 ms	489 -> 568 MB
332 modules	758 ms (708-827)	378 ms (352-420)	-50%	1255 -> 1139 ms	257 -> 278 MB

repro on published 8.3.8 by flipping the option: https://github.com/hood/vite-ssr-pretransform-repro

npm i && npm run gen && npm run bench

RSS goes up a bit, more transforms in flight at once.

things worth a look

• custom environments flip to true too (snapshot updated). they load through the same module runner, so same win, but lmk if you'd rather keep it to consumer === 'server'.
• modules that are imported but never executed (vitest mocks, see How to disable Pre-transform error log? vitest-dev/vitest#7345) now get transformed and can log a Pre-transform error, same as the client env does today. opt out is server.preTransformRequests: false. vitest might want to set it explicitly.

tests

• pnpm test-unit, pnpm test-serve, pnpm test-build on this branch
• all ssr playgrounds pass (ssr, ssr-html, hmr-ssr, environment-react-ssr, ssr-deps, ssr-webworker, ...), no Pre-transform error logs. ssr-html already asserts on that
• no new test, the existing preTransformRequests config test covers the default

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AI disclosure: helped myself w/ Claude Code for profiling and digging through git history.