diff --git a/.agents/skills/lib.sh b/.agents/skills/lib.sh
index 11fe96c..5f4a816 100644
--- a/.agents/skills/lib.sh
+++ b/.agents/skills/lib.sh
@@ -429,7 +429,7 @@ except Exception:
       split_dir=""
       if [ -n "$sample_pane" ]; then
         layout_raw=$(_real_herdr pane layout --pane "$sample_pane" 2>/dev/null || echo "")
-        read -r split_dir split_target < <(printf '%s' "$layout_raw" | python3 -m lib_py.layout --min-cols "${MAM_MIN_PANE_COLS:-40}" --min-rows "${MAM_MIN_PANE_ROWS:-20}" --sample-pane "$sample_pane" 2>/dev/null || echo "right $sample_pane")
+        read -r split_dir split_target < <(printf '%s' "$layout_raw" | python3 -m lib_py.layout --min-cols "${MAM_MIN_PANE_COLS:-15}" --min-rows "${MAM_MIN_PANE_ROWS:-0}" --sample-pane "$sample_pane" 2>/dev/null || echo "right $sample_pane")
         split_dir="${split_dir:-right}"
         sample_pane="${split_target:-$sample_pane}"
       fi
diff --git a/.agents/skills/lib_py/layout.py b/.agents/skills/lib_py/layout.py
index b73445c..6f4697f 100644
--- a/.agents/skills/lib_py/layout.py
+++ b/.agents/skills/lib_py/layout.py
@@ -70,8 +70,8 @@ def extract_panes(data: Dict[str, Any]) -> List[PaneInfo]:
 
 def compute_2xk_layout(
     data: Dict[str, Any],
-    min_cols: int = 40,
-    min_rows: int = 20,
+    min_cols: int = 15,
+    min_rows: int = 0,
     max_columns: Optional[int] = None,
     default_anchor_id: Optional[str] = None
 ) -> LayoutDecision:
@@ -90,8 +90,8 @@ def compute_2xk_layout(
     if len(panes) == 1:
         p = panes[0]
         # In 2xK grid, 1 pane -> 2 panes: split down to create top and bottom rows
-        # Check height overflow if dimensions known
-        if p.height > 0 and p.height // 2 < min_rows:
+        # Check height overflow only if min_rows > 0 is explicitly configured
+        if min_rows > 0 and p.height > 0 and p.height // 2 < min_rows:
             # If height is too small for 2 rows, try splitting right if width allows
             if p.width > 0 and p.width // 2 >= min_cols:
                 return LayoutDecision(target_pane_id=p.pane_id, direction="right", reason="single_pane_height_constrained")
@@ -153,8 +153,8 @@ def compute_2xk_layout(
 
     if singleton_col is not None:
         target_p = singleton_col[0]
-        # Check height
-        if target_p.height > 0 and target_p.height // 2 < min_rows:
+        # Check height only if min_rows > 0
+        if min_rows > 0 and target_p.height > 0 and target_p.height // 2 < min_rows:
             return LayoutDecision(target_pane_id=target_p.pane_id, direction="overflow", is_overflow=True, reason="singleton_height_overflow")
         return LayoutDecision(target_pane_id=target_p.pane_id, direction="down", reason="fill_singleton_column")
 
@@ -176,7 +176,7 @@ 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 40 default).
+    legitimate 0 survives (MAM_MIN_PANE_COLS=0 means 0, not the 15 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
@@ -198,8 +198,8 @@ def _env_int(*names: str, default: Optional[int] = None) -> Optional[int]:
 
 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", default=40))
-    parser.add_argument("--min-rows", type=int, default=_env_int("MAM_MIN_ROWS", "MAM_MIN_PANE_ROWS", default=20))
+    parser.add_argument("--min-cols", type=int, default=_env_int("MAM_MIN_COLS", "MAM_MIN_PANE_COLS", default=15))
+    parser.add_argument("--min-rows", type=int, default=_env_int("MAM_MIN_ROWS", "MAM_MIN_PANE_ROWS", default=0))
     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")
diff --git a/.mam.env.example b/.mam.env.example
index 40d486d..38338f5 100644
--- a/.mam.env.example
+++ b/.mam.env.example
@@ -128,13 +128,14 @@
 #default: 3
 # SKS_EMPTY_GIVEUP=3
 
-# Minimum columns a pane must retain after a vertical split (2xK layout engine).
-#default: 40
-# MAM_MIN_PANE_COLS=40
+# Minimum columns a pane must retain after a horizontal/column split (2xK layout engine).
+#default: 15
+# MAM_MIN_PANE_COLS=15
 
-# Minimum rows a pane must retain after a horizontal split (2xK layout engine).
-#default: 20
-# MAM_MIN_PANE_ROWS=20
+# Minimum rows a pane must retain after a vertical split (2xK layout engine).
+# Set to 0 to disable vertical row constraints (terminal scrollback handles height).
+#default: 0
+# MAM_MIN_PANE_ROWS=0
 
 # Maximum number of columns a workspace may grow to before the engine reports
 # 'overflow' (which makes lib.sh create a fresh workspace instead of splitting).
diff --git a/tests/test_layout.py b/tests/test_layout.py
index 218fafc..f2818a9 100644
--- a/tests/test_layout.py
+++ b/tests/test_layout.py
@@ -287,7 +287,7 @@ split_dir=""
 # Exact snippet from lib.sh:429-435
 if [ -n "$sample_pane" ]; then
   layout_raw=$(_real_herdr pane layout --pane "$sample_pane" 2>/dev/null || echo "")
-  read -r split_dir split_target < <(printf '%s' "$layout_raw" | python3 -m lib_py.layout --min-cols "${{MAM_MIN_PANE_COLS:-40}}" --min-rows "${{MAM_MIN_PANE_ROWS:-20}}" --sample-pane "$sample_pane" 2>/dev/null || echo "right $sample_pane")
+  read -r split_dir split_target < <(printf '%s' "$layout_raw" | python3 -m lib_py.layout --min-cols "${{MAM_MIN_PANE_COLS:-15}}" --min-rows "${{MAM_MIN_PANE_ROWS:-0}}" --sample-pane "$sample_pane" 2>/dev/null || echo "right $sample_pane")
   split_dir="${{split_dir:-right}}"
   sample_pane="${{split_target:-$sample_pane}}"
 fi
@@ -435,11 +435,11 @@ _ZERO_TRAP = {"result": {"panes": [
 
 
 def test_j1_env_zero_min_cols_matches_flag_zero():
-    """J-1: MAM_MIN_PANE_COLS=0 must mean 0, not fall through to the 40 default."""
-    flag = _run_layout(_ZERO_TRAP, ("--min-cols", "0"))
+    """J-1: MAM_MIN_PANE_COLS=0 must mean 0, not fall through to the 15 default."""
+    flag = _run_layout(_ZERO_TRAP, ("--min-cols", "0", "--min-rows", "20"))
     assert flag["direction"] == "right" and flag["reason"] == "single_pane_height_constrained"
     for var in ("MAM_MIN_COLS", "MAM_MIN_PANE_COLS"):
-        assert _run_layout(_ZERO_TRAP, (), {var: "0"}) == flag, var
+        assert _run_layout(_ZERO_TRAP, ("--min-rows", "20"), {var: "0"}) == flag, var
 
 
 def test_j1_env_zero_min_rows_matches_flag_zero():
@@ -452,8 +452,8 @@ def test_j1_env_zero_min_rows_matches_flag_zero():
 def test_j1_nonzero_and_malformed_env_behaviour_unchanged():
     """Behaviour neutrality: non-zero env still applies, and a lone typo still
     lands on the documented default instead of crashing on a None comparison."""
-    assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_PANE_COLS": "25"}) == \
-           _run_layout(_ZERO_TRAP, ("--min-cols", "25"))
+    assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_PANE_COLS": "25", "MAM_MIN_PANE_ROWS": "20"}) == \
+           _run_layout(_ZERO_TRAP, ("--min-cols", "25", "--min-rows", "20"))
     assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_PANE_COLS": "abc"}) == _run_layout(_ZERO_TRAP)
 
 
@@ -465,32 +465,41 @@ def test_j1b_invalid_alias_does_not_shadow_the_documented_var():
     Empty values already fell through (`if raw:`); this makes invalid values
     behave the same way. When every candidate is unusable, `default` still wins.
     """
-    good = _run_layout(_ZERO_TRAP, (), {"MAM_MIN_PANE_COLS": "25"})
+    good = _run_layout(_ZERO_TRAP, ("--min-rows", "20"), {"MAM_MIN_PANE_COLS": "25"})
     assert good["direction"] == "right"
     # 별칭이 깨져 있어도 문서화된 변수가 적용된다
-    assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_COLS": "foo",
+    assert _run_layout(_ZERO_TRAP, ("--min-rows", "20"), {"MAM_MIN_COLS": "foo",
                                         "MAM_MIN_PANE_COLS": "25"}) == good
     # 0 도 마찬가지 (J-1 과의 상호작용)
-    assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_COLS": "foo",
+    assert _run_layout(_ZERO_TRAP, ("--min-rows", "20"), {"MAM_MIN_COLS": "foo",
                                         "MAM_MIN_PANE_COLS": "0"}) == \
-           _run_layout(_ZERO_TRAP, ("--min-cols", "0"))
+           _run_layout(_ZERO_TRAP, ("--min-cols", "0", "--min-rows", "20"))
     # 모든 후보가 무효면 문서화된 기본값으로 흡수 (Rev.1 불변식 보존)
     assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_COLS": "foo",
                                         "MAM_MIN_PANE_COLS": "bar"}) == _run_layout(_ZERO_TRAP)
 
 
-def test_default_min_cols_is_40():
-    """Verify compute_2xk_layout default min_cols is 40.
-    With width 80 (width//2 = 40):
-    - min_cols=40 -> 40 >= 40 -> split right (new column).
-    - min_cols=60 -> 40 < 60 -> overflow.
-    Default invocation (no min_cols passed) must split right.
+def test_default_min_cols_is_15_and_min_rows_is_0():
+    """Verify compute_2xk_layout default min_cols is 15 and min_rows is 0.
+    With 1 pane of 54x23:
+    - min_rows=0 -> splits down without height overflow
+    With 2 panes of 30x23 (width//2 = 15):
+    - min_cols=15 -> 15 >= 15 -> split right (new column).
+    - min_cols=40 -> 15 < 40 -> overflow.
+    Default invocation (no min_cols/min_rows passed) must split right for 30 cols.
     """
+    # 1. 1 pane of 54x23 splits down (no height constraint)
+    p1_54x23 = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 54, "height": 23}}]}}
+    d1 = compute_2xk_layout(p1_54x23)
+    assert d1.direction == "down"
+    assert not d1.is_overflow
+
+    # 2. 2 panes with width 30 (30 // 2 = 15 == min_cols 15) -> splits right cleanly
     payload = {
         "result": {
             "panes": [
-                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 80, "height": 40}},
-                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 80, "height": 40}},
+                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 30, "height": 20}},
+                {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 30, "height": 20}},
             ]
         }
     }
@@ -500,118 +509,79 @@ def test_default_min_cols_is_40():
     assert decision.reason == "new_column_right"
 
 
-def test_80_col_2_column_splitting_boundary():
-    """Verify width >= 80 cols allows 2-column splitting with default min_cols=40,
-    while width < 80 (e.g. 79) triggers column_width_overflow.
+def test_30_col_2_column_splitting_boundary():
+    """Verify width >= 30 cols allows 2-column splitting with default min_cols=15,
+    while width < 30 (e.g. 29) triggers column_width_overflow.
     """
-    # 80 cols: 80 // 2 = 40 == min_cols(40) -> splits right
-    payload_80 = {
+    # 30 cols: 30 // 2 = 15 == min_cols(15) -> splits right
+    payload_30 = {
         "result": {
             "panes": [
-                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 80, "height": 40}},
-                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 80, "height": 40}},
+                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 30, "height": 20}},
+                {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 30, "height": 20}},
             ]
         }
     }
-    d80 = compute_2xk_layout(payload_80)
-    assert d80.direction == "right"
-    assert not d80.is_overflow
+    d30 = compute_2xk_layout(payload_30)
+    assert d30.direction == "right"
+    assert not d30.is_overflow
 
