diff --git a/CMakeLists.txt b/CMakeLists.txt
index 010bb7db..76238089 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -141,7 +141,8 @@ if(WIN32)
   if(TERMFORGE_BUILD_SOURCE_CONPTY_EXPERIMENT)
     add_executable(conpty_source_margin_probe experiments/conpty/margin_probe.cpp)
     add_executable(conpty_source_backend_probe experiments/conpty/backend_probe.cpp)
-    foreach(target conpty_source_margin_probe conpty_source_backend_probe)
+    add_executable(conpty_source_margin_controls experiments/conpty/margin_controls_probe.cpp)
+    foreach(target conpty_source_margin_probe conpty_source_backend_probe conpty_source_margin_controls)
       termforge_warnings(${target})
       target_compile_definitions(${target} PRIVATE NOMINMAX WIN32_LEAN_AND_MEAN _WIN32_WINNT=0x0A00
         TERMFORGE_CONPTY_SOURCE_EXPERIMENT=1)
@@ -370,6 +371,7 @@ if(BUILD_TESTING)
   termforge_add_python_test(measure -m unittest experiments.measure.test_measure experiments.measure.test_r54_contract.CostPlanTests -v)
   termforge_add_python_test(binary_paths -m unittest experiments.test_build_paths -v)
   termforge_add_python_test(conpty_margin_contract -m unittest experiments.conpty.test_margin_contract -v)
+  termforge_add_python_test(conpty_margin_controls -m unittest experiments.conpty.test_margin_controls -v)
   termforge_add_python_test(benchmark_tools -m unittest discover -s benchmarks/tests -v)
   termforge_add_python_test(differential -m unittest discover -s experiments/differential -p test_*.py -v)
   termforge_add_python_test(ime_inventory -m unittest research.ime.test_hosted_inventory research.ime.test_prepare_hosted research.ime.test_product_ime -v)
diff --git a/docs/EVIDENCE.md b/docs/EVIDENCE.md
index 11c12d3f..657ef767 100644
--- a/docs/EVIDENCE.md
+++ b/docs/EVIDENCE.md
@@ -52,6 +52,7 @@ R1 固定总出口的源码为 `ce9b24d`，早期 `2dc8d6d` / `9b16acc` 仍分
 | 纯 AST 夹具的生命周期记录 | [#40](https://github.com/JavaZeroo/termforge/issues/40)、[计时、进度与回收验证](../research/ime/results/2026-10-26-inventory-lifecycle/validation.json)、[专用 CI 40253727745](https://github.com/JavaZeroo/termforge/actions/runs/40253727745) | 旧 10 秒 AST 夹具及专用 CI 记录启动、AST 和 Job0；原超时根因未确定。诊断增强见 #40 阶段保留，不由一次 CI 成功结项。 |
 | 原生 margin 逐字段合同与历史修复候选（#56 仍开放） | [合同、源码与路径](research/conpty-native-margin-path.md)、[独立 oracle](../experiments/conpty/margin_contract.py)、[2026-10-26固定运行](../experiments/conpty/results/2026-10-26-native-margin-path/validation.json) | 当时系统与官方原生 final 仍红，官方80列两次原5秒生命周期失败保留；补丁当时仅可应用。后续真实同源构建/运行另列，不改写旧失败。 |
 | 固定源码 ConPTY margin 运行对照（#56 限定实验） | [构建身份、运行与复验](research/conpty-source-margin-runtime.md)、[白名单验证](../experiments/conpty/results/2026-10-27-source-margin-runtime/validation.json) | 同源baseline与patched，原175B两尺寸native red→green；四阶段文本/格属性/光标、末端文本和VT-off反例独立检查，共8次自然退出/EOF/Job0。15个API/身份场景及8个清单拒绝通过；显式样式、历史、resize、完整产品未验，未选择后端。 |
+| 源码 ConPTY 主屏与重复切屏对照（#56 限定实验） | [输入、预期与结果](research/conpty-source-margin-controls.md)、[白名单验证](../experiments/conpty/results/2026-10-27-source-margin-controls/validation.json) | 三场景×两尺寸×同源两版共12次；主屏均正确，默认备用屏/重复h/l为具体旧错误→原生全部正确，两版末端最终文字均正确；全部自然退出/EOF/Job0。独立输入不替代原175B，样式/历史/resize及产品未验。 |
 | ConPTY 系统/固定官方后端的同源 margin A/B（#41、#47 未关闭） | [合同与第一方来源](research/conpty-margin-backends.md)、[固定 175B 与 16 case 结果](../experiments/conpty/results/2026-10-26-margin-backends/validation.json) | 相同 175B、两网格/两 mode/两 fresh：系统末端 margin 错，固定官方后端的末端正确；CHAR_INFO 仍错。禁用 VT 由窄屏反例拒绝；仅诊断可行性，不证明 PR #50 或 main 联合整合通过。 |
 | 实验输入 worker 持块与停止（#62） | [sender fence 合同](research/sender-fence.md)、[固定源码与实际字段](../experiments/shell/results/2026-10-26-sender-fence/validation.json) | `519a3f3` 的系统/官方各两进程、每次 stop/cancel/竞争，共 12 条实际 worker 记录，均 join/Job0；另有各一次原 focus 单测和各 2/2 纯 CTest。明确修正旧 never-read/output-first 不能保证 16KiB 的夹具假设，同 EXE 旧顺序仍红。实现仅在 PR #50 实验整合，main 未包含；probe 未链接候选 VT，纯 EOF 为模拟，#53 UI/3MB/768B/八会话及完整官方矩阵未验收。 |
 | 实验 UI 未完成粘贴（#53） | [机制与边界](research/ui-paste-fence.md)、[旧固定记录](../experiments/shell/results/2026-10-26-ui-paste-fence/validation.json)、[组合修复](research/resize-replay-cost.md)、[最终同源码记录](../experiments/shell/results/2026-10-26-replay-cost-and-close/validation.json) | `eae4b6a` 单窗口两轮、真实EOF/无GO负例及两轮原八会话data-only通过；行键复用及关闭期间不回复分别有诊断/因果回归，原completed/stage45/退出错误保留。完整CTest54/56仍有Vim59、resize43、main7/ui52与shell180秒期限；未计真实CF/IME、完整后端或性能通过。 |
diff --git a/docs/FEATURES.md b/docs/FEATURES.md
index b6bc7f8a..2e3401b0 100644
--- a/docs/FEATURES.md
+++ b/docs/FEATURES.md
@@ -16,7 +16,7 @@
 | 显式候选 main：`termforge.4` + 系统 ConPTY | `TERMFORGE_BUILD_CANDIDATE_ADAPTER=ON`；按 [ADR-0003](adr/0003-core-reference-and-reuse.md)保留为可评估实验，正式核心选型待用户确认 | [固定来源](../experiments/candidates/alacritty/PROVENANCE.md)、[适配边界](../experiments/core/CANDIDATE.md)与 [#39 字素合同](research/streaming-graphemes.md)；候选正确性通过不关闭系统 ConPTY 或 R2 父项 |
 | 实验分支：`termforge.5` + 固定官方 ConPTY | [PR #50（Draft）](https://github.com/JavaZeroo/termforge/pull/50)，`.4` 联合源码 `3e5b96d` 的[真实基线](research/joint-conpty-baseline.md)保留，尚未合并 main 或通过产品整体验收 | [#51 原生 viewport 修复](research/native-viewport-resize.md)的原 resize/Unicode 及原生样本、[#88 回显完成判据](research/workspace-restore-transport-oracle.md)的原保存/恢复/钳制分别通过；[#87 完整记录检查点](research/workflow-record-checkpoint.md)有受控旧红/新绿及最终同源码两轮原八会话 data-only。最新官方完整回归 56/57、8 项内部 skip，[Vim #52](https://github.com/JavaZeroo/termforge/issues/52)仍红，[MSYS输入边界](research/vim-msys-input-boundary.md)已定位捕获样本的Ctrl-O丢失位置，后续[隔离运行库补丁](research/vim-msys-runtime-prototype.md)在重建基点red后原方法四轮通过；正式固定运行库验收未完成，[#63 工作区残尾](research/workspace-native-viewport.md)已由同EXE单变量与运输回放确认现有viewport修复覆盖，原UI/主区三轮重复两批及完整shell通过；更早缺运输样本保留未知。[#53 UI fence](research/ui-paste-fence.md)与[行键复用/关闭回复](research/resize-replay-cost.md)、[#62 worker 夹具](research/sender-fence.md)各自限定通过。终端 margin 与原生状态分列，#47 及完整后端仍开放；旧失败和历史运输缺口保留 |
 
