FEATURE-ci-darwin-header-deadline: Preserve native launcher signal defaults

Restore each available SIGPIPE, SIGXFZ and SIGXFSZ to SIG_DFL immediately before the diagnostic Python launcher execs the native suite, matching direct Popen restore_signals behavior. Keep UID/context/token checks, native code, buffered traces, assertions, budgets and exact archive bindings unchanged. A real native signal-report helper demonstrates RED ignored dispositions through the prior Python exec fragment and GREEN defaults matching direct Popen after restoration. Workflow/Python/shell syntax and non-root rejection checks pass; privileged Darwin execution remains pending.

Author: etr

.github/workflows/v3-package-validation.yml

@@ -221,11 +221,14 @@ jobs:
               graph = audit.dependency_graph([str(executable)])
               matrix.check_linkage(graph, 'shared', prefix)
               receipt['dependencies'] = graph
-              launch = ('import json,os,sys; assert os.geteuid() == 0; '
+              launch = ('import json,os,signal,sys; assert os.geteuid() == 0; '
                   'assert not any(key in os.environ for key in ("GH_TOKEN", "GITHUB_TOKEN")); '
                   'context=dict(uid=os.getuid(),euid=os.geteuid(),gid=os.getgid(),egid=os.getegid(),cwd=os.getcwd(),'
                   'runtime={key:os.environ.get(key) for key in ("PATH","DYLD_LIBRARY_PATH","LD_LIBRARY_PATH","V3_PACKAGE_TOOLCHAIN")}); '
                   'print("V3_DIAGNOSTIC_CONTEXT " + json.dumps(context),flush=True); '
+                  'signal.signal(signal.SIGPIPE, signal.SIG_DFL) if hasattr(signal, "SIGPIPE") else None; '
+                  'signal.signal(signal.SIGXFZ, signal.SIG_DFL) if hasattr(signal, "SIGXFZ") else None; '
+                  'signal.signal(signal.SIGXFSZ, signal.SIG_DFL) if hasattr(signal, "SIGXFSZ") else None; '
                   'os.execvpe(sys.argv[1],sys.argv[1:],os.environ)')
               result = command([sys.executable, '-c', launch, str(executable)], source / 'test', runtime, timeout=180, allow_failure=True)
               print(result, end='', flush=True)

specs/tasks/FEATURE-ci-darwin-header-deadline.md

@@ -73,6 +73,12 @@ flags. The build stage asserts EUID 0 and token absence. A final assert-and-exec
 launcher records the actual test process UID/GID, cwd and selected runtime
 search environment before replacing itself with the unchanged test executable;
 its EUID must be 0 and its environment must exclude both token variables.
+Immediately before native exec, that launcher restores each available SIGPIPE,
+SIGXFZ and SIGXFSZ to SIG_DFL. This preserves the original direct subprocess
+signal setup after Python startup would otherwise reintroduce ignored
+signals. [Python subprocess documentation](https://docs.python.org/3/library/subprocess.html#subprocess.Popen)
+defines this default `restore_signals` behavior. This is an execution comparator
+correction, not an established explanation of the deadline failure.
 
 Buffered runner-context run `39978609885`, job `120499691522`, subsequently
 finishes successfully with four tests, 52 checks and zero failures/skips. It
@@ -176,8 +182,14 @@ original required gate remain incomplete. For the privilege-only follow-up,
 YAML, both Python stages and all macOS shell syntax pass; artifact/overlay code,
 permissions, other jobs and all C++ files are unchanged. An actual local env
 check proves both token variables are stripped while ordinary context survives;
-the literal test launcher rejects local EUID 1000 before exec. These are setup
-checks; native sudo/build/test EUID 0 execution remains pending.
+the literal test launcher rejects local EUID 1000 before exec. A real tiny C
+signal-report helper then demonstrated RED: direct Popen starts with available
+SIGPIPE/SIGXFSZ defaults, while the prior Python exec fragment inherits ignored
+dispositions. GREEN: the corrected literal signal/exec fragment yields identical
+native defaults. SIGXFZ is checked when available. This proves the focused signal
+correction locally, without claiming root execution; all native code and archive
+bindings remain unchanged. These are setup checks; native sudo/build/test EUID 0
+execution remains pending.
 
 The caller reviews/publishes only this task branch and dispatches the existing
 workflow, then resumes this same worktree with actual native evidence. No root