[CI] dotnet/MSBuild intermittently exits 139 during restore and truncates binlogs

[dalexsoto]

Additional info to collect

Copilot: please collect the following information for each occurrence of this issue:

• Any crash reports for the crashed process. Upload them to the issue, or if that's not possible, create gists.
• We have minidumps enabled for some parts of the build (DOTNET_DbgMiniDumpName); collect whether the crash created a minidump or not, and if so, a link to the artifact where the minidump was uploaded.

Failure signature

The dotnet process hosting MSBuild 18.9.3 (18.9.3+d88a8f149, SDK 10.0.400-preview.0.26360.120) intermittently exits with status 139 during the first second of project restore/evaluation:

Process dotnet exited with 139

The abrupt process death leaves the corresponding binlog truncated. Structured binlog analysis reports System.IO.EndOfStreamException: Unable to read beyond the end of the stream and a 0.0-second failed build.

Confirmed occurrences

PR / head	Build and job	Failing variation
#26200 / 966f7cc95666adf0926c09964990868e5f161864	14718622 - linker_tvos	dont link/tvOS - simulator/Debug
#26202 / 1f6d35df981f18fd18fb67e70d4def97495f1daa	14718710 - interdependent-binding-projects	interdependent-binding-projects/Mac Catalyst/Debug
#26204 / e91862693a70d34dfd66bcc1d6967fe986fb464b	14718779 - linker_macos	link all/macOS/Debug

First observed: 2026-07-21 13:36 UTC. Latest observed: 2026-07-21 14:37 UTC. Recurrence: 3 jobs across 3 distinct monitored PRs.

Diagnosis and impact

This is nondeterministic CI infrastructure/tooling behavior rather than a source compilation failure:

• It occurs in unrelated projects on tvOS, Mac Catalyst, and macOS.
• The process dies during restore/evaluation before a product error is emitted.
• Other variations in the same jobs complete successfully.
• The only apparent binlog errors are consequences of the truncated stream.

Each occurrence fails an otherwise independent simulator-test job. The current workaround is to rerun failed jobs after confirming the PR is conflict-free and retry budgets permit it. The linked artifacts and task logs have limited retention.

[dalexsoto]

New affected PR: #26188 @ fc3b9163c9b6de1eee35029949ae395174253e51, build 14718729, job monotouch_maccatalyst. The NativeAOT restore ended with Process dotnet exited with 139; xharness then reported The Writer is closed or in error state while parsing the abruptly truncated log.

Also observed in a second job on already-listed PR #26202: monotouch_maccatalyst, where MSBuild property evaluation exited 139. The signature now covers 5 jobs across 4 monitored PRs. Build 14718729 is still cancelling, so no retry has been requested.

[dalexsoto]

New affected PR: #26198 @ 0a8a95dd2f117727a1b51b46e043def81ca7664a, build 14720520, job xcframework. The iOS simulator build died during restore/evaluation with Process dotnet exited with 139, leaving the build log truncated.

The signature now covers 6 jobs across 5 monitored PRs. Build 14720520 remains in progress, so no retry has been requested.

[dalexsoto]

Two new exit-139 occurrences:

• New affected PR [xtro-sharpie] Handle typedef-level API_UNAVAILABLE on enums. Fixes #26166. #26168 @ cb951d2a3a87ffbf459387f3712efb80961ab6f8: build 14720939, job dotnettests_ios. MlaunchTest.GetMlaunchInstallArguments died during dotnet build with exit 139, and the binlog ended in EndOfStreamException.
• Already-listed PR [tests] Truncate command output in DotNet.ExecuteCommand failure messages #26188 @ fc3b9163c9b6de1eee35029949ae395174253e51: build 14720595, job monotouch_tvos. The Debug LinkSdk variation died during restore/evaluation with Process dotnet exited with 139.

The signature now covers 8 jobs across 6 monitored PRs. Both builds remain active, so no retry has been submitted; retained artifacts may expire.

[dalexsoto]

PR #26198 retry update: build 14720520 completed terminal, with no prior retries or equivalent build active. Simulator_tests attempt 2 was accepted at 00:34 UTC to rerun xcframework and introspection. Two separately counted stage requests were accepted for this PR; current budget is 2 lifetime / 2 on this head.

[dalexsoto]

Retry outcome: merged PR #26204 build 14718779 simulator_tests attempt 2 completed successfully at 23:17 UTC. The previously exit-139 linker_macos job passed, and the overall build completed succeeded at 00:27 UTC.

[dalexsoto]

Retry outcome: PR #26200 build 14718622 simulator_tests attempt 2 completed with the previously exit-139 linker_tvos job succeeding.

[dalexsoto]

Retry outcome: PR #26202 build 14718710 simulator_tests attempt 2 completed successfully. The previously exit-139 interdependent-binding-projects and monotouch_maccatalyst jobs both passed; the overall build result is succeeded.

[dalexsoto]

PR #26168 build 14720939 is now terminal, but no retry was submitted for the exit-139 dotnettests_ios job. Known same-head build 14719254 is omitted from retained build-list history and its saved timeline is empty, so lifetime/head retry counters cannot be established safely.

[dalexsoto]

Final retry outcome: merged PR #26198 build 14720520 simulator_tests attempt 2 completed successfully. The previously exit-139 xcframework job passed, the overall build succeeded, and the PR merged at 01:43 UTC.

[dalexsoto]

New affected PR: #26208 @ 34b9f4d4972752561d6769b7f1ef0fbe276e049c, build 14718968, simulator_tests attempt 2 job monotouch_ios. The Release NativeAOT variation died during restore/evaluation with Process dotnet exited with 139.

The signature now covers 9 jobs across 7 monitored PRs. Attempt 3 was accepted at 02:22 UTC to rerun monotouch_ios; reconciled budget is 3 lifetime/current-head retries.

[dalexsoto]

External retry update: Azure simulator_tests attempt 2 became active around 05:34 UTC for PR #26168 build 14720939 and PR #26188 build 14720595, rerunning their previously recorded exit-139 jobs. No retry was initiated by this monitor.

[dalexsoto]

External retry outcome: PR #26168 build 14720939 simulator_tests attempt 2 completed successfully. The previously exit-139 dotnettests_ios job passed, and the overall build succeeded.