-另有默认关闭的[源码 ConPTY margin 探针实验](research/conpty-source-margin-runtime.md)：固定同源 baseline/patched 对照在原175B两尺寸取得原生四阶段 red→green，VT-off反例保持一致。它只构建独立探针，尚未成为产品后端；样式、历史、resize及完整合同仍由 #56/#41 跟踪。
+另有默认关闭的[源码 ConPTY margin 探针实验](research/conpty-source-margin-runtime.md)：固定同源 baseline/patched 对照在原175B两尺寸取得原生四阶段 red→green，VT-off反例保持一致。后续[主屏与重复切屏对照](research/conpty-source-margin-controls.md)以独立输入完成12次原生/末端验证，补充默认备用屏区域和重复h/l的限定证据。它只构建独立探针，尚未成为产品后端；样式、历史、resize及完整合同仍由 #56/#41 跟踪。
 
 以下能力默认指已合并实现；某个配置的通过结果不能转用于另一个配置。R1 的真实系统 CF/拼音验收属于固定自研核心配置，不外推到候选 `.4` 或实验后端联合配置。
 
diff --git a/docs/research/conpty-source-margin-controls.md b/docs/research/conpty-source-margin-controls.md
new file mode 100644
index 00000000..7805f167
--- /dev/null
+++ b/docs/research/conpty-source-margin-controls.md
@@ -0,0 +1,44 @@
+# 源码 ConPTY：主屏与重复切屏的原生对照
+
+同源 margin 补丁在三个补充场景中符合预先固定的结果：主屏单独滚动保持正确；新建或再次进入备用屏使用默认全屏滚动区域；返回主屏和重复离开备用屏后恢复原来的 `2;3r`。未修补版在后两个场景出现具体预期错误，修补版通过全部原生阶段。实际运输的最终主屏在两版中均正确，不能用末端正确掩盖原生错误。
+
+这是 [#56](https://github.com/JavaZeroo/termforge/issues/56) 的独立补充实验。预期依据是既有 R2 每缓冲区 margin 合同和固定上游状态路径，运行前已记录在 issue；WindTerm 2.7.0 对这些场景的实际行为仍未知。本结果不验收 WindTerm 等价、不选择产品后端，也不关闭 #56/#41。
+
+## 固定输入与观测边界
+
+沿用[原 175B 对照](conpty-source-margin-runtime.md)的同源 baseline/patched：Terminal `dc8ae365847d41f62d1ebca93815bb00959bc12f`、构建 run `40449292015` 和已审核的双文件 SHA、variant/summary/patch receipt。本次未修改上游补丁或重新构建上游。
+
+三个场景各在 `80×24`、`12×7` 下运行 baseline/patched 一次，共 12 次，只开 VT；无自动重试。输入由独立 controls 探针发送，原 175B、四阶段 probe/oracle 和既有期限不变。新场景使用 `CTRL_DONE`，字节数与原负载分列。
+
+| 场景 | 80×24 / 12×7 字节数 | 运行前固定的原生预期 | 未修补版实际结果 | 修补版实际结果 |
+|---|---:|---|---|---|
+| `main-only` | 99 / 99 | 无备用屏；主屏 `2;3r` 滚动，区域外不变 | before/final 均正确 | before/final 均正确 |
+| `default-alt` | 150 / 149 | 主屏区域不传给新备用屏；物理底部换行应全屏滚动；返回后仍为主屏区域 | alt 未全屏滚动：保留 `ALT_TOP`，`ALT_LAST` 被覆盖；其余阶段正确 | before/alt/restored/final 全部正确 |
+| `repeat-alt` | 221 / 220 | alt1 的 `4;5r` 不传给再次创建的 alt2；两次离开后主屏仍为 `2;3r` | alt2 同样未全屏滚动；final 出现 `REGION_CIXED`；其余阶段正确 | before/alt1/alt2/restored/final 全部正确 |
+
+每个阶段分别检查 `ReadConsoleOutputCharacterW` 文本、完整 `CHAR_INFO` 字符/属性、光标及 viewport top。预期为字面值，不使用候选 parser 生成；baseline 必须符合上述具体旧状态，异常、生命周期失败或其他文字错误均不计为有效反例。没有设置 SGR，属性检查只证明初始属性保持。
+
+12 次都自然退出 37、读端 EOF 109，creation flags=0，内层子进程清零，外层 Job 为 active0/total4/terminated0，无强制取消。每次仍为 5 秒 child wait、15 秒外期限、共享 5 秒 cleanup；离线候选回放另由既有 trace 入口管理。两版实际运输的最终文字和 alternate=false 均符合预期；没有观测末端逐阶段光标、属性或实际呈现。
+
+## 源码、构建与验证身份
+
+- 本地实际运行源码 `edec26bb3c4d04858a667a96debf69c139476172`，工作树干净；参与文件 SHA、探针、trace、输入、运输、每阶段捕获及监督记录 SHA 见[脱敏清单](../../experiments/conpty/results/2026-10-27-source-margin-controls/validation.json)。
+- Windows 11 x64 build 26200；VS17 / MSVC 19.42.34433 / SDK 26100，Release x64。controls 探针 SHA `a71c94795806a40062ace7788ee69cfbac0cd8a274765dce6b28aa6d7f33c7ee`；`.5` trace SHA `5941d4569d0ae146eb005f12ecfb15014bc06c18ee48d1c9460824ab65df93d3`。
+- 新旧 margin 判据与 GO/回收回归 17/17，通过耗时 0.375 秒；原 loader/API/清理回归 14/14、零跳过，1.020 秒。后者复用前一批相同源码的原探针 EXE，运行本次修改后的 Python supervisor；不冒充重新编译原探针。两个实际 stdout 日志均保存在本地并记录 SHA，时长仅为测试诊断。
+- `TERMFORGE_BUILD_SOURCE_CONPTY_EXPERIMENT` 仍默认 OFF；新增 `conpty_source_margin_controls` 独立目标。仅 supervisor 增加可选参数和期限，既有 API 调用默认仍为 20 秒。纯 controls 判据纳入 Windows/Linux CTest，不依赖 native DLL；原生矩阵需显式运行。
+
+私有原件位于 `local/r56-margin-controls/matrix-1`；公开清单仅含合成场景结果、必要身份和文件哈希，不包含绝对路径、原生二进制、原始运输或用户状态。
+
+## 复验与剩余范围
+
+先按[源码构建说明](../../experiments/conpty/upstream/README.md)取得并审核固定 run 的 baseline/patched。使用全新的输出目录：
+
+```powershell
+cmake -S . -B local/source-controls-build -A x64 -DTERMFORGE_BUILD_SOURCE_CONPTY_EXPERIMENT=ON -DTERMFORGE_BUILD_CANDIDATE_ADAPTER=OFF -DTERMFORGE_CONPTY_BACKEND_DIR= -DBUILD_TESTING=OFF
+cmake --build local/source-controls-build --config Release --target conpty_source_margin_controls --parallel 2
+cargo +1.92.0 build --manifest-path experiments/candidates/alacritty/Cargo.toml --locked --release --bin termforge-alacritty-trace
+python -m experiments.conpty.source_margin_controls --baseline local/source-baseline --patched local/source-patched --probe local/source-controls-build/bin/Release/conpty_source_margin_controls.exe --candidate-trace experiments/candidates/alacritty/target/release/termforge-alacritty-trace.exe --output local/source-controls-new
+python -m unittest experiments.conpty.test_margin_controls -v
+```
+
+本次只补无备用屏、默认备用屏区域、重复 h/l 的真实交叉。显式样式、非零光标保存恢复、历史隔离/压力、resize、查询/API 写入、完整产品工作流、性能及维护升级仍未验证；原 175B 的 VT-off 证据属于前一批，不能合并成同批更大矩阵。原系统/官方失败、#52、#97 和 #99 的独立失败继续保留。正式方案仍由 #34 提交证据及取舍，经用户确认后生效。
diff --git a/docs/research/conpty-source-margin-runtime.md b/docs/research/conpty-source-margin-runtime.md
index 9b6e7f95..fcd05c64 100644
--- a/docs/research/conpty-source-margin-runtime.md
+++ b/docs/research/conpty-source-margin-runtime.md
@@ -24,7 +24,7 @@
 
 ## 隔离入口与身份拒绝
 
-`TERMFORGE_BUILD_SOURCE_CONPTY_EXPERIMENT` 默认 OFF，仅建立 `conpty_source_margin_probe` 与 `conpty_source_backend_probe`，不能与产品 `TERMFORGE_CONPTY_BACKEND_DIR` 同时启用。只有这两个目标编译新的 source factory；默认及官方 factory 仍严格接受各自原身份。产品 bundle、默认后端和 PR #50 的固定官方配置均未切换。
+`TERMFORGE_BUILD_SOURCE_CONPTY_EXPERIMENT` 默认 OFF，本次使用 `conpty_source_margin_probe` 与 `conpty_source_backend_probe`；后续[补充对照](conpty-source-margin-controls.md)另增加 `conpty_source_margin_controls`。只有这三个独立目标编译 source factory，不能与产品 `TERMFORGE_CONPTY_BACKEND_DIR` 同时启用；默认及官方 factory 仍严格接受各自原身份。产品 bundle、默认后端和 PR #50 的固定官方配置均未切换。
 
