Regression: linux-arm64-{debug,profile,release}/linux-arm64-flutter-gtk.zip stopped publishing after #180235 — flutter build linux broken on arm64 hosts #190893

Help us understand the severity of this issue

• breakage; unable to contribute or trigger builds will no workarounds
• inconvenient workarounds exist, but significant effort required
• needed for a Flutter team-wide priority (already agreed upon)
• nice-to-have; none of the above

What do you need help with

Disclaimer: I used Claude to prepare this bug report. However, manual checking confirms that there aren't any arm64 releases where they're expected to be.

Steps to reproduce:

1. On an arm64 Linux host (reproduced on a GitHub Actions ubuntu-24.04-arm runner, Ubuntu 24.04.3), clone Flutter's master channel:
   git clone https://github.com/flutter/flutter.git -b master --depth 1
2. Run flutter build linux --release --target lib/main.dart on a standard Flutter desktop project.

Expected behavior: Build succeeds, same as on an x64 host.

Actual behavior:
Failed to download https://storage.googleapis.com/flutter_infra_release/flutter//linux-arm64-debug/linux-arm64-flutter-gtk.zip. Ensure you have network connectivity and then try again.
Exception: 404
Error: Process completed with exit code 1.

Root cause — this is a regression, and I've bisected it to the exact commit:

Checked artifact availability against the flutter_infra_release GCS bucket directly (not just relying on flutter build output):

• Monthly samples back to 2026-01-10 all had working linux-arm64-debug/linux-arm64-flutter-gtk.zip (HTTP 200), same as linux-x64-debug. This worked fine for months.
• Daily samples through 2026-08-05 were still fine.
• Bisecting the commit range on 2026-08-05, the artifact goes from present to missing between two adjacent commits:
  • 8ebfb2e (2026-08-05T16:52:00Z) → 200
  • e4c0224 (2026-08-05T17:21:41Z) → 404
• The breaking commit is e4c0224, PR Separate ARM64 Linux Desktop and Embedded engine builds to fix CJK and non-ASCII font rendering #180235, "Separate ARM64 Linux Desktop and Embedded engine builds to fix CJK and non-ASCII font rendering" (@krystic Chung). Every commit since — checked 37 consecutive commits through 2026-08-09 plus the reported failure's commit d083e4795ac8710b70d277b7866df2446bf5f2f6 — is 404.
• For contrast, linux-x64-debug/linux-x64-flutter-gtk.zip is 200 for every one of those same commits, before and after.

PR #180235 intentionally split the old combined ARM64 Linux CI builder into two: linux_arm_host_engine (embedded, no fontconfig) and a new linux_arm_host_desktop_engine (desktop, with fontconfig), with the latter intended to produce linux-arm64-flutter-gtk.zip for debug/profile/release at what should be the same artifact path flutter_tools already expects. Based on the bucket contents, that new desktop builder does not appear to be publishing to that path — either it isn't running, is misconfigured, or is gated off. What is present under linux-arm64/ (flat, no debug/profile/release split) is artifacts.zip, font-subset.zip, impeller_sdk.zip, linux-arm64-embedder.zip — a different set, seemingly for the separate Embedder API (see #172911/#173067), not for flutter_tools' desktop build pipeline.

Impact: flutter build linux (and flutter run -d linux) is broken on any arm64 Linux host on master channel, consistently since 2026-08-05, not intermittent.

Flutter doctor: (attach flutter doctor -v output from an arm64 host on master — diagnosed via direct GCS bucket inspection rather than a first-party doctor capture)

Related: #172911 / #173067 (Embedder API prebuilts, same platform, likely unrelated pipeline but worth cross-checking in case of a shared CI shard issue).