refactor(new_editor): split utility window semantics from workspace

docs/plan/NewEditor_WorkspaceUtilityWindowSemanticSplitPlan_2026-04-22.md

@@ -1,7 +1,7 @@
 # NewEditor Workspace Utility Window Semantic Split Plan
 
 Date: 2026-04-22
-Status: In Progress
+Status: Implementation Complete, Manual Verification Pending
 
 ## 0. Execution Progress
 
@@ -29,6 +29,34 @@ What is intentionally not done yet:
 
 This means the root shell/content ownership boundary has been extracted first, while feature semantics remain unchanged for safety.
 
+### Completed on 2026-04-22
+
+Phase C, Phase D, and Phase E implementation are now in place.
+
+Completed changes:
+
+1. a first-class utility window domain now exists:
+   - `EditorUtilityWindowKind`
+   - `EditorWindowOpenUtilityWindowRequest`
+   - `EditorUtilityWindowCoordinator`
+   - `EditorUtilityWindowRegistry`
+2. color picker open intent no longer routes through detached workspace mutation
+3. the color picker now opens through utility-window coordination and utility content
+4. color picker has been removed from:
+   - `UIEditorPanelRegistry`
+   - shell hosted-panel composition
+   - workspace detached-panel request plumbing
+5. `openDetachedPanel` has been deleted from frame transfer routing
+6. `UIEditorWindowWorkspaceController::OpenPanelInNewWindow(...)` has been deleted
+7. `toolWindow` and related workspace utility inference have been deleted
+8. detached floating-window placement logic is now shared instead of duplicated
+9. `XCUIEditorApp` Debug build passes after this phase
+
+What is intentionally not claimed yet:
+
+1. manual GUI regression verification is still required for the matrix in section 10
+2. no drag/drop or panel movement was automated during this step
+
 ## 1. Objective
 
 This plan solves the problem from the architectural root, not by adding another special case.