 source factory 只允许表中两个 SHA 对，分别报告 `source-dc8-r56-baseline-run40449292015` / `source-dc8-r56-patched-run40449292015`。Python 入口另核对原始 summary、patch、精确 variant 字段与类型、文件大小和 SHA；布尔值不能以 0/1 代替。DLL 与 EXE 在加载期间保持只读共享句柄；create/resize/close 使用同一模块，模块存活至会话和子进程回收之后。
 
@@ -63,6 +63,6 @@ python -m experiments.conpty.source_margin_run --baseline local/source-baseline
 python -m experiments.conpty.source_backend_check --baseline local/source-baseline --patched local/source-patched --official local/official-conpty-1.25 --probe-directory local/source-margin-build/bin/Release --output local/source-backend-new
 ```
 
-待补无备用屏、重复 h/l、默认 margin、非零光标和显式样式、历史隔离、resize、查询及 API 写入的真实交叉；上游 focused 测试虽覆盖重复 h/l，不能代替这些原生运行。之后仍需实际产品联合源码、支持平台、资源与维护/升级验证，并由 #34 提出正式方案供用户确认。
+无备用屏、重复 h/l、默认 margin 的后续 12 次[原生补充对照](conpty-source-margin-controls.md)已单独记录，不更改或扩充本批 175B 结果。非零光标和显式样式、历史隔离、resize、查询及 API 写入仍待真实交叉；之后还需实际产品联合源码、支持平台、资源与维护/升级验证，并由 #34 提出正式方案供用户确认。
 
 独立的 [#97 candidate-scroll 退出超时](https://github.com/JavaZeroo/termforge/issues/97)发生于 parent `5c073e4` 的 candidate/system push CI：正确末帧已经产生，但原 20 秒期限未自然结束。它不是本 175B 输入，同 HEAD 的其他 CI 成功不能覆盖该失败；此处的源构建修补也不构成其因果修复。原官方 80 列 5 秒失败、Vim #52、完整 R2、WindTerm 行为等价、性能与实际呈现均没有由本实验验收。
diff --git a/experiments/conpty/margin_controls.py b/experiments/conpty/margin_controls.py
new file mode 100644
index 00000000..bcd9c106
--- /dev/null
+++ b/experiments/conpty/margin_controls.py
@@ -0,0 +1,74 @@
+"""Literal native outcomes for independent source ConPTY control workloads."""
+from __future__ import annotations
+
+
+def expected_source(case, columns, rows):
+    expected_native(case, columns, rows)  # Fixed workload/grid validation.
+    parts = [b"\x1b[2J\x1b[HTOP_FIXED\r\nREGION_A\r\nREGION_B\r\nBOTTOM_FIXED\r\n\x1b[2;3r"]
+    if case != "main-only":
+        if case == "repeat-alt":
+            parts.append(b"\x1b[?1049hALT_OUTSIDE\r\n\x1b[4;1HALT_A\r\nALT_B\x1b[4;5r\x1b[5;1H\nALT_C\nALT_D")
+        parts.append(b"\x1b[?1049h\x1b[HALT_TOP\x1b[" + str(rows).encode("ascii") + b";1HALT_LAST\r\nALT_DONE")
+        parts.append(b"\x1b[?1049l\x1b[?1049l" if case == "repeat-alt" else b"\x1b[?1049l")
+    parts.append(b"\x1b[3;1H\nREGION_C\nREGION_D\x1b[6;1HCTRL_DONE\r\n")
+    return b"".join(parts)
+
+
+def expected_native(case, columns, rows):
+    if (columns, rows) not in ((80, 24), (12, 7)) or case not in ("main-only", "default-alt", "repeat-alt"):
+        raise ValueError("fixed native control and grid required")
+
+    def state(lines, cursor):
+        return {"lines": lines + [""] * (rows - len(lines)), "cursor": cursor}
+
+    before = state(["TOP_FIXED", "REGION_A", "REGION_B", "BOTTOM_FIXED"], [0, 0])
+    result = {"before": before}
+    if case != "main-only":
+        if case == "repeat-alt":
+            result["alt1"] = state(["ALT_OUTSIDE", "", "", "ALT_C", "ALT_D"], [4, 5])
+        result["alt2" if case == "repeat-alt" else "alt"] = state(
+            [""] * (rows - 2) + ["ALT_LAST", "ALT_DONE"], [rows - 1, 8])
+        result["restored"] = before
+    result["final"] = state(["TOP_FIXED", "REGION_C", "REGION_D", "BOTTOM_FIXED", "", "CTRL_DONE"], [6, 0])
+    return result
+
+
+def _evaluate(stages, expected, columns, rows):
+    if set(stages) != set(expected):
+        raise ValueError("native control stages differ")
+    for capture in stages.values():
+        if (capture["columns"], capture["rows"]) != (columns, rows):
+            raise ValueError("native control grid changed")
+    # No control selects SGR. Compare all cells against the initial attribute;
+    # this checks preservation, without choosing a portable default color.
+    attribute = stages["before"]["cells"][0][0][1]
+    results = {}
+    for name, target in expected.items():
+        actual = stages[name]
+        wanted = [[(ord(character), attribute) for character in line.ljust(columns)]
+                  for line in target["lines"]]
+        fields = {"text": actual["lines"] == target["lines"],
+                  "cell_text": actual["cell_lines"] == target["lines"],
+                  "cells_and_attributes": actual["cells"] == wanted,
+                  "cursor": [actual["cursor_row"], actual["cursor_column"]] == target["cursor"],
+                  "viewport": actual["top"] == 0}
+        results[name] = dict(fields, passed=all(fields.values()))
+    return {"stages": results, "passed": all(row["passed"] for row in results.values()),
+            "initial_native_attribute": attribute, "full_r2_contract_verified": False}
+
+
+def evaluate_native(stages, case, columns, rows):
+    return _evaluate(stages, expected_native(case, columns, rows), columns, rows)
+
+
+def matches_unpatched_prediction(stages, case, columns, rows):
+    expected = expected_native(case, columns, rows)
+    if case != "main-only":
+        # With the main region still active, LF at the physical bottom clamps
+        # instead of scrolling. ALT_DONE overwrites ALT_LAST; ALT_TOP remains.
+        expected["alt2" if case == "repeat-alt" else "alt"] = {
+            "lines": ["ALT_TOP"] + [""] * (rows - 2) + ["ALT_DONE"], "cursor": [rows - 1, 8]}
+    if case == "repeat-alt":
+        expected["final"] = {"lines": ["TOP_FIXED", "REGION_A", "REGION_B", "REGION_CIXED", "REGION_D", "CTRL_DONE"] + [""] * (rows - 6),
+                             "cursor": [6, 0]}
+    return _evaluate(stages, expected, columns, rows)["passed"]
diff --git a/experiments/conpty/margin_controls_probe.cpp b/experiments/conpty/margin_controls_probe.cpp
new file mode 100644
index 00000000..6e6b6069
--- /dev/null
+++ b/experiments/conpty/margin_controls_probe.cpp
@@ -0,0 +1,103 @@
+// Independent native controls for the fixed-source ConPTY margin experiment. MIT.
