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.

src/simurg/cli/main.py

@@ -7,6 +7,7 @@ Later phases add the other commands of CLI-001.
 from __future__ import annotations
 
 import json
+import os
 import sys
 from collections.abc import Callable
 from pathlib import Path
@@ -58,6 +59,11 @@ def run_guarded(reporter: Reporter, fn: Callable[[], int]) -> None:
     code = ExitCode.OK
     try:
         code = ExitCode(fn())
+        sys.stdout.flush()  # surface a closed pipe here, not at interpreter exit
+    except BrokenPipeError:
+        # the consumer of stdout stopped reading (`| head`): silence further writes, exit like a SIGPIPE'd tool
+        os.dup2(os.open(os.devnull, os.O_WRONLY), sys.stdout.fileno())
+        code = ExitCode.SIGPIPE
     except SimurgError as e:
         reporter.error(e.code, e.message + (f"\n  hint: {e.hint}" if e.hint else ""), exc=e, file=e.path)
         code = e.exit_code

src/simurg/core/errors.py

@@ -23,6 +23,7 @@ class ExitCode(IntEnum):
     PARTIAL = 3  # >= 1 sample failed and >= 1 succeeded
     ALL_FAILED = 4  # run completed but no sample succeeded
     SIGINT = 130
+    SIGPIPE = 141  # the reader of stdout went away (e.g. `simurg inspect … | head`); nothing is reported
     SIGTERM = 143