test: review round 2 of Issue #71 (line breaks, unreadable registry, shim anchor)

- parity and create with real line breaks in the name;
- stop with malformed YAML (no DB) or a corrupt DB refuses (exit 1);
- test_layout: the shim heredoc anchor follows the { ... } > "$tmp_file"
  form (the rule it checks is unchanged);
- S11: base re-pinned to 0fc162e, which changes the shim's sanitize body.

Refs #71

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_issue23_24_startup_path.py

@@ -303,7 +303,7 @@ def test_s11_this_branch_does_not_change_the_generated_shim(mam_sandbox):
     too (one sanitize definition written in with `declare -f`, agent attach
     resolved, no silent wrong name), so the base is that commit."""
     repo = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-    base = os.environ.get("MAM_BASE_SHA", "5cd72d2")
+    base = os.environ.get("MAM_BASE_SHA", "0fc162e")
     show = subprocess.run(["git", "show", "%s:.agents/skills/lib.sh" % base],
                           capture_output=True, text=True, cwd=repo)
     if show.returncode != 0: