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/lib_py/layout.py

@@ -172,24 +172,34 @@ def compute_2xk_layout(
     return LayoutDecision(target_pane_id=rightmost_top_pane.pane_id, direction="right", reason="new_column_right")
 
 
-def _env_int(*names: str) -> Optional[int]:
-    """First non-empty env var among *names, parsed as int. Bad values are
-    ignored rather than raised: a typo in an operator's shell must not take the
-    whole layout call down (lib.sh would silently fall back to 'right')."""
+def _env_int(*names: str, default: Optional[int] = None) -> Optional[int]:
+    """First *valid* int among the env vars in *names*, else `default`.
+
+    `default` is an explicit parameter rather than an `or` at the call site so a
+    legitimate 0 survives (MAM_MIN_PANE_COLS=0 means 0, not the 60 default).
+
+    An unparsable value is skipped rather than raised or treated as terminal: a
+    typo in an operator's shell must not take the whole layout call down (lib.sh
+    would silently fall back to 'right'), and must not shadow a later candidate
+    that IS set correctly -- MAM_MIN_COLS is a legacy alias while
+    MAM_MIN_PANE_COLS is the name .mam.env.example documents, so aborting on the
+    first bad value would discard the documented setting. Empty values already
+    fell through; this makes invalid values behave the same way.
+    """
     for n in names:
         raw = os.environ.get(n, "").strip()
         if raw:
             try:
                 return int(raw)
             except ValueError:
-                return None
-    return None
+                continue
+    return default
 
 
 def main():
     parser = argparse.ArgumentParser(description="Compute 2xK grid TUI layout split direction")
-    parser.add_argument("--min-cols", type=int, default=_env_int("MAM_MIN_COLS", "MAM_MIN_PANE_COLS") or 60)
-    parser.add_argument("--min-rows", type=int, default=_env_int("MAM_MIN_ROWS", "MAM_MIN_PANE_ROWS") or 20)
+    parser.add_argument("--min-cols", type=int, default=_env_int("MAM_MIN_COLS", "MAM_MIN_PANE_COLS", default=60))
+    parser.add_argument("--min-rows", type=int, default=_env_int("MAM_MIN_ROWS", "MAM_MIN_PANE_ROWS", default=20))
     parser.add_argument("--max-cols", type=int, default=_env_int("MAM_MAX_COLS", "MAM_MAX_PANE_COLS"))
     parser.add_argument("--sample-pane", type=str, default=None)
     parser.add_argument("--json", action="store_true", help="Output full JSON decision")