fix(preview): stop flattenTree overflowing the stack on a huge directory

[pedrofrxncx]

The bug

flattenTree (the file-explorer's tree→row flattener, apps/web/src/components/sandbox/preview/file-explorer/utils.ts) recursed into an expanded directory's children and merged the result back with rows.push(...flattenTree(...)). Spreading an array into a call's argument list is bounded by the JS engine's max-arguments limit, well below what a legitimate sandbox directory can hold (build output, generated assets, a large node_modules/.bin-style dump, etc.) — once a single expanded directory has enough direct children (~700k in this engine), the spread throws RangeError: Maximum call stack size exceeded and the whole file explorer crashes instead of rendering a (possibly slow but working) tree.

The fix

Replaced the spread-push with a plain for...of loop appending one row at a time — same output, no argument-list ceiling. Net change: +8/-1 in utils.ts.

Failure scenario + regression test

Expanding a directory with a very large number of direct children (build output, a huge asset dump, etc.) crashed the whole panel. Added a test in utils.test.ts building a 700,000-child directory and asserting flattenTree returns all rows instead of throwing — this reproducibly threw the RangeError before the fix (confirmed by hand against the old spread-based implementation) and passes after it.

How a reviewer confirms

bun test apps/web/src/components/sandbox/preview/file-explorer/utils.test.ts — 33 pass / 0 fail.

Checks run locally

• bun run fmt — clean
• cd apps/web && bunx tsc --noEmit — clean
• bun test apps/web/src/components/sandbox/preview/file-explorer/utils.test.ts — 33 pass / 0 fail
• bunx oxlint on both changed files — 0 warnings / 0 errors

Full CI validates the rest.

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Summary by cubic

Prevents the file explorer from crashing when expanding a directory with a very large number of children. Previously flattenTree used rows.push(...flattenTree(...)), which hit the engine’s max-arguments limit and threw; now it appends rows in a loop and renders the full tree.

• Change is limited to flattenTree: replace spread-push with a for...of loop. Output is identical; no API changes.
• Adds a regression test that builds a directory with 700,000 children and asserts flattenTree returns all rows without throwing.

^{Written for commit c94cb0b. Summary will update on new commits.}