feat(IMP-09): PR 2 — 2-D dynamic dispatch for 5 preset families

Stage 3 lock implementation: extend build_layout_css dispatch beyond
the horizontal-2 / vertical-2 1-D dynamic paths. T / inverted-T /
side-T-left / side-T-right / 2x2 now flow through a 2-D track solver
instead of the fr_default sink, with length-locked heights_px (R) +
widths_px (C) on every return path (default and override).

PR 2 scope (u1~u5):
  - u1: _aggregate_zone_signals_per_track — per-row + per-col virtual
    zones via max(weight) + max(min_height_px) of single-span zones,
    falling back to all-span when a track has none.
  - u2: _build_grid_dynamic_2d default builder — feeds virtual zones
    into compute_zone_layout + compute_zone_layout_cols; emits
    computation="2d_dynamic_aggregated", dynamic_rows=True,
    dynamic_cols=True.
  - u3: _override_to_grid_tracks override builder — single-span
    aggregation (max h per row, max w per col), normalize, multiply
    by avail_h/avail_w, last-element diff absorb; emits
    computation="user_override_geometry"; falls back to u2 when
    total_h or total_w == 0.
  - u4: build_layout_css dispatcher wiring — topology in
    {T, inverted-T, side-T-left, side-T-right, 2x2} routes to
    _build_grid_dynamic_2d (default) or _override_to_grid_tracks
    (override); legacy [override-warning] stderr removed for the
    5 presets; step08 trace gains a 2-D-aware print line that fires
    before the dynamic_rows / dynamic_cols branches.
  - u5: PR 1 lock test test_top_1_bottom_2_fr_default_populates_geometry
    renamed to test_top_1_bottom_2_dynamic_2d_populates_geometry and
    flipped to PR 2 reality (computation="2d_dynamic_aggregated",
    dynamic_rows=True, dynamic_cols=True).

Fixtures: 10 build_layout_css (5 presets × {default, override}) +
5 retry_gate *_dynamic_2d.yaml locking the retry gate skip reason
"dynamic_cols (2-D topology) ... IMP-09 lock" for the 5 presets.

Tests: python -m pytest -q tests = 104 passed (Stage 2 baseline
10 RED → GREEN, 0 regressions). Kei archive
(build_containers_type_b / page_structure) untouched —
rg "build_containers_type_b|page_structure" src/phase_z2_pipeline.py
returns 0 hits.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/phase_z2/fixtures/build_layout_css/grid-2x2_default.yaml

@@ -0,0 +1,43 @@
+input:
+  layout_preset: grid-2x2
+  zones_data:
+  - position: top-left
+    template_id: MOCK_top-left
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: top-right
+    template_id: MOCK_top-right
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: bottom-left
+    template_id: MOCK_bottom-left
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: bottom-right
+    template_id: MOCK_bottom-right
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  override_zone_geometries: null
+expected_layout_css:
+  areas: '"top-left top-right" "bottom-left bottom-right"'
+  cols: 583px 583px
+  rows: 286px 285px
+  heights_px:
+  - 286
+  - 285
+  widths_px:
+  - 583
+  - 583
+  ratios:
+  - 0.489
+  - 0.487
+  width_ratios:
+  - 0.494
+  - 0.494
+  computation: 2d_dynamic_aggregated
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/grid-2x2_override.yaml

@@ -0,0 +1,63 @@
+input:
+  layout_preset: grid-2x2
+  zones_data:
+  - position: top-left
+    template_id: MOCK_top-left
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: top-right
+    template_id: MOCK_top-right
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: bottom-left
+    template_id: MOCK_bottom-left
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: bottom-right
+    template_id: MOCK_bottom-right
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  override_zone_geometries:
+    top-left:
+      x: 0
+      y: 0
+      w: 0.55
+      h: 0.4
+    top-right:
+      x: 0.55
+      y: 0
+      w: 0.45
+      h: 0.4
+    bottom-left:
+      x: 0
+      y: 0.4
+      w: 0.55
+      h: 0.6
+    bottom-right:
+      x: 0.55
+      y: 0.4
+      w: 0.45
+      h: 0.6
+expected_layout_css:
+  areas: '"top-left top-right" "bottom-left bottom-right"'
+  cols: 641px 525px
+  rows: 228px 343px
+  heights_px:
+  - 228
+  - 343
+  widths_px:
+  - 641
+  - 525
+  ratios:
+  - 0.4
+  - 0.6
+  width_ratios:
+  - 0.55
+  - 0.45
+  computation: user_override_geometry
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/left-1-right-2_default.yaml