-    # 79 cols: 79 // 2 = 39 < min_cols(40) -> overflow
-    payload_79 = {
+    # 29 cols: 29 // 2 = 14 < min_cols(15) -> overflow
+    payload_29 = {
         "result": {
             "panes": [
-                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 79, "height": 40}},
-                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 79, "height": 40}},
+                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 29, "height": 20}},
+                {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 29, "height": 20}},
             ]
         }
     }
-    d79 = compute_2xk_layout(payload_79)
-    assert d79.direction == "overflow"
-    assert d79.is_overflow
-    assert d79.reason == "column_width_overflow"
+    d29 = compute_2xk_layout(payload_29)
+    assert d29.direction == "overflow"
+    assert d29.is_overflow
+    assert d29.reason == "column_width_overflow"
 
 
-def test_90_col_single_workspace_multi_pane_tiling():
-    """Verify complete 1 -> 2 -> 3 -> 4 pane tiling in a 90-col single workspace.
-    - 1 pane (90x40): splits down to p1(90x20), p2(90x20)
-    - 2 panes: splits right to start col 2 -> p3(45x40)
-    - 3 panes: fills singleton col 2 down -> p4(45x20)
-    - 4 panes (2x2 grid): 5th agent overflows because 45 // 2 = 22 < 40
+def test_54x23_compact_viewport_single_workspace_multi_pane_tiling():
+    """Verify complete 1 -> 2 -> 3 -> 4 pane tiling in standard 80x24 (54x23 content area) workspace.
+    - 1 pane (54x23): splits down to p1(54x11), p2(54x11)
+    - 2 panes: splits right (54//2 = 27 >= 15) to start col 2 -> p3(27x23)
+    - 3 panes: fills singleton col 2 down -> p4(27x11)
+    - 4 panes (2x2 grid): 5th agent overflows because 27 // 2 = 13 < 15
     """
-    # 1 -> 2
-    p1_layout = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 90, "height": 40}}]}}
+    # 1 -> 2 (splits down)
+    p1_layout = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 54, "height": 23}}]}}
     d1 = compute_2xk_layout(p1_layout)
     assert d1.direction == "down"
     assert d1.target_pane_id == "p1"
+    assert not d1.is_overflow
 
-    # 2 -> 3
+    # 2 -> 3 (splits right)
     p2_layout = {"result": {"panes": [
-        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 90, "height": 20}},
-        {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 90, "height": 20}},
+        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 54, "height": 11}},
+        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 54, "height": 11}},
     ]}}
     d2 = compute_2xk_layout(p2_layout)
     assert d2.direction == "right"
     assert d2.target_pane_id == "p1"
     assert not d2.is_overflow
 
-    # 3 -> 4
+    # 3 -> 4 (fills singleton col 2 down)
     p3_layout = {"result": {"panes": [
-        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 45, "height": 20}},
-        {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 45, "height": 20}},
-        {"pane_id": "p3", "rect": {"x": 45, "y": 0, "width": 45, "height": 40}},
+        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 27, "height": 11}},
+        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 27, "height": 11}},
+        {"pane_id": "p3", "rect": {"x": 53, "y": 1, "width": 27, "height": 23}},
     ]}}
     d3 = compute_2xk_layout(p3_layout)
     assert d3.direction == "down"
     assert d3.target_pane_id == "p3"
     assert not d3.is_overflow
 