+#include <windows.h>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <stdexcept>
+#include <string>
+#include <vector>
+#include "session.hpp"
+#include "../shell/workflow_fixture.hpp"
+
+static void require(bool ok, const char* message) {
+    if (!ok) throw std::runtime_error(message);
+}
+static void save(const std::filesystem::path& path, const std::string& bytes) {
+    std::ofstream stream(path, std::ios::binary);
+    stream.write(bytes.data(), bytes.size()); stream.close();
+    require(bool(stream), "control artifact write failed");
+}
+static void write(const std::string& bytes) {
+    DWORD count = 0;
+    require(WriteFile(GetStdHandle(STD_OUTPUT_HANDLE), bytes.data(),
+                      static_cast<DWORD>(bytes.size()), &count, nullptr) && count == bytes.size(),
+            "control output failed");
+}
+static std::vector<std::pair<std::string, std::string>> stages(const std::wstring& name, int rows) {
+    require(name == L"main-only" || name == L"default-alt" || name == L"repeat-alt", "fixed control required");
+    std::vector<std::pair<std::string, std::string>> result{{"before",
+        "\x1b[2J\x1b[HTOP_FIXED\r\nREGION_A\r\nREGION_B\r\nBOTTOM_FIXED\r\n\x1b[2;3r"}};
+    if (name != L"main-only") {
+        if (name == L"repeat-alt") result.emplace_back("alt1",
+            "\x1b[?1049hALT_OUTSIDE\r\n\x1b[4;1HALT_A\r\nALT_B\x1b[4;5r\x1b[5;1H\nALT_C\nALT_D");
+        result.emplace_back(name == L"repeat-alt" ? "alt2" : "alt",
+            "\x1b[?1049h\x1b[HALT_TOP\x1b[" + std::to_string(rows) + ";1HALT_LAST\r\nALT_DONE");
+        result.emplace_back("restored", name == L"repeat-alt" ? "\x1b[?1049l\x1b[?1049l" : "\x1b[?1049l");
+    }
+    result.emplace_back("final", "\x1b[3;1H\nREGION_C\nREGION_D\x1b[6;1HCTRL_DONE\r\n");
+    return result;
+}
+static void client(const std::wstring& name, const std::filesystem::path& directory, int rows) {
+    require(SetConsoleOutputCP(CP_UTF8) && SetConsoleMode(GetStdHandle(STD_OUTPUT_HANDLE),
+            ENABLE_PROCESSED_OUTPUT | ENABLE_WRAP_AT_EOL_OUTPUT | ENABLE_VIRTUAL_TERMINAL_PROCESSING),
+            "control mode failed");
+    std::string source;
+    for (const auto& stage : stages(name, rows)) {
+        write(stage.second); source += stage.second;
+        tf_shell_test::WorkflowOptions options;
+        options.capture = directory / stage.first; options.generation = 1;
+        tf_shell_test::workflow_capture_console(options, stage.first);
+    }
+    save(directory / "source.bin", source);
+}
+
+int wmain(int argc, wchar_t** argv) {
+    try {
+        require(argc == 6, "control arguments required");
+        const bool wide = std::wstring(argv[4]) == L"80" && std::wstring(argv[5]) == L"24";
+        const bool narrow = std::wstring(argv[4]) == L"12" && std::wstring(argv[5]) == L"7";
+        require(wide || narrow, "fixed control grid required");
+        const COORD size{static_cast<SHORT>(wide ? 80 : 12), static_cast<SHORT>(wide ? 24 : 7)};
+        const bool child = std::wstring(argv[1]) == L"--client";
+        const std::wstring name = argv[child ? 2 : 1];
+        (void)stages(name, size.Y); // Reject an unknown workload before acquiring resources.
+        BOOL owned = FALSE;
+        const auto directory = std::filesystem::absolute(argv[3]);
+        if (child) {
+            require(IsProcessInJob(GetCurrentProcess(), nullptr, &owned) && owned, "owned Job required");
+            client(name, directory, size.Y); return 37;
+        }
+
+        // The owner assigns this host to its Job before allowing any backend
+        // load or child creation. This retains the original bounded GO gate.
+        char go[4]{}; size_t used = 0;
+        while (used < sizeof(go)) {
+            DWORD count = 0;
+            if (!ReadFile(GetStdHandle(STD_INPUT_HANDLE), go + used, 1, &count, nullptr) || count != 1) break;
+            if (go[used++] == '\n') break;
+        }
+        require(std::string(go, used) == "GO\n" || std::string(go, used) == "GO\r\n", "GO required");
+        require(IsProcessInJob(GetCurrentProcess(), nullptr, &owned) && owned, "owned Job required");
+        auto backend = tf_conpty::Backend::reviewed_source_side_by_side(argv[2]);
+        wchar_t self[32768]{};
+        const DWORD length = GetModuleFileNameW(nullptr, self, 32768);
+        require(length && length < 32768, "control executable path failed");
+        tf_conpty::Session session(backend);
+        session.start(self, L"--client " + name + L" \"" + directory.wstring() + L"\" " +
+                      argv[4] + L" " + argv[5], {}, {}, size);
+        const bool waited = session.wait_exit(5000);
+        save(directory / "transport.prefix.bin", session.output());
+        session.close();
+        save(directory / "transport.bin", session.output());
+        std::cout << std::boolalpha << "{\"waited\":" << waited << ",\"side_by_side\":true"
+          << ",\"creation_flags\":" << session.backend_creation_flags()
+          << ",\"exit_code\":" << session.exit_code << ",\"read_error\":" << session.read_error
+          << ",\"capture_overflow\":" << session.capture_overflow
+          << ",\"forced_reader_cancel\":" << session.forced_reader_cancel
+          << ",\"forced_process_cancel\":" << session.forced_process_cancel
+          << ",\"cleanup_complete\":" << session.cleanup_complete
+          << ",\"active_children_after\":" << session.active_after
+          << ",\"backend_identity\":\"" << session.backend_identity() << "\"}\n";
+        return waited && session.exit_code == 37 && session.cleanup_complete ? 0 : 1;
+    } catch (const std::exception& error) { std::cerr << error.what() << '\n'; return 2; }
+}
diff --git a/experiments/conpty/results/2026-10-27-source-margin-controls/validation.json b/experiments/conpty/results/2026-10-27-source-margin-controls/validation.json
new file mode 100644
index 00000000..5fb7e04f
--- /dev/null
+++ b/experiments/conpty/results/2026-10-27-source-margin-controls/validation.json
@@ -0,0 +1,1667 @@
+{
+  "schema": "termforge-source-margin-controls-v1",
+  "upstream_source": "dc8ae365847d41f62d1ebca93815bb00959bc12f",
+  "generated_utc": "2026-10-27T05:46:36.962112+00:00",
+  "build_run": "40449292015",
+  "source": "edec26bb3c4d04858a667a96debf69c139476172",
+  "working_tree_dirty": false,
+  "source_files": {
+    "CMakeLists.txt": "9afd4590855f90d0e467824a49fc75a6f24b0d88ba7f4ff4ad92764239b682b3",
+    "experiments/conpty/backend.hpp": "af672718af8c05e90a26576e317b6ac9295fbee76f3f0298371060a9d167f5bb",
+    "experiments/conpty/session.hpp": "242ac8aa13f3fd56675b2ddefaaf207e5f4c8d3ef8e703260aaed2f0c41677aa",
+    "experiments/conpty/test_backend.py": "ab371ff7fbf196061451b96009a8260afb35473c1d05b2f99dda66e2b6a9bbba",
+    "experiments/conpty/margin_controls_probe.cpp": "bf4193ed091b83b50f095623c9bbc406b63646e92dfac552cae1818fd9fc1a18",
+    "experiments/conpty/margin_controls.py": "7bab11200188a30eaeac4de56b2f35a365def83651fe19e17e54e43e2740060c",
+    "experiments/conpty/source_margin_controls.py": "b1159026480e52fde97f7b0e36824bded9fb394f70846c94bffa767e063b3df6",
+    "experiments/conpty/margin_run.py": "99e6caf18224ce7b41307355066db70eacb810bc0626b15d3af09c9a89439ed2",
+    "experiments/conpty/source_margin_run.py": "26d07c9f912b1bb68b89d33a989ee80189230002869df83a572a22e7b2f6f657",
+    "experiments/conpty/run.py": "c8eef1e36b6d200b2d508cef91eaa5ca79a91fa87c5daf6265b2475c31dce329",
+    "experiments/candidates/alacritty/run.py": "2d83240506bf03b4da92f7b2dc85adf40446aff25cd0f0dbe08132b611c2627e",
+    "experiments/shell/workflow_fixture.hpp": "332d73699320a6f503fc212417a4d3820b82cc2d3feb3d1fffe3930660d57453",
+    "experiments/shell/workflow_checks.py": "f186ff0f5335c26fc5c4f0286961981dfd6af8fbaafc789e2bc50058486efa44"
+  },
+  "platform": "Windows-11-10.0.26200-SP0",
+  "probe_sha256": "a71c94795806a40062ace7788ee69cfbac0cd8a274765dce6b28aa6d7f33c7ee",
+  "trace_sha256": "5941d4569d0ae146eb005f12ecfb15014bc06c18ee48d1c9460824ab65df93d3",
+  "pair_receipts": {
+    "baseline": {
+      "schema": "termforge-upstream-conpty-variant-v1",
+      "upstream_source": "dc8ae365847d41f62d1ebca93815bb00959bc12f",
+      "workflow_run": "40449292015",
+      "production_patch_applied": false,
