Electron Releases

Description of Change

Publish jobs spend a large chunk of their wall clock outside the build itself; this trims the two biggest non-build items without changing any released file formats.

• dsym.tar.xz is now written with multi-threaded xz (bsdtar --options xz:threads=0; XZ_OPT=-T0 under GNU tar). "Zip Symbols" was 25–47 min on every macOS publish job because xz was single-threaded over ~7 GB of dSYMs. Output is still a plain .xz stream.
• Symbol zips (pdb.zip, dsym-snapshot.zip, debug.zip, symbols.zip) use deflate level 6 instead of 9. #48766 added -9 for the 2 GB asset limit; measured below, it only buys ~0.4% (~8 MB on the 1.93 GB win-x64 pdb.zip) for ~1.7x the time — "Zip Symbols" was 8–16 min on Windows.
• "Zip Symbols" now only runs when the build was asked for symbols. Every testing and PGO build passes generate-symbols: false (the input was declared but never read), and symbols.zip/pdb.zip/dSYM archives are only consumed by the release uploader (move-artifacts.sh already tolerates their absence), yet each Windows PR build spent 8–13 min zipping PDBs — it's the largest remaining step on a fully cached build.
• Publish and release-build jobs pass generate-test-artifacts: false: nothing consumes src_artifacts (12.5 min of msys cp -r + tar per Windows publish job, 8 × 143–787 MB uploads per release) or the linux arm64 cross-arch snapshot (5.7 min) outside test jobs. The mksnapshot_args fixup was behind the same flag but is also read by @electron/mksnapshot from the released zip, so it now also runs for is-release builds.

Measured on a 512 MiB slice of an unstripped electron binary (Linux, one core unless noted):

Reference timings are from the v45.0.0-nightly.20260808 / v44.0.0-beta.2 publish runs.

Checklist

• I have built and tested this change
• I have filled out the PR description
• I have reviewed and verified the changes

Verified make_zip / make_tar_xz locally against both GNU tar and bsdtar (archives list and xz -t cleanly), lint --py passes, and copy-pipeline-segment-publish.js --check is still in sync. The macOS/Windows "Zip Symbols" step time on this PR's own CI is the real check for the xz change; the publish-flag change is only exercised by a publish run.

Release Notes

Notes: none