v1.39.2.0 fix: bun run build crashes on Windows from subshell-with-redirection

[scarson]

Summary

Fixes #1530.

bun run build crashes on Windows + Git Bash + bun 1.3.13 with:

error: Subshells with redirections are currently not supported.

The current package.json scripts.build contains three ( git rev-parse HEAD 2>/dev/null || true ) > path/.version patterns. Bun's bundled shell on Windows rejects all single-line forms of "swallow stderr, swallow exit code, write stdout to a file" — brace groups, subshells-with-redirect, and dual-redirect commands all fail. The only safe option is to delegate to bash.

The same root cause produced the v1.38.0.0 → v1.39.1.0 ping-pong between brace groups and subshells (CHANGELOG v1.39.1.0 notes the brace-group regression; this PR notes that the v1.39.1.0 fix swapped to a different Bun-shell-hostile pattern). See #1530 for the full RCA and the matrix of Bun shell limitations observed.

Changes

• scripts/write-versions.sh (new) — bash script that writes git rev-parse HEAD to all three .version files. Mirrors the precedent of browse/scripts/build-node-server.sh. Handles git-missing case cleanly; setup's existing safety net backfills missing .version files at install time, so an empty file is acceptable.
• package.json scripts.build — replace the three subshell-with-redirect patterns with bash scripts/write-versions.sh. Net result: one shorter command instead of three POSIX-spelled-but-Bun-shell-rejected ones.
• test/build-script-shell-compat.test.ts — strengthen coverage:
  • Existing no bash brace groups test kept.
  • New no subshell-with-redirection patterns test — catches the v1.39.1.0 regression that this PR fixes.
  • New no command with both stderr-suppress and stdout-redirect test — catches the third Bun-shell-hostile form so future inline rewrites can't sneak it in.
  • Existing must be a subshell test replaced with .version writes are delegated to a bash script — gates on the right property (delegation), not the previously-incorrect property (subshell prefix).

Why a regex test is still useful

The strengthened regex test catches all three currently-observed Bun-shell-hostile patterns and prevents reintroduction. It does not predict future Bun shell limitations. A complementary follow-up would be to execute bun run build (or a parse-only probe) under windows-free-tests.yml — flagged in #1530 as a recommendation but out of scope for this PR.

Test plan

• bun test test/build-script-shell-compat.test.ts → 4 pass, 0 fail (Windows 11 + bun 1.3.13)
• bun run build end-to-end on Windows → exit 0; all three .version files contain the correct HEAD SHA
• ./setup end-to-end on Windows → "gstack ready (claude)."
• CI: standard Linux pipeline runs against the new test
• CI: windows-free-tests.yml runs the new test (currently includes test/build-script-shell-compat.test.ts per its existing test-list)

Out of scope

• Executing bun run build itself under Windows CI as a regression net (mentioned as a recommendation in bun run build crashes on Windows: "Subshells with redirections are currently not supported" #1530).
• Pushing the bash-script pattern to other multi-redirect inline forms elsewhere in the codebase (no others observed via grep, but a sweep is a separate concern).

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