@@ -0,0 +1,38 @@
+input:
+  layout_preset: left-1-right-2
+  zones_data:
+  - position: left
+    template_id: MOCK_left
+    content_weight:
+      score: 0.5
+    min_height_px: 200
+  - position: right-top
+    template_id: MOCK_right-top
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: right-bottom
+    template_id: MOCK_right-bottom
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  override_zone_geometries: null
+expected_layout_css:
+  areas: '"left right-top" "left right-bottom"'
+  cols: 777px 389px
+  rows: 286px 285px
+  heights_px:
+  - 286
+  - 285
+  widths_px:
+  - 777
+  - 389
+  ratios:
+  - 0.489
+  - 0.487
+  width_ratios:
+  - 0.658
+  - 0.33
+  computation: 2d_dynamic_aggregated
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/left-1-right-2_override.yaml

@@ -0,0 +1,53 @@
+input:
+  layout_preset: left-1-right-2
+  zones_data:
+  - position: left
+    template_id: MOCK_left
+    content_weight:
+      score: 0.5
+    min_height_px: 200
+  - position: right-top
+    template_id: MOCK_right-top
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: right-bottom
+    template_id: MOCK_right-bottom
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  override_zone_geometries:
+    left:
+      x: 0
+      y: 0
+      w: 0.4
+      h: 1.0
+    right-top:
+      x: 0.4
+      y: 0
+      w: 0.6
+      h: 0.5
+    right-bottom:
+      x: 0.4
+      y: 0.5
+      w: 0.6
+      h: 0.5
+expected_layout_css:
+  areas: '"left right-top" "left right-bottom"'
+  cols: 466px 700px
+  rows: 286px 285px
+  heights_px:
+  - 286
+  - 285
+  widths_px:
+  - 466
+  - 700
+  ratios:
+  - 0.5
+  - 0.5
+  width_ratios:
+  - 0.4
+  - 0.6
+  computation: user_override_geometry
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/left-2-right-1_default.yaml

@@ -0,0 +1,38 @@
+input:
+  layout_preset: left-2-right-1
+  zones_data:
+  - position: left-top
+    template_id: MOCK_left-top
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: left-bottom
+    template_id: MOCK_left-bottom
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: right
+    template_id: MOCK_right
+    content_weight:
+      score: 0.5
+    min_height_px: 200
+  override_zone_geometries: null
+expected_layout_css:
+  areas: '"left-top right" "left-bottom right"'
+  cols: 389px 777px
+  rows: 286px 285px
+  heights_px:
+  - 286
+  - 285
+  widths_px:
+  - 389
+  - 777
+  ratios:
+  - 0.489
+  - 0.487
+  width_ratios:
+  - 0.33
+  - 0.658
+  computation: 2d_dynamic_aggregated
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/left-2-right-1_override.yaml

@@ -0,0 +1,53 @@
+input:
+  layout_preset: left-2-right-1
+  zones_data:
+  - position: left-top
+    template_id: MOCK_left-top
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: left-bottom
+    template_id: MOCK_left-bottom
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: right
+    template_id: MOCK_right
+    content_weight:
+      score: 0.5
+    min_height_px: 200
+  override_zone_geometries:
+    left-top:
+      x: 0
+      y: 0
+      w: 0.35
+      h: 0.6
+    left-bottom:
+      x: 0
+      y: 0.6
+      w: 0.35
+      h: 0.4
+    right:
+      x: 0.35
+      y: 0
+      w: 0.65
+      h: 1.0
+expected_layout_css:
+  areas: '"left-top right" "left-bottom right"'
+  cols: 408px 758px
+  rows: 343px 228px
+  heights_px:
+  - 343
+  - 228
+  widths_px:
+  - 408
+  - 758
+  ratios:
+  - 0.6
+  - 0.4
+  width_ratios:
+  - 0.35
+  - 0.65
+  computation: user_override_geometry
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/top-1-bottom-2_default.yaml