-    # 4 -> 5 (overflow to new workspace)
+    # 4 -> 5 (overflow to new workspace because 27 // 2 = 13 < 15)
     p4_layout = {"result": {"panes": [
-        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 45, "height": 20}},
-        {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 45, "height": 20}},
-        {"pane_id": "p3", "rect": {"x": 45, "y": 0, "width": 45, "height": 20}},
-        {"pane_id": "p4", "rect": {"x": 45, "y": 20, "width": 45, "height": 20}},
-    ]}}
-    d4 = compute_2xk_layout(p4_layout)
-    assert d4.direction == "overflow"
-    assert d4.is_overflow
-    assert d4.reason == "column_width_overflow"
-
-
-def test_100_col_single_workspace_multi_pane_tiling():
-    """Verify complete 1 -> 2 -> 3 -> 4 pane tiling in a 100-col single workspace."""
-    # 1 -> 2
-    p1_layout = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 100, "height": 40}}]}}
-    d1 = compute_2xk_layout(p1_layout)
-    assert d1.direction == "down"
-
-    # 2 -> 3
-    p2_layout = {"result": {"panes": [
-        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 100, "height": 20}},
-        {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 100, "height": 20}},
-    ]}}
-    d2 = compute_2xk_layout(p2_layout)
-    assert d2.direction == "right"
-    assert not d2.is_overflow
-
-    # 3 -> 4
-    p3_layout = {"result": {"panes": [
-        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 50, "height": 20}},
-        {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 50, "height": 20}},
-        {"pane_id": "p3", "rect": {"x": 50, "y": 0, "width": 50, "height": 40}},
-    ]}}
-    d3 = compute_2xk_layout(p3_layout)
-    assert d3.direction == "down"
-    assert d3.target_pane_id == "p3"
-    assert not d3.is_overflow
-
-    # 4 -> 5 (overflow to new workspace)
-    p4_layout = {"result": {"panes": [
-        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 50, "height": 20}},
-        {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 50, "height": 20}},
-        {"pane_id": "p3", "rect": {"x": 50, "y": 0, "width": 50, "height": 20}},
-        {"pane_id": "p4", "rect": {"x": 50, "y": 20, "width": 50, "height": 20}},
+        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 27, "height": 11}},
+        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 27, "height": 11}},
+        {"pane_id": "p3", "rect": {"x": 53, "y": 1, "width": 27, "height": 11}},
+        {"pane_id": "p4", "rect": {"x": 53, "y": 12, "width": 27, "height": 11}},
     ]}}
     d4 = compute_2xk_layout(p4_layout)
     assert d4.direction == "overflow"
diff --git a/tests/test_tier1_unit.py b/tests/test_tier1_unit.py
index 8ed5c20..a472104 100644
--- a/tests/test_tier1_unit.py
+++ b/tests/test_tier1_unit.py
@@ -865,88 +865,85 @@ def test_lib_sh_new_session_passes_mam_ws_label(mam_sandbox):
 
 
 # ==============================================================================
-# FEATURE: 2xK Grid Layout Engine (min_cols=40 & multi-pane workspace tiling)
+# FEATURE: 2xK Grid Layout Engine (min_cols=15 & min_rows=0 multi-pane workspace tiling)
 # ==============================================================================
 
-def test_layout_default_min_cols_40_in_tier1():
-    """Verify default min_cols=40 behavior across compute_2xk_layout in Tier 1 suite."""
+def test_layout_default_min_cols_15_in_tier1():
+    """Verify default min_cols=15 behavior across compute_2xk_layout in Tier 1 suite."""
     from lib_py.layout import compute_2xk_layout
 
-    # 1. 2 panes in 80 col width (80 // 2 = 40 == min_cols 40) -> splits right cleanly
-    payload_80 = {
+    # 1. 2 panes in 30 col width (30 // 2 = 15 == min_cols 15) -> splits right cleanly
+    payload_30 = {
         "result": {
             "panes": [
-                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 80, "height": 40}},
-                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 80, "height": 40}}
+                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 30, "height": 20}},
+                {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 30, "height": 20}}
             ]
         }
     }
-    decision = compute_2xk_layout(payload_80)
+    decision = compute_2xk_layout(payload_30)
     assert decision.direction == "right"
     assert not decision.is_overflow
     assert decision.reason == "new_column_right"
 
-    # 2. 2 panes in 79 col width (79 // 2 = 39 < min_cols 40) -> column_width_overflow
-    payload_79 = {
+    # 2. 2 panes in 29 col width (29 // 2 = 14 < min_cols 15) -> column_width_overflow
+    payload_29 = {
         "result": {
             "panes": [
-                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 79, "height": 40}},
-                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 79, "height": 40}}
+                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 29, "height": 20}},
+                {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 29, "height": 20}}
             ]
         }
     }
-    decision_overflow = compute_2xk_layout(payload_79)
+    decision_overflow = compute_2xk_layout(payload_29)
     assert decision_overflow.direction == "overflow"
     assert decision_overflow.is_overflow
     assert decision_overflow.reason == "column_width_overflow"
 
