feat: make crosswalk and stop-line offsets solvable

Step 1 of the control-marking task, and deliberately server-only: no handle is
drawn yet. This project already shipped a range handle for `profile.interval`,
which compileGeometry ignores, so the control dragged and changed nothing. The
consumer comes first now.

Two kinds join the taxonomy — `junction-crosswalk-inset` and
`junction-stop-line-offset`, both on the existing `junction-approach` anchor. The
solver writes them onto the approach entry, `applyDirectJunctionPlans` carries
them onto the compiled approach, and `compileControlMarkings` reads them in place
of the module constants it used for every junction. They move markings without
reshaping the junction, so unlike width and cutback they deliberately do not
trigger a boundary recompute.

`applyJunctionConstraint` becomes an explicit switch. Its trailing `else` had
meant every kind that was not approach-width fell through to the cutback
validator, so a new kind would have been silently validated and written as a
cutback. The same non-exhaustive shape in the test fixture's `valueFor` is fixed
the same way, and now throws for an unnamed kind rather than answering with a
corner radius.

design.md's taxonomy is updated with it — a test asserts the two cannot drift,
which is what caught the omission.

Measured on a 41-road workspace with 8 crossings: both constraints change their
marking geometry, neither drags the other, and out-of-range blocks instead of
clamping. That measurement is not in the suite: the synthetic junction resolves
`junction_inset_m` to 0 because its crossing never binds to a plan, and the
committed OSM fixture has no crossings at all. The tests assert the wiring the
handles will depend on — values reaching the approach entry, distinct branches,
blocking diagnostics — and the gap is recorded in the test itself.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.trellis/tasks/08-26-direct-manipulation-road-editor/design.md

@@ -37,6 +37,8 @@ type RoadConstraintKind =
   | 'junction-approach-width'
   | 'junction-cutback'
   | 'junction-corner-radius'
+  | 'junction-crosswalk-inset'
+  | 'junction-stop-line-offset'
 ```
 
 | kind | 锚点 | value | 单位与含义 | 所有者 |
@@ -47,8 +49,18 @@ type RoadConstraintKind =
 | `junction-approach-width` | `junction-approach` | `{ widthMeters }` | 米 | JunctionTools |
 | `junction-cutback` | `junction-approach` | `{ cutbackMeters }` | 米 | JunctionTools |
 | `junction-corner-radius` | `junction-corner` | `{ radiusMeters }` | 米 | JunctionTools |
+| `junction-crosswalk-inset` | `junction-approach` | `{ insetMeters }` | 米，斑马线距路口边界的退让 | 主地图 / JunctionTools |
+| `junction-stop-line-offset` | `junction-approach` | `{ offsetMeters }` | 米，停止线沿进口后退的距离 | 主地图 / JunctionTools |
 
-这 6 个 kind 与 PRD 首期范围一一对应（外缘、步行带、车道分隔 + 进口、cutback、角部），没有多余项也没有缺口。
+前 6 个 kind 对应 PRD 首期范围（外缘、步行带、车道分隔 + 进口、cutback、角部）。
+
+后 2 个于 2026-08-28 追加，是「更多元素可直接操纵」方向的第一类扩展：控制标线的**位置**
+成为可编辑参数。它们不改变路口形状，只移动标线，因此不触发路口边界重算。
+放置是否成立的判据（`STOP_LINE_MAX_APPROACH_DISTANCE_METERS` 等）不在此范围内。
+
+新增 kind 的前提：**几何阶段必须已经消费它**。本项目曾为 `profile.interval` 交付过
+一个拖动无效果的手柄（见 `08-26-direct-edit-map-editor/research/interval-not-applied.md`），
+所以扩展 kind 时先证明 `compileGeometry()` 读取该参数，再画任何手柄。
 
 `transition: 'smoothstep' | 'linear'`，默认 `smoothstep`，作用于 interval 两端回归基线的过渡段。
 

.trellis/tasks/08-26-direct-manipulation-road-editor/task.json

@@ -23,7 +23,9 @@
     "08-26-direct-edit-solver-api",
     "08-26-direct-edit-map-editor",
     "08-26-direct-edit-junction-tools",
-    "08-27-junction-dominated-roads"
+    "08-27-junction-dominated-roads",
+    "08-28-edit-interaction-polish",
+    "08-28-junction-control-offsets"
   ],
   "parent": null,
   "relatedFiles": [