+      "focused_adapter_result": "expected-failure",
+      "full_adapter_verified": false,
+      "patch_sha256": "dc27377e399bd0217a0b76e16cc89f087c1b781929e4c958ad30c3a475322b81",
+      "files": {
+        "OpenConsole.exe": {
+          "sha256": "fabdc934d9755c405fe848251905e8c0e70a2bf7702b8ed7ccd104eec6591588",
+          "bytes": 1146880
+        },
+        "conpty.dll": {
+          "sha256": "9d165745cce4b29a5818a45c23f68e962b3a3140c2e00566bd17fee970fdd9d1",
+          "bytes": 108544
+        }
+      }
+    },
+    "patched": {
+      "schema": "termforge-upstream-conpty-variant-v1",
+      "upstream_source": "dc8ae365847d41f62d1ebca93815bb00959bc12f",
+      "workflow_run": "40449292015",
+      "production_patch_applied": true,
+      "focused_adapter_result": "passed",
+      "full_adapter_verified": true,
+      "patch_sha256": "dc27377e399bd0217a0b76e16cc89f087c1b781929e4c958ad30c3a475322b81",
+      "files": {
+        "OpenConsole.exe": {
+          "sha256": "1c8f071f6e4779ec297fb041af4eaea39be29b6920cef625ab91d1cbc20c79cb",
+          "bytes": 1147392
+        },
+        "conpty.dll": {
+          "sha256": "9d165745cce4b29a5818a45c23f68e962b3a3140c2e00566bd17fee970fdd9d1",
+          "bytes": 108544
+        }
+      }
+    }
+  },
+  "deadlines": {
+    "child_seconds": 5,
+    "outer_seconds": 15,
+    "cleanup_seconds": 5
+  },
+  "planned_executions": 12,
+  "comparisons": [
+    {
+      "case": "main-only",
+      "columns": 80,
+      "rows": 24,
+      "baseline_matches_prediction": true,
+      "patched_native_passed": true,
+      "both_terminal_finals_passed": true,
+      "passed": true
+    },
+    {
+      "case": "default-alt",
+      "columns": 80,
+      "rows": 24,
+      "baseline_matches_prediction": true,
+      "patched_native_passed": true,
+      "both_terminal_finals_passed": true,
+      "passed": true
+    },
+    {
+      "case": "repeat-alt",
+      "columns": 80,
+      "rows": 24,
+      "baseline_matches_prediction": true,
+      "patched_native_passed": true,
+      "both_terminal_finals_passed": true,
+      "passed": true
+    },
+    {
+      "case": "main-only",
+      "columns": 12,
+      "rows": 7,
+      "baseline_matches_prediction": true,
+      "patched_native_passed": true,
+      "both_terminal_finals_passed": true,
+      "passed": true
+    },
+    {
+      "case": "default-alt",
+      "columns": 12,
+      "rows": 7,
+      "baseline_matches_prediction": true,
+      "patched_native_passed": true,
+      "both_terminal_finals_passed": true,
+      "passed": true
+    },
+    {
+      "case": "repeat-alt",
+      "columns": 12,
+      "rows": 7,
+      "baseline_matches_prediction": true,
+      "patched_native_passed": true,
+      "both_terminal_finals_passed": true,
+      "passed": true
+    }
+  ],
+  "passed": true,
+  "full_r2_contract_verified": false,
+  "product_backend_selected": false,
+  "presented_done": null,
+  "unmeasured": [
+    "styled_source",
+    "history_stress",
+    "resize",
+    "queries_and_api_writes",
+    "terminal_stage_cursors",
+    "full_product",
+    "performance",
+    "WindTerm_equivalence"
+  ],
+  "raw_summary_sha256": "49a51e9fe31591c689203b54eedf5a7b75c93db5fb74a4062d1ddbdf00732004",
+  "build": {
+    "generator": "Visual Studio 17 2022",
+    "compiler": "MSVC 19.42.34433.0",
+    "sdk": "10.0.26100.0",
+    "configuration": "Release x64",
+    "source_experiment": true,
+    "candidate_adapter": false,
+    "product_backend_dir": "",
+    "build_testing": false,
+    "target": "conpty_source_margin_controls",
+    "configure_log_sha256": "80e9aa25bb3337065aa412f06d5a7e652814a181df9128b8d2fbf86db9b493f6",
+    "build_log_sha256": "20716d99571de46a12aedb7431f6eff87ed76668e0c444e7adc30780c5daf56c",
+    "cmake_cache_sha256": "45df1ee5960f8231049fc23a5eb3cd84297c696c747005ff8b5af60a3ed65be6"
+  },
+  "checks": {
+    "margin_regressions": {
+      "tests": 17,
+      "passed": 17,
+      "skipped": 0,
+      "seconds": 0.375,
+      "stdout_log_sha256": "7090c04a72c484bcf76445e60d14136db7b247111a69552ae0abce8135e2f030"
+    },
+    "loader_regressions": {
+      "tests": 14,
+      "passed": 14,
+      "skipped": 0,
+      "seconds": 1.02,
+      "stdout_log_sha256": "6b49c108d84db78da015c7b6f95d8691216ee7d50510f7f4bf80157942dc244e"
+    },
+    "original_margin_probe_sha256": "060abdbb7e4c885f77e2617fe0ca1f5b7e0550d6c3a851f918d1836b3afb6b83",
+    "original_backend_probe_sha256": "2d921cc7d82f912ab87a9a6d0c73d9e6e7acfcde00d0d88020d3997d5732d1c7",
+    "binary_source_files_unchanged_since_parent": true,
+    "original_probe_build_scope": "Reused the preceding build; the native probe source and shared headers are unchanged. The current Python harness was executed."
+  },
+  "samples": {
+    "baseline-80x24-main-only": {
+      "status": "completed",
+      "case": "main-only",
+      "columns": 80,
+      "rows": 24,
+      "source_bytes": 99,
+      "source_sha256": "562efe17a5fc38ef1f6c0d2178909529d410a564153af2096fd65385774b7d78",
+      "transport_bytes": 140,
+      "transport_sha256": "298ef170a31e6b682bd03e6df50fa63501bba6a4d50b93068d238de5b11c98d6",
+      "native_contract": {
+        "stages": {
+          "before": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          },
+          "final": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          }
+        },
+        "passed": true,
+        "initial_native_attribute": 7,
+        "full_r2_contract_verified": false
+      },
+      "unpatched_prediction_matches": true,
+      "native_cursor": {
+        "before": [
+          0,
+          0
+        ],
+        "final": [
+          6,
+          0
+        ]
+      },
+      "native_cell_sha256": {
+        "before": "fe9016196e03b264cce22f628f67b778fe1e6a3aeb160ed53effc153b1ff6651",
+        "final": "cd50199bb35507012250c82e89282232990e58c8dfa12d014002837520780135"
+      },
+      "terminal_alternate": false,
+      "terminal_final_passed": true,
+      "lifecycle": {
+        "status": "completed",
+        "failure_code": null,
+        "returncode": 0,
+        "outer_job_after": {
+          "active": 0,
+          "total": 4,
+          "terminated": 0
+        },
+        "outer_job_after_forced_cleanup": null,
+        "forced_cleanup": false,
+        "job_assigned": true,
+        "process_reaped": true,
+        "streams_drained": true,
+        "cleanup_errors": [],
+        "native": {
+          "waited": true,
+          "side_by_side": true,
+          "creation_flags": 0,
+          "exit_code": 37,
+          "read_error": 109,
+          "capture_overflow": false,
+          "forced_reader_cancel": false,
+          "forced_process_cancel": false,
+          "cleanup_complete": true,
+          "active_children_after": 0,
+          "backend_identity": "source-dc8-r56-baseline-run40449292015"
+        },
+        "error": null
+      },
+      "native_stage_files": {
+        "before": {
+          "console.json": "2cc9905011e52755ad390a7ef9ea8c84ced519ae8272f6806e0d6c0c0801d328",
+          "console.bin": "4279b6605b0fb08728ce75e50e7b24eaf2d75e39e3d44b12b0f41d2e6ba8343b",
+          "cells.bin": "fe9016196e03b264cce22f628f67b778fe1e6a3aeb160ed53effc153b1ff6651"
+        },
+        "final": {
+          "console.json": "44791e13f43dc0e3d8f5f85e3a0fe43d0efd140d92c44874183ae37ba75b6805",
+          "console.bin": "b397c51fdcda4e4c05dd0f99994518461c063798e3485b36f1fa7922902116d8",
+          "cells.bin": "cd50199bb35507012250c82e89282232990e58c8dfa12d014002837520780135"
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+          "cells.bin": "17469e5eb0c1cfa2577d55e2f5870e4d478f650f2d4a9d72c330094bec23ccc6"
+        },
+        "restored": {
+          "console.json": "d846fba64eedf13310f9b819d2ef8d5cec418b79617be1aaab3ebee496de85c2",
+          "console.bin": "f3f613e2347734671af75bb4747b55ebc89ea0c2b1994b5efd7a86152aa80b10",
+          "cells.bin": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3"
+        },
+        "final": {
+          "console.json": "7e0a4e914d3163ba1eed10904852c8fb8a392c585f53612d2e96395c65cb5931",
+          "console.bin": "ae750de80c88d1345983e4ff3af5c96f9d83f550efe08480233b9d4f593b0465",
