docs(studio-3d): 阶段 6 交付说明（正确性与失效状态）+ 接口骨架同步

- What:
  1. `docs/architecture/studio-3d-stages.md` 新增「阶段 6：运行正确性与失效状态（批次 A）—— 已完成」：
     做（epoch/字段级来源/设备几何身份/加载请求号/工具与重编包）、验收表格（含两份探针的
     before/after 与全量计数）、"这一阶段抓到的" 7 条、兼容说明 6 条；文首进度改成阶段 6 已完成、
     7/8/9 未开始；依赖关系图扩展为 6→7/8→9。
  2. `docs/architecture/studio-3d-contracts.pyi` 与本阶段的契约改动同步：`SceneState` 加 `'stale'`；
     `SurfaceFieldFrame`/`RenderFrame` 加 `computed_frame_id`；`ExpectedGeometry` 加 `source_geometry_id`
     并注明米制 id 何时为空；`SceneAssets` 加 `source_geometry_id`/`compatible_sensor_model`/
     `compatible_hardware_revisions`；`ThreeDCoordinator.__init__` 加 `clock`/`stale_grace_s`，新增
     `note_field_failure()`/`show_rest()`/`epoch`/`last_presented()`。
- Why: 规格 §13 要求每阶段同时交出实现、测试、输入样例、失败样例、兼容说明与平台诊断报告；阶段 6 的
  契约改动（`SceneState`、两个 `computed_frame_id`、`ExpectedGeometry`/`SceneAssets` 的新身份字段、
  协调器新参数）必须先落到接口骨架里，否则下一阶段会照着过期文档实现。审查报告本身不修改
  （`_review_scene3d_20260914/` 保持原样），结论与反号证据写进本仓文档。
- Verification:
  · 阶段末全量复核（与本提交同一工作树）：apps/studio 234 项 0 失败（14 跳过 = offscreen 下的真 GL 用例，
    用 `QT_QPA_PLATFORM=windows` 单独跑为 14 项 0 失败 0 跳过）；shared 316 项 0 失败 1 跳过；
    `ui_check` 587 项 0 失败；`locale_check` 0 缺失（zh/en 各 398 键，仅有键集合相同）；
    `validate_scene.py` 对重编发布包 `source geometry recorded 46a03a5fbac1eace` 等全项 ok。
  · 复现证据：`.repro/probe_stage6_r1.py`（R1/R7-b 反号）、`.repro/probe_stage6_device.py`
    （R3：同尺寸不同映射被拒、表面不同被拒、设备不声明 → unverified），输出 JSON 与扫描件留在 `.repro/`。
- Not in this change: 不改代码（本提交只动文档与接口骨架）；阶段 7/8/9 的计划条目（二维后端统一、
  回放入口收口、能力控件、限速与真实统计、保护包密钥注入、ARM 与 2 小时门禁）尚未开始；
  真机上"算法链失败时 `VRAW` 是否也过期"这一条仍待实测（风险项已写进阶段 6 小节）。

docs/architecture/studio-3d-contracts.pyi

@@ -8,7 +8,7 @@ by NDArray. See studio-3d-design.md for threading and validation requirements.
 """
 from dataclasses import dataclass
 from pathlib import Path
-from typing import Generic, Literal, Mapping, Protocol, TypeAlias, TypeVar
+from typing import Callable, Generic, Literal, Mapping, Protocol, TypeAlias, TypeVar
 from concurrent.futures import Executor
 
 import numpy as np
@@ -28,7 +28,7 @@ Role: TypeAlias = Literal['sensing', 'housing', 'reference']
 Quality: TypeAlias = Literal['calibrated', 'approximate', 'display_only']
 Profile: TypeAlias = Literal['desktop33', 'gles30']
 OfferResult: TypeAlias = Literal['accepted', 'replaced', 'stale', 'disabled', 'invalid']
-SceneState: TypeAlias = Literal['disabled', 'loading', 'ready', 'live', 'no_data', 'suspended', 'unavailable']
+SceneState: TypeAlias = Literal['disabled', 'loading', 'ready', 'live', 'no_data', 'suspended', 'unavailable', 'stale']
 
 
 @dataclass(frozen=True)
@@ -75,6 +75,7 @@ class SurfaceFieldFrame:
     displacement_sensor_m: F32 | None  # [H,W,3]; base displacement BEFORE display gain.
     displacement_quality: Quality | None
     diagnostic: Diagnostic | None
+    computed_frame_id: int | None  # Frame the array was computed for; None = unstated.
 
 
 @dataclass(frozen=True)
@@ -118,9 +119,10 @@ class CameraPreset:
 class ExpectedGeometry:
     sensor_model: str
     hardware_revision: str
-    geometry_id: str
+    geometry_id: str  # Metre-scaled shape identity; '' when the device cannot state it.
     field_domain_id: str
     shape_hw: tuple[int, int]
+    source_geometry_id: str  # Unit-free surface identity a device CAN reproduce.
 
 
 @dataclass(frozen=True)
@@ -133,6 +135,9 @@ class SceneAssets:
     binding: SurfaceBinding  # v1 supports exactly one sensing part.
     camera_presets: tuple[CameraPreset, ...]
     bounds_sensor_m: F32  # [2,3]: min, max.
+    source_geometry_id: str  # Unit-free source geometry this asset was built from.
+    compatible_sensor_model: str
+    compatible_hardware_revisions: tuple[str, ...]  # '*' means any revision.
 
 
 @dataclass(frozen=True)
@@ -172,6 +177,7 @@ class RenderFrame:
     valid: Mask  # [N].
     scalar_descriptor: FieldDescriptor
     diagnostics: tuple[Diagnostic, ...]
+    computed_frame_id: int | None  # Carried through so the display side re-checks it.
 
 
 @dataclass(frozen=True)
@@ -345,17 +351,23 @@ class Sensor3DWidget(QOpenGLWidget):
 
 class ThreeDCoordinator:
     def __init__(self, widget: Sensor3DWidget, composer: SceneComposer,
-                 executor: Executor, max_fps: int = 30) -> None: ...
+                 executor: Executor, max_fps: int = 30, *,
+                 clock: Callable[[], float] = ..., stale_grace_s: float = 1.0) -> None: ...
     def activate(self, assets: SceneAssets, source_id: str) -> int: ...
     def submit(self, frame: SurfaceFieldFrame) -> OfferResult: ...
+    def note_field_failure(self, item: Diagnostic | None = None) -> None: ...
     def tick(self) -> None: ...
     def set_visible(self, visible: bool) -> None: ...
     def set_settings(self, settings: DisplaySettings) -> None: ...
+    def show_rest(self) -> None: ...
     def close(self) -> None: ...
     @property
     def state(self) -> SceneState: ...
     @property
     def generation(self) -> int: ...
+    @property
+    def epoch(self) -> int: ...
+    def last_presented(self) -> tuple[FrameIdentity, float] | None: ...
 
 
 class ThreeDPanel(QWidget):