Add pure combined Allocation Arrange planner with exact source and geometry checks

crates/oa-desktop/src/allocation_drag.rs

@@ -13,6 +13,11 @@ use oa_core::{
 };
 use std::collections::{BTreeMap, BTreeSet};
 
+// The pure planner is verified before its App gesture adapter is connected.
+#[allow(dead_code)]
+#[path = "allocation_drag/arrange.rs"]
+pub mod arrange;
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Destination {
     LayoutOnly,
@@ -76,6 +81,11 @@ pub enum Refusal {
 
 pub fn capture(p: &Project, diagram: Id, work: Id, placement: Id) -> Result<Scope, Refusal> {
     validate_candidate(p).map_err(|e| Refusal::InvalidCandidate(e.to_string()))?;
+    capture_validated(p, diagram, work, placement)
+}
+
+/// Collect work facts after the caller's single complete Project validation.
+fn capture_validated(p: &Project, diagram: Id, work: Id, placement: Id) -> Result<Scope, Refusal> {
     let d = p.diagrams.get(&diagram).ok_or(Refusal::StaleScope)?;
     let root = p.elements.get(&work).ok_or(Refusal::StaleScope)?;
     if !root.kind().is_work()