+          "cells.bin": "3143631df305f659111e37d5a4a81be0b4c1ad63957cc73c3a162f7ec1c782d7"
+        }
+      },
+      "transport_prefix_sha256": "6f36d5c80521c6b16edeb5255b5ee7c76140ac9b6e953ff0af7f0256fd01b325",
+      "supervision_summary_sha256": "53233abedb9bc62a5f7bbdc241403891ed825b16572c6ea9c37c89ffe3189cb5"
+    },
+    "baseline-12x7-repeat-alt": {
+      "status": "completed",
+      "case": "repeat-alt",
+      "columns": 12,
+      "rows": 7,
+      "source_bytes": 220,
+      "source_sha256": "2b68cea085a519f73306b02b702c685aa0dba44d780c8619e0e3ef7b202d1dcd",
+      "transport_bytes": 263,
+      "transport_sha256": "7859bdb124e0b8ed7858a5d090648dc30948d81c56948c0942313cead0e79161",
+      "native_contract": {
+        "stages": {
+          "before": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          },
+          "alt1": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          },
+          "alt2": {
+            "text": false,
+            "cell_text": false,
+            "cells_and_attributes": false,
+            "cursor": true,
+            "viewport": true,
+            "passed": false
+          },
+          "restored": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          },
+          "final": {
+            "text": false,
+            "cell_text": false,
+            "cells_and_attributes": false,
+            "cursor": true,
+            "viewport": true,
+            "passed": false
+          }
+        },
+        "passed": false,
+        "initial_native_attribute": 7,
+        "full_r2_contract_verified": false
+      },
+      "unpatched_prediction_matches": true,
+      "native_cursor": {
+        "before": [
+          0,
+          0
+        ],
+        "alt1": [
+          4,
+          5
+        ],
+        "alt2": [
+          6,
+          8
+        ],
+        "restored": [
+          0,
+          0
+        ],
+        "final": [
+          6,
+          0
+        ]
+      },
+      "native_cell_sha256": {
+        "before": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3",
+        "alt1": "c7b9b5456a0566673db0a45765f1de63ac3ae76501da1be8cc3f0aadf848b3b7",
+        "alt2": "2bb287dce6b1d142599046e30596417ed0ea1abdff31f81471cb2c03fe46e34a",
+        "restored": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3",
+        "final": "ca4f1e7fdd65663604cfe2eb8c50a838839adac9ac7bcf10fd22a342058efba7"
+      },
+      "terminal_alternate": false,
+      "terminal_final_passed": true,
+      "lifecycle": {
+        "status": "completed",
+        "failure_code": null,
+        "returncode": 0,
+        "outer_job_after": {
+          "active": 0,
+          "total": 4,
+          "terminated": 0
+        },
+        "outer_job_after_forced_cleanup": null,
+        "forced_cleanup": false,
+        "job_assigned": true,
+        "process_reaped": true,
+        "streams_drained": true,
+        "cleanup_errors": [],
+        "native": {
+          "waited": true,
+          "side_by_side": true,
+          "creation_flags": 0,
+          "exit_code": 37,
+          "read_error": 109,
+          "capture_overflow": false,
+          "forced_reader_cancel": false,
+          "forced_process_cancel": false,
+          "cleanup_complete": true,
+          "active_children_after": 0,
+          "backend_identity": "source-dc8-r56-baseline-run40449292015"
+        },
+        "error": null
+      },
+      "native_stage_files": {
+        "before": {
+          "console.json": "0ff49b4ca941a2569ba6b6e88be65a2d371bdeebb1ec02c1028c720d84a74e6e",
+          "console.bin": "f3f613e2347734671af75bb4747b55ebc89ea0c2b1994b5efd7a86152aa80b10",
+          "cells.bin": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3"
+        },
+        "alt1": {
+          "console.json": "c9144171f486448d88de93fc4f6f4d0bc602a77b5b748136f34757b4d638bdc8",
+          "console.bin": "c2e8954d37be9bfc2b600951255d9410a9873e9259b7980ed41785de97e863c3",
+          "cells.bin": "c7b9b5456a0566673db0a45765f1de63ac3ae76501da1be8cc3f0aadf848b3b7"
+        },
+        "alt2": {
+          "console.json": "2253a902f36fc1d407ab5d72faf6d928f6ee8df10f5c947a0d27a24d2e6259de",
+          "console.bin": "be8621c984e3f28209bbc97d377e78b8ecd01ca4f2600129c72181f0230f7744",
+          "cells.bin": "2bb287dce6b1d142599046e30596417ed0ea1abdff31f81471cb2c03fe46e34a"
+        },
+        "restored": {
+          "console.json": "d846fba64eedf13310f9b819d2ef8d5cec418b79617be1aaab3ebee496de85c2",
+          "console.bin": "f3f613e2347734671af75bb4747b55ebc89ea0c2b1994b5efd7a86152aa80b10",
+          "cells.bin": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3"
+        },
+        "final": {
+          "console.json": "f318dcc781710db4d4695dd2906b401edf6d44710d30d5d5a59574b29b4fb58c",
+          "console.bin": "ad734bcaaac7c400337e93737f2a3c0f99993bbd7e0bdd8ca80278b1e0ef386a",
+          "cells.bin": "ca4f1e7fdd65663604cfe2eb8c50a838839adac9ac7bcf10fd22a342058efba7"
+        }
+      },
+      "transport_prefix_sha256": "ef90cd86ca36da979fe06820f50ec8695a0ed86b46288f6de74ab8a07bef8e6e",
+      "supervision_summary_sha256": "661250217a88ffca8b79f59e301f5d89766fde825a36a274ab0090f5ec7552b5"
+    },
+    "patched-12x7-repeat-alt": {
+      "status": "completed",
+      "case": "repeat-alt",
+      "columns": 12,
+      "rows": 7,
+      "source_bytes": 220,
+      "source_sha256": "2b68cea085a519f73306b02b702c685aa0dba44d780c8619e0e3ef7b202d1dcd",
+      "transport_bytes": 263,
+      "transport_sha256": "7859bdb124e0b8ed7858a5d090648dc30948d81c56948c0942313cead0e79161",
+      "native_contract": {
+        "stages": {
+          "before": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          },
+          "alt1": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          },
+          "alt2": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          },
+          "restored": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          },
+          "final": {
+            "text": true,
+            "cell_text": true,
+            "cells_and_attributes": true,
+            "cursor": true,
+            "viewport": true,
+            "passed": true
+          }
+        },
+        "passed": true,
+        "initial_native_attribute": 7,
+        "full_r2_contract_verified": false
+      },
+      "unpatched_prediction_matches": false,
+      "native_cursor": {
+        "before": [
+          0,
+          0
+        ],
+        "alt1": [
+          4,
+          5
+        ],
+        "alt2": [
+          6,
+          8
+        ],
+        "restored": [
+          0,
+          0
+        ],
+        "final": [
+          6,
+          0
+        ]
+      },
+      "native_cell_sha256": {
+        "before": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3",
+        "alt1": "c7b9b5456a0566673db0a45765f1de63ac3ae76501da1be8cc3f0aadf848b3b7",
+        "alt2": "17469e5eb0c1cfa2577d55e2f5870e4d478f650f2d4a9d72c330094bec23ccc6",
+        "restored": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3",
+        "final": "3143631df305f659111e37d5a4a81be0b4c1ad63957cc73c3a162f7ec1c782d7"
+      },
+      "terminal_alternate": false,
+      "terminal_final_passed": true,
+      "lifecycle": {
+        "status": "completed",
+        "failure_code": null,
+        "returncode": 0,
+        "outer_job_after": {
+          "active": 0,
+          "total": 4,
+          "terminated": 0
+        },
+        "outer_job_after_forced_cleanup": null,
+        "forced_cleanup": false,
+        "job_assigned": true,
+        "process_reaped": true,
+        "streams_drained": true,
+        "cleanup_errors": [],
+        "native": {
+          "waited": true,
+          "side_by_side": true,
+          "creation_flags": 0,
+          "exit_code": 37,
+          "read_error": 109,
+          "capture_overflow": false,
+          "forced_reader_cancel": false,
+          "forced_process_cancel": false,
+          "cleanup_complete": true,
+          "active_children_after": 0,
+          "backend_identity": "source-dc8-r56-patched-run40449292015"
+        },
+        "error": null
+      },
+      "native_stage_files": {
+        "before": {
