Checkpoint source 7 workflows and in-progress diagram authoring redesign

Preserve current core, source, REST, desktop, recovery, documentation and validation work, including AGENTS.md and the development summary. This is a work-in-progress checkpoint: the new compact palette has outstanding compilation errors and native acceptance; earlier passing gates retain their documented scope.

crates/oa-server/src/store.rs

@@ -13,6 +13,10 @@ use std::{
     sync::{Mutex, MutexGuard},
 };
 
+#[cfg(test)]
+#[path = "store_preparation_gate.rs"]
+pub(crate) mod preparation_gate;
+
 pub const MAX_MODEL_BYTES: usize = 8 * 1024 * 1024;
 pub const MAX_SOURCE_PROJECT_BYTES: usize = 8 * 1024 * 1024;
 pub const MAX_OBJECTS: usize = 5_000;
@@ -89,6 +93,8 @@ pub enum StoreError {
 
 pub struct Store {
     inner: Mutex<StoreInner>,
+    #[cfg(test)]
+    preparation_gate: Mutex<Option<preparation_gate::Armed>>,
     // Keep the OS lock alive for the store's entire lifetime, including requests.
     _directory_lock: File,
 }
@@ -242,6 +248,8 @@ impl Store {
     ) -> ApiResult<(StoredProject, bool)> {
         let current = self.checked(id, expected)?;
         let prepared = PreparedProject::replacement(&current, decoded)?;
+        #[cfg(test)]
+        self.wait_after_preparation(id, expected, &prepared)?;
         self.lock()?.replace(id, expected, prepared)
     }
 
@@ -381,6 +389,8 @@ impl Store {
             }
         }
         Ok(Self {
+            #[cfg(test)]
+            preparation_gate: Mutex::new(None),
             inner: Mutex::new(StoreInner {
                 directory,
                 projects,