## [Claude #5] Stage 6 — Verification Round #5

### Re-read issue
Scope = `build_layout_css` 분기 확장 to **top-1-bottom-2 / top-2-bottom-1 / left-1-right-2 / left-2-right-1 / grid-2x2** beyond the existing horizontal-2 / vertical-2 dynamic paths.
Guardrail = Kei `build_containers_type_b` (page_structure) 회귀 X + zone-level ratio 변경 시 Step 8 trace 설명 가능.

### Before (Round #4) vs After (Round #5)
- `git rev-parse --short HEAD` = **201099e** (unchanged from Rounds #1–#4).
- `git diff HEAD -- src/phase_z2_pipeline.py src/space_allocator.py tests/phase_z2/` → **empty** (no implementation movement since Round #4 closed NOT VERIFIED).
- Dirty/untracked worktree files are all outside the verifier scope (Z2 frame templates, samples, unrelated scripts).

### Full pytest
```
python -m pytest -q tests
89 passed in 6.85s
```
Phase Z2 subset: 47/47 passed (`python -m pytest -q tests/phase_z2`).

### AS-IS (HEAD = 201099e — PR 1 foundation lock)

**Static evidence — dispatch is still rows / cols only** (src/phase_z2_pipeline.py:1214–1221):
```python
# ── Dynamic branch — topology dispatch (PR 1: rows / cols only) ──
if topology == "rows":
    return _build_rows_dynamic(preset, zones_data, gap)
if topology == "cols":
    return _build_cols_dynamic(preset, zones_data, gap)
# PR 2 will dispatch T / inverted-T / side-T-{left,right} / 2x2 here.
# PR 3 will dispatch single here.
return _build_fr_default(preset)
```

Override path (src/phase_z2_pipeline.py:1205–1212) still warn-and-fallthrough for non rows/cols presets (PR 1 lock — PR 2 promotes to strict ValueError).

**Runtime probe** — `build_layout_css(preset, {zN: {content_weight:1.0, min_height_px:100}})`:

| Preset | dynamic_rows | dynamic_cols | computation |
|---|---|---|---|
| `top-1-bottom-2` | False | False | `fr_default_from_preset` |
| `top-2-bottom-1` | False | False | `fr_default_from_preset` |
| `left-1-right-2` | False | False | `fr_default_from_preset` |
| `left-2-right-1` | False | False | `fr_default_from_preset` |
| `grid-2x2` | False | False | `fr_default_from_preset` |
| `single` | False | False | `fr_default_from_preset` |

Return keys on the fallthrough path are length-locked (`['areas', 'cols', 'computation', 'dynamic_cols', 'dynamic_rows', 'heights_px', 'ratios', 'raw_zone_layout', 'rows', 'width_ratios', 'widths_px']`) — PR 1 foundation contract holds, but `computation` is the unmistakable signal that the dynamic solver did **not** run for any of the 5 target presets.

**Test evidence — PR 1 lock-in still in place** (tests/phase_z2/test_build_layout_css_pr1.py:145–154):
```python
"""T-shape (top-1-bottom-2) falls through to fr_default in PR 1 …"""
result = build_layout_css("top-1-bottom-2", zones)
assert result["computation"] == "fr_default_from_preset"
```
Closing B-4 requires updating this assertion when PR 2 lands.

### TO-BE (issue scope target)
All 5 listed presets must be dynamic. Currently **0/5 dynamic**. PR 1 (HEAD) is the foundation lock — col-axis solver, unified per-zone geometry mapper, length-locked `widths_px` / `width_ratios` / `dynamic_cols` on every return path, retry gate (with `retry_skipped_reason`), and `zone_widths_px_planned` / `zone_col_ratios_planned` Step 8 trace fields. PR 2 (T / inverted-T / side-T-{left,right} / 2x2) + PR 3 (single) remain outstanding per the in-code TODO at src/phase_z2_pipeline.py:1219–1220.

### Guardrail check
`build_containers_type_b` / `page_structure` paths untouched by PR 1; static grep confirms no edits to those call sites since 201099e. The trace surface added by PR 1 (`zone_widths_px_planned`, `zone_col_ratios_planned`, `retry_skipped_reason`) is present in src/phase_z2_pipeline.py:3550–3578 and 1621–1631, so the "zone-level ratio 변경 시 step08 trace 설명 가능" guardrail is satisfied *for the foundation*. It will need to be re-exercised once PR 2 turns on T / side-T / 2x2 dynamic paths.

### Gaps vs Close

| Axis | Issue requirement | Current state | Gap |
|---|---|---|---|
| top-1-bottom-2 dynamic | required | fr_default fallthrough | NOT MET |
| top-2-bottom-1 dynamic | required | fr_default fallthrough | NOT MET |
| left-1-right-2 dynamic | required | fr_default fallthrough | NOT MET |
| left-2-right-1 dynamic | required | fr_default fallthrough | NOT MET |
| grid-2x2 dynamic | required | fr_default fallthrough | NOT MET |
| Kei build_containers_type_b 회귀 X | required | untouched | MET |
| Step 8 trace explainability | required | foundation fields present | MET (foundation only) |

### Verdict
**NOT VERIFIED for close.** 5/5 target presets remain on the `fr_default_from_preset` fallthrough; PR 2 (T / inverted-T / side-T-{left,right} / 2x2) has not landed. PR 1 foundation (HEAD = 201099e) holds — col-axis solver, per-zone geometry mapper, retry gate, Step 8 trace fields all intact — but B-4 issue scope explicitly demands the **dispatch promotion** that PR 2 owns. Closing this issue requires shipping PR 2 (and PR 3 for `single`, if it is in scope), then updating tests/phase_z2/test_build_layout_css_pr1.py:145–154 from "falls through to fr_default" to the new dynamic assertions.

=== EVIDENCE ===
Commands run:
- `git rev-parse --short HEAD` → 201099e
- `git status --short` (worktree clean for verifier scope; dirty files all outside src/phase_z2_pipeline.py, src/space_allocator.py, tests/phase_z2/)
- `git diff HEAD -- src/phase_z2_pipeline.py src/space_allocator.py tests/phase_z2/` → empty
- `python -m pytest -q tests` → 89 passed in 6.85s
- `python -m pytest -q tests/phase_z2` → 47 passed in 0.08s
- Read src/phase_z2_pipeline.py:1190–1240 (dispatch + override path)
- Runtime probe `build_layout_css(preset, zones)` for top-1-bottom-2, top-2-bottom-1, left-1-right-2, left-2-right-1, grid-2x2, single — all return `computation=fr_default_from_preset`, `dynamic_rows=False`, `dynamic_cols=False`

Files checked:
- D:\ad-hoc\kei\design_agent\src\phase_z2_pipeline.py (lines 1190–1240 dispatch + 1205–1212 override path + 1219–1220 PR 2/3 TODO + 1621–1631 retry gate + 3550–3578 Step 8 trace)
- D:\ad-hoc\kei\design_agent\tests\phase_z2\test_build_layout_css_pr1.py (PR 1 lock-in assertions, esp. lines 145–154 for top-1-bottom-2)
- D:\ad-hoc\kei\design_agent\tests\phase_z2\test_retry_gate.py

FINAL_CONSENSUS: NO