+          "console.json": "0ff49b4ca941a2569ba6b6e88be65a2d371bdeebb1ec02c1028c720d84a74e6e",
+          "console.bin": "f3f613e2347734671af75bb4747b55ebc89ea0c2b1994b5efd7a86152aa80b10",
+          "cells.bin": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3"
+        },
+        "alt1": {
+          "console.json": "c9144171f486448d88de93fc4f6f4d0bc602a77b5b748136f34757b4d638bdc8",
+          "console.bin": "c2e8954d37be9bfc2b600951255d9410a9873e9259b7980ed41785de97e863c3",
+          "cells.bin": "c7b9b5456a0566673db0a45765f1de63ac3ae76501da1be8cc3f0aadf848b3b7"
+        },
+        "alt2": {
+          "console.json": "1d0cce7996e41de52f5399433caa8a2397c19a8ab5caff37a072fce707e7d695",
+          "console.bin": "127f85391d796833c9f5e9a6ac970ab4fa3fc369ebfb8df5214291504940c6a1",
+          "cells.bin": "17469e5eb0c1cfa2577d55e2f5870e4d478f650f2d4a9d72c330094bec23ccc6"
+        },
+        "restored": {
+          "console.json": "d846fba64eedf13310f9b819d2ef8d5cec418b79617be1aaab3ebee496de85c2",
+          "console.bin": "f3f613e2347734671af75bb4747b55ebc89ea0c2b1994b5efd7a86152aa80b10",
+          "cells.bin": "323107891dd2f32c2be1fecd7ae03379c96f8fe38eff938ece8f19eeebe6dbf3"
+        },
+        "final": {
+          "console.json": "7e0a4e914d3163ba1eed10904852c8fb8a392c585f53612d2e96395c65cb5931",
+          "console.bin": "ae750de80c88d1345983e4ff3af5c96f9d83f550efe08480233b9d4f593b0465",
+          "cells.bin": "3143631df305f659111e37d5a4a81be0b4c1ad63957cc73c3a162f7ec1c782d7"
+        }
+      },
+      "transport_prefix_sha256": "ef90cd86ca36da979fe06820f50ec8695a0ed86b46288f6de74ab8a07bef8e6e",
+      "supervision_summary_sha256": "53233abedb9bc62a5f7bbdc241403891ed825b16572c6ea9c37c89ffe3189cb5"
+    }
+  }
+}
diff --git a/experiments/conpty/source_margin_controls.py b/experiments/conpty/source_margin_controls.py
new file mode 100644
index 00000000..30955187
--- /dev/null
+++ b/experiments/conpty/source_margin_controls.py
@@ -0,0 +1,149 @@
+"""One bounded source-pair comparison for three additional native controls."""
+from __future__ import annotations
+
+import argparse
+from datetime import datetime, timezone
+import json
+from pathlib import Path
+import platform
+import subprocess
+
+from experiments.candidates.alacritty.run import run_trace
+from experiments.conpty.margin_controls import (
+    evaluate_native, expected_native, expected_source, matches_unpatched_prediction,
+)
+from experiments.conpty.margin_run import sha256, validate_lifecycle
+from experiments.conpty.source_margin_run import identity, reviewed_pair, ROOT, RUN, UPSTREAM
+from experiments.conpty.test_backend import BackendTests
+from experiments.shell.workflow_checks import validate_console_window
+
+CASES = ("main-only", "default-alt", "repeat-alt")
+GRIDS = ((80, 24), (12, 7))
+
+
+def inspect_case(directory, trace, case, columns, rows):
+    source = (directory / "source.bin").read_bytes()
+    if source != expected_source(case, columns, rows):
+        raise ValueError("fixed control source changed")
+    transport = (directory / "transport.bin").read_bytes()
+    if not 0 < len(transport) <= 8192:
+        raise ValueError("control transport bound")
+    expected = expected_native(case, columns, rows)
+    states = {stage: validate_console_window(directory, expected_role=stage,
+                                             expected_generation=1, prefix=stage)
+              for stage in expected}
+    report, records = run_trace(trace, transport, rows, columns, 100,
+                                [len(transport)], directory / "replay")
+    if report["passed"] is not True:
+        raise ValueError("control replay rejected")
+    final = records[-1]
+    lines = ["".join(cell["text"] for cell in line if cell.get("width", 1)).rstrip()
+             for line in final["screen"]["cells"]]
+    alternate = bool(final["mode_bits"] & (1 << 12))
+    return {"source_bytes": len(source), "source_sha256": sha256(directory / "source.bin"),
+            "transport_bytes": len(transport), "transport_sha256": sha256(directory / "transport.bin"),
+            "native_contract": evaluate_native(states, case, columns, rows),
+            "unpatched_prediction_matches": matches_unpatched_prediction(states, case, columns, rows),
+            "native_lines": {stage: row["lines"] for stage, row in states.items()},
+            "native_cursor": {stage: [row["cursor_row"], row["cursor_column"]] for stage, row in states.items()},
+            "native_cell_sha256": {stage: sha256(directory / (stage + ".cells.bin")) for stage in expected},
+            "terminal_lines": lines, "terminal_alternate": alternate,
+            "terminal_final_passed": lines == expected["final"]["lines"] and not alternate}
+
+
+def compare(samples):
+    results = []
+    for columns, rows in GRIDS:
+        for case in CASES:
+            baseline = samples[f"baseline-{columns}x{rows}-{case}"]
+            patched = samples[f"patched-{columns}x{rows}-{case}"]
+            completed = all(row.get("status") == "completed" for row in (baseline, patched))
+            qualified = (completed and baseline["unpatched_prediction_matches"] and
+                         baseline["native_contract"]["passed"] == (case == "main-only"))
+            repaired = completed and patched["native_contract"]["passed"]
+            terminal = completed and all(row["terminal_final_passed"] for row in (baseline, patched))
+            results.append({"case": case, "columns": columns, "rows": rows,
+                            "baseline_matches_prediction": qualified,
+                            "patched_native_passed": repaired, "both_terminal_finals_passed": terminal,
+                            "passed": qualified and repaired and terminal})
+    return results
+
+
+def run(baseline, patched, probe, trace, output):
+    pairs = {name: reviewed_pair(folder, name) for name, folder in
+             (("baseline", baseline), ("patched", patched))}
+    probe, trace = Path(probe).resolve(strict=True), Path(trace).resolve(strict=True)
+    output = Path(output).resolve()
+    output.mkdir(parents=True, exist_ok=False)
+    subject = BackendTests()
+    subject.out, subject.serial = output / "_private" / "supervision", 0
+    sources = ["CMakeLists.txt", "experiments/conpty/backend.hpp", "experiments/conpty/session.hpp",
+               "experiments/conpty/test_backend.py", "experiments/conpty/margin_controls_probe.cpp",
+               "experiments/conpty/margin_controls.py", "experiments/conpty/source_margin_controls.py",
+               "experiments/conpty/margin_run.py", "experiments/conpty/source_margin_run.py",
+               "experiments/conpty/run.py", "experiments/candidates/alacritty/run.py",
+               "experiments/shell/workflow_fixture.hpp", "experiments/shell/workflow_checks.py"]
+    summary = {"schema": "termforge-source-margin-controls-v1", "upstream_source": UPSTREAM,
+               "generated_utc": datetime.now(timezone.utc).isoformat(), "build_run": RUN,
+               "source": subprocess.check_output(["git", "rev-parse", "HEAD"], cwd=ROOT, text=True).strip(),
+               "working_tree_dirty": bool(subprocess.check_output(["git", "status", "--porcelain"], cwd=ROOT)),
+               "source_files": {name: sha256(ROOT / name) for name in sources},
+               "platform": platform.platform(), "probe_sha256": sha256(probe), "trace_sha256": sha256(trace),
+               "pair_receipts": {name: receipt for name, (_, receipt) in pairs.items()},
+               "deadlines": {"child_seconds": 5, "outer_seconds": 15, "cleanup_seconds": 5},
+               "planned_executions": 12, "samples": {}, "comparisons": [], "passed": False,
+               "full_r2_contract_verified": False, "product_backend_selected": False,
+               "presented_done": None,
+               "unmeasured": ["styled_source", "history_stress", "resize", "queries_and_api_writes",
+                              "terminal_stage_cursors", "full_product", "performance", "WindTerm_equivalence"]}
+
+    def save():
+        (output / "summary.json").write_text(json.dumps(summary, indent=2) + "\n", encoding="utf-8")
+
+    try:
+        # Exactly one execution per planned cell; failed cells remain failed.
