fix(export): create the output directory for every format

[stn1slv]

What

exportSlides now creates the directory of --output once, before the browser starts, so every format can write into a path that does not exist yet.

Why

Whether a missing output directory is an error depends on the format:

slidev export slides.md --format pdf  --output dist/slides.pdf    # works, creates dist/
slidev export slides.md --format pptx --output dist/slides.pptx   # ENOENT

The writers disagree about whose job it is. page.pdf({ path }) creates the directory, since Playwright creates parent directories, and genPagePng calls fs.mkdir(..., { recursive: true }), which Markdown also goes through. Everything that calls fs.writeFile directly does not, which covers both PowerPoint formats and, less obviously, --format pdf --per-slide: that path renders each slide into a buffer, merges them and writes the result itself, so it never touches the Playwright call that would have created the directory.

Tested on v53.0.0 against a deck with no dist/ folder:

Command	Before	After
--format pdf	works	works
--format pdf --per-slide	ENOENT	works
--format png	works	works
--format md	works	works
--format pptx	ENOENT	works
--format pptx-editable	ENOENT	works

dist/ is where most people put an export, and it is what the docs use in their examples, so this is easy to hit on a fresh checkout.

Tests

packages/slidev/node/commands/export.test.ts is new, and it is the first test around exportSlides. A real export needs a browser and a dev server, but the test never gets that far. importPlaywright asks getRoots for the user root, and that throws without an entry, so every call rejects before anything renders. The directory is created before that point, so the assertion still says whether the step ran. Each rejection is matched against that known failure, otherwise an error thrown by the mkdir itself would satisfy the test instead of failing it. Four of the five cases fail without the one-line fix, and the file runs in milliseconds with no browser.

Notes

The fs.mkdir call sits before chromium.launch, so an unwritable path fails straight away instead of after the whole deck has rendered. It does nothing when the directory already exists, or when --output has no directory part.

For PNG, --output names a directory rather than a file, so this creates its parent and the existing fs.mkdir in genPagePng still creates the directory itself.

A narrower fix would be to add the same call at each failing write site, in genPagePdfPerSlide, genPagePptx and packages/slidev/node/commands/pptx/index.ts. That leaves the shared path alone but keeps the difference between formats. I am happy to switch if you prefer it.

pnpm lint passes. vitest run reports the same 11 failures with and without this change, in api-snapshots.test.ts and node/syntax/integration.test.ts, so they look like snapshot drift on main.

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