diff --git a/docs/superpowers/specs/2026-05-13-phase-b4b-design.md b/docs/superpowers/specs/2026-05-13-phase-b4b-design.md
index b3ecce1..e160d3b 100644
--- a/docs/superpowers/specs/2026-05-13-phase-b4b-design.md
+++ b/docs/superpowers/specs/2026-05-13-phase-b4b-design.md
@@ -123,11 +123,15 @@ server's reply. Outbound is the only block.
 
 One new file + edits to `GameWindow.cs`.
 
-**New:** `src/AcDream.App/Rendering/WorldPicker.cs` — static helper
-class in `AcDream.App.Rendering` namespace. Two pure methods, no
-state, no DI. Lives next to `GameWindow.cs` because the picker
-shares `WorldEntity` shape knowledge with the rendering layer (uses
-`.ServerGuid` + `.Position`).
+**New:** `src/AcDream.Core/Selection/WorldPicker.cs` — static helper
+class in `AcDream.Core.Selection` namespace. Two pure methods, no
+state, no DI. **Lives in Core** (not App) because it has no App-layer
+dependencies: it operates on `WorldEntity` (Core) plus
+`System.Numerics` matrices/vectors. Putting it in Core also means it
+can be unit-tested via the existing `AcDream.Core.Tests` project; no
+new test project required (`AcDream.App.Tests` does not exist as of
+2026-05-13 and creating it would add more LOC than the picker
+itself).
 
 **Edited:** `src/AcDream.App/Rendering/GameWindow.cs`:
 1. Rename field `_selectedTargetGuid` → `_selectedGuid` (project-wide
@@ -299,8 +303,8 @@ player walks through doorway
 
 ### Testing
 
-**Unit tests** — `tests/AcDream.App.Tests/Rendering/WorldPickerTests.cs`
-(new file):
+**Unit tests** — `tests/AcDream.Core.Tests/Selection/WorldPickerTests.cs`
+(new file in existing test project):
 
 | Test | Scenario | Asserts |
 |---|---|---|
@@ -363,8 +367,8 @@ This is one slice. No further sub-slicing.
 
 | Step | Files | LOC | Subagent? |
 |---|---|---|---|
-| 1. Write `WorldPickerTests.cs` (TDD: tests first) | `tests/AcDream.App.Tests/Rendering/WorldPickerTests.cs` (new) | ~80 | Yes (Sonnet) — bounded TDD task |
-| 2. Create `WorldPicker.cs` static helper | `src/AcDream.App/Rendering/WorldPicker.cs` (new) | ~50 | Same agent as step 1 |
+| 1. Write `WorldPickerTests.cs` (TDD: tests first) | `tests/AcDream.Core.Tests/Selection/WorldPickerTests.cs` (new) | ~80 | Yes (Sonnet) — bounded TDD task |
+| 2. Create `WorldPicker.cs` static helper | `src/AcDream.Core/Selection/WorldPicker.cs` (new) | ~50 | Same agent as step 1 |
 | 3. Rename `_selectedTargetGuid` → `_selectedGuid` in `GameWindow.cs` | 1 file edit | ~5 sites | Manual or Sonnet |
 | 4. Add 3 switch cases + 3 helper methods in `GameWindow.OnInputAction` | 1 file edit | ~40 | Manual or Sonnet |
 | 5. `dotnet build` + `dotnet test` green | — | — | Manual |