+        for columns, rows in GRIDS:
+            for case in CASES:
+                for variant, (directory, _) in pairs.items():
+                    name = f"{variant}-{columns}x{rows}-{case}"
+                    folder = output / "_private" / name
+                    folder.mkdir(parents=True)
+                    sample = {"status": "failed", "case": case, "columns": columns, "rows": rows,
+                              "supervision_case": subject.serial}
+                    stage = "native_execution"
+                    try:
+                        lifecycle = subject.invoke(directory, case, executable=probe,
+                                                   arguments=(folder, columns, rows), timeout=15)
+                        sample["lifecycle"] = lifecycle
+                        stage = "lifecycle_validation"
+                        job = lifecycle["outer_job_after"]
+                        if (lifecycle["returncode"] != 0 or lifecycle["error"] is not None or
+                                job["active"] != 0 or job["total"] < 1 or job["terminated"] != 0):
+                            raise ValueError("control native probe failed")
+                        validate_lifecycle(lifecycle["native"], True, backend_identity=identity(variant))
+                        stage = "capture_and_replay_validation"
+                        sample.update(inspect_case(folder, trace, case, columns, rows), status="completed")
+                    except Exception as error:
+                        sample["error_type"] = type(error).__name__
+                        sample["failure_stage"] = stage
+                    summary["samples"][name] = sample
+                    save()
+        summary["comparisons"] = compare(summary["samples"])
+        summary["passed"] = all(row["passed"] for row in summary["comparisons"])
+    finally:
+        save()
+    return summary
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    for name in ("baseline", "patched", "probe", "candidate-trace", "output"):
+        parser.add_argument("--" + name, type=Path, required=True)
+    args = parser.parse_args()
+    result = run(args.baseline, args.patched, args.probe, args.candidate_trace, args.output)
+    print(json.dumps({"passed": result["passed"], "comparisons": result["comparisons"]}))
+    return int(not result["passed"])
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/experiments/conpty/test_backend.py b/experiments/conpty/test_backend.py
index 47b64cdd..eedd7888 100644
--- a/experiments/conpty/test_backend.py
+++ b/experiments/conpty/test_backend.py
@@ -21,7 +21,7 @@ def setUp(self):
         self.out = Path(tempfile.mkdtemp(prefix="run-", dir=base))
         self.serial = 0
 
-    def invoke(self, directory, mode="--host", *, executable=None):
+    def invoke(self, directory, mode="--host", *, executable=None, arguments=(), timeout=20):
         job = process = None
         stdout = stderr = b""
         result = {"status": "failed", "failure_code": None, "returncode": None,
@@ -42,14 +42,15 @@ def cleanup_fault(code):
         try:
             job = OwnedJob()
             stage = "process_start"
-            process = subprocess.Popen([str(executable or binary("conpty_backend_probe")), mode, str(directory)],
+            process = subprocess.Popen([str(executable or binary("conpty_backend_probe")), mode, str(directory),
+                                        *map(str, arguments)],
                                        stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                                        creationflags=subprocess.CREATE_NO_WINDOW)
             stage = "job_assign"
             job.assign(process.pid)
             result["job_assigned"] = True
             stage = "process_communicate"
-            stdout, stderr = process.communicate(b"GO\n", timeout=20)
+            stdout, stderr = process.communicate(b"GO\n", timeout=timeout)
             result["streams_drained"] = True
             stage = "stream_evidence"
             (private / "host.stdout.bin").write_bytes(stdout)
diff --git a/experiments/conpty/test_margin_controls.py b/experiments/conpty/test_margin_controls.py
new file mode 100644
index 00000000..1a72c8ac
--- /dev/null
+++ b/experiments/conpty/test_margin_controls.py
@@ -0,0 +1,78 @@
+"""Independent literal captures and corruption gates for native margin controls."""
+import copy
+import unittest
+
+from experiments.conpty.margin_controls import evaluate_native, matches_unpatched_prediction
+
+
+def capture(lines, cursor, columns=12, rows=7):
+    padded = lines + [""] * (rows - len(lines))
+    return {"columns": columns, "rows": rows, "top": 0,
+            "lines": padded, "cell_lines": padded.copy(),
+            "cells": [[(ord(c), 7) for c in line.ljust(columns)] for line in padded],
+            "cursor_row": cursor[0], "cursor_column": cursor[1]}
+
+
+class NativeMarginControlTests(unittest.TestCase):
+    def main_only(self):
+        return {"before": capture(["TOP_FIXED", "REGION_A", "REGION_B", "BOTTOM_FIXED"], (0, 0)),
+                "final": capture(["TOP_FIXED", "REGION_C", "REGION_D", "BOTTOM_FIXED", "", "CTRL_DONE"], (6, 0))}
+
+    def test_main_region_preserves_outside_and_rejects_corrupted_fields(self):
+        original = self.main_only()
+        self.assertTrue(evaluate_native(original, "main-only", 12, 7)["passed"])
+        self.assertTrue(matches_unpatched_prediction(original, "main-only", 12, 7))
+        for field in ("lines", "cell_lines", "cells", "cursor_row", "cursor_column", "top"):
+            changed = copy.deepcopy(original)
+            if field in ("lines", "cell_lines"):
+                changed["final"][field][0] = "REGION_A"
+            elif field == "cells":
+                changed["final"][field][0][0] = (ord("T"), 4)
+            else:
+                changed["final"][field] += 1
+            with self.subTest(field=field):
+                self.assertFalse(evaluate_native(changed, "main-only", 12, 7)["passed"])
+                self.assertFalse(matches_unpatched_prediction(changed, "main-only", 12, 7))
+
+    def test_new_alternate_has_full_screen_margins_and_qualifies_specific_old_failure(self):
+        sample = self.main_only()
+        sample["alt"] = capture(["", "", "", "", "", "ALT_LAST", "ALT_DONE"], (6, 8))
+        sample["restored"] = copy.deepcopy(sample["before"])
+        self.assertTrue(evaluate_native(sample, "default-alt", 12, 7)["passed"])
+        self.assertFalse(matches_unpatched_prediction(sample, "default-alt", 12, 7))
+        old = copy.deepcopy(sample)
+        old["alt"] = capture(["ALT_TOP", "", "", "", "", "", "ALT_DONE"], (6, 8))
+        result = evaluate_native(old, "default-alt", 12, 7)
+        self.assertFalse(result["passed"])
+        self.assertEqual([name for name, stage in result["stages"].items() if not stage["passed"]], ["alt"])
+        self.assertTrue(matches_unpatched_prediction(old, "default-alt", 12, 7))
+        old["before"]["cursor_row"] = 1
+        self.assertFalse(matches_unpatched_prediction(old, "default-alt", 12, 7))
+
+    def test_repeated_alternate_and_main_requests_keep_the_hidden_main_region(self):
+        sample = self.main_only()
+        sample["alt1"] = capture(["ALT_OUTSIDE", "", "", "ALT_C", "ALT_D"], (4, 5))
+        sample["alt2"] = capture(["", "", "", "", "", "ALT_LAST", "ALT_DONE"], (6, 8))
+        sample["restored"] = copy.deepcopy(sample["before"])
+        self.assertTrue(evaluate_native(sample, "repeat-alt", 12, 7)["passed"])
+        self.assertFalse(matches_unpatched_prediction(sample, "repeat-alt", 12, 7))
+        old = copy.deepcopy(sample)
+        old["alt2"] = capture(["ALT_TOP", "", "", "", "", "", "ALT_DONE"], (6, 8))
+        old["final"] = capture(["TOP_FIXED", "REGION_A", "REGION_B", "REGION_CIXED", "REGION_D", "CTRL_DONE"], (6, 0))
+        result = evaluate_native(old, "repeat-alt", 12, 7)
+        self.assertEqual([name for name, stage in result["stages"].items() if not stage["passed"]], ["alt2", "final"])
+        self.assertTrue(matches_unpatched_prediction(old, "repeat-alt", 12, 7))
+        old["restored"]["cells"][0][0] = (ord("T"), 4)
+        self.assertFalse(matches_unpatched_prediction(old, "repeat-alt", 12, 7))
+
+    def test_missing_stage_and_wrong_grid_are_rejected(self):
+        with self.assertRaises(ValueError):
+            evaluate_native({"before": self.main_only()["before"]}, "main-only", 12, 7)
+        with self.assertRaises(ValueError):
+            evaluate_native(self.main_only(), "main-only", 80, 24)
+        with self.assertRaises(ValueError):
+            evaluate_native(self.main_only(), "unknown", 12, 7)
+
+
+if __name__ == "__main__":
+    unittest.main()