runtime:mayMoreStackMove: TestLockOSThreadExit failures

[gopherbot]

#!watchflakes
default <- pkg == "runtime:mayMoreStackMove" && test == "TestLockOSThreadExit"

Issue created automatically to collect these failures.

Example (log):

=== RUN   TestLockOSThreadExit
    proc_test.go:987: /home/swarming/.swarming/w/ir/x/t/go-build3987034283/testprog.exe LockOSThreadMain (9.641368ms): ok
    proc_test.go:993: /home/swarming/.swarming/w/ir/x/t/go-build3987034283/testprog.exe LockOSThreadAlt: signal: trace/breakpoint trap (core dumped)
    proc_test.go:995: want "OK\n", got ""
--- FAIL: TestLockOSThreadExit (0.03s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "runtime:mayMoreStackMove" && test == "TestLockOSThreadExit"

2026-08-14 15:05 go1.27-linux-amd64-longtest-git2.24.0 release-branch.go1.27@996e69fe runtime:mayMoreStackMove.TestLockOSThreadExit (log)

=== RUN   TestLockOSThreadExit
    proc_test.go:987: /home/swarming/.swarming/w/ir/x/t/go-build3987034283/testprog.exe LockOSThreadMain (9.641368ms): ok
    proc_test.go:993: /home/swarming/.swarming/w/ir/x/t/go-build3987034283/testprog.exe LockOSThreadAlt: signal: trace/breakpoint trap (core dumped)
    proc_test.go:995: want "OK\n", got ""
--- FAIL: TestLockOSThreadExit (0.03s)

— watchflakes