 
-def test_layout_single_workspace_90_100_cols_tiling_tier1():
-    """Verify 3-4 agents tiling in standard 90-100 col terminal windows within a single workspace."""
+def test_layout_single_workspace_54x23_compact_tiling_tier1():
+    """Verify 3-4 agents tiling in standard 80x24 (54x23 content) terminal windows within a single workspace."""
     from lib_py.layout import compute_2xk_layout
 
-    for total_w in [90, 100]:
-        half_w = total_w // 2
+    # Step 1: 1 pane -> 2 panes (split down without height constraint)
+    p1 = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 54, "height": 23}}]}}
+    d1 = compute_2xk_layout(p1)
+    assert d1.direction == "down"
+    assert d1.target_pane_id == "p1"
+    assert not d1.is_overflow
 
-        # Step 1: 1 pane -> 2 panes (split down)
-        p1 = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": total_w, "height": 40}}]}}
-        d1 = compute_2xk_layout(p1)
-        assert d1.direction == "down"
-        assert d1.target_pane_id == "p1"
-        assert not d1.is_overflow
+    # Step 2: 2 panes -> 3 panes (split right to open 2nd column)
+    p2 = {"result": {"panes": [
+        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 54, "height": 11}},
+        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 54, "height": 11}}
+    ]}}
+    d2 = compute_2xk_layout(p2)
+    assert d2.direction == "right"
+    assert d2.target_pane_id == "p1"
+    assert not d2.is_overflow
 
-        # Step 2: 2 panes -> 3 panes (split right to open 2nd column)
-        p2 = {"result": {"panes": [
-            {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": total_w, "height": 20}},
-            {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": total_w, "height": 20}}
-        ]}}
-        d2 = compute_2xk_layout(p2)
-        assert d2.direction == "right"
-        assert d2.target_pane_id == "p1"
-        assert not d2.is_overflow
+    # Step 3: 3 panes -> 4 panes (split singleton 2nd column down)
+    p3 = {"result": {"panes": [
+        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 27, "height": 11}},
+        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 27, "height": 11}},
+        {"pane_id": "p3", "rect": {"x": 53, "y": 1, "width": 27, "height": 23}}
+    ]}}
+    d3 = compute_2xk_layout(p3)
+    assert d3.direction == "down"
+    assert d3.target_pane_id == "p3"
+    assert not d3.is_overflow
 
-        # Step 3: 3 panes -> 4 panes (split singleton 2nd column down)
-        p3 = {"result": {"panes": [
-            {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": half_w, "height": 20}},
-            {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": half_w, "height": 20}},
-            {"pane_id": "p3", "rect": {"x": half_w, "y": 0, "width": half_w, "height": 40}}
-        ]}}
-        d3 = compute_2xk_layout(p3)
-        assert d3.direction == "down"
-        assert d3.target_pane_id == "p3"
-        assert not d3.is_overflow
-
-        # Step 4: 4 panes (2x2 complete) -> 5th agent overflows to fresh workspace
-        p4 = {"result": {"panes": [
-            {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": half_w, "height": 20}},
-            {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": half_w, "height": 20}},
-            {"pane_id": "p3", "rect": {"x": half_w, "y": 0, "width": half_w, "height": 20}},
-            {"pane_id": "p4", "rect": {"x": half_w, "y": 20, "width": half_w, "height": 20}}
-        ]}}
-        d4 = compute_2xk_layout(p4)
-        assert d4.direction == "overflow"
-        assert d4.is_overflow
-        assert d4.reason == "column_width_overflow"
+    # Step 4: 4 panes (2x2 complete) -> 5th agent overflows to fresh workspace (27 // 2 = 13 < 15)
+    p4 = {"result": {"panes": [
+        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 27, "height": 11}},
+        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 27, "height": 11}},
+        {"pane_id": "p3", "rect": {"x": 53, "y": 1, "width": 27, "height": 11}},
+        {"pane_id": "p4", "rect": {"x": 53, "y": 12, "width": 27, "height": 11}}
+    ]}}
+    d4 = compute_2xk_layout(p4)
+    assert d4.direction == "overflow"
+    assert d4.is_overflow
+    assert d4.reason == "column_width_overflow"