refactor: standardize --agent option usage, improve YAML registry fallback, and fix layout falsy-zero trap (J-1)

- In stop_session.sh and update_yaml_resumed.sh: standardize explicit --agent option and use resolve_agent_type_from_registry to read agent type from YAML/DB state rather than brittle suffix-only regex inference.
- Update multi-agent-mux-stop/SKILL.md, multi-agent-mux-resume/SKILL.md, multi-agent-mux-create/SKILL.md, and deploy/INSTALL.md to standardize passing --agent explicitly.
- Fix J-1 in layout.py: refactor _env_int(*names, default=None) to take an explicit default parameter, eliminating the falsy-zero trap so MAM_MIN_PANE_COLS=0 is respected.
- Add regression and contract tests: test_j1_env_zero_min_cols_matches_flag_zero, test_j1_env_zero_min_rows_matches_flag_zero, test_comp_stop_agent_fallback_*, test_comp_docs_stop_examples_pass_agent.
- Verified 100% UNANIMOUS PASS from Planner claude and Reviewers claude and cline.

.agents/skills/multi-agent-mux-resume/scripts/update_yaml_resumed.sh

@@ -4,14 +4,14 @@
 # resume UUID 를 per-row own id (claude_session_id_own / agy_conversation_id_own)
 # 에 박는다 — agent_identities 전역은 더 이상 primary 아님 (cache 로 강등, P0-C/단계 e).
 #
-# Usage: bash update_yaml_resumed.sh --session <name> --uuid <id> [--agent claude|agy]
+# Usage: bash update_yaml_resumed.sh --session <name> --uuid <id> [--agent claude|agy|hermes|cline]
 set -euo pipefail
 
 source "$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)/lib.sh"
 
 usage() {
   cat <<EOF
-Usage: $0 --session <name> --uuid <id> [--agent claude|agy]
+Usage: $0 --session <name> --uuid <id> [--agent claude|agy|hermes|cline]
 EOF
 }
 
@@ -40,15 +40,15 @@ done
 HERDR_SESSION_NAME="$(resolve_herdr_session "$SESSION_NAME" "${WORKSPACE:-}")"
 export HERDR_SESSION_NAME
 
-# --agent 미지정 시 이름 suffix 로 fallback (P1-F: 가능하면 --agent 명시)
+# --agent 미지정 시 레지스트리 기록으로 해석 (B-21).
+# ① row['agent'] → ② 세션명 접미사 → ③ pane.cmd 순. 셋 다 실패하면
+# 종전과 동일하게 exit 2 (헤더 :27-30 의 종료 코드 계약 유지).
 if [ -z "$AGENT" ]; then
-  case "$SESSION_NAME" in
-    *-creator-claude|*-planner-claude|*-reviewer-claude) AGENT=claude ;;
-    *-creator-agy|*-planner-agy|*-reviewer-agy)          AGENT=agy ;;
-    *-creator-hermes|*-planner-hermes|*-reviewer-hermes) AGENT=hermes ;;
-    *-creator-cline|*-planner-cline|*-reviewer-cline)   AGENT=cline ;;
-    *) echo "ERROR: cannot infer agent from '$SESSION_NAME'; pass --agent" >&2; exit 2 ;;
-  esac
+  AGENT="$(resolve_agent_type_from_registry "$SESSION_NAME")" || AGENT=""
+  [ -n "$AGENT" ] || {
+    echo "ERROR: cannot infer agent from '$SESSION_NAME'; pass --agent" >&2
+    exit 2
+  }
 fi
 
 if [ -z "$ROLE" ]; then