CLI: a closed stdout pipe exits 141 silently (was E_INTERNAL); example avoids head under pipefail

Found by the P10 fresh-VM run: `simurg inspect … | head` raised BrokenPipeError, reported as
an internal error, and stopped examples/gsa_demo.sh (set -o pipefail). run_guarded now flushes
stdout inside the guard and maps BrokenPipeError to ExitCode.SIGPIPE (141) without a message.
p10.sh: SKIP_DOCKER/SKIP_CONDA, clearer digest report; p10t.sh runs build+pip+tutorial only.

tests/unit/test_cli_errors.py

@@ -93,3 +93,18 @@ def test_locale_independent_output(tmp_path) -> None:  # type: ignore[no-untyped
         assert r.returncode == 0, r.stderr
         outs.add(r.stdout)
     assert len(outs) == 1
+
+
+def test_closed_stdout_is_not_an_internal_error(tmp_path) -> None:  # type: ignore[no-untyped-def]
+    # `simurg inspect … | head`: the reader goes away; the CLI must exit like a SIGPIPE'd tool (141), silently
+    f = _files(tmp_path)
+    p = subprocess.Popen(
+        [sys.executable, "-m", "simurg.cli.main", "inspect", "--json", str(f["bpm"]), str(f["egt"]), str(f["idat"])],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+    )
+    assert p.stdout is not None and p.stderr is not None
+    p.stdout.close()  # nobody reads stdout
+    err = p.stderr.read().decode()
+    assert p.wait() == 141, err
+    assert "E_INTERNAL" not in err and "Traceback" not in err and "Exception ignored" not in err