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-stop/scripts/stop_session.sh

@@ -13,7 +13,9 @@
 # 옵션:
 #   --session <name>        — 대상 세션 (필수)
 #   --agent <type>          — claude | agy | hermes | cline
-#                             (미지정 시 세션명 접미사로 추론; 추론 실패 시 exit 2)
+#                             (권장: 항상 명시. 미지정 시 레지스트리 기록으로
+#                              해석 — agent 필드 → 세션명 접미사 → pane.cmd;
+#                              셋 다 실패하면 exit 2)
 #   --reason <reason>       — 상태 전이 사유 (stop_reason). 기본값 manual_stop
 #   --purge-conversation    — 디스크의 conversation artifact 까지 삭제.
 #                             status=terminated, resumable=false 로 전이하며
@@ -32,7 +34,7 @@ set -euo pipefail
 
 # shellcheck disable=SC1091
 _script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-_lib_sh="$(cd "$_script_dir/../.." 2>/dev/null || pwd)/lib.sh"
+_lib_sh="$(cd "$_script_dir/../.." && pwd)/lib.sh"
 [ -f "$_lib_sh" ] || _lib_sh="${WORKSPACE_ROOT:-$PWD}/.agents/skills/lib.sh"
 source "$_lib_sh"
 
@@ -43,8 +45,9 @@ Usage: $0 --session <name> [--agent claude|agy|hermes|cline] [--reason <reason>]
 
 Arguments:
   --session <name>     — target session name (required)
-  --agent <type>       — claude | agy | hermes | cline
-                         (inferred from the session-name suffix when omitted)
+  --agent <type>       — claude | agy | hermes | cline (recommended: always pass it)
+                         (falls back to the registry record: agent field ->
+                          session-name suffix -> pane.cmd)
   --reason <reason>    — stop_reason field (default: manual_stop)
   --purge-conversation — also delete on-disk conversation artifacts;
                          status becomes terminated and resume is impossible
@@ -97,15 +100,15 @@ fi
 HERDR_SESSION_NAME="$(resolve_herdr_workspace "$SESSION_NAME" "${WORKSPACE:-$WORKSPACE_ROOT}")"
 export HERDR_SESSION_NAME
 
-# --agent 미지정 시 이름 suffix 로 fallback (P1-F)
+# --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
 
 # 세션이 YAML 에 있는지 + 해당 row 의 워크스페이스 cwd 및 delegate_job_id 추출.