@@ -0,0 +1,38 @@
+input:
+  layout_preset: top-1-bottom-2
+  zones_data:
+  - position: top
+    template_id: MOCK_top
+    content_weight:
+      score: 0.5
+    min_height_px: 200
+  - position: bottom-left
+    template_id: MOCK_bottom-left
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: bottom-right
+    template_id: MOCK_bottom-right
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  override_zone_geometries: null
+expected_layout_css:
+  areas: '"top top" "bottom-left bottom-right"'
+  cols: 583px 583px
+  rows: 314px 257px
+  heights_px:
+  - 314
+  - 257
+  widths_px:
+  - 583
+  - 583
+  ratios:
+  - 0.537
+  - 0.439
+  width_ratios:
+  - 0.494
+  - 0.494
+  computation: 2d_dynamic_aggregated
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/top-1-bottom-2_override.yaml

@@ -0,0 +1,53 @@
+input:
+  layout_preset: top-1-bottom-2
+  zones_data:
+  - position: top
+    template_id: MOCK_top
+    content_weight:
+      score: 0.5
+    min_height_px: 200
+  - position: bottom-left
+    template_id: MOCK_bottom-left
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: bottom-right
+    template_id: MOCK_bottom-right
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  override_zone_geometries:
+    top:
+      x: 0
+      y: 0
+      w: 1.0
+      h: 0.3
+    bottom-left:
+      x: 0
+      y: 0.3
+      w: 0.5
+      h: 0.7
+    bottom-right:
+      x: 0.5
+      y: 0.3
+      w: 0.5
+      h: 0.7
+expected_layout_css:
+  areas: '"top top" "bottom-left bottom-right"'
+  cols: 583px 583px
+  rows: 171px 400px
+  heights_px:
+  - 171
+  - 400
+  widths_px:
+  - 583
+  - 583
+  ratios:
+  - 0.3
+  - 0.7
+  width_ratios:
+  - 0.5
+  - 0.5
+  computation: user_override_geometry
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/top-2-bottom-1_default.yaml

@@ -0,0 +1,38 @@
+input:
+  layout_preset: top-2-bottom-1
+  zones_data:
+  - position: top-left
+    template_id: MOCK_top-left
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: top-right
+    template_id: MOCK_top-right
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: bottom
+    template_id: MOCK_bottom
+    content_weight:
+      score: 0.5
+    min_height_px: 200
+  override_zone_geometries: null
+expected_layout_css:
+  areas: '"top-left top-right" "bottom bottom"'
+  cols: 583px 583px
+  rows: 257px 314px
+  heights_px:
+  - 257
+  - 314
+  widths_px:
+  - 583
+  - 583
+  ratios:
+  - 0.439
+  - 0.537
+  width_ratios:
+  - 0.494
+  - 0.494
+  computation: 2d_dynamic_aggregated
+  dynamic_rows: true
+  dynamic_cols: true

tests/phase_z2/fixtures/build_layout_css/top-2-bottom-1_override.yaml

@@ -0,0 +1,53 @@
+input:
+  layout_preset: top-2-bottom-1
+  zones_data:
+  - position: top-left
+    template_id: MOCK_top-left
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: top-right
+    template_id: MOCK_top-right
+    content_weight:
+      score: 0.25
+    min_height_px: 200
+  - position: bottom
+    template_id: MOCK_bottom
+    content_weight:
+      score: 0.5
+    min_height_px: 200
+  override_zone_geometries:
+    top-left:
+      x: 0
+      y: 0
+      w: 0.6
+      h: 0.4
+    top-right:
+      x: 0.6
+      y: 0
+      w: 0.4
+      h: 0.4
+    bottom:
+      x: 0
+      y: 0.4
+      w: 1.0
+      h: 0.6
+expected_layout_css:
+  areas: '"top-left top-right" "bottom bottom"'
+  cols: 700px 466px
+  rows: 228px 343px
+  heights_px:
+  - 228
+  - 343
+  widths_px:
+  - 700
+  - 466
+  ratios:
+  - 0.4
+  - 0.6
+  width_ratios:
+  - 0.6
+  - 0.4
+  computation: user_override_geometry
+  dynamic_rows: true
+  